# Alternate source for Millet-Hybrid PCB



## n_maher

Please read this thread if you would like to learn more about the revisions to Peter Millet's Hybrid headphone amplifier.


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## comabereni

I think a couple people have built, or are building, this P2P. Perhaps you should start an interest check thread to see if a few members might want to try it that way as a group. You might even be able to build in some upgrades that would be difficult with the PCB. I'd be interested in trying this P2P.

 -coma


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## jamont

I agree that $40 seems a little high for this, it is a high quality board, however.

 The gerber files are available on Pete Millett's web site. If you get a few people together to share, you can probably have boards manufactured for under $40 each.


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## sbelyo

When I got my board it was $25.00 from DIYCable.com.

 But the main reason why it's a tad expensive is if you were to have it made with the soldermask and silkscreen in small quantities like less than 50 it would cost around $30.00

 It's a thick board with heavy copper.

 Pete also posts the eagle brd file and the gerber drill file so you can have them made yourself.

 I was thinking of trying to lay it out in Express PCB and have them make the boards as they would at least be the same price as diycable if you ordered 4 or 6. I's like to remove all the board mounted rca's, power jack, switch etc. That will make the board smaller. Also I'd like to make the space for metalized film caps bigger so that you could try solen or something else without any trouble.

 It's still worth paying $40.00 for it though. It's a sweet sounding amp.


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## n_maher

[edit]

 I'd love it, and help however I could, if some one wanted to streamline this board as you suggested and see if there was any interest in a group buy. 

 Nate


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## comabereni

vksy emailed me earlier today to share his not-yet-built Millett Hybrid P2P layout. He's done a good job and it looks pretty straightforward to me, but it's not yet tested. He's the one who posted yesterday about using diamond buffers with the Millett. Modifications include parallel tubes (2 per channel) and the possibility of diamond buffers. Pete has commented on the modifications but hasn't built, tested, or heard anything like it, so can't vouch for how it would sound. Pete said paralleling tubes increases Gm and lowers noise (at least on paper).

 I want to do this P2P Millett myself. vksy said total cost for amp and (Tangent's) LM317 PSU (not including case, knobs, shipping) was just ~$135.

 -coma

 P.S. Even the Dynahi boards were only around $8/pair, so I know what you mean. I think it all comes down to "do you want to make things easy".


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## drewd

A few enterprising people could get together and send the Eagle .brd file to PCB Fab Express and have the boards made for about $19 each with a five day turn. I've used them for protos and the quality is good (the silkscreen can be a little blurry sometimes).

 -Drew


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## n_maher

Consider me looking into it - I'll be contacting PCB Fab tomorrow to check on pricing and lead time for a larger order, say 25 boards. Might be time to put together my first group buy...

 Thanks for the help Drew!

 Nate


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## comabereni

Let us know. I'd probably be in for a board, maybe two, in that price range.


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## bg4533

Quote:


  Originally Posted by *comabereni* 
_Let us know. I'd probably be in for a board, maybe two, in that price range._

 

Same here.


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## blip

Depending on price / improvements to the DIY cables board, I'd probably be in for at least one. 

 I'd definitely be down if someone wanted to use economies of scale to make a cheaper kit version of this.


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## Unclewai

+1 here. I know nothing about making the board. But if there's an organizer happens to be in Seattle area, I can help out on shipping them out.


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## aeroes

Count me in please.


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## MisterX

I would suggest you check out Imagineering.... 
 Between their prototype deal and their second order discount  they gotcha covered pretty well for a "small" order like this.


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## dsavitsk

Assuming that it is alright with Pete, I'd be in for one.

 Among changes I can think of off the top of my head 

 - there are some long traces in the original where power and signal run the length of the board that can be shortened by moving some components around
 - space for an alps blue or a noble pot would be great
 - there is in general a lot of space on the board, and it could be compacted to about half its size without too much difficulty -- this should lower the cost a bit
 - the heatsinks are unnecessary
 - the 8 pin DIP version of the buffers are cheaper and might save a bit of board space as well

 -d


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## n_maher

Okay, so it seems like there's plent of interest in putting together the required order from PCB Fab - which only requires a quantity of 5.

 I'll also follow MisterX suggestion of taking a lot at the alternate vendor. 

 I'm working with someone to modify the current board layout and I'll also be in touch with Mr. Millett to make sure that he has no issues with any of this. As I see it right now the group would like to make the following changes:

 1. remove most board mounted components (jack, rca, power, switch)
 2. make room for an Alps RK27 pot
 3. modify buffer locations to allow use of DIP 8 components
 4. compress the board as much as phsyically possible

 At the current time I have no real desire to try any of the more exotic mods suggested like paralleling tubes or adding diamond buffers. This board will be for those of us looking to build pretty much a bone stock MH amp.

 I'll update this thread when I have anything significant to add or for review of a modified layout. In the mean time I have no issues with people posting there interest but this isn't meant as a group buy thread, yet 
	

	
	
		
		

		
			





.

 Regards,

 Nate


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## comabereni

Sounds great. Count me in for a definite two if these come in at ~$20. Perhaps we can do a PCB later on with the spiffy upgrades after it's been built and tested.

 -coma


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## Nisbeth

This sounds interesting, I'm definitely subscribing to this thread 
	

	
	
		
		

		
		
	


	





 /U.


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## n_maher

Okay, drewd has been kind enough to offer his board editing/creating skills as the board size is not able to be edited in the free version of Eagle. 

 THANKS DREW!

 At this time would anyone like to augment the list of changes I posted above? I'd like to keep this version of the board as true to the original design as possible (for $$ reasons). The idea of a well thought out, non PTP, approx. $100 tube amp is too much to ask for. 

 And thanks to MisterX for the alternate vendor suggestions. It would seem highly likely that the boards could be had for under $20 and relatively quickly.

 Nate


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## vksy

Quote:


 the $40 that DIYCable.com wants seems like highway robbery 
 

I totally agree that a $40 board is a bit much for what is supposed to be a beginner's tube project. I'm certain this turns off potential builders for that fact alone. I hope Nate's effort works out for everyone.

  Quote:


 The idea of a well thought out, non PTP, approx. $100 tube amp is too much to ask for 
 

It's possible. Keeping board cost at a minimum is key. The price just for the amp excluding shipping, case, psu, and minor stuff is about $75.

  Quote:


 modify buffer locations to allow use of DIP 8 components 
 

DIP-8 sockets give you 2 modding options without much fuss: rolling and paralleling buffers. Sijosae's P2P diamond buffer is another possibility. His layout isn't much bigger than a quarter and easily mounts on a DIP-8 socket. I have not tried it though, and my post on the subject is dead pretty much. It looks like I'm the guinea pig.

  Quote:


 I have no real desire to try any of the more exotic mods suggested like paralleling tubes or adding diamond buffers 
 

Diamond buffers may sound high-end, but it's just ~$5 in parts from DigiKey. Keep in mind BUF634's costs $8+ for TO-220 and $6+ for DIP-8, so I would hardly call DB's exotic. I admit 4 tubes doubles your replacement/rolling cost, but it looks fun to experiment on without the risk of being zapped by high voltages.

  Quote:


 Perhaps we can do a PCB later on with the spiffy upgrades after it's been built and tested 
 

I'm way past the stock board at this point. I want to have fun with Pete's amp, and a prefab just doesn't provide enough flexibility. Pete was very helpful in listing component changes in order to make the tweaks work. He also noted they look good on paper but questions whether I'll get better results. I'm looking at this as a learning exercise. If my P2P puts out even a squeek, I'm happy.

 I'll let you know how it turns out. This won't happen until summer though.


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## evo_lution

I'd be interested in a board- i tried contacting DIYCable.com several times about shipping to the UK, but got no reply


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## tess

I'm in as well, 

 have had the same problems as evo_lution, doesn't seem to want to send to the UK.


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## individual6891

Count me in too... Go team UK!


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## sbelyo

If someone changes the board for better then I'll take one as well.


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## blip

Things I'd definitely like to see:

 1) DIP-8 Buffers - Both to provide the option of diamond buffers and easy buffer rolling / replacement. I think this is the most important change.

 2) Off-Board Inputs, Outputs, Volume etc. - I like to do all such things off-board (esp. because I think I would probably integrate it into a pre-amp).

 3) As others have already noted - the smaller it is the cheaper it will be... which is a definite plus!

 4) But on the other hand, if we could avoid an ultra-tight spacing of pads (obviously this can't be done for every section of the board) it would make the board easier to newbies... and fumbly DIYers!

 5) I'd also love to see someone put this together into kit form so that we can all save on shipping... plus they could probably still make a little profit and sell it for cheaper because of the economy of scale.


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## bg4533

The BUF634 is fairly popular around here. Maybe someone should design a diamond buffer module that will drop in and replace it.

 On a related note, if the board is redesigned to handle DIP8 buffers please leave a little room around the socket for a diamond buffer.


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## drewd

I just got an email from Pete Millett blessing this undertaking - I emailed him earlier today because I thought that since it's his original design, it would be nice to make sure that he didn't have any objections to me tearing his board apart. He even offered to put links on his webpage to whatever we eventually come up with.

 What a class act...

 I've spent a little bit of time going over the board and removing most of the on-board input and output components. I've also added an ALPS "Blue Velvet" volume control in parallel with the Panasonic EV-J, a la the PIMETA.

 There is room on the board to use both the socketed BUF634 and a discrete diamond buffer, with a jumper to select between the two. That is an option, however there are several implementations of the circuit, so I guess that we'd have to come to an agreement over which would be best. I can also leave space around the DIP8 part so that a custom board could be used. Perhaps that might be a project to run in parallel with this one instead of putting too many options onto the main PCB. I'd be happy to work out space requirements on the main PCB if somebody wants to work on an off-board diamond buffer.

 Peter's web site discusses the features of the board. Please speak up if there is more (or less) that you'd like to see on the board and I'll see what can be done to accomodate everything. Nate and I agree that there's no big rush on this - I don't think that he has any deadline in mind yet, so please let your creative juices flow!

 -Drew


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## n_maher

An updated board is already forming, I've already seen a preview 
	

	
	
		
		

		
		
	


	




 . Drew and I are currently working on the the basic list of mods and are exploring the idea of having both buffer types on board with a jumper to switch between the two. We'll see how that shakes out.

 I don't think there is any great need to compress the board down super tight. Reducing the board size some will happen by default in removal of all the board mounted components. How much we persue reduction beyond this point is a yet to be determined quantity.

 So stay tuned, I expect that we'll have a layout for review in the next couple of days. Seeing as Drew is voluteering his time and effort to do this there's no way I'm going to pressure him at all 
	

	
	
		
		

		
		
	


	




.

 Nate


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## n_maher

Evidently Drew beat me to the reply above hehehe.

 I also spoke with Peter to get the go-ahead with this project and have to agree with Drew, absolute class act.


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## individual6891

Will a diamond buffer be absolutely necessary? Modifying another circuit are you absolutely sure you can guarantee stability?..Which would require extensive prototype testing..

 Diamond buffers designed from scratch to fit a specific circuit run into stability problem - is there such a thing "universal diamond buffer" out there? I maybe wrong, but I was under the impression that diamond buffers were very sensitive to the components around it..


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## drewd

Quote:


  Originally Posted by *individual6891* 
_Will a diamond buffer be absolutely necessary? Modifying another circuit are you absolutely sure you can guarantee stability?..Which would require extensive prototype testing..

 Diamond buffers designed from scratch to fit a specific circuit run into stability problem - is there such a thing "universal diamond buffer" out there? I maybe wrong, but I was under the impression that diamond buffers were very sensitive to the components around it.._

 

Yep, that's a problem. What I was getting at was that there are quite a few topologies out there. There is not one universal diamond buffer, but several different implementations. Component selection is, of course, the key.

 It may be best to leave the output buffer as a DIP8 part and not even mess with trying to get something on the PCB. That would make the whole prototyping issue much easier by reducing the number of things that can go wrong. It also would let me reduce the board size and still leave an option for those who want to pursue a diamond buffer.

 To answer your question, no, a discrete diamond buffer is not necessary.

 -Drew


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## individual6891

Does the BUF634T get hot in the millet hybrid circuit? Of course a DIP8 package would be preferred, but maybe there was a reason pete chose the TO220 package?


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## dsavitsk

Quote:


  Originally Posted by *individual6891* 
_Does the BUF634T get hot in the millet hybrid circuit?_

 

It doesn't even get warm. The heatsinks are totally unnecessary.

 -d


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## drewd

Quote:


  Originally Posted by *individual6891* 
_Does the BUF634T get hot in the millet hybrid circuit? Of course a DIP8 package would be preferred, but maybe there was a reason pete chose the TO220 package?_

 

No more than in any other headphone amplifier. The BUF634's thermal protection circuit kicks in at 175C which is very, very hot. I suspect that he chose the TO220 package because it is the most thermally conservative one available. Pete didn't address his choice of buffer package in the AudioXpress write-up, but considering Ohm's law, the output buffers ought not to dissipate more power from this amplifier than from a solid state model.

 -Drew


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## individual6891

Dip-8 it is then


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## bg4533

Dip8 will also allow for easy stacking of BUF634s like in the Pimeta. 

 My only other suggestion is to allow plenty of space for electrolytic and film caps. It might be nice to give multiple hole options so people can easily use the Blackgates or Panasonics of their choice.


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## drewd

I've started on the redesign of Pete Millett's amplifier. I've reduced the board size from 32 square inches to about 26. There is still plenty of work to do, especially with the electrolytic cap placement and some of the currently awkward routing, but this should give everyone a feel for where the board is headed. I've left some space around the buffers for anyone who wants to experiment a bit. There is not enough space around some of the caps and I'll fix that. The signal inputs have a nice ground plane except for one spot on the left channel grid input.

 Please, please, please, if you have any interest in this project, post some suggestions for things that you'd like to see included in a basic, low cost, easy to build entry level tube amplifier.

 Board image (no fill): http://img.photobucket.com/albums/v4...wd/millett.jpg

 Board image (fill): http://img.photobucket.com/albums/v4...llett_fill.jpg

 Rendered image: http://img.photobucket.com/albums/v4...ybrid_head.jpg

 -Drew


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## n_maher

Drew, I know this runs contrary to the current layout (which I like a lot 
	

	
	
		
		

		
		
	


	




 ) but I think conventionally minded people might have expected the volume on the short end of the board with the tubes running back in line behind it. That way you might fit this thing in a standard hammond case (not my plan) and use an external powersupply. 

 Personally I'm envisioning it in a case somewhat like your Ascent with a center pot just like you've got it now. But that's just me.

 Any thoughts?

 Nate


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## individual6891

Aye, a lengthway PCB would allow for a larger variety of enclosure options.. Maybe even a possibility of fitting into into eurocard size?


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## Nisbeth

Drew, could you possibly change the trimpots on the board to Bourns type 3296? They are a bit larger, but much easier to find replacements for than the current type 
	

	
	
		
		

		
		
	


	





 /U.


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## drewd

Roger dodger on the three previous suggestions!

 -Drew


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## drewd

A quick update. This is single Eurocard sized, 100x160mm. The usual caveats apply - very preliminary and needs substantial refinement, but I'm interested to hear if the general layout seems acceptable.

http://img.photobucket.com/albums/v4...brid_head3.jpg

 -Drew


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## individual6891

Yeah that looks quite nice..

 Any chance of leaving about 3-4mm space on the sides (down the lengths) so they might fit better in cases with PCB slots (hammond, bopla etc). Also make sure there's enough space for mounting holes in the corners for those who don't use a euro-card pcb enclosure.

 Also any chance of changing the trimmer pot to use 3 x 0.1inch spacings as Nisbeth suggested? Or maybe even a way of using both layouts like you have done in with the vol pot? Though this isn't a major issue, the trimmer pot spacing is still widely available, just though some people may prefer to use the bourns.


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## Nisbeth

Quote:


  Originally Posted by *drewd* 
_A quick update. This is single Eurocard sized, 100x160mm. The usual caveats apply - very preliminary and needs substantial refinement, but I'm interested to hear if the general layout seems acceptable._

 

Sure does !
	

	
	
		
		

		
		
	


	




 /U.


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## drewd

Quote:


  Originally Posted by *individual6891* 
_Yeah that looks quite nice..

 Any chance of leaving about 3-4mm space on the sides (down the lengths) so they might fit better in cases with PCB slots (hammond, bopla etc). Also make sure there's enough space for mounting holes in the corners for those who don't use a euro-card pcb enclosure.

 Also any chance of changing the trimmer pot to use 3 x 0.1inch spacings as Nisbeth suggested? Or maybe even a way of using both layouts like you have done in with the vol pot? Though this isn't a major issue, the trimmer pot spacing is still widely available, just though some people may prefer to use the bourns._

 

Yes, I'll adjust the routing to leave some space for the grooves and I'll put some mounting holes in the corners - good ideas.

 I'll also use the Bourns trimmers. I'm going to look through the DigiKey and Mouser catalogs and make sure that the component sizes on the board match what is available from those catalogs.

 -Drew


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## comabereni

Quote:


  Originally Posted by *n_maher* 
_Drew, I know this runs contrary to the current layout (which I like a lot 
	

	
	
		
		

		
			





 ) but I think conventionally minded people might have expected the volume on the short end of the board with the tubes running back in line behind it. That way you might fit this thing in a standard hammond case (not my plan) and use an external powersupply. _

 

Not that anyone asked for my vote, but I like it the way it is (edit: was). For whatever personal aesthetics matter in these decisions, I'd enjoy seeing the tubes side-by-side behind the pot rather than in-line behind the pot like the diycable Millett board I own. 

 -coma

 P.S. Looks like I voted too late. If the revisions make casing this thing easier for everyone, that's the way to go. I can lift the pot (or tubes) off the board when I do my case.


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## skyskraper

awww he's right side by side would look much cooler


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## blip

Side-by-side tubes would be better but I would prefer a cleaner circuit to a better looking board. Anyway, up to you Drewd.

 Looks good so far!


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## dsavitsk

How about putting a second place to connect the input wires that's closer to the pot? Then, if you like to run the signal through the board you can, or you can run wire to the other input spot.

 -d


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## comabereni

I heard the original tube sockets descibed in Pete's article are discontinued and harder to come by now. I don't know how most of you are planning to case this up, but perhaps it would make sense to plan this around tube sockets mounted off the PCB. I've been enjoying a little tube-rolling with my Millett Hybrid and get a bit nervous pushing and pulling on the sockets connected to the PCB. Probably not a real concern--mostly stems back to how many motherboards I've killed flexing them, but I'd rather they be mounted to something sturdier. It'll take a taller enclosure to get it all inside unless you cut (ugly) holes in the top, so perhaps the tube sockets can be mounted sideways inside an enclosure or on top of the case as a few have done.

 Just some food for thought--you can always solder to the pads and mount off-board in any orientation as is, but the PCB footprint could be even smaller if the board was designed that way.

 -coma


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## individual6891

Quote:


  Originally Posted by *comabereni* 
_I heard the original tube sockets descibed in Pete's article are discontinued and harder to come by now. I don't know how most of you are planning to case this up, but perhaps it would make sense to plan this around tube sockets mounted off the PCB. I've been enjoying a little tube-rolling with my Millett Hybrid and get a bit nervous pushing and pulling on the sockets connected to the PCB. Probably not a real concern--mostly stems back to how many motherboards I've killed flexing them, but I'd rather they be mounted to something sturdier. It'll take a taller enclosure to get it all inside unless you cut (ugly) holes in the top, so perhaps the tube sockets can be mounted sideways inside an enclosure or on top of the case as a few have done.

 Just some food for thought--you can always solder to the pads and mount off-board in any orientation as is, but the PCB footprint could be even smaller if the board was designed that way.

 -coma_

 

Not really. If you read his article you can google his source:

http://www.tubesandmore.com/

 One of them is out of stock, but he lists at least 4 alternative tubes.

 ..It's just a problem for Euro DIYers..


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## Nisbeth

Quote:


  Originally Posted by *individual6891* 
_..It's just a problem for Euro DIYers.. 
	

	
	
		
		

		
		
	


	


_

 

 It shouldn't be. Have a look at www.amplimo.nl (under "high-end audio") 
	

	
	
		
		

		
		
	


	





 /U.


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## vksy

I'm not raining on anyone's parade, but people need to do their homework before jumping on this bandwagon. 7-pin miniature board mount sockets are not available from tubesandmore.com anymore. So kiss that $0.50 socket goodbye. There's a pretty picture on their site, but it doesn't mean they have one. I called them last week for my own Millett project, but who knows these days, I could have talked to a 14-year old with a part time job. 

 I found other places which are more expensive, but there's no guarantee if their stock can support this endeavor. It might be worth considering to include sockets in the group buy as well. There are also surplus online shops that sell them cheap, but I didn't bother contacting them because they didn't have nice pictures like these three:

http://store.tubedepot.com/sk-7pinpc.html 
http://thetubestore.com/7pinminisocket.html 
http://www.angela.com/catalog/tube-sockets/7.pin.html 

 Again, I'm not being harsh, but let's put this in perspective, retro gear is getting harder and harder to come by. The last thing we want is a group buy for 50 boards only to find out later it takes six months to find sockets.

 As for the board itself, some sockets come with center posts, so it would be a good idea to work that into the new design.


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## comabereni

Another possible reason to at least consider planning this PCB with the tube sockets outboard--you could then go with the socket of choice, or socket available, should sockets not be part of this group buy and you find yourself not getting around to sourcing your own or completing this amp in the near future.

 -coma


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## dsavitsk

Many of the alternative sockets can be soldered onto the pads of the old millett board even though though it is not specifically meant for them. You just set the socket on top of the PCB and put enough solder to make a strong surface mount type joint. This is how mine is done (I had to use a snip to cut the center post off of the socket) and it has worked fine. Also, Pete emailed me a list of alternative sources for sockets that I can dig up if anyone needs them. 

 So, please leave space on the board for the sockets. You can always mount them off the board if you want, but to require it is a bad plan. (the whole point of tubes being outside the case is for heat dissipation, and these tubes don't get hot enough that this is an issue. Also, they are so small that outside mounting looks cheesy)

 -d


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## drewd

Parts Connexion also carries the 7 pin mini sockets at $1.20 or $1.50 for gold plated. I don't think that availability of the sockets will be a terribly big issue.

 I agree that a second set of input pads would be a nice feature and I'll implement that.

 The socket pads on the board make off-board mounting pretty simple.

 I'll try to implement all of the ideas that are brought up. Obviously the inline versus left/right layouts are kind of exclusive...

 I'll post a revised layout later this evening.

 -Drew


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## comabereni

Quote:


  Originally Posted by *drewd* 
_Parts Connexion also carries the 7 pin mini sockets at $1.20 or $1.50 for gold plated. I don't think that availability of the sockets will be a terribly big issue._

 

Say the word that this Parts Connection socket will fit and I'll pick mine up with my next order in case I decide to board mount my tubes. I'm not pushing hard for off-board sockets, just bringing up things to consider. I can just solder to the pads of whatever design if finalized. 

 Just for the record, top-mounted tubes wouldn't look small and silly if this new PCB was small enough--they just look silly sitting atop the large footprint case required by the diycable PCB. It's all about proportions.

 -coma


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## slindeman

I've used the sockets from theTubeStore and from PartsConnexion. They both work great. I slightly prefer the ones from the PartsConnexion because the tubes insert a little easier.


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## blip

Personally I like to order my parts from 2-3 sources max... more than that and you are paying out half of the expense of the project in shipping! So is there any place that carries both the tubes & the sockets? If not then I'd definitely be in favor of bundling the socket with the board. Heck, I wouldn't be opposed to bundling starting tubes with the board.


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## comabereni

Quote:


  Originally Posted by *blip* 
_Personally I like to order my parts from 2-3 sources max... more than that and you are paying out half of the expense of the project in shipping! So is there any place that carries both the tubes & the sockets? If not then I'd definitely be in favor of bundling the socket with the board. Heck, I wouldn't be opposed to bundling starting tubes with the board._

 

If you only want a pair of tubes to start, it might be difficult coming to a concensus on what to include as there is a difference in sound between tubes I've tried yet no clear "winner". That said, I believe it would probably come down to either the 12AE6A or the 12FK6 for most people. I'd definitely recommend getting both if assembling a "starter bundle".

 I've listened to the 12AE6, 12AE6A, 12FK6, 12FM6, and tried the 12EL6 (doesn't work even though mentioned as a possibility in Pete's article). The only tube reported to work that I haven't heard yet is the 12AJ6, but will have a set later this week. There have been recent discussions on Millett amp tube selection/compatibility:

http://www6.head-fi.org/forums/showt...ghlight=12ae6a 
http://www6.head-fi.org/forums/showt...ghlight=12ae6a 

 -coma


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## drewd

The latest iteration of the board.

 Regarding board size versus tube size, this board is the same size as a PPA circuit board.

 I've tweaked the routing a little bit, changed the bias adjustment pots to Bourns and added an extra set of inputs closer to the volume control. Also added mounting holes for those who want to use a non-Eurocard case.

Board layout 

Rendered PCB 

 As usual, suggestions, criticism and complaints are welcome!

 -Drew

 EDIT: Fixed mangled links


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## MisterX

Nice work.... chances of replacing the BUF634 with Intersills?


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## comabereni

Quote:


  Originally Posted by *drewd* 
_Regarding board size versus tube size, this board is the same size as a PPA circuit board._

 

It looks nice. How big is the PPA circuit board?

 -coma


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## MisterX

6.3 × 3.925" or 160 ×100mm


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## comabereni

Neat--so it's almost an inch narrower and a half-inch shorter. Good work.

 It looks like most of the entire left side of the board is just for the pot. It would be neat if there was a way for those of us still wanting to compress the board size further and move the pot off the board and between the tubes to cut the pot end of the board off completely (appx. 1/5 of the board length) and still have some pads to solder the pot to. Only that 1K resistor (??) and 220UF_16U cap (??) are sitting in the way (correct me if I'm not identifying these properly). Anyway, would it even be possible if the pot were moved to the left a little for the resistor to be turned 90-degrees and maybe an optional set of pot pads to be located in-board a little? If so, the board length could maybe be reduced another inch for those of us not planning to use a standard enclosure. The "Team Head-Fi" printing could be moved to right/back end of the board so it wouldn't get cut off.

 Just say "no". ( 
	

	
	
		
		

		
		
	


	




 ) It would be pretty neat if this was designed to permit an alternative PCB/case configuration, but I'm not expecting anything. There are always compromises and this is better than the original at around half the price.

 Again, good job. 

 -coma


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## drewd

Quote:


  Originally Posted by *MisterX* 
_Nice work.... chances of replacing the BUF634 with Intersills? 
	

	
	
		
		

		
		
	


	


_

 

You are an evil, evil man.


----------



## drewd

Added pads for off-board pots. Moved some components on the left side of the board a little bit to make room for the pads and associated extra trace.

Board render 

Board image 

 I'm sleepy...


----------



## comabereni

**AWESOME**


----------



## individual6891

Quote:


  Originally Posted by *comabereni* 
_It looks like most of the entire left side of the board is just for the pot. It would be neat if there was a way for those of us still wanting to compress the board size further.

 -coma_

 

The point is keeping the board size eurocard isn't it? 160x100mm ..so that it can fit standard eurocard enclosures as mentioned.

 Regarding the pot pads - you can easily mount an offboard pot simply from the ALPs pot's pads. It's not difficult looking at a datasheet to figure the pinouts - why complicate the circuit further still? You don't see external pot pads in other designs..I prefer post #61 layout.

  Quote:


  Originally Posted by *drewd* 
_I'm sleepy..._

 

It's looking pretty impressive so far, good work ... get some sleep


----------



## comabereni

Quote:


  Originally Posted by *individual6891* 
_The point is keeping the board size eurocard isn't it? 160x100mm ..so that it can fit standard eurocard enclosures as mentioned.

 Regarding the pot pads - you can easily mount an offboard pot simply from the ALPs pot's pads. It's not difficult looking at a datasheet to figure the pinouts - why complicate the circuit further still?_

 

Hey now, let's not undo progress 
	

	
	
		
		

		
		
	


	




. This last revision permits some radical custom orientation and enclosure options for those of us with a bandsaw and not afraid to use it. 
	

	
	
		
		

		
		
	


	




 Doesn't #67 fit in a eurocard enclosure and do everything #61 does anyway?

 -coma


----------



## individual6891

It further complicates the circuit by adding unnecessary pads.. How many other PCB layouts have you seen with external pot pads in addition to it's PCB component?

  Quote:


 This last revision permits some radical custom orientation 
 

I wouldn't exactly call it radical, you're simply slicing 1 inches of board space, and sure there are cases that maybe (I wouldn't know why though) accomodate 100mm x 135mm PCBs (?!?), but how many have you found?


----------



## n_maher

At this point I think that we should hold the board design where we've got it unless there are concerns about the circuit layout. Component and options wise I think we've acheived what was the original goal of this project. Mainly to get rid of all the board mounted components (save for the pot) and add some increased functionality to the original design. There isn't going to be any single design that deals with everyone's desires 
	

	
	
		
		

		
		
	


	




. If a lot of folks are wanting a tweaked, hotrodded MH than I think it would make sense for them to pursue this on their own. I'd really like to keep this version as true to the original design as possible. If we decide to go through another round of tweaks I'll let everyone know. 

 For now Drew and I have begun talking about how we're going to handle the prototype testing phase. I'll update this thread as more information becomes available. My sincere hope is to have this amp built alongside an M3, PPA V2 and Dynalo for comparisons. That may take a minor miracle though.

 Thanks to everyone for their input, I for one am really pleased with the most recent board layout. Most of all, thanks again to Drew for volunteering his time and knowledge. 

 Nate


----------



## skyskraper

eurocard is nice but why not give options 
	

	
	
		
		

		
		
	


	




 who knows what people want to do with the circuit


----------



## individual6891

Quote:


  Originally Posted by *n_maher* 
_At this point I think that we should hold the board design where we've got it unless there are concerns about the circuit layout. Component and options wise I think we've acheived what was the original goal of this project. Mainly to get rid of all the board mounted components (save for the pot) and add some increased functionality to the original design. There isn't going to be any single design that deals with everyone's desires 
	

	
	
		
		

		
		
	


	




. If a lot of folks are wanting a tweaked, hotrodded MH than I think it would make sense for them to pursue this on their own. I'd really like to keep this version as true to the original design as possible. If we decide to go through another round of tweaks I'll let everyone know. 

 For now Drew and I have begun talking about how we're going to handle the prototype testing phase. I'll update this thread as more information becomes available. My sincere hope is to have this amp built alongside an M3, PPA V2 and Dynalo for comparisons. That may take a minor miracle though.

 Thanks to everyone for their input, I for one am really pleased with the most recent board layout. Most of all, thanks again to Drew for volunteering his time and knowledge. 

 Nate_

 

That sounds cool.

 Just from curiosity, is there anyone from USA willing to distribute some tubes/sockets to europeans? We're still having difficulties with some stock (nice source though nisbeth, but very very expensive!).


----------



## comabereni

Quote:


  Originally Posted by *individual6891* 
_It further complicates the circuit by adding unnecessary pads.. How many other PCB layouts have you seen with external pot pads in addition to it's PCB component?

 I wouldn't exactly call it radical, you're simply slicing 1 inches of board space, and sure there are cases that maybe (I wouldn't know why though) accomodate 100mm x 135mm PCBs (?!?), but how many have you found?_

 

I agree this last revision was a step beyond the necessary, but I'm grateful for it. It opens up custom size, orientation and enclosure options. I personally see no reason to go back to an earlier version unless the earlier version is better than this last one. 

 In fact, I'm buying Drew dinner as soon as he sends his PayPal address (thanks!) 
	

	
	
		
		

		
		
	


	




.

 -coma


----------



## comabereni

Quote:


  Originally Posted by *individual6891* 
_That sounds cool.

 Just from curiosity, is there anyone from USA willing to distribute some tubes/sockets to europeans? We're still having difficulties with some stock (nice source though nisbeth, but very very expensive!)._

 

I will help you with tubes and sockets.


----------



## individual6891

Quote:


  Originally Posted by *comabereni* 
_I've listened to the 12AE6, 12AE6A, 12FK6, 12FM6

 -coma_

 

How do these compare? Are there audiogrades of these tubes? The only tube sources I've been looking at was tubesandmore.com and they seem pretty cheap.. but to be honest I don't know the status of tube suppliers over the pond


----------



## comabereni

Quote:


  Originally Posted by *individual6891* 
_How do these compare? Are there audiogrades of these tubes? The only tube sources I've been looking at was tubesandmore.com and they seem pretty cheap.. but to be honest I don't know the status of tube suppliers over the pond 
	

	
	
		
		

		
		
	


	


_

 

I believe Pete's reasoning behind using these tubes was due to their wide availability, low cost, and safety. I am not aware of recent iterations or better quality versions. As I understand it, they were designed for AM car radio back in their day and they sound fine. My Millett amp completely dominates a Grado RA-1 clone I also have, and many people swear by their RA-1. There is no contest. 

 As for how one tube compares to another, there have been several posts on this recently and I provided some links above. But summarizing here from my favorite to least favorite, I like the 12FK6, 12AE6A, 12FM6, 12AE6. I don't know where the 12AJ6 fits in yet, but should know later this week. These might be (though I'm not certain) all the tubes that work with this amp, but it's plenty. Even more, it's kind of exciting that they sound noticeably different from each other--the 12AE6A is clear, intimate and punchy, the 12FK6 sounds wide, deep and detailed, the 12FM6 is laid back and has a kind "traditional" tube sound like I remember from back when I was a kid, the 12AE6 (IMO) is like a weak 12AE6A, bass not as punchy or defined. I could be wrong about the 12AE6--haven't given it a careful listen recently.

 -coma


----------



## individual6891

The 12AE6A, 12FK6 and 12FM6 look very interesting. 
	

	
	
		
		

		
		
	


	




 Any idea how shipping to europe could be handled? What american sources are best for these tubes?


----------



## Nisbeth

Quote:


  Originally Posted by *individual6891* 
_It further complicates the circuit by adding unnecessary pads.. How many other PCB layouts have you seen with external pot pads in addition to it's PCB component?_

 

FWIW (and I know I'm a bit late), I also think the layout in post 61 looks much better. It's cleaner and less cluttered, and unless I absolutely needed the extra inch I could gain by chopping off the end of the pcb, why should I wire my pot to the end of an input trace that's nearly twice as long as the one going to the alps pads and criss-crosses through the entire amplifier? If the pot isn't going be mounted on board anyway, why not just wire the input directly to the pot? Bear in mind that the off-board pot mounting isn't the default option but only for "exotic" case styles and so you might have additional airwiring in the first place. Also, the only reason I can see for chopping off the end of the PCB is if you have a case that can only accept a board that's 135 mm wide. Since the pot takes up the same amount of space in the case regardless of where it's mounted, it will only be in very special circumstances that it will be any advantage to have a board that's smaller than Eurocard size, because in most cases the extra inch will not matter - even if the pot is mounted off-board 
	

	
	
		
		

		
		
	


	





 The layout from post #61 looks nearly perfect to me. The only minor changes I would suggest (and I'm being really anal here), is to move C5 and C6 slightly forward so the line up perfectly with C14 and C15 on the other side for better symmetry (I said I was being anal 
	

	
	
		
		

		
		
	


	




) and also add a ground pad next to the alternate input pads 
	

	
	
		
		

		
		
	


	




 Other than this little rant, great project and great work drew and nate 
	

	
	
		
		

		
		
	


	




 I'm looking forward to building this one (sometime) 
	

	
	
		
		

		
		
	


	





 /U.


----------



## n_maher

Nisbeth,

 Drew and I are taking your suggestion under consideration as it really does make a lot of sense. If people are really concerned about in correctly wiring the pot pads I'm sure that a diagram could be provided to make it more user friendly. 

 To the rest,
 The schematic schedule goes a little like this - with any luck independant review of the board will be completed early this week and the prototype boards will be ordered before the end of the week. It's then a min. of 5 days for production plus another couple days for shipment. I hope to have the full compliment of parts ready when the proto-boards arrive so that at least one working prototype can be assembled a week after that (3rd week of April). If all goes well with the testing of the prototype I think we might be looking at a production run sometime around the first week of May. I don't anticipate finding anything wrong with the prototype as the circuitry is essentially the same as the original PMH design but I'd rather be safe than sorry. 

 As always, I'll periodically update the thread with any relevant information.

 Nate


----------



## blip

Good stuff. Thanks for taking the lead on the design/testing.

 Do you have an estimate on the boards cost yet?


----------



## comabereni

I guess I don't understand why anyone should care if the board now permits different options--90-degree orientation, shorter length, custom cases, etc. As is, it's still the same size, still fits in the eurocard case, and the tubes are in the same place. Why limit it for those who might want to shorten the board and mount a pot or stepped attenuator between the tubes (above or below) and have it in as small a footprint as possible with the tubes equidistant from the pot and the edge? 

 For those planning to put theirs in a eurocard case, nothing that will be visible from the outside has changed--it just got a little more condensed, so unless it makes no sense from an electrical or an ease of construction standpoint, why would we want to undo work and eliminate options? I only made my recommendation because it was obvious the pot end of the board in #61 was already sparse and could see a cool alternate case option if the components were tightened up a little and alternate pot pads provided. Evidently Drew saw that as well or he would have ignored my suggestion.

 -coma


----------



## n_maher

Coma,

 The only reason that I can see to not follow your suggestions would be if it complicates the boards in a negative way. As I said, Drew and I are taking this under consideration, nothing final in any regard has been decided upon. As you said if it has no electrical or construction penalty its win/win for everyone. Drew is the brains behind this operation and I'll defer to him on this matter.

 Blip,

 Preliminary estimates put it in the $10 to $20 range (plus shipping costs). We won't know for sure until later on in the game. The prototype boards are going to be ordered from Drew's supplier at a cost of $19/ea but there may be a possibility of that going down for the group buy (if one forms). I'll do my best to find the cheapest, best option for that when the time comes. 

 Nate


----------



## individual6891

Quote:


  Originally Posted by *comabereni* 
_I guess I don't understand why anyone should care if the board now permits different options--90-degree orientation, shorter length, custom cases, etc._

 

The board is a lot more cluttered and complicated.. The track lengths are unnecessarily long just to accomodate this feature.

 Also read:
http://www6.head-fi.org/forums/showp...9&postcount=17

  Quote:


  Originally Posted by *amb* 
_
 Within an amp like the PPA or M³ where the volume control is board-mounted, and the pcb trace paths from the output of the volume control to the input of the active stage (the opamps) are short.

 This actually brings up an aspect of stepped attenuators that is worth considering. While the propect of precision resistors and great interchannel matching of a SA is a good thing, the large size of the SA almost always requires off-board mounting and hand-wiring, increasing the distance between it and the following active stage. This could lead to susceptibility of noise induction, reduced bandwidth and channel separation. So, if you use a SA, keep the wires as short as possible. For a purely passive preamp that is basically impossible to do, and this is why I don't really like the idea of a passive preamp._

 

...Sure, keeping the pot pads would have a small benefit and broaden options, but there are disadvantages involved too?

  Quote:


  Originally Posted by *comabereni* 
_why would we want to undo work?_

 

The original layout was completely reworked by drew, so I'm sure he doesn't mind such a small change and I'm sure he saves each revision. It's not simply down to that fact that work is being undone.. I mean if my opinion was to strap on octal pads because 7 pin sockets are difficult to source, then sure it's a benefit for me - but then again it's not necessarily the best option..


----------



## individual6891

If you move the RLED and LED pads behind the pot like you have done with #67, then it would allow a larger C2 size to match the other electrolytic diameters..


----------



## PhilipYork

I will order the revised PCB when it comes to a group order.


----------



## drewd

This is the latest board. I'm just tweaking things now. The only significant tweak that I did was to change the routing for the external pot pads so that they will have no effect if they are not used. There is a set of pads to be jumpered that will enable the external pot pads. If they are not enabled, they are out of the input circuit.

 My R&D buddies at my day job gave it a quick look and saw no problems. Of course, we're all high speed digital engineers, so all they were looking for were shorts or opens...they saw five inches of parallel trace and just about panicked.

 This is the last chance for changes, I think. Please let me know if you see anything that should be changed or if you think that I've done something wrong. 

 Take a look at Pete's web site for his write-up on the board, including the AudioXpress article.

Board Image 

Rendered Board 

 -Drew


----------



## Nisbeth

Drew, looks like you've come up with some thing everyone can be happy about 
	

	
	
		
		

		
		
	


	




 My only suggestions are really only minor:

 1) Put a pair of mounting holes on the left side of the board in what will be the corners of the board if you cut off the pot section.

 2) Reroute the trace that goes through the pins of C2 - there's plenty of space to go around it.

 3) (The really anal one 
	

	
	
		
		

		
		
	


	




) Move the R_BW jumper closer to the buffer. Then move R7 down and C12 a bit to the right to make the board symmetrical 
	

	
	
		
		

		
		
	


	





 /U.

  Quote:


  Originally Posted by *drewd* 
_My R&D buddies at my day job gave it a quick look and saw no problems. Of course, we're all high speed digital engineers, so all they were looking for were shorts or opens...they saw five inches of parallel trace and just about panicked._

 

Haha, one of my friends is an HF design engineer. His idea of a "low frequency" device is basically an FM-radio, so we're not always "on the same wavelength" so to speak when discussing circuit design


----------



## drewd

'Tis done!


  Quote:


  Originally Posted by *Nisbeth* 
_Drew, looks like you've come up with some thing everyone can be happy about 
	

	
	
		
		

		
		
	


	




 My only suggestions are really only minor:

 1) Put a pair of mounting holes on the left side of the board in what will be the corners of the board if you cut off the pot section.

 2) Reroute the trace that goes through the pins of C2 - there's plenty of space to go around it.

 3) (The really anal one 
	

	
	
		
		

		
		
	


	




) Move the R_BW jumper closer to the buffer. Then move R7 down and C12 a bit to the right to make the board symmetrical 
	

	
	
		
		

		
		
	


	



_


----------



## individual6891

Quote:


  Originally Posted by *drewd* 
_This is the last chance for changes, I think. Please let me know if you see anything that should be changed or if you think that I've done something wrong. 
 -Drew_

 

Any chance of increasing C2's diameter to match the other electrolytics? At the moment it looks like it's half (!!?!) the diameter of the others..


----------



## blip

The new board is excellent! Great balance of features v. simplicity... I'm impressed!

 Only comment is that (and maybe it is just the way it looks on the image) but it looks like some of the labels overlap each other making them a bit hard to read. I'm being too anal but, if you could reduce font or something to clean that up a bit that would be cool. (But like I say I'm being WAY too anal at this point)

 Yeah HF engineers are a world apart. They don't really see wires, they see antennas!


----------



## individual6891

Oh yeah, label the pcb components, c1 r1 etc.. Didn't notice this until blip pointed something similar out..


----------



## Nisbeth

Quote:


  Originally Posted by *individual6891* 
_Any chance of increasing C2's diameter to match the other electrolytics? At the moment it looks like it's half (!!?!) the diameter of the others.._

 

FWIW, I don't have problem with C2 being smaller than the rest of the caps. IMHO it looks better that way and a 16mm cap (which I'm guessing the others are) would have an insanely high voltage rating at that value - something which clearly isn't necessary. Short version - leave it be! 
	

	
	
		
		

		
			






 /U.

 EDIT: Blip, I've tried asking him what I should be paying attention to when laying out boards for 25 MHz digital circuits (HF in my world - DC with a bit of ripple in his...). His reply was basically "nothing"


----------



## drewd

Quote:


  Originally Posted by *individual6891* 
_Any chance of increasing C2's diameter to match the other electrolytics? At the moment it looks like it's half (!!?!) the diameter of the others.._

 

C2 and C11 are just cathode bypass caps - their value isn't critical and they are sized to fit an Elna Cerafine cap, which is about as boutique of a cap as you should need in this application.

 Nonetheless, I'll work at it a little bit and see if I can add a third pad to C2 and C11 to allow for a larger cap.

 -Drew


----------



## individual6891

I guess I just found it funny looking that it was so small compared to the rest, it's more of an asthetic problem than practical so only a minor comment 
	

	
	
		
		

		
		
	


	




 Else, it looks fine - still not 100% happy with the external pot "option", but heck, tis up to you in the end.

 Great work drew,

 -andy


----------



## comabereni

When it comes time to sourcing tubes, and anything that can be bought from the same vendor as those tubes (sockets?), I'd be happy to handle a group buy for these items. I am too inexperienced, and really too busy, to manage assembling the rest of the components, but I have bought various tubes compatible with this amp from a few different sources now--something like 40 or so tubes of the five known types that work, so I wouldn't mind taking care of this part. There may be no price advantage for United States buyers, but maybe it would make sense anyway for reasons discussed below. For our brethren in Europe, Asia, Australia, etc., there might be a price advantage. I made this offer to Andy/individual6891 up-thread, but am extending it to others now.

 I think everyone should at least have a pair of 12AE6A's and 12FK6's, not so much the 12FM6 unless you like real slow and laid back. Don't know about the 12AJ6 yet--hopefully soon. The 12AE6 is probably not worth looking at unless you just want it to try. These tubes come up all the time on Ebay--some are really cheap, like $1.10 for the 12FK6 and $3.00 shipping + .25 for each additional tube. Antique Electronics was also pretty reasonable and they probably also have the sockets we can use.

 Here's something else to consider--there is often no choice of brands when buying from these vendors. I honestly haven't been able to tell a difference between different brands in my somewhat limited rolling experience (to the point that all the tube pairs I use now are different brands from each other even though I have identical pairs to choose from sitting in storage waiting for these to burn out), but if we pool together to acquire a large stock of tubes, I can at least try to pair tubes together so you might not have to use one GE and one Raytheon. And when we run out of identical brands, I can continue to try to match internal plate geometries (I have noticed some 12AE6A's (for example) have a different internal plate geometery than a 12AE6A from a different manufacturer. In other cases, internal geometries are identical across two or three different brands of the same tube.) Most sellers won't be hassled with this--if you buy just a couple tubes, there's a good chance you'll end up with an unmatched set despite their claim to "try" to send you the same thing. When they do occasionally bundle tubes of the same brand together, they often ask more for these. I'll do it to the best of my ability as a favor to all of you. 

*EDIT (3/29): Perhaps if our order is large enough, I might be able to lean on a tube seller to ensure every tube has a mate so we only end up with like pairs. Even more, maybe I can get us a discount (not likely, but I'll ask). Otherwise, this might not be such an attractive thing for amp builders in the US if you can get the same price and have equal chances of getting matched tubes (or not) elsewhere. If I can't get a guarantee of matched tubes, one or two of you is bound to end up with unmatched sets, unless I buy several extra and take *all* the hits--i.e. more tubes than I need and none of them match 
	

	
	
		
		

		
		
	


	




.*

 Thanks,

 -coma


----------



## drewd

Quote:


  Originally Posted by *individual6891* 
_Oh yeah, label the pcb components, c1 r1 etc.. Didn't notice this until blip pointed something similar out.._

 

They are labeled - it may be a little hard to see on the layout because it's a little busy and the image isn't all that big. And they did not come out on the render, but they will be part of the silkscreen when it's manufactured.

 I'll push things around as best as I can to keep the text from overlapping.

 -Drew


----------



## skyskraper

one request id like to make but im not sure if space will permit it without moving some of the traces around, a second set of output pads. a trivial request i know, but it would be nice


----------



## cetoole

Going to have to watch this, looks great so far.


----------



## blip

comabereni, I might be interested in buying a tube set from you if you get that set-up. Keep us up-to-date as your plans develop.

 While we are talking about tubes, PM's site had an interesting link on low-voltage tubes that I haven't seen anyone mention: http://www.duntemann.com/12vtubes/12vtubesindex.htm. Looks like some good info.


----------



## skyskraper

did we decide what tube socket from tubesandmore we need?


----------



## guzzler

Regards the whole tube socket debate, remember you don't actually need a socket 
	

	
	
		
		

		
		
	


	




 check out sijosae's tube hybrid over at HeadWize to see the (cheaper) alternative. Won't be as durable, but easily replaced, and good to last if you're careful with it. 

 Individual, there will be somewhere in the UK that stocks the right tube sockets if you're concerned, just need to hunt a little 
	

	
	
		
		

		
		
	


	




 g


----------



## sijosae

guzzler, thanks. ^_^

 I found female pins of the D-sub connector fit exactly to the tube pins.
 I highly recommend following substitution. (As we know, Headwize is temporarily down.)


----------



## bg4533

That is a pretty good idea with the pins. I imagine at least some people want to chassis mount their tubes though.


----------



## CedMan

Looking good guys, please count me in for at least a couple.


----------



## individual6891

Quote:


  Originally Posted by *bg4533* 
_That is a pretty good idea with the pins. I imagine at least some people want to chassis mount their tubes though._

 

Looks like the tubes can also fit into those sockets..
  Quote:


 I found female pins of the D-sub connector fit exactly to the tube pins. 
 

Thanks Sijosae/Guzzler for the recommendation.

 By the way, thanks comabereni for organising the tube distribution.. Would help some people a lot, including meh!


----------



## n_maher

We are going to close the "suggestions" phase of this and limit any changes beyond this to minor tweaks. I think that we've gotten some really good feedback on board design and layout. Drew is finishing up the last of these and I think we'll see the final board layout sometime in the next day or so. Please hold requests for boards until an official "Group Buy" thread is started, which I don't expect to happen for the better part of a month. At this point we know that there is enough interest to support the minimum order size so it'll happen provided that the prototypes check out ok.

 Thanks for everyone's input and help on this.

 Nate


----------



## drewd

This is the final cut on the prototype:

Board Image

Board Render 

 I'm ordering the protos today from Imagineering. They have a five day turn on proto orders, so I should have them around the middle of next week. I'm ordering enough parts to build up two amplifiers and then I'll run them through my test gear and post the results. If all goes well and no significant changes need to be made, Nate should be able to open the group buy late next week.

 Thanks again to everyone who offered suggestions and encouragement!

 -Drew


----------



## individual6891

How about a tube illumination LED in the middle of the socket sijosae style? Looks like +v tracks are quite near this area, just the resistor to deal with..


----------



## skyskraper

yes very cool idea


----------



## Nisbeth

Quote:


  Originally Posted by *individual6891* 
_How about a tube illumination LED in the middle of the socket sijosae style? Looks like +v tracks are quite near this area, just the resistor to deal with.._

 

Good idea if the room is there. Consider using 1206 or 0805 LEDs and resistors to save some space 
	

	
	
		
		

		
		
	


	




 An additional advantage would be that most SMD LEDs have wider viewing angles than leaded ones 
	

	
	
		
		

		
		
	


	





 /U. 

 EDIT:Just remembered that 0805 LEDs fit nicely on a set of standard LED pads so you don't have to go the SMD route, even if it would still be helpful for the resistor


----------



## comabereni

Tube illuminating LEDs--very cool!! The 12FK6 glows nicely, but the 12AE6A and 12FM6 are pretty dim in comparison--nothing like a little red glow boost. I'd actually rather have that over an on/off LED.

 Hey, Drew doesn't need any sleep! 
	

	
	
		
		

		
		
	


	




 P.S. Drew, you shouldn't have posted an image of the final prototype--the suggestions will never end 
	

	
	
		
		

		
		
	


	




. Another obvious problem is that trace under the left tube--this might mean shuffling everything around again. Maybe you should call it done, Drew, but it's up to you. 
	

	
	
		
		

		
		
	


	




 Nate warned us only "minor tweaks"--not sure where this would fit with that, but it's cool.


----------



## skyskraper

ive seen a few tube amps with blue under the tube. the red + blue = cool


----------



## individual6891

Just having looked at the schematic, datasheet and the original pcb..

 I'm concerned over these components:

 C6/C15 - 0.01uF Ceramic
 C5/C14 - 0.22uF Film (Polyester/Polypropylene)
 C9/C18 - 100uF Electrolytic

 From the BUF634 datasheet:
  Quote:


 Power supplies should be bypassed with capacitors connected close
 to the device pins. 
 

and

  Quote:


 For best results, use a ground plane type circuit board layout
 and bypass the power supplies with 0.1uF ceramic chip
 capacitors at the device pins in parallel with solid tantalum
 10uF capacitors. 
 

The electrolytic is not a major problem, but the other 2 might pose a problem. They are very close on Pete's original layout and no where near on the alt design, somewhat worrying.

 If you look on the PIMETA layout using the BUF634, the bypass film caps are pretty much 10mm from it's pin.


----------



## dsavitsk

Quote:


  Originally Posted by *individual6891* 
_How about a tube illumination LED in the middle of the socket sijosae style?_

 

As long as they are optional. I find this kind of stuff a bit too tacky.


----------



## individual6891

And also, I can't believe I didn't mention this before..

 R/L Bias shouldn't be left as a jumper, instead a resistor pad should be used to control the bandwidth of the BUF634 chip. The chip benefits with about 220R resistance between BW pin (pin1 on the dip8 package) and ground. Distortion decreases as bandwidth goes up (by decreasing resistance) up to 220R, and then increases again as resistance drops below 220R. The R/L Bias jumper is essentially zero resistance.


----------



## Nisbeth

Quote:


  Originally Posted by *individual6891* 
_R/L Bias shouldn't be left as a jumper, instead a resistor pad should be used to control the bandwidth of the BUF634 chip. The chip benefits with about 220R resistance between BW pin (pin1 on the dip8 package) and ground. Distortion decreases as bandwidth goes up (by decreasing resistance) up to 220R, and then increases again as resistance drops below 220R. The R/L Bias jumper is essentially zero resistance._

 

You're right that measurements indicate the the BUF has lower distortion with 220R in the BW-pin, but you'll still find many people who will swear it sounds better at "full power". If you want to experiment, you can always tombstone a resistor on the jumper pads (even though it looks a bit stupid). Personally, I run my BUFs with BW shorted to V- whenever current consumption isn't an issue (and I intend to continue doing so 
	

	
	
		
		

		
		
	


	




 ) 


 /U.


----------



## 00940

I'd say the same for the film caps decoupling the power pins of the tubes. They're pretty far away while kept near the tubes on Pete's layout.

 It's difficult to see how continuous are your groundplanes from the posted pics. Could you export a pic with only the bottom and a pic with only the top ?


----------



## drewd

Quote:


 These bypass caps are no where near the buffer on the current design, somewhat worrying.

 If you look on the PIMETA layout using the BUF634, the bypass film caps are pretty much 10mm from it's pin. 
 

In practice, it is not a problem. For our bandwidth needs the buffers actually work quite well with no capacitors at all. In fact, if you look at the MINT schematic, there are no bypass caps at all. I've built quite a few headphone amps with no bypass caps with no audible or measurable performance issues.

 For high bandwidth implementations that use power and ground planes, the caps are necessary to decouple the induced high frequency noise on the planes from the power connections on the chip. They also resolve ground bounce problems. But in our application, neither of these should be a problem.

 Nonetheless, when I put the amp on a scope, that's one of the things that I'll be checking for. But the note that you saw on the datasheet is applicable to high frequency operations, such as video. We're nowhere near those frequencies.

 I'll thoroughly test the board with and without the caps and post the results.

 -Drew


----------



## individual6891

Quote:


  Originally Posted by *drewd* 
_
 I'll thoroughly test the board with and without the caps and post the results.

 -Drew_

 

Sounds great


----------



## drewd

Quote:


  Originally Posted by *00940* 
_I'd say the same for the film caps decoupling the power pins of the tubes. They're pretty far away while kept near the tubes on Pete's layout.

 It's difficult to see how continuous are your groundplanes from the posted pics. Could you export a pic with only the bottom and a pic with only the top ?_

 

Top of the board 

Bottom of the board 

 Gang, when I mentioned a page or two ago that we were finishing up the design, that was your cue to jump in with this sort of stuff. I can stop the proto order if this is something that is a really big problem, but it would be an awfully lot easier if these suggestions came up during the design process.

 Thanks,

 -Drew


----------



## 00940

Sorry, I honnestly didn't follow that thread earlier. The pcb as it is now is, more than probably, perfectly fine for audio frequencies. But you'll expose yourself to audio perfectionnists (unjustly perhaps). The Pete Millet's layout is more "audiophile attractive", with clearly seperated L/R section and a more continuous groundplane.


----------



## individual6891

Quote:


  Originally Posted by *drewd* 
_In practice, it is not a problem. For our bandwidth needs the buffers actually work quite well with no capacitors at all. In fact, if you look at the MINT schematic, there are no bypass caps at all. I've built quite a few headphone amps with no bypass caps with no audible or measurable performance issues.

 -Drew_

 

Soz about noticing this at the latest point, but personally my pimeta sounds better than the mint due to a huge number of a differences, who's to say this isn't one of them? I know it'd probably not make a difference in the end, but say someone compared the pmillet layout to this design, _some_ people (and i mean a very small number) will be able to hear the subtle differences due to the layout. I don't think I'm one of them "leet-ears", but it's nice to discuss possible improvements.

  Quote:


  Originally Posted by *Nisbeth* 
_you can always tombstone a resistor on the jumper pads (even though it looks a bit stupid /U._

 

I was going to do this initially (vertically mounting the resistor) so thats why I didn't bring it up but I dunno, IMO the BUF634 sounds better with a bandwidth limiting resistor, but it's probably personal opinion.

  Quote:


  Originally Posted by *drewd* 
_Gang, when I mentioned a page or two ago that we were finishing up the design, that was your cue to jump in with this sort of stuff. -Drew_

 

..Well the first design was only posted 4 days ago (post #37). Prototyping didn't even last a week, I'm not too surprised suggestions keep coming in..

  Quote:


 The pcb as it is now is, more than probably, perfectly fine for audio frequencies. 
 

..This is most probably true and I'd still happily invest in the PCB, but regarding the performance of the board, you never know


----------



## n_maher

Quote:


  Originally Posted by *individual6891* 
_
 ..Well the first design was only posted 4 days ago (post #37). Prototyping didn't even last a week, I'm not too surprised suggestions keep coming in.._

 

In my opinion the protyping process isn't over, it's just begun. We're going to test what appears to be a working configuration and report back. If there are issues we'll seek suggestions for change. You can rest assured that I'm not going to move forward with letting anyone else invest money in this project until I'm sure that it works, and works well at that. It'll be my money and that alone flowing down the toilet if modifications are needed to the prototype design. There simply will not be a group buy until several working protos have been built and tested in at least a few different configurations. But remember, we're building a stock Millet-Hybrid here, if folks want to break from the standard design they're on there own. I simply can't afford to test all the possibilities for people. 

  Quote:


  Originally Posted by *individual6891* 
_..This is most probably true and I'd still happily invest in the PCB, but regarding the performance of the board, you never know 
	

	
	
		
		

		
		
	


	


_

 

And I guess I'm willing to trust a guy who's not only tested versions of the PIMETA, MINT and others but who has designed and tested his own amps. I know for a fact that Drew doesn't take the idea of assigning his name to a project or product lightly, and neither do I. 

 The prototype order has been placed. The building will hopefully begin next week. I ask that you all be patient with this process as Drew and I both work full time jobs in addition to Head-Fi.

 Your humble tube-servant,

 Nate


----------



## blip

I think it should be just fine. As I understand it those caps are mostly just insurance at audio frequencies, we should be fine with a little more distance on them.

 Besides that (unless I'm missing something), if it is a problem then I think it could be fairly easily rectified by mounting them to the buffer pins themselves... just think of it like a gainclone. Maybe not cosmetically perfect but it shouldn't be a major eye-sore. (Esp. if you mount them on the back of the board).


----------



## individual6891

Quote:


  Originally Posted by *blip* 
_Besides that (unless I'm missing something), if it is a problem then I think it could be fairly easily rectified by mounting them to the buffer pins themselves... just think of it like a gainclone. Maybe not cosmetically perfect but it shouldn't be a major eye-sore. (Esp. if you mount them on the back of the board)._

 

If I wanted to do that, I'd have gone P2P.. but that isn't the point of this project.


----------



## drewd

OK, OK, I'm over my temper tantrum 
	

	
	
		
		

		
		
	


	




 I changed the layout to put the bypass caps adjacent to the parts that they are bypassing. The protos are on order and I'll have them on Wednesday. I've ordered enough parts to build two complete amplifiers.

 Regarding tubes and sockets: I ordered two 12AE6As ($4.95 each) and two 12FK6s ($3.95 each) from tubedepot.com. They also have the PCB mount 7 pin mini socket. I called them on the phone and they verified that the tubes will fit the sockets. I didn't talk to them about matching tubes.

 Price-wise, for two amplifiers, the parts bill was:

 Tubes and sockets: $30.00 (tubedepot.com)
 Generic electronic parts: $24.00 (DigiKey and Mouser)
 Elna and Wima caps: 51.50 (Welborne Labs)

 Total: $105.50 (for two amps' worth of parts), including shipping.

 Add in the cost of either the Pansonic EV-J or ALPS Blue Velvet pot, input and output jacks, switch, knob, enclosure and whatever else I've forgotten.

 A single amp should come in at around $100, plus the cost of the PCB, if you don't get too terribly extravagent with the accessories. 

 Pete Millett's BOM in the AudioXpress article is correct for the PCB except for R2 and R5 which are Bourns 3296W, DigiKey P/N 3296W-502-ND. External hardware is obviously not specific to the PCB.

 Thanks to everyone who is supporting this project!

 -Drew


----------



## individual6891

Quote:


  Originally Posted by *drewd* 
_OK, OK, I'm over my temper tantrum 
	

	
	
		
		

		
		
	


	




 I changed the layout to put the bypass caps adjacent to the parts that they are bypassing. The protos are on order and I'll have them on Wednesday. I've ordered enough parts to build two complete amplifiers.
_

 

Thanks a lot drew, do you have a layout / render of the new design?

  Quote:


  Originally Posted by *drewd* 
_
 Regarding tubes and sockets: I ordered two 12AE6As ($4.95 each) and two 12FK6s ($3.95 each) from tubedepot.com. They also have the PCB mount 7 pin mini socket. I called them on the phone and they verified that the tubes will fit the sockets. I didn't talk to them about matching tubes.

 Price-wise, for two amplifiers, the parts bill was:

 Tubes and sockets: $30.00 (tubedepot.com)
 Generic electronic parts: $24.00 (DigiKey and Mouser)
 Elna and Wima caps: 51.50 (Welborne Labs)

 Total: $105.50 (for two amps' worth of parts), including shipping.

 Add in the cost of either the Pansonic EV-J or ALPS Blue Velvet pot, input and output jacks, switch, knob, enclosure and whatever else I've forgotten.

 A single amp should come in at around $100, plus the cost of the PCB, if you don't get too terribly extravagent with the accessories. 

 Pete Millett's BOM in the AudioXpress article is correct for the PCB except for R2 and R5 which are Bourns 3296W, DigiKey P/N 3296W-502-ND. External hardware is obviously not specific to the PCB.

 Thanks to everyone who is supporting this project!

 -Drew_

 

Looking on target for the $100 price mark!

 I'd like to take this opportunity to thanking drew for making all this possible and putting up with our constant criticisms 
	

	
	
		
		

		
		
	


	




*[size=small]Thanks[/size]*


----------



## drewd

Ask and ye shall receive!

Rendered board 

Top 

Bottom 

Both Layers 

 This is not the very latest and greatest version - I rerouted the filament heater trace so that it does not split C2. To do that, I connected Pin 3 of VT1 to V+, routed Pin 4 to Pin 3 of VT2 and grounded Pin 4 of VT2 - just the opposite of how it had been connected. It cleaned the routing up quite a bit

 I know that the planes are a little bit broken up - I've tried to compensate for that by liberally sprinkling vias all over the place. The board is at the shop and the finished protos will be back next Wednesday.

 -Drew


----------



## doobooloo

Very interesting!


----------



## comabereni

Quote:


  Originally Posted by *drewd* 
_Ask and ye shall receive!
 -Drew_

 

Gorgeous! I can hardly wait...


----------



## drewd

A preliminary BOM is at http://www.shellbrooklab.com/hybrid. The BOM that Pete has on his website and in the article has the wrong part numbers for the electrolytic caps.

 This is the BOM that I am going to use to build the first couple of protos. I'm more than amenable to suggestions for alternate parts and I'd be happy to adjust the BOM to reflect them.

 Thanks again to everyone for the great input!

 -Drew


----------



## Nisbeth

Looks good 
	

	
	
		
		

		
		
	


	




 What lead spacing do you have on the board for the Wima caps? Welborne claims it's 38 mm which is clearly incorrect (unless it's 1600V and not 160V). The ones I have on hand are 15mm LS which matches the information on Wima's website. Perhaps you could update the BOM with size/LS-information for each part?


 /U.


----------



## slindeman

Thanks for the hard work drewd!

 Some alternative parts and/or distributors:

 C3-C5, C8, C12-C14 - Digikey P3224-ND (.22uF 50V 2% Panasonic Polypropylene 15mm ls, 20mm x 9.5mm body)
 C3-C5, C8, C12-C14 - Mouser 1429-2224 (.22uF 250V Xicon Metallized Polypropylene 15mm lead spacing)
 C6, C15 - Mouser 80-C410C103K5R
 D2 - Mouser 511-P6KE30A
 PF1 - Mouser 650-RXE050
 R2,R6 - Mouser 652-3296W-1-502

 You left off the buffers from the list, and the potentiometer. You also might want to mention that they will want a switch and possibly an LED

 Some general thoughts on parts:

 For those that want to save money, use Panasonic FC or FM for the PS caps and just buy boutique caps for the output coupling caps (C7 and C16). Other candidates for boutique parts are the buffer output resistors (R4 and R9). Those resistors can also be jumpered for those that want low output impedance. 

 For the output caps I used Nichicon Muse KZ 470uF 50V. I think you definitely want higher than 100uF if you will use low impedance headphones with this. With 32 ohm headphones and 100uF caps you would get 3db down at 50Hz for the high-pass filter.

 Pete has said that 50V caps are fine for every cap on the board. I bet 35V would even suffice. I mean there's only 24V-30V on the board anyway.


----------



## comabereni

Quote:


  Originally Posted by *drewd* 
_A preliminary BOM is at http://www.shellbrooklab.com/hybrid. The BOM that Pete has on his website and in the article has the wrong part numbers for the electrolytic caps.

 This is the BOM that I am going to use to build the first couple of protos. I'm more than amenable to suggestions for alternate parts and I'd be happy to adjust the BOM to reflect them.

 Thanks again to everyone for the great input!

 -Drew_

 

Thanks Drew. We've had mentioned in this thread several times allowances on the PCB for various upgraded components--it might be nice if the BOM also mentioned the optional upgrade components to do a maxed out version, for those us too inexperienced to properly identify and remember to order the alternate parts.

 -coma


----------



## comabereni

I've started to contact tube sellers I've dealt with to find out what stock they have on hand of the 12AE6A and 12FK6. I am asking that all tubes be matched pairs and for a price discount for a larger order. Right now I'm just getting an idea of what can be bulk purchased before I pull the trigger. Also, I've only contacted the first seller on my list so far--will see what he says before moving down the list.

 Those prices listed by Drew of $4.95/ea and $3.95/ea are probably 2x to 4x what they can be purchased for elsewhere even without a discount, but tubedepot.com might still make sense if combined with other parts for shipping. I'm attempting to save everyone ~$10.00 off those prices for four tubes you'll want anyway and will work to guarantee matched sets. If I am successful with the tubes, I'll also order the tube sockets so you can get these things from me and save $$.

 Will let you know what I find out.

 Thanks,

 -coma


----------



## bg4533

What is the max voltage PSU that will work with this amp? I see 24V is the default. Some have said 28V is better. Will 30V work? I have a few Elpac WM071s that should work well if so.

 Tangent just released his Tread regulator board. It should be a nice and cheap power supply option. It looks like it should be under $25 (not including case) , easy to build and should outperform the Elpacs and other wallwarts.


----------



## dsavitsk

Quote:


  Originally Posted by *bg4533* 
_What is the max voltage PSU that will work with this amp? I see 24V is the default. Some have said 28V is better. Will 30V work? I have a few Elpac WM071s that should work well if so.

 Tangent just released his Tread regulator board. It should be a nice and cheap power supply option. It looks like it should be under $25 (not including case) , easy to build and should outperform the Elpacs and other wallwarts._

 

With the first Millett I built, I initially used the PS suggested by Pete. (I later built a STEPS and the improvement was dramatic. I am actually putting my steps in a buffered passive pre I am building, so the Millett is going to get a Vellman next) 

 Anyhow, out of curiosity I measured the wallwart. It turned out to be 32V, notwithstanding that it says 24V right on it. I didn't notice any ill effects from running the amp at 32V, but YMMV.

 -d


----------



## comabereni

Quote:


  Originally Posted by *bg4533* 
_What is the max voltage PSU that will work with this amp? I see 24V is the default. Some have said 28V is better. Will 30V work? I have a few Elpac WM071s that should work well if so._

 

Pete's original article says: "The supply does not need to be regulated; any voltage between 20V and 28V is fine." That said, I ran mine at 30V for some time with no ill effects, but my PSU is regulated. The Millett amp doesn't like 36V I found out. The tubes glow nice and pretty--until they start to "sizzle", "crackle" and "pop" (like a breakfast cereal, I suppose). 
	

	
	
		
		

		
			





. Of course I'm replying based on my experience, not on an analysis of the circuit's components. I'll leave that for someone else.

 -coma


----------



## dsavitsk

Quote:


  Originally Posted by *bg4533* 
_It looks like it should be under $25 (not including case)._

 

I think you are a little low here. The PCB is $5, shipping from Tangent is a few bucks, the transformer is $16, shipping from DigiKey will be at least 4, so without the rest of the parts, it is already pushing $30. This is still cheap, but I would guess more like $40 to do it right. Of course, if you are ordering other stuff from both Tangent and DigiKey/Mouser, you can save a bit on shipping -- but it is still more like $30 for parts.

 -d


----------



## comabereni

I settled on Astron linear regulated PSU's for most of my audio equipment and have a stack of them on the floor next to my PC. For the Millett amp, I went with the LS-18A. It is a 28VDC PSU that puts out, as the model # indicates, something like 18A. I bought it cheap, around $25 + shipping on Ebay. It's overkill for one amp and they are ugly if you need to put yours on a desktop or in a rack, but these used supplies are inexpensive for linear regulated power without having to DIY. They are also variable within a certain range, though I don't know what that range is.

Looking at this page, I see there are 10A and 4A versions of this PSU. They would be very inexpensive on Ebay. I suspect most of you guys probably want to DIY your own power supplies, but if not, these are good and cheap off Ebay when they come available.


----------



## bg4533

Quote:


  Originally Posted by *dsavitsk* 
_I think you are a little low here. The PCB is $5, shipping from Tangent is a few bucks, the transformer is $16, shipping from DigiKey will be at least 4, so without the rest of the parts, it is already pushing $30. This is still cheap, but I would guess more like $40 to do it right. Of course, if you are ordering other stuff from both Tangent and DigiKey/Mouser, you can save a bit on shipping -- but it is still more like $30 for parts.

 -d_

 

I figured using the 500ma AC wallwart from Mouser that Tangent has listed should be fine. It only costs $5.89

 I ignored shipping in my estimates too. I usually order stuff for multiple projects at a time, so I just tend to ignore shipping costs when talking about a single project.


----------



## individual6891

Quote:


  Originally Posted by *comabereni* 
_I've started to contact tube sellers I've dealt with to find out what stock they have on hand of the 12AE6A and 12FK6. I am asking that all tubes be matched pairs and for a price discount for a larger order. Right now I'm just getting an idea of what can be bulk purchased before I pull the trigger. Also, I've only contacted the first seller on my list so far--will see what he says before moving down the list.

 Those prices listed by Drew of $4.95/ea and $3.95/ea are probably 2x to 4x what they can be purchased for elsewhere even without a discount, but tubedepot.com might still make sense if combined with other parts for shipping. I'm attempting to save everyone ~$10.00 off those prices for four tubes you'll want anyway and will work to guarantee matched sets. If I am successful with the tubes, I'll also order the tube sockets so you can get these things from me and save $$.

 Will let you know what I find out.

 Thanks,

 -coma_

 



 Anyword on the 12FM6?

 What distributors have you been looking at?

 Can't wait to hear word on tube/socket prices - the key to this project


----------



## comabereni

Quote:


  Originally Posted by *individual6891* 
_Anyword on the 12FM6?

 What distributors have you been looking at?

 Can't wait to hear word on tube/socket prices - the key to this project 
	

	
	
		
		

		
		
	


	


_

 

So far I've only contacted Walt "radiotinkerer" Eby, seller on Ebay. He is looking through his cache of tubes to see what he can dig up. If I don't hear from him soon (tonight), I'll broaden my search to include more Ebay sellers in search of several paired tubes at a discount price (or not). 

 I mentioned to Walt primarily wanting 12AE6A's and 12FK6's, but that I might want a few 12FM6's as well. I know some of you want to try this tube just to try it, but I can almost guarantee it will not see much use if you have 12AE6A's and/or 12FK6's. It just isn't in the same league.

 Someone come to a decision about which socket will satisfy most of us so I can prepare to order if/when I find tubes. I'd personally like a socket with gold contacts if there is one--or at least something *not cheap* that I don't have to question every time I insert a tube.

 I will organize a hasty group buy when I find tubes so I don't overbuy. I've got enough tubes for my own personal use already.

 -coma


----------



## drewd

Tubedepot.com sent matched sets - two RCA 12AE6As and two GE 12FK6s. comabereni is right, they are kind of expensive, but I didn't really check around much for prices.

 I'll start working on some alternate parts for the BOM in a few minutes as well as posting the specs for the component sizes.

 -Drew


----------



## dsavitsk

Quote:


  Originally Posted by *comabereni* 
_I mentioned to Walt primarily wanting 12AE6A's and 12FK6's, but that I might want a few 12FM6's as well. I know some of you want to try this tube just to try it, but I can almost guarantee it will not see much use if you have 12AE6A's and/or 12FK6's. It just isn't in the same league._

 

Interestingly, this is, or can be, very power supply dependent. When I was using the PS suggested by Pete, the 12FM6 was far superior to the 12AE6A. The 12AE6A was harsh and bright while the 12FM6 was smooth and pleasant. When I switched to the STEPS, the sound was similar to how you describe with the 12AE6A being the superior tube.

 -d


----------



## drewd

I've updated the web page with some additional parts recommendations and links. I still have a few things to add, but it's getting late and I'm getting sleepy. I keep thinking that if I didn't waste a third of my life sleeping I could get so much more done!

 -Drew


----------



## comabereni

Quote:


  Originally Posted by *dsavitsk* 
_Interestingly, this is, or can be, very power supply dependent. When I was using the PS suggested by Pete, the 12FM6 was far superior to the 12AE6A. The 12AE6A was harsh and bright while the 12FM6 was smooth and pleasant. When I switched to the STEPS, the sound was similar to how you describe with the 12AE6A being the superior tube.

 -d_

 

I never listened to 12AE6A's or 12FM6's with the 24V wall-wart since I switched to 28V linear before I bought them. I still have a 24V unit--I should use it again to see for myself what happens with all the different tubes. I only listened to 12AE6's with 24V and never noticed deficiencies, but now think the 12AE6 sounds inferior to almost everything. Maybe the 12AE6 and 12FM6 really shine with the cheap psu's.

 This psu-dependent tube issue casts doubt on every conclusion I've come to about tubes with this amp 
	

	
	
		
		

		
		
	


	




 (except that the amp running at around 28V really sings with the 12AE6A and 12FK6--that much is certain).


----------



## comabereni

Deleted nonsense to keep ever-growing thread readable.


----------



## drewd

By the way, if you haven't figured it out from the board layout, these tubes are small. Very, very small:


----------



## doobooloo

Quote:


  Originally Posted by *drewd* 
_By the way, if you haven't figured it out from the board layout, these tubes are small. Very, very small:






_

 

Cute!


----------



## blip

Just did a Mouser only bill of materials for the amp. (Baisically, I was trying to see how cheap it could theoretically be made for and still use somewhat decent components) It covers everything except resistors (which you may already have laying around), tube stuff, powersupply and volume control (still trying to find the best one at Mouser). Enjoy:

 C1, C7, C9, C10, C16, C18, C19
 Nichicon UVR Radial Electrolytic 50V 100Uf 8X11.5 (647-UPR1H101MPH)
 .45/each

 C2, C11Nichicon UPW Radial Electrolytic 25V 220uF 8x11.5 (647-UPW1E221MPD)
 .50/each

 C3-C5, C8, C12-C14, C17 
 Vishay/Roederstein Metallized Polyester Film 0.22uF 63V 5% (75-MKT1817422064)
 .34/each

 C6, C15
 Kemet Molded Axial Ceramic Capacitors 50V X7R 0.01uF 10% (80-C114C103K5R)
 .24/each

 D2
 Vishay Semiconductor Transient Voltage Suppressors DO-204AC 600W 30V Unidirectional (625-P6KE30A)
 .15/each

 D3, D4 
 Central Semi Diodes DO-35 .56mA Current Regulating Diode (610-1N5291)
 1.78/each

 PF1
 Raychem Radial Lead Resettable Fuses Crimped Radial Lead .5A 72V 40A Imax (650-RXE050)
 .54/each

 R2, R6
 Bourns Multi-Turn Trimmer Potentiometers BULK 3/8" 5Kohms Sealed Vertical Adjust (652-3296W-1-502)
 2.20/each

 IC1, IC2 
 Texas Instruments Amplifiers DIP-8 High-Speed Buffer (595-BUF634P)
 6.45/each

 Total28.90


 Personally I'd rather order from Digikey (for Panasonic caps and volume control) but I couldn't find an equivalent for the current regulating diode 
	

	
	
		
		

		
		
	


	




. 

 Anyway, $30 before shipping for most of the non-tube guts of this amp is pretty good. If we get the PCB price low, this could become the new budget favorite.


----------



## .: ZMN :.

Just out of curiosity,

 is there a possibility in the design for the tubes to be installed on the back side of the PCB or does that not make much sense? 

 I thought with reverse mounting the tubes, they can stick out as far as possible from the enclosure. Looks cool, and would cool them better as well. All other parts would then face downwards. 

 I've had some experience lately with building a tube headamp and found that the big capacitors were in the way; the tubes were only sticking outside the enclosure 1/3th of their height, so i had to make larger holes to get decent ventilation.

 I guess it can be done by mirroring part of the design, but I am no expert on what can or cannot be done with PCBs.


----------



## comabereni

*Tube Search Update*

 I sent emails to the following tube sellers this morning:

 - Antique Electronic Supply (www.tubesandmore.com)
 - "Heavenly Tubes and More" (ebay seller)
 - "the-radio-tube-supply-company" (ebay seller)
 - "radiotinkerer" (ebay seller, followup email)
 - "CJ's Tube Supply" (ebay seller)

 I asked each seller for matched brand pairs and a price discount based on an estimate of 25 pairs of the 12AE6A and another 25 pairs of the 12FK6, plus a few of the 12FM6 and 12AJ6. 
 __________________________________________________ _________

 Word back from the-radio-tube-supply-company:

 [size=x-small]*"ALL TUBE PRICES ARE LISTED AT www.radiotubesupply.com THAT IS THE WAREHOUSE.I DO NOT OFFER A DISCOUNT ON THESE TUBES,MOST ARE ONLY ABOUT $3.00 TUBES NEW,AFTER PULLING THEM AND TESTING THEM,THE TIME INVOLVED IS HARDLY WORTH THE $3.00 I CHARGE. I DO NOT MATCH TUBES ON A TUBE TESTER ANYMORE WE USED TO AT $5.00 A MATCHED SET,BUT IT BACAME TO PAINFULL AND TO MUCH TIME,BEST I CAN DO IS MATCH BRANDS,BUT ONCE AGAIN I DO NOT LIKE DOING THAT EITHER.I SIMPLY SELL TUBES BY THE NUMBER,AT OVER 300 EMAILS A DAY AND NEAR 100 BOXES TO PACK A DAY I HAVE LITTLE TIME TO GO HUNTING. THE GIRLS IN THE WAREHOUSE ARE NOT ALLOWED TO HUNT THROUGH THE TUBES AND SORT BY CONSTRUCTION ECT. THANK YOU,roy 

 ROY GOLDEN 
 23 DELAWARE AVE. 
 POLAND OHIO 
 44514 
 USA 
www.radiotubesupply.com "*[/size]

 I emailed him back about specific availability and the cost of shipping a medium sized box of tubes and Roy said he should have all the tubes we need at $3.00 ea and $12.00 shipping for each lot of ~50 tubes. 

*"I SHOULD HAVE THE TUBES,IN PAIRS,WHEN YOUR READY MAKE ME A LIST,BETWEEN 5 WAREHOUSES I WILL FIND THEM.SHIPPING FOR 50 SMALL TUBES IS ABOUT $12.00 OFF HAND.LET ME KNOW WHEN YOUR READY. THANK YOU,roy"
*
 __________________________________________________ _________

 Word back from Heavenly Tubes and More:

*"Thank you for your interest in my items. All that I have to sell is listed in my store - not nearly the quantities you are looking for - in fact all I have from your list are three 12AE6's.

 Good luck,
 Kim
 heavenlytubes"
*
 __________________________________________________ _________

 Word back from radiotinkerer:

*"I am doubtful that I will be able to offer much, if any, help. This is a hobby, and most items are acquired in small quantities at auctions, estate sales, Hamfests, etc."
*
 __________________________________________________ _________

 Word back from CJ's Tube Collection (ebay seller):

*"Sorry I have nowhere near the quantities you need. Regards, Chris"*

 __________________________________________________ _________

 Word back from Antique Electronics:

 "The only tube we have is the 12AE6 that we can come up with that may
 pairs at $3.10 per tube. Dwight"

 __________________________________________________ _________


*[size=small]Conclusions[/size]*

 I think the group-buy isn't going to happen. It is looking like we can score super cheap tubes on Ebay, but not in large quantities. Or we can score large quantities, but not at the best prices. No one wants to give a discount, so you'd might as well buy them directly.

 What I recommend (from least to most expensive):

 1) Keep your eyes on Ebay for the cheapest tubes and buy extras for your friends out of the U.S.

 2) Buy from Antique Electronics with their rather low prices. I think I bought all but their last 12FK6 a couple weeks ago. Also, all six 12FK6's I received were a different brand. Here's a list with their prices:

 12FK6 - $1.40
 12AE6A - $3.10
 12FM6 - $1.80
 12AJ6 - $2.50

 3) Buy from Roy at www.radiotubesupply.com with his 5 warehouses and tubes at $3.00 each. It appears he can keep us in reasonably priced tubes for a long time to come.

 4) Buy from www.tubedepot.com when you order your sockets. Higher prices, but you can get everything at the same time for convenience and also combine shipping.

 5) Keep looking 
	

	
	
		
		

		
		
	


	




. PARTS CONNEXION might have what you need, but I'm too tired to search through their PDF format catalog and don't see a search box.

 Finally, I didn't check with Antique Electronics regarding socket availability. If they have the sockets and tubes in stock, they are probably the best one-stop shop for these items with the best overall shipped price.

 -coma


----------



## sbelyo

Roy is a good guy.... Actually I like buying tubes from him more than anyone else. He responds very quickly consdiering the volume (700,000 a year) of tubes he sells. If he does have the time he will match the brands for you. I just bought 6 six sets of different brands of 12fm6 and 12fk6. IMO the 12ae6 isn't worth owning more than one pair to just see if the circuit works. The 12FK6 is where the detail is for sure. The 12FM6 is somewhere in between. Although I haven't rolled all my fk's and fm's through the circuit yet.


----------



## comabereni

Quote:


  Originally Posted by *sbelyo* 
_Roy is a good guy.... Actually I like buying tubes from him more than anyone else. He responds very quickly consdiering the volume (700,000 a year) of tubes he sells. If he does have the time he will match the brands for you. I just bought 6 six sets of different brands of 12fm6 and 12fk6. IMO the 12ae6 isn't worth owning more than one pair to just see if the circuit works. The 12FK6 is where the detail is for sure. The 12FM6 is somewhere in between. Although I haven't rolled all my fk's and fm's through the circuit yet._

 

And I notice Roy doesn't list the 12AE6A separately from the 12AE6, so it might be difficult to get ahold of the "A" from him. He replied regarding this question with: *"12AE6,OR 12AE6A,I DO NOT KNOW HOW MANY I HAVE OF A TYPES .THANK YOU,roy"*

 IMO, the 12AE6A is the "sweetest" sounding of all the tubes--it's really special, but I still think I like the 12FK6 best. Actually, it's probably genre dependent.

 -coma


----------



## sbelyo

Quote:


  Originally Posted by *comabereni* 
_And I notice Roy doesn't list the 12AE6A separately from the 12AE6, so it might be difficult to get ahold of the "A" from him. He replied regarding this question with: *"12AE6,OR 12AE6A,I DO NOT KNOW HOW MANY I HAVE OF A TYPES .THANK YOU,roy"*_

 

I got a pair of westinghouse 12AE6A's from him

  Quote:


  Originally Posted by *comabereni* 
_IMO, the 12AE6A is the "sweetest" sounding of all the tubes--it's really special, but I still think I like the 12FK6 best. Actually, it's probably genre dependent.

 -coma_

 

I'll have to give the 12ae6a another listen with the steps 1.2 I just built. What's your supply voltage and bias when you listen with the 12ae6a?


----------



## comabereni

Quote:


  Originally Posted by *sbelyo* 
_I'll have to give the 12ae6a another listen with the steps 1.2 I just built. What's your supply voltage and bias when you listen with the 12ae6a?_

 

Supply voltage has been 27.8V for awhile. I usually bias the tubes at ~18V. I'm using one GE and one Tung-Sol right now. I think I remember reading you get a little extra headroom before clipping biasing the tubes at the upper end of the range, so haven't really tried any of my tubes much below 17V and can't comment on that affects how they sound. The 12AE6A set like I have it is my wife's favorite--I must admit it really sounds sweet.

 When I get some time after my 12AJ6's arrive, I'll do a comprehensive shootout to include all the tubes, varying bias levels, switching between ~28V linear and 24V wallwart, etc.

 -coma


----------



## Thaddy

Comabereni, I suggest you give the guys at http://www.vacuumtubes.net/ a call. This is who I use to get my tubes, and they are $2 a pop, with an extra $2 fee if you want them matched. It seems they have a bug stock too, so maybe they can offer a discount? Maybe just by waiving the shipping fee or discout the matching fee? I've only dealt with them about 4 times, but everytime I call back and say "Hey, it's Zack, I'm looking for new tubes!", they instantly recognize me from my previous purchases. 

 I saw the 4 places you sent email too weren't very helpful, so hopefully my friends at Radio Electric Supply can help


----------



## comabereni

Quote:


  Originally Posted by *Thaddy* 
_Comabereni, I suggest you give the guys at http://www.vacuumtubes.net/ a call. This is who I use to get my tubes, and they are $2 a pop, with an extra $2 fee if you want them matched. It seems they have a bug stock too, so maybe they can offer a discount? Maybe just by waiving the shipping fee or discout the matching fee? I've only dealt with them about 4 times, but everytime I call back and say "Hey, it's Zack, I'm looking for new tubes!", they instantly recognize me from my previous purchases. 

 I saw the 4 places you sent email too weren't very helpful, so hopefully my friends at Radio Electric Supply can help
	

	
	
		
		

		
		
	


	


_

 

Hey Thaddy-- I think I'm done now. Those prices are pretty low, just a little more than Antique Electronics for some tubes, a little less for others, and it also appears they'll sift through their stock. Perhaps it makes more sense for U.S. builders to deal directly and for non-U.S. builders to make a buddy over here willing to buy local and ship overseas as this rolls out. I think inexpensive tube acquisition will be easiest in smaller groups/quantities. After being chastised for asking for a discount on $3 tubes, I think I would feel silly asking for a discount on $2 tubes 
	

	
	
		
		

		
		
	


	




. Still, if anyone else wants to give it a try...

 My overseas tube buddy is individual6891. I'm planning to sell him matched tubes from my personal stash 
	

	
	
		
		

		
		
	


	




.

 -coma


----------



## comabereni

The 12AJ6 doesn't work. 

 At least not in my original Millett hybrid set at ~28V. Loud, "scratchy" distortion when adjusting the pot, significant "hissing" sound in the background behind the music, which music only plays at diminished volume. As gain is increased, the bias on the tubes also climbs until it maxes out and then the sound goes from "thin" to heavily distorted.

 So, add this tube to the 12EL6 as non-compatible. It did occur to me with sbelyo's recent observations that tube sound quality might possibly be supply voltage dependent that this tube might play nice at a lower (or higher) voltage within a range the rest of the components on this board could withstand without starting to smoke. Perhaps the 12EL6 too (?), I don't know. Problem is my PSU is on the bottom of a heavy stack of PSUs and the case must be unscrewed to get access to the voltage pot. and it's more than I have time for this afternoon.

 Finally, I cracked open a new pair of Tung-Sol 12AE6's (non-"A" version) and they sound pretty nice biased at 18V and ~28VDC supply. So perhaps my earlier observation that this tube is clearly inferior to its 12AE6A brother is unsupported--maybe it was the Raytheon tubes I was using, or poor memory, or both, or neither, or some combination thereof 
	

	
	
		
		

		
		
	


	




. (EDIT: Shortly after writing these new impressions on the 12AE6, my wife walked in the room and asked what tubes were in since the music now sounded "muddy". 
	

	
	
		
		

		
		
	


	




 I give up.--just get the 12AE6A 
	

	
	
		
		

		
		
	


	




).


----------



## sbelyo

I think the problem with the aj, and el's is that they want more than the 0.56 ma of current. I'll wait for this new board to foo,a round with my idea as $40.00 from diycable is a little steep for building one to mess around with. I'll be tube rolling tomorrow with a few sets I bought from roy. Power supply will be a steps at 24V and headphone will be HD-580's

 We'll see what happens.


----------



## klappar

Anyone know if there are any matching tubes from Russian/Soviet product lines for this amp? In Europe they migth be easier to find.


----------



## art633

Perhaps we should all step back a bit and remember what these tubes where designed for!
 Automotive, 12v ( well 13.8 fully charge – if my brain cell is correct ) so running at 28v or more could be a problem. In the Millet design with the heaters and ‘HT’ supply being common then these higher voltages will result in short tube life AND in the case of AL’s & EL’s distortion. 

 With a maximum plate potential of 30volts and 11 to 14 volts (12.5v recommended) - data from RCA circa 1959 Pete has got it right - 24v PSU.

 My experiences with space charge tubes like these is, 24v is the max or better still 18v with a higher plate current of .8 to 1.2mA. OK so it is VERY tube dependant we need to play around a lot.

 Check out the data sheets at http://hereford.ampr.org/cgi-bin/tube?tube=
 or see Blip's link in post #101

 Great work Drew and everyone else, I'm in for some PCBS too if managment (my wife) approves!

 Martin


----------



## sbelyo

I often wondered about decreasing the voltage and increasing the current as well. It's definitely something to play with when I finish all my projects.

 I aslo gave the 12ae6a another listen @24Vdc and 18V bias setting. I now like it. I would say it's equal to the 12fm6.

 Also I don't really think matching these tube is that important in this circuit, No? As long as they're the same brand, I think that's good enough.


----------



## individual6891

Just to let you guys know. Pete's moved his pages.

 New homepage is at:

http://www.pmillett.com/

 Hybrid pages are here:

http://www.pmillett.com/hybrid_head.htm


----------



## art633

Quote:


  Originally Posted by *sbelyo* 
_Also I don't really think matching these tube is that important in this circuit, No? As long as they're the same brand, I think that's good enough._

 

I sure agree with that. Same brand, same construction etc..... where are not talking "hi-end".


----------



## comabereni

Quote:


  Originally Posted by *art633* 
_I sure agree with that. Same brand, same construction etc..... where are not talking "hi-end"._

 

Pete says on this page :

 "Anyway, so far I've had really nice results using a 12AE6A triode, running on a B+ of 36V, with a plate load of a 1N5291 0.56mA constant-current diode! Gives a gain of 10, fairly low output impedance, and runs right to the rails before clipping... but still has nice single-ended-triode distortion characteristics, on the order of 0.2% at 1V RMS output."

 -coma


----------



## sbelyo

I would think that because we can adjust the bias that matching isn't really that key. Usually people match tubes because of fixed bias values, or re-tubing an old circuit or a pair of mono amps.


----------



## art633

Quote:


  Originally Posted by *comabereni* 
_Pete says on this page :

 "Anyway, so far I've had really nice results using a 12AE6A triode, running on a B+ of 36V, with a plate load of a 1N5291 0.56mA constant-current diode! Gives a gain of 10, fairly low output impedance, and runs right to the rails before clipping... but still has nice single-ended-triode distortion characteristics, on the order of 0.2% at 1V RMS output."

 -coma_

 

I read that too. In my experience( some 30+ yrs ) with low volt tubes running at hi plate levels decreases their life VERY rapidly. Maybe depends on make. I know some of pentodes in the same group (eg 6AQ5/EL95 at 180v one of my favs) can run hi, but the ones we're looking at here will not. 

 M


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## drewd

The proto boards are sitting on the front porch. And I'm sitting at my desk at work... 
	

	
	
		
		

		
			





 I'll post some pictures later tonight...and start building tomorrow.

 -Drew


----------



## drewd

The protos are in!

Top 
Bottom

 I've gone over them pretty closely and I don't see any electrical problems. I haven't received the parts from Welborne Labs yet, but I'll build one up as much as possible tomorrow.

 The silkscreen layer needs some work as far as organizing and updating a couple of things.

 I'll keep everyone posted!

 -Drew


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## comabereni

hubba hubba 
	

	
	
		
		

		
		
	


	




. This is going to be FUN. (I assume you noticed Pete's new web address announced up-thread).

 -coma


----------



## individual6891

Initial board looks good..

 Just some things to notice:

 The LEFT Input trace isn't 100% straight

 Also some traces could be routed better


----------



## comabereni

Since this seems to be the primary Millett amp thread lately, I thought I'd mention how great this amp is as a preamp. My 1212m arrived yesterday and I thought I'd try the card connected directly to my Tripath/T-amp. Okay, but not great. Putting the Millett hybrid (back) in the chain takes the T-amp to a whole new level of performance. I have always been happy with my office system: AV710 --> Millett --> T-amp --> Paradigm Atoms. Same goes now for the 1212m. Drew told me we should be able to wire these new boards for preamp duty.


----------



## skyskraper

mmm i might have to build one as a pre and one as a hp amp. 

 care to post the instructions for making it a pre?


----------



## drewd

Things got a little slow at work today, so I put one of the protos together in the lab. I'm still waiting for the film caps from Welborne, so there are no bypass caps in the circuit. And, naturally, the CRD for the right channel is bad, so the plate voltage is zero and...no output from that channel. But the left channel works 
	

	
	
		
		

		
		
	


	




Photo 1 
Photo 2 
Thar she glows 

 There are a couple of small problems on the board. One is that the Panasonic pot is not properly grounded. That's fixed. The other is that the silkscreen layer is a little bit disorganized. I'm working on that now.

 I'm going over the board again with an eye toward individual6891's comments.

 Skyskraper, as far as making the amp work as a preamp, you should not have to do anything to it. The amp should do a great job driving a high impedance load like a power amp. Output cap selection becomes pretty easy - anything over 47uF will work just fine. Pete briefly touches on that in the AudioXpress article available on his web site.

 We're getting there!

 -Drew


----------



## comabereni

[size=medium]NICE[/size]

 (Now to figure out how to make the 12AJ6 work since I have 11 of them 
	

	
	
		
		

		
		
	


	




)


----------



## drewd

Both channels work now - a big whoops on my part! When I was trying to clean up the routing, I grounded the left channel's plate CRD. That shut off the right channel (go figure). I cut a couple of traces, jumpered them and *poof*, the amp works great.











 With 12FK6 tubes and about 13.8V bias on a 30V regulated power supply, it really sings - even without the film bypass caps.

 So, that problem is fixed in the layout and I've done some routing changes that cleaned up the board a bit. I'll post that later this evening.

 -Drew


----------



## Thaddy

Drewd, that looks really nice. I feel proud to be a Millet owner right now 
	

	
	
		
		

		
			





 I'm getting that itch again...I might have to spring for a nicer model this summer. I have a feeling the Millet will be all the rave at Head-Fi soon!


----------



## drewd

Thanks Thaddy!

 Here's a picture of the rough case job that I finished a few minutes ago:






 Also, here are links to the latest PCB revisions. The revisions are all minor and aimed at fixing the two major problems with the prototype and resolving some small routing issues.

Render
Top
Bottom 
Both Layers 

 As before, I really appreciate everybody's input. I don't want to make any tremendous changes to the board, but I'll try to implement as much as I can before we reach a consensus that it's finished. Then it's in Nate's hands!

 -Drew


----------



## comabereni

Drew,

 The only thing I can think of to recommend, and only to be polite to the original designer, is to remove or replace the word "improved". I suggest "designed", or "version", or something similar. If it sounds the same or better then it certainly is improved, but we should probably leave it unsaid. 
	

	
	
		
		

		
		
	


	




 -coma

 P.S. RE the particular amp shown above, I wonder if it would be possible to be able to adjust tube bias from the outside of the case so you wouldn't have to unscrew it to swap tubes out? I have a hard enough time landing my jewelers screwdriver on the trimpots in full view, so it might be difficult without mounting them somehow flush with the top plate. As is, you have to pull the tubes, slide the cover off, insert new tubes, adjust bias, pull the tubes, slide the cover back on, reinsert tubes (correct?). For the tube rollers amongst us planning to use a standard case, perhaps a mod that permits a top panel to be removed to expose the bias test pins and trim pots without having to slide anything off would be helpful.


----------



## slindeman

Quote:


  Originally Posted by *comabereni* 
_P.S. RE the particular amp shown above, I wonder if it would be possible to be able to adjust tube bias from the outside of the case so you wouldn't have to unscrew it to swap tubes out? I have a hard enough time landing my jewelers screwdriver on the trimpots in full view, so it might be difficult without mounting them somehow flush with the top plate. As is, you have to pull the tubes, slide the cover off, insert new tubes, adjust bias, pull the tubes, slide the cover back on, reinsert tubes (correct?). For the tube rollers amongst us planning to use a standard case, perhaps a mod that permits a top panel to be removed to expose the bias test pins and trim pots without having to slide anything off would be helpful._

 

One thing I thought about doing when I built my last Millet Hybrid, but didn't in the end, was to mount the trimpots on the bottom side of the board and cut holes in the bottom panel of the amp to get access to them. You would also have to cut holes in the bottom panel where the test points are. Then you could just turn the amp on its side and adjust the bias from the bottom. No need to open the case.


----------



## n_maher

Quote:


  Originally Posted by *drewd* 
_Thanks Thaddy!

 Here's a picture of the rough case job that I finished a few minutes ago...

 As before, I really appreciate everybody's input. I don't want to make any tremendous changes to the board, but I'll try to implement as much as I can before we reach a consensus that it's finished. Then it's in Nate's hands!

 -Drew_

 

Drew,

 Looks great! And I completely agree with Coma's suggestion to change the board name to "Team-Head-Fi Modified" or some such thing.

 For the group,

 We should have 6 prototypes up and running before the end of the month. Due to vacation plans that I have for the last week of April it looks like the group buy for the boards will be started on May 1. We'll leave the "suggestions period" open until then with the understanding that nothing major is going to be considered.

 The group buy will be handled in a separate thread and there will most likely be a two week ordering phase, unless some one can tell me a good reason for letting it go longer. This should get folks their board(s) by the end of May. Drew has all of the build info on his site and there are established sources for all the parts so I think we're good to go.

 Nate


----------



## Thaddy

Does anyone know of a case that is big enough to house both of the Millet PCB and a STEPS PSU? As these get more popular, I'm sure a larger case will be needed. I suppose the Par Metal cases work, but do they allow enough room for the tubes to be placed inside?

 Looks really nice Drewd!


----------



## amb

Thaddy, the Par Metal 20-series cases are available in a variety of sizes, heights, finish, and other options. You can also order custom sizes. There is no problem getting one that would fit everything perfectly.


----------



## Thaddy

Quote:


  Originally Posted by *amb* 
_Thaddy, the Par Metal 20-series cases are available in a variety of sizes, heights, finish, and other options. You can also order custom sizes. There is no problem getting one that would fit everything perfectly._

 

Thanks, I actually have my Millet built into a Par case, but it's situated so the tubes are sticking out. I was unaware that you could have them custom built


----------



## individual6891

Also any chance of that centre mounted LED lighting up the tubes? If it's too much of a squeeze, then nevermind - I'm sure someone can figure out some ingenius mounting for it


----------



## drewd

I think that putting the trimpots on the bottom of the amp is an excellent idea. Since I used the Panasonic pot on the amp pictured above, the PCB is actually about four "slots" up in the board so that the volume knob would be more centered on the front panel. It is definitely a hassle to adjust the bias when changing tubes in the amp as it sits right now. comabereni is right about the torturous process to swap them out.

 Regarding the "improved" moniker, Pete actually suggested that himself. But I do agree, I'm not all that comfortable saying that it's improved. I'll change that to something a little less strident.

 Also, in the interest of flexibility, are there any requests for pots other than the EV-J and Blue Velvet? Those two work together centered on the board, but there is plenty of space to the left of those for something else, like the RK097 or whatever else might strike somebody's fancy.

 Finally, I left space around C11 and C2 for larger caps. I used a couple of 470uF/25V Elna Cerafines that are 12.mm (I think) instead of the 10mm caps that are spec'd. They fit just fine. Incidentally, I would not recommend that large a value of cap in those positions - 47uF to 100uF is just fine.

 -Drew


----------



## dsavitsk

Quote:


  Originally Posted by *Thaddy* 
_Does anyone know of a case that is big enough to house both of the Millet PCB and a STEPS PSU? As these get more popular, I'm sure a larger case will be needed. I suppose the Par Metal cases work, but do they allow enough room for the tubes to be placed inside?_

 

Here's my old one with a STEPS in a Par-Metal case


----------



## blip

I like the RK097 (great price/performance ratio) but I wouldn't worry about adding it to the board.... I personally prefer wiring everything off board myself. 

 As for the caps, has anyone done much experimenting with different values?


----------



## drewd

Quote:


  Originally Posted by *blip* 
_As for the caps, has anyone done much experimenting with different values?_

 

The first proto that I built used a bunch of el-cheapo Nichicon 1000uF, 50V caps in all of the 100uF positions. The second one used Elna Silmic 2 100uF caps. I used Elna Cerafine 470uF caps for C2 and C11 in both cases. I can't hear a difference - however - since I haven't received the Wima film caps from Welborne Labs yet, there probably isn't much of a conclusion to draw yet.

 I've also ordered some Panasonic FC electrolytics and BC film caps from Digi-Key, so I'll build up number three with those and see if there is any difference.

 If you're looking for the caps that will have the most effect on sound, that would be C4, C7, C13 and C16. In combination with R4 and R9 (and your headphones), they will set the -3dB point of the amp's potential frequency response, plus, of course, the audio signal itself is traveling through them. Remember that this is a budget amp (although a pretty good one), so if you buy reasonably priced caps like Panasonic FC or FM for the other positions, you can splurge a little on C4, C7, C13 and C16. Roughly speaking, Fc = 1/(2*Pi*(Rout+Rheadphones)*C). Pete Millett suggests that anything above a 47uF cap will work and that seems pretty reasonable. Note that Fc (the corner frequency) doesn't represent the lower end of the amp's frequency response, but the -3dB point that the amp would be capable of. It might not go down that far - but we're talking about 25Hz with a 47uF cap and 100 ohm headphones. Bump the cap up and the frequency change is inversely proportional to the cap size. There is plenty of room for boutique output caps on the board.

 -Drew


----------



## art633

Quote:


  Originally Posted by *drewd* 
_Regarding the "improved" moniker, Pete actually suggested that himself. But I do agree, I'm not all that comfortable saying that it's improved. I'll change that to something a little less strident.

 -Drew_

 

What are folks thoughts on "Millet Re-Visited" ?

 M


----------



## sbelyo

Millett 2.0


----------



## comabereni

Quote:


  Originally Posted by *sbelyo* 
_Millett 2.0_

 

Gets my vote 
	

	
	
		
		

		
			





 Or, 

 Millett 2.0 Head-Amp
 Head-Fi.org Team Project
 April 2005


----------



## skyskraper

its not really a 2.0 as in new design. 

 "Head-Fi Reorganized Millett Hybrid" would be a good one


----------



## sbelyo

Quote:


  Originally Posted by *skyskraper* 
_its not really a 2.0 as in new design. _

 

That is true... But it looks nothing like the original either


----------



## comabereni

How about:

 Peter Millett Headphone Amplifier
 www6.head-fi.org Team Project
 April 2005

 Says exactly what it is. Gives credit to Pete. Gives credit to us. No implied circuit revision.

 Then list Pete's web address on a separate area of the board. By listing where and when this version was developed as well as the original designer's address, future builders know where to look to find out how to put it together.


----------



## drewd

We probably don't need to agonize over how to name the board - remember, I told Pete what we were doing and his response was to call it an improved hybrid. Well, I can't say that it is for a fact improved (other than fixing a couple of small problems on his original board file), but I think that it's safe to say that it is modified. So that's what I called it when I fixed a few issues last night. Here is the result:

Top
Bottom 
Both 
No Planes 
Render

Really, really big image of both layers (Danger, Will Robinson!) 

 There is no provision for putting LEDs under the tubes - the mini seven pin sockets are very small and do not have a hole in them for the light to shine through. However, an enterprising soul could hand wire an LED underneath the socket across the heater pin to ground. It would light up under the socket. 

 I'm looking over the board now for dumb errors (like the ground vias that I stuck in a couple of signal traces), so if as many people as possible can squint at the big image and see if I missed anything, I'd appreciate it. It's on my server, so I can just about guarantee that it will be slower than molasses to download...sorry.

 As far as listening goes, I've been changing between the 12FK6 and the 12AE6A today. With 30V and 13.8V bias, the 12FK6 is a hands down winner, however I'm *still* waiting for my film caps to arrive from Welborne, so it's just running on electrolytics except for one ceramic cap per channel (C6, C15).

 Somebody mentioned that this could be the CMOY of the tube world - I think that's true. It's easily buildable in an hour or two and it really does sound very good.

 -Drew


----------



## n_maher

Drew,

 Once again, thanks for all your efforts and being so giving of your time to modify the board layouts. I can't wait to get building this weekend!

 For the record, Welborne has been slower than molasses on this. I can't say that I've experienced this with them in the past so let's hope this is just an isolated thing (that we're both going through). But their stuff was the ordered on the same day as everthing else and the are physically closer than some of the other places to me, yet it's still not here 3 days after the last of the other stuff 
	

	
	
		
		

		
		
	


	




...

 And Tube Depot was super to deal with, shipped stuff even though they were in the middle of moving their entire facility and sent matched tubes.

 Look for pictures of yet another prototype on Monday.

 Nate


----------



## drewd

Welborne Labs finally came through. Here's proto number two - I'll put it in a case on Sunday.











 I haven't had time to listen to number one with the film caps in it yet. It's just sitting there...tantalizing me...sigh...

 -Drew


----------



## individual6891

Regarding the film bypass caps, could you add alternative hole spacings down to 5mm pitch to allow for small caps? I mean polypropylenes are ideal here, but not a necessity. This would allow you to use for example the smaller Wima MK4 series polyesters caps.

 Thanks, good work on the board btw


----------



## drewd

Quote:


  Originally Posted by *individual6891* 
_Regarding the film bypass caps, could you add alternative hole spacings down to 5mm pitch to allow for small caps? I mean polypropylenes are ideal here, but not a necessity. This would allow you to use for example the smaller Wima MK4 series polyesters caps._

 

Yep, no problem. I'll make that change to the board.

 -Drew


----------



## bg4533

What is the height from the bottom of the board to the top of the tubes? Are all of the tubes the same height?


----------



## Thaddy

Quote:


  Originally Posted by *bg4533* 
_What is the height from the bottom of the board to the top of the tubes? Are all of the tubes the same height?_

 

Yeah the ones I have are all the same height, which is just under 2 inches I think.

 Oh, and for clarification, I have the 12FK6's, 12FM6's, and 12AE6A's.


----------



## drewd

Quote:


  Originally Posted by *bg4533* 
_What is the height from the bottom of the board to the top of the tubes? Are all of the tubes the same height?_

 

It's about 2.75". All of the tubes that I have are the same size.

 Here's the latest proto. Looks good, sounds good.

 I've added the pads for smaller film caps to the board. I think that at this point, I'm tossing the ball to Nate!

 -Drew


----------



## comabereni

Quote:


  Originally Posted by *drewd* 
_Here's the latest proto. Looks good, sounds good.
 -Drew_

 

It does look good. You could probably fit a Sonic Impact Tripath amp board inside that enclosure too. SET sound quality on a budget? (T-amp sounds much better with tube preamp, also read the followup message to the link). Would have to do something about power since the circuits require different voltages. I know I'm going off-topic. I'm not looking to start a new discussion here--just throwing an idea out.

 Great work on the prototype. Just needs the wood finished now.

 -coma


----------



## Thaddy

Quote:


  Originally Posted by *comabereni* 
_It does look good. You could probably fit a Sonic Impact Tripath amp board inside that enclosure too. SET sound quality on a budget? (T-amp sounds much better with tube preamp, also read the followup message to the link). Would have to do something about power since the circuits require different voltages. I know I'm going off-topic. I'm not looking to start a new discussion here--just throwing an idea out.

 Great work on the prototype. Just needs the wood finished now.

 -coma_

 

Coma, that would be really cool if someone could incorporate a T Amp into the same case as the Millet. I'm drooling at the fact that I could have a Millet for my cans and a T Amp for my Paradigm Atoms...all driven by a STEPS in the same case 
	

	
	
		
		

		
		
	


	




 edit: Drewd, which tubes are you using? Also, which ones are you favorites?


----------



## comabereni

Quote:


  Originally Posted by *Thaddy* 
_Coma, that would be really cool if someone could incorporate a T Amp into the same case as the Millet. I'm drooling at the fact that I could have a Millet for my cans and a T Amp for my Paradigm Atoms...all driven by a STEPS in the same case 
	

	
	
		
		

		
		
	


	


_

 

Don't forget a line out for a powered subwoofer 
	

	
	
		
		

		
		
	


	




.


----------



## Thaddy

Quote:


  Originally Posted by *comabereni* 
_Don't forget a line out for a powered subwoofer 
	

	
	
		
		

		
			





._

 

Ohh my...now we're cookin' with fire!

 But I'm one of those guys who thinks 2.0 is perfect for music, so no sub-out for me


----------



## Unclewai

Yes, I am planning to incorporate the millet pre-amp into the T-amp also. I thought you just have to split an extra RCA to the powered subwoofer from the millet pre-amp? 
 I hope we can exchange ideas on how to put the millet pre-amp and t-amp together once the pcb is available.

 Thaddy, a subwoofer really helps out on music listening, it fills the lower extension which bookshelf just can't produce well.


----------



## Thaddy

Quote:


  Originally Posted by *Unclewai* 
_Thaddy, a subwoofer really helps out on music listening, it fills the lower extension which bookshelf just can't produce well._

 

Oh I know, that's why I have the HD580's 
	

	
	
		
		

		
		
	


	




 I'm not a fan of subs for some reason, I just prefer my music in 2.0 when listening with speakers.


----------



## bg4533

Quote:


  Originally Posted by *comabereni* 
_It does look good. You could probably fit a Sonic Impact Tripath amp board inside that enclosure too. SET sound quality on a budget? (T-amp sounds much better with tube preamp, also read the followup message to the link). Would have to do something about power since the circuits require different voltages. I know I'm going off-topic. I'm not looking to start a new discussion here--just throwing an idea out.

 Great work on the prototype. Just needs the wood finished now.

 -coma_

 

I would build your own PSU. you could get a big center tapped or dual secondary transformer and go from there. Use one tap to get what you want for the TAmp and both for the Millet.


----------



## drewd

Quote:


  Originally Posted by *Thaddy* 
_Drewd, which tubes are you using? Also, which ones are you favorites?_

 

I've got 12AE6A, 12FK6 and 12FM6. I like the 12FK6 the best, with a 30V regulated PS and about 14V bias. This is with a set of DT880's. With my Grado SR225's, I found that I had to double up on the buffers.

 -Drew


----------



## Thaddy

Quote:


  Originally Posted by *drewd* 
_I've got 12AE6A, 12FK6 and 12FM6. I like the 12FK6 the best, with a 30V regulated PS and about 14V bias. This is with a set of DT880's. With my Grado SR225's, I found that I had to double up on the buffers.

 -Drew_

 

I agree Drewd, out of the 3 different types I've tried, my Tung-Sol 12FK6's are my favorites


----------



## n_maher

Well, in addition to Drew's two prototypes I've now built a working one as well. I can echo previous sentiments that the 12FK6 tubes are definitely my preference over the 12AE6As. I tested it briefly using these tubes with both my Senn 600's and Grado 225's and I can also say that Drew is correct in finding that stacked buffers are probably a necessity for Team Grado (more current needed). I'll be testing it with my Etys (P and S) tonight.

 I do have one more question for the "group" in terms of how the group buy will be administered. I will be the primary organizer of this and as such I feel compelled to tell people that I'm going to be on vacation from April 22 through the 1st of May. I'm wondering if the masses think that the entire process should be left until after I return or if people think that it would just make sense to have the ordering phase run until after I get back.

 For sure it won't start until mid next week so that the other prototypers get a chance to build and confirm the success of the design. But if no one has an issue with it I'd suggest that it start on the 20th and run through the 4th. The order would then be place and so on and so forth. So please offer up your thoughts on this. 

 Late thing of note - pricing is as of yet undetermined and ultimately will be based on the quantity ordered. Based on my estimation if we get over 100 boards ordered we should be looking at around $10/board + shipping and handling. Not too shabby compared to the original $40 a board!

 Nate


----------



## skyskraper

i say let it run whilst you're away


----------



## individual6891

Quote:


  Originally Posted by *skyskraper* 
_i say let it run whilst you're away 
	

	
	
		
		

		
		
	


	


_

 

^ditto on this 
	

	
	
		
		

		
		
	


	




 BTW Coma, received the tubes today - they're teeny huh? 
	

	
	
		
		

		
		
	


	




 Thanks again


----------



## comabereni

Quote:


  Originally Posted by *individual6891* 
_BTW Coma, received the tubes today - they're teeny huh? 
	

	
	
		
		

		
		
	


	




 Thanks again_

 

Thanks for letting me know, you're welcome.

 -coma


----------



## drewd

Somebody asked about putting LEDs under the tubes (and I'm too lazy to search through the thread 
	

	
	
		
		

		
		
	


	




 ). I'm pretty sure that I said that the mini 7 pin sockets have no hole in the bottom and there's not a lot of room under them for a part...but...I was fooling around yesterday and put a Lumiled Luxeon LED in the center, on top of the buffers. It looks pretty interesting:

Picture 1 

Closeup

 It's hard to see in the pictures, but the tips of the tubes get sort of a black light look. It's kind of eerie.

 -Drew


----------



## Magsy

Heh totally awesome, I just have to build for the looks alone!! 

 Job well done


----------



## CedMan

That's just what I wanted to do, it looks awesome. As for the groupbuy I am cool eitherway. 
	

	
	
		
		

		
		
	


	




 Can't wait ... lol


----------



## n_maher

Drew,

 Care to pull aside the curtain and show us how you did that? I think I get what you're saying, just two leds mounted near the buffers to project light at the tubes but I'm from mizzou, so could you show me?

 Looks wild, man!

 Nate


----------



## drewd

Quote:


  Originally Posted by *n_maher* 
_Care to pull aside the curtain and show us how you did that? I think I get what you're saying, just two leds mounted near the buffers to project light at the tubes but I'm from mizzou, so could you show me?_

 

Easier than that, even. I used one of these:






 It came from here I ordered mine from Future Electronics when they first came out, but I'm pretty sure that you can get them from Digi-Key or Mouser. The part number is LXHL-DR01.

 Hook it up to the LED pads on the board, a little 3M double sided foam tape on top of the buffers and instant light.

 It's extremely bright - you really don't want to look right at it.

 -Drew


----------



## individual6891

They use up like 300mA though don't they?


----------



## jerb

you werent planning on using this thing battery powered were you?

 as for the led's, ive been following this thread and in the very beginning i wanted to put led's under the tubes and in the very beginning it would have been as easy as drilling a hole under the tubes but as the board progressed you guys added two traces under the tubes. Not that i mind sacrificing looks for sound but it was defiantly a let down... very good idea with the luxons Btw.


----------



## n_maher

jerb,

 Even if we'd put traces under the boards it still wouldn't have really helped the fact that the tube sockets don't have a hole to let the light shine through.

 At least that was my reasoning behind not pushing for it. Besides, I think it looks just fine the way it is...

 [edit] Evidently drew is still working on the boards...


----------



## drewd

Quote:


  Originally Posted by *individual6891* 
_They use up like 300mA though don't they?_

 

Max current is 350mA. With a 1K resistor in series, the current is down to 24mA.

  Quote:


  Originally Posted by *jerb* 
_in the very beginning i wanted to put led's under the tubes and in the very beginning it would have been as easy as drilling a hole under the tubes_

 

You mean like this?






 (Don't kill me)

 -Drew


----------



## jerb

Yeah that was what i was going to do with a drill press but two traces were added under the tube socket to the left.

 its fine though the luxeons will work as an alternative and:
  Quote:


 (Don't kill me) 
 

why would i go and do something like that?


----------



## jerb

Quote:


 Even if we'd put traces under the boards it still wouldn't have really helped the fact that the tube sockets don't have a hole to let the light shine through. 
 

im sorry i was under the impression that the tube sockets were hollow in the center and that tubes would allow light to shine through from the bottom, i know sijose (sry i spelled it wrong) commonly puts LED's under his tubes... sorry for my ignorance


----------



## n_maher

Quote:


  Originally Posted by *jerb* 
_im sorry i was under the impression that the tube sockets were hollow in the center and that tubes would allow light to shine through from the bottom, i know sijose (sry i spelled it wrong) commonly puts LED's under his tubes... sorry for my ignorance_

 

nonononono, it's probably me who's ignorant here, not you 
	

	
	
		
		

		
		
	


	




. The only tube sockets that I'd find for mini tubes like this amp uses don't have holes, but I'm sure I haven't found them all. I just did a bit of research on Sijosae's amp and it uses a different (9-pin mini) and I found several sockets for those tubes with a hollow center. It is quite possible that some of the other mini 7-pin sockets have hollow centers, but pictures that I've found so far are inconclusive.

 That said, I think Drew might have been referring to me killing him given that he's still tweaking the board! Which of course is fine by me!

 And I do think that the tubes glow nicely without the aid of an internal led though...


----------



## skyskraper

nice work on the illumination drew! care to give us more details about the hole or is it simply a hole and we mount the luxeons underneath and their circuits seperate?

 edit: surely some of the tube sockets could be drilled to mount an led? i must confess tube ignorance at this point and don't know if there's other stuff going on in the sockets.


----------



## jerb

if you read through this thread (which at this point is a quite tedious task) there is a want for LED's under the tubes. If it would be possible to include holes on the board as seen in the render several posts up i think it will be taken advantage of. also for all of you who would rather go for a more traditional look you could simply ignor these holes, because they are under the tubes no one will notice if you dont put anything there.


 just my .02 if its impratical then feel free to dismiss my comments

 P.S Great job on this project, its people like you that keep this fourm (my favorite) thriving


----------



## n_maher

the render that you see above is the most current version of the board that we'll be sending for the production run. In the end Drew was able to make the holes work with the layout so everyone wins, I think 
	

	
	
		
		

		
		
	


	




 .

 Nate

 [size=xx-small]P.s. I'll probalby use the holes too! 
	

	
	
		
		

		
		
	


	




 [/size]


----------



## jerb

as far as the holes go im glad to see that they've been encorperated into the design, i dont think they will bother anyone who doesnt want to use them but are an added bonus to those who do have plans for them. another opiton is to add a switch on the led so if you dont want under-lit tubes you could always turn the LED off

 another option that could look very cool is a RGB led that cycles gently through a series of colors. a How-To artical can be found on Bit-tech

 EDIT-More specificaly the How-To Guide can be found Here might be nice to add a relaxing effect to the already layed back sound of tubes


----------



## dsavitsk

Quote:


  Originally Posted by *drewd* 
_With my Grado SR225's, I found that I had to double up on the buffers._

 

Interestingly, (using RS-1s) I've found that running my Millett through my Pimeta sounds better than either of them do on their own. Essentially using the Pimeta as a super buffer. Part of me thinks that my next project may be combining a 12ae6a gain stage with a discrete buffer stage ... the other part of me thinks that at that point I may as well just use a better tube.

 On a side note, on my Millett I just replaced the "stock" 100uF elna cerafine output caps with some 470uF Nichicon caps for Percy. With Grados, there is a bit more deep bass, and maybe a bit more fullness, but the difference is not huge. Probably worth the $3.50, though.

 -d


----------



## drewd

Quote:


  Originally Posted by *skyskraper* 
_nice work on the illumination drew! care to give us more details about the hole or is it simply a hole and we mount the luxeons underneath and their circuits seperate?_

 

In my amp, the luxeon star LED board is just taped to the top of the buffers with double sided tape - no hole. It's kind of a hokey setup, but from the outside, it looks neat. The holes in the production board are .25 inch, so a standard T1-3/4 LED will stick through. There are plenty of bright LEDs that will really light things up, even if there is no hole in the bottom of the socket.

  Quote:


 edit: surely some of the tube sockets could be drilled to mount an led? i must confess tube ignorance at this point and don't know if there's other stuff going on in the sockets. 
 

I think that the sockets can be drilled to let the light through. All four of mine are mounted and in cases, so I can't see now, but if my memory serves me (which is no sure thing), the center is just a metal plug.

 -Drew


----------



## individual6891

The hole idea's pretty interesting - what's the diameter size in mm?

 But just wondering if there is any space to run a LED/resistor pads in the middle of the tube sockets from the +v and ground?


----------



## n_maher

Quote:


  Originally Posted by *individual6891* 
_The hole idea's pretty interesting - what's the diameter size in mm?_

 

1/4" = 6.35mm


----------



## drewd

Quote:


  Originally Posted by *individual6891* 
_But just wondering if there is any space to run a LED/resistor pads in the middle of the tube sockets from the +v and ground?_

 

I'll take a look at it, but I wouldn't hold my breath - it's a little crowded and the ground plane is cut up enough as it is. But I'll do my best.

 -Drew


----------



## comabereni

Quote:


  Originally Posted by *jerb* 
_another option that could look very cool is a RGB led that cycles gently through a series of colors. a How-To artical can be found on Bit-tech

 EDIT-More specificaly the How-To Guide can be found Here might be nice to add a relaxing effect to the already layed back sound of tubes_

 

It should be easy enough to wire an on/off switch to the LEDs from underneath without anything on the board. That color cycling circuit is pretty neat--just stick a couple of these under the Millett PCB for a cool disco effect. Now you just need a way to make them pulse with the music. 
	

	
	
		
		

		
			





 -coma


----------



## number1sixerfan

Does anyone have an older millet that they could lend out to borrow? I want to hear how they sound before I invest in one. I have flawless heat and feedback here. I'd even rent it,lol.


----------



## comabereni

Quote:


  Originally Posted by *number1sixerfan* 
_Does anyone have an older millet that they could lend out to borrow? I want to hear how they sound before I invest in one. I have flawless heat and feedback here. I'd even rent it,lol._

 

I'll loan you mine. PM me to make arrangements.

 -coma


----------



## individual6891

Quote:


  Originally Posted by *comabereni* 
_ Now you just need a way to make them pulse with the music. 
	

	
	
		
		

		
		
	


	




 -coma_

 

Velleman have loadsa these types of kits...

Sound to Light 

Pocket Sound Meter 

Programmable 2 LED Flasher 

White LED Strobscope 

 Top one's probably the one you're looking for


----------



## Buzzerbro

Hello Drew,

What are the dimensions of the amplifier PCB. I am trying to determine which Hammond’s chassis to buy from Mouser.  

http://www.mouser.com/catalog/621/1248.pdf

By the way I already build a Millet Headphone amp a couple of months ago and it sounds great. I have 3 different pairs of tube sockets and they all have holes in the middle. I bought them from vacuumtubes.net part # PCP7 (Socket Ceramic chassis ) and PC7 (Socket phenolic PC mount)

 Thanks,
 Buzzerbro


----------



## multibit16

Hi guys,

 I have been reading this thread with interest because I've been wanting to build a nice tube headphone amp for a while.
 So how do these things sound regarding quality?
 I currently have a JLH Chiarra and Cmoy amp, it would also be nice if this would make a good pre amp 

 Cheers

 Leo


----------



## number1sixerfan

Quote:


  Originally Posted by *comabereni* 
_I'll loan you mine. PM me to make arrangements.

 -coma_

 

Thanks for the kind jesture. Can't wait to hear it.


----------



## drewd

Quote:


  Originally Posted by *Buzzerbro* 
_What are the dimensions of the amplifier PCB. I am trying to determine which Hammond’s chassis to buy from Mouser.  _

 

It measures 6.3" x 3.96", a perfect fit for the 1455N1601...well, perfect, except that in either you'll have to cut holes in the lid for the tubes. The pictures of mine are in a 1455N1601 with the board in the third or fourth slot from the bottom so that the volume control is centered on the face of the amplifier. The amp _might_ fit in the 1455L1601 if you can find shorter caps. It definitely will not fit with a Blue Velvet pot, though.

 The nice thing about the 1455N1601 case is that there is some room underneath the board for something clever, like, for instance, some batteries. OK, a LOT of batteries. I think that an enterprising person could fit enough AA batteries under there, along with a PPA-style charger to get reasonable performance from the amp. Maybe I'll give that a shot once I get through this week's backlog of projects!

 Thanks for the source on the sockets, also!

 -Drew


----------



## drewd

Quote:


  Originally Posted by *multibit16* 
_I have been reading this thread with interest because I've been wanting to build a nice tube headphone amp for a while.
 So how do these things sound regarding quality?
 I currently have a JLH Chiarra and Cmoy amp, it would also be nice if this would make a good pre amp_

 

I've been listening to a prototype pretty steadily for the past week and a half or so. I use a set of Beyer DT880s almost exclusively and the amp seems to be tailor made for those headphones.

 It has very palpable bass and well-defined mids. I notice that as time has gone by either the treble has been improving or I've gotten used to it - probably a combination of the two. I haven't had time to throw it on RMAA to see if there's any monkey business going on.

 My gut feeling is that it has the warmth and presence that you expect from tubes, but with a low-end solid-state kick. In particular, if you have headphones that are a little overbearing on the high end, this amplifier is an excellent combo. I notice this particularly with my Grado SR225s. The only drawback is that there seems to be a bit too much gain form them and a subtle flip of the wrist can be deafening. I'm working on that - I suspect that selecting the right values for D3 and D4 will tune the gain a bit.

 On the flip side, high impedance headphones don't have enough gain at this point. My HD580s need nearly the full travel of the pot to get loud. Again, I'll be working with the two CRDs to see if it's possible to get enough gain to drive 300 ohm headphones with some authority.

 The amp that I've been testing is pretty much outfitted the way that Pete Millett suggested, except that the electrolytic caps are Silmics. The volume control is a Blue Velvet and the tubes are GE 12FK6's (for the most part). I'm using a Radio Shack 13.8V/30V power supply and the bias is set at about 13.8V.

 As a preamp, it works quite nicely. I've used it briefly to drive a pair of Carver monoblocks into a set of Acoustat 1+1s and I was very impressed - as with the Grados, the Acoustats can be a little aggressive on the high end and the Millett Hybrid does an excellent job of taming that a bit.

 I kind of suspect that when I toss it on RMAA, I'll see that its frequency response isn't all that flat. But I'm pretty darned happy with it, particularly in its price to performance ratio.

 -Drew


----------



## dsavitsk

Quote:


  Originally Posted by *drewd* 
_I've been listening to a prototype pretty steadily for the past week and a half or so. I use a set of Beyer DT880s almost exclusively and the amp seems to be tailor made for those headphones.

 It has very palpable bass and well-defined mids. I notice that as time has gone by either the treble has been improving or I've gotten used to it - probably a combination of the two. I haven't had time to throw it on RMAA to see if there's any monkey business going on.

 My gut feeling is that it has the warmth and presence that you expect from tubes, but with a low-end solid-state kick. In particular, if you have headphones that are a little overbearing on the high end, this amplifier is an excellent combo. I notice this particularly with my Grado SR225s. The only drawback is that there seems to be a bit too much gain form them and a subtle flip of the wrist can be deafening._

 

I'll second this impression of this amp. The gain issue is going to depend a lot on source. With a NOS DAC with no output buffer, I have to turn the volume past 1:00 with my RS-1s. With my Cary cdp, I am barely past 8:00.

  Quote:


  Originally Posted by *drewd* 
_As a preamp, it works quite nicely. I've used it briefly to drive a pair of Carver monoblocks into a set of Acoustat 1+1s and I was very impressed - as with the Grados, the Acoustats can be a little aggressive on the high end and the Millett Hybrid does an excellent job of taming that a bit._

 

When I tried it as a pre, driving long (6m) cables into a sumo amp w/ B&W speakers (a load that my Melos does a great job with), it performed very badly. The bottom end was hollow and flabby. I only mention this to note that system matching matters here, as everywhere.

 Last thing to note is that power supply matters a lot with this amp. You may find that switching from the RS one to something like a steps will change the amps basic character - probably for the better 
	

	
	
		
		

		
		
	


	




 Thanks for the update drewd.

 -d


----------



## jamont

Quote:


  Originally Posted by *dsavitsk* 
_Last thing to note is that power supply matters a lot with this amp._

 

This was also noted a couple of years ago by those of us who built this amp on Millett's PCB. The renewed interest makes me think that this amp might benefit from something better than a LM317 based PS - a Sulzer or Jung regulator perhaps. Maybe the mysterious YJPS would be just the thing here


----------



## cetoole

Can't wait for the group buy, I hope something is worked out so that it works well with 300 ohm cans, otherwize, I might be forced to buy some Grados or Alessandros to go along with my HD580's 
	

	
	
		
		

		
		
	


	




 + 
	

	
	
		
		

		
		
	


	




 = Yum. Sorry about my wallet indeed. Just got the T-Amp today to go with it, this will be fun. Anyone have any idea what Hammond I will need to fit the (modded) T-Amp in with the Millet? Also, any links to how the wood panels are added to the Hammonds, like in drewd's sample?


----------



## blip

Hmmm... The high impedance performance thing worries me... Look forward to hearing more feedback on it from existing Millet owners.

 Failing that, I guess I could always use the millet as a pre-amp for another gain stage... Like maybe for my pimeta or some kind of simple voltage gain stage.


----------



## Thaddy

I'm using my Millet right now with my HD580's and the volume is at about 9 o'clock. Also, my EMU-0404 is at about 75%-80%. I don't seem to be having any problems driving my Sennheisers.

 I'm really excited about these new PCB's, this summer I plan on selling my current Millet to fund for another Millet with a Steps PSU and an input selector. Hey, maybe I'll even get a DACT
	

	
	
		
		

		
		
	


	




 But first, one of you DIY guys have to build it for me 
	

	
	
		
		

		
		
	


	




 edit: If anyone is up for it, shoot me a PM and we can talk in more detail.


----------



## sbelyo

I wouldn't be too woried about driving the sennheisers. As long as your source is good quality I don't think you'll have to bring it past the 3/4 position.


----------



## Buzzerbro

Quote:


 Hmmm... The high impedance performance thing worries me... Look forward to hearing more feedback on it from existing Millet owners.

 Failing that, I guess I could always use the millet as a pre-amp for another gain stage... Like maybe for my pimeta or some kind of simple voltage gain stage. 
 

Millett explains what to do if you have high impedance headphones in his article. Check out page 5 of the pdf. 

http://www.pmillett.com/file%20downloadss/ax_hybrid.pdf


----------



## art633

Quote:


  Originally Posted by *Buzzerbro* 
_Millett explains what to do if you have high impedance headphones in his article. Check out page 5 of the pdf. 

http://www.pmillett.com/file%20downloadss/ax_hybrid.pdf_

 

I was just thinking that - the RTFM method, Read The screw**g Manual first, sometimes known to work 
	

	
	
		
		

		
			





 Another thought to increase the gain is to reduce the CRD's impedance(AC resistance) with a small cap across it, 6.8uF for example. I've done this in the past on plate _current to voltage convertors_ (in English a resistor) and jfet/bjt CCS's to good effect. No idea on IN5291's CRD's though! Sounds like play time again..........

 Thanks for the mini review Drewd, nice that it's good on my favourite 'phones, DT880s.

 M


----------



## art633

Quote:


  Originally Posted by *dsavitsk* 
_Last thing to note is that power supply matters a lot with this amp. You may find that switching from the RS one to something like a steps will change the amps basic character - probably for the better 
	

	
	
		
		

		
		
	


	


_

 

 Quote:


  Originally Posted by *jamont* 
_This was also noted a couple of years ago by those of us who built this amp on Millett's PCB. The renewed interest makes me think that this amp might benefit from something better than a LM317 based PS - a Sulzer or Jung regulator perhaps. Maybe the mysterious YJPS would be just the thing here 
	

	
	
		
		

		
		
	


	


_

 


 Surely this is correct for ANY amp. The YJPS is a mystery to me too, any chance of a link - pretty please.

 M


----------



## drewd

Quote:


  Originally Posted by *art633* 
_Another thought to increase the gain is to reduce the CRD's impedance(AC resistance) with a small cap across it, 6.8uF for example. I've done this in the past on plate current to voltage convertors (in English a resistor) and jfet/bjt CCS's to good effect. No idea on IN5291's CRD's though! Sounds like play time again.........._

 

I wonder about using the JFET cascode with a pot, something like the PPA's bias system. Like you said, it's play time! Time to break out the project board again.

 -Drew


----------



## n_maher

Given people's desire to tweak this a bit more I'm going to hold off starting the group buy till we have at least explored the adjustable bias option.

 N


----------



## multibit16

Quote:


  Originally Posted by *drewd* 
_I've been listening to a prototype pretty steadily for the past week and a half or so. I use a set of Beyer DT880s almost exclusively and the amp seems to be tailor made for those headphones.

 It has very palpable bass and well-defined mids. I notice that as time has gone by either the treble has been improving or I've gotten used to it - probably a combination of the two. I haven't had time to throw it on RMAA to see if there's any monkey business going on.

 My gut feeling is that it has the warmth and presence that you expect from tubes, but with a low-end solid-state kick. In particular, if you have headphones that are a little overbearing on the high end, this amplifier is an excellent combo. I notice this particularly with my Grado SR225s. The only drawback is that there seems to be a bit too much gain form them and a subtle flip of the wrist can be deafening. I'm working on that - I suspect that selecting the right values for D3 and D4 will tune the gain a bit.

 On the flip side, high impedance headphones don't have enough gain at this point. My HD580s need nearly the full travel of the pot to get loud. Again, I'll be working with the two CRDs to see if it's possible to get enough gain to drive 300 ohm headphones with some authority.

 The amp that I've been testing is pretty much outfitted the way that Pete Millett suggested, except that the electrolytic caps are Silmics. The volume control is a Blue Velvet and the tubes are GE 12FK6's (for the most part). I'm using a Radio Shack 13.8V/30V power supply and the bias is set at about 13.8V.

 As a preamp, it works quite nicely. I've used it briefly to drive a pair of Carver monoblocks into a set of Acoustat 1+1s and I was very impressed - as with the Grados, the Acoustats can be a little aggressive on the high end and the Millett Hybrid does an excellent job of taming that a bit.

 I kind of suspect that when I toss it on RMAA, I'll see that its frequency response isn't all that flat. But I'm pretty darned happy with it, particularly in its price to performance ratio.

 -Drew_

 


 Cheers Drew!

 Well I just hope a UK group buy will be organised some time, I'm certainly interested in building one, Excellent work on the pcb by the way 
	

	
	
		
		

		
		
	


	



 I've been trying to find something diy to go with my AvondaleNCC200 amp, a nice valve pre seemed a good idea and being a headphone amp as well is a bonus, Its currently being used with a highly modified Naim Nac pre.
 My main amp is a highly modified Kit88 valve amp from WAD which I'm happy with but I'd like to try and get the solid state pre for the NCC200 improved.
 Both my dacs are NOS so they deserve something nice to amplify the signal 
	

	
	
		
		

		
		
	


	




 Leo


----------



## Magsy

Well I'm sure the guys will ship over to us 
	

	
	
		
		

		
		
	


	



 If there are a large number of uk'ers then I'll distro if needs be...


----------



## Tyll Hertsens

Just thought I'd let you guys know we've been following this thread with interest because we are about to introduct a version of this amp as well. Joe W. (our engineer) and Pete have been collaberating on the effort but Pete really did most of the work. We will be shipping the a pair each of the 12AE6A, 12FM6, and 12FK6 with the amp. It will have the unusual feature of a switch on the front to change the bias for each tube type.

 Origionally the idea was to have a Lush, Lusher, Lushest switch on the front panel and drive the tubes farther and farther into 2nd order distortions, but we found the tubes work so well over a variety of bias voltage that we chaged the switch to set the optimal bias for each tube type. (Of course you would have to open the box to fine tweak it.)

 I was listening to our version of this amp the other day with my Overture DAC fed by the digital out of my iRiver IHP140. I have some industrial trance music ripped at 128kbs that I normally just skip ove cause it's so harsh. But the Millett Hybrid design does wonders with harsh recordings, and I actually sat and listened witout realizing I was on a crap recording for quite a while. 

 You guys have done a great job, and any of you on the fence about doing this project should feel great about stepping in and building one. I love mine.


----------



## dsavitsk

Quote:


  Originally Posted by *n_maher* 
_Given people's desire to tweak this a bit more I'm going to hold off starting the group buy till we have at least explored the adjustable bias option._

 

Is this an invitation to tweak?

 Would we be able to add a tle2426 at some point to give the buffers +/- voltage -- essentially giving them their own power supply. From Pete's article, I got the impresion that the reason for the DC offset, and thus the reason for the electrolytic output caps, was because the buffer only got the + part of the voltage. Perhaps by adding a virtual ground, we could get rid of the caps?

 On that note, we could also use diamond buffers of some design, rather than the monolithic buffers. Here's a nice thread on the topic, with a drop in replacement by sijosae at the end.

  Quote:


  Originally Posted by *Tyll Hertsens* 
_Just thought I'd let you guys know we've been following this thread with interest because we are about to introduct a version of this amp as well._

 

That's pretty cool. I have the sense that had this been introduced a year and a half ago that I would never have gotten into diy in the first place. I am not sure if this is good or bad.

 -d


----------



## Thaddy

Tyll, are you planning on having this amp with you on the road? My original plan was to get a _really_ nice version of the Millet, but now I'm very tempted to wait until I get a chance to either hear HeadRoom's version or read some reviews on it.

 Man, just when I think I'm happy with my current Millet, two more come into the picture!

 Comabereni, didn't we say this amp would be huge in the future? Well, I think the future is now


----------



## Tyll Hertsens

Quote:


  Originally Posted by *Thaddy* 
_Tyll, are you planning on having this amp with you on the road?_

 

Yup.


----------



## n_maher

Quote:


  Originally Posted by *dsavitsk* 
_Is this an invitation to tweak? Would we be able to add a tle2426 at some point to give the buffers +/- voltage..._

 

I said tweak, as in to change slightly 
	

	
	
		
		

		
		
	


	




. I don't think that means adding entire sections to the board. This project always has, I hope will continue to be, an effort to SLIGHTLY modify Pete's original design with an eye towards keeping costs low and adding flexibility to the design. Remember that this all got started in an effort to just find a lower priced stock Millett board. If folks are really interested in diamond buffers and more exotic mods like the change of buffers that you suggested I'd say it's time for your own thread. One final thing to keep in mind is that some of us have poured a fair amount of time and money into this with no expectation to get any of it back. It's absolutely been worth it so far.

  Quote:


  Originally Posted by *Tyll Hertsens* 
_Just thought I'd let you guys know we've been following this thread with interest because we are about to introduct a version of this amp as well._

 

Tyll, that's very cool, I can't wait to see it, unfortunately your "tour" won't make it within several hundred miles of me. Headroom sold me my first real set of headphones (Ety 4ps) long before I knew of a place called Head-Fi. I don't know if my wallet will ever recover.

 Nate


----------



## sbelyo

Quote:


  Originally Posted by *n_maher* 
_I said tweak, as in to change slightly 
	

	
	
		
		

		
		
	


	


_

 

Well put...

  Quote:


  Originally Posted by *n_maher* 
_This project always has, I hope will continue to be, an effort to SLIGHTLY modify Pete's original design with an eye towards keeping costs low and adding flexibility to the design._

 

Definitely want to stay on track with the original design for certain. It works and sounds good for a reason. All we would want to do is have more spacing and pads for different ic's, caps etc.

  Quote:


  Originally Posted by *n_maher* 
_Remember that this all got started in an effort to just find a lower priced stock Millett board._

 

This has been a success

  Quote:


  Originally Posted by *n_maher* 
_If folks are really interested in diamond buffers and more exotic mods like the change of buffers that you suggested I'd say it's time for your own thread._

 

You can build those by hand and use pins from a dip socket. When completed, they will snap in just like a dip chip. There's no need to re re design. This board is all about flexability.

  Quote:


  Originally Posted by *n_maher* 
_One final thing to keep in mind is that some of us have poured a fair amount of time and money into this with no expectation to get any of it back.
 Nate_

 

I know and fully appreciate what has progressed so far... Thanks Nate and Drew A++++

 This is just my $0.02


----------



## skyskraper

well if we can get rid of the electrolytic output caps and reduce offset we might get an even better sounding amp 
	

	
	
		
		

		
		
	


	




 i'm not knowledgable enough to really know what im talking about and im sure its not as simple as simply adding a tle for the buffers and pulling out a few caps.

 if we are still tweaking the board, can we _please_ have a second set of output pads ? 
	

	
	
		
		

		
		
	


	




 also, id like to put this to the buyers, can we add the cost of the prototype boards given away to testers and tooling to the final cost of the boards to help compensate the guys who are out of pocket developping the new boards?


----------



## art633

Quote:


  Originally Posted by *skyskraper* 
_...also, id like to put this to the buyers, can we add the cost of the prototype boards given away to testers and tooling to the final cost of the boards to help compensate the guys who are out of pocket developping the new boards?_

 

This would certainly would get my vote - if not toooo much. I'm on a dam tight budget at present - being laidoff do SUCK!

 For my .1cents worth big mods should be left as a further development project, yeah I know diamonds do sound very interesting but lets get this re-vamp of the 'straight' design finished first. I have some other ideas too - for now though they are just in my head 
	

	
	
		
		

		
			





 /paper sketches and for another yet to come thread.

 M


----------



## drewd

I've been pretty continuously working on the board with small tweaks and changes. One of them freed up a fair amount of room in the center of the board around the buffers so that there is now enough room for an enterprising person to come up with a diamond buffer design that would plug into the two buffer sockets. I've helped out a bit by lining up the buffers and separating them by a standard distance (it escapes me right now, but it's either two or three DIP sockets).

 Regarding the DC offset, all I can say is welcome to the world of single ended triode tubes. A dual power supply for the buffers will not get rid of the offset - they are only current devices - they put out the same voltage that goes in and, because the plate is loaded with the CRD from V+, there is going to be a DC offset no matter what. The best thing to do is to make sure that the output caps are very good. This is one place where I can easily recommend a boutique cap without feeling a little uneasy.

 I'm assuming that the request for a second set of output pads is for the preamplifier guys - correct me if I'm wrong. I'll put a second set of pads at the back of the board for that.

 I've also made a little bit more room around some of the caps, particularly the output caps, both film and electrolytic. The tube locations are now the same distance from the front as from the back (that freed up the room around the buffers). There is also an empty area at the back of the board to allow for input and power jacks.

 I'm going to see if a JFET cascode will do any better than the CRD for loading the plate. If nothing else, it's maybe half the price of a CRD. Also, the idea that Tyll mentioned, of providing multiple preset bias levels is very interesting and something that I'd certainly like to look into. I'll see if I can fit in a circuit to do that if there is interest.

 That's about enough for one night for me. By the way, Tyll, that's really cool to hear about the Headroom plans! When I emailed Pete last month he said that you guys must have really liked his amplifier because when he left it there he never saw it again! 
	

	
	
		
		

		
		
	


	




 -Drew


----------



## skyskraper

at the back of the board is fine, or next to the current set of pads would be fine also to save any re arrangement of or extra traces. i like to put two headphone outs on my amps if there is space in the enclosure 
	

	
	
		
		

		
		
	


	




 nice work on the jfet cascode, crd's are a bit harder to come by for people who don't order from mouser 
	

	
	
		
		

		
		
	


	




 headroom switch: yes yes yes


----------



## bg4533

Quote:


  Originally Posted by *dsavitsk* 
_Would we be able to add a tle2426 at some point to give the buffers +/- voltage -- essentially giving them their own power supply. 
 -d_

 

You would also probably want to buffer it for a bit of extra power. That is a significant change at this point.

 I have used Blackgate NXs for coupling and I don't think I can tell a difference with or without them. A 220uF NX is only about $5.


----------



## dsavitsk

Quote:


  Originally Posted by *drewd* 
_Regarding the DC offset, all I can say is welcome to the world of single ended triode tubes. A dual power supply for the buffers will not get rid of the offset - they are only current devices - they put out the same voltage that goes in and, because the plate is loaded with the CRD from V+, there is going to be a DC offset no matter what._

 

I see, I guess I misunderstood Pete's article.

  Quote:


  Originally Posted by *bg4533* 
_You would also probably want to buffer it for a bit of extra power. That is a significant change at this point.

 I have used Blackgate NXs for coupling and I don't think I can tell a difference with or without them. A 220uF NX is only about $5._

 

I had been thinking of using one or per-anders' buffers (per a recommendation from guzzler), but my sense is that it is a totally different amp at that point, and might deserve a different tube.

 fwiw, I replaced the stock output caps in mine with 470uF Nichicon Muse caps from Percy and the amp sounds pretty good.

 -d


----------



## guzzler

d; re the Per-Anders buffers; I've not actually listened to them yet 
	

	
	
		
		

		
		
	


	




 I'm away for a couple of months, so if you'd like them to try out, I'll pop them in the post for you. They do have decoupling to a ground line between +/-, so I'm not sure how that would fit in to the Millett design. I suggest you get in touch with Per before going ahead, I'm sure he'll be willing to help.

 regards (and put me in for a board.... not that I need it 
	

	
	
		
		

		
		
	


	




)

 g


----------



## Finch&Music

I am following this thread in the last two weeks with great interest. When the 'new' version of the Millet amp can fully drive my Sennheiser 650 'to make music' I am considering to build one. 

 I am glad you take some more time to make the development of the new board more complete. Doing so it will take the endproduct to a higher level, even within the already given performance/cost relationchip. For me this is inspiring confidence in relation to your endproduct. 

 For me it is not a problem to spread some costs of the prototype boards over the production boards. I do not expect too much financial effect, so what are we talking about (some good coupling caps will cost you much more I am afraid). No one wants to build up a sub optimised ampboard. Rather an already optimised (and still flexible and easy to build) board than one that leaves a little too much to desire (f.e. only suitable for some phones) or a board that needs too much individual tweaking afterwards to get it right. In both situations it will scare off no so expierenced, but at the same time musically critical builders (your primary target group, I suppose). 

 As with all amps the quality of the psu in the end is decisive for the musical performance of the amp itself. A flaw psu can spoil every good amp and/or board design. Some other posters already pointed that out when they find out in reality that this amp is sensitive to a given psu. I have searched for information in old threads on this topic for this specific amp, but could not find specific information or experience with supplies on the 'older' version of the Millet amp. Do you know some links? 

 I am not surprised, that a steps (or similar psu's with some more VA) performed 'better to good' in relation to less beefier supplies. IMO, in this amp-case you should always use a relatively powerfull supply, because the supply lines for the tubeheaters only already needs 0,15 A each, let alone the dynamic supply loads for the other sections of the tubes and the buffer(-s). In the old days this tubes were supplied by a car-battery with always ample Amp reverve. So in that implementation there was principally never a problem with a reservoir for current or voltage. 

 But how about this implementation? With which supply specs are you and some experimenters testing the prototypes? What are the minimum requirements when using a 'normal' supply in a 'normal' situation for this amp? IMO workbench supplies are in most cases much beefier supplies than the supplies that will be used in the reality of listening to music in the home. Wich reserve should a prospective builder take into account (or are the specified on board amounts of electrolyitics more than sufficient for a proper functioning of the amp)?

 Just out of interest and I am not in any way an expert on (tube-)electronics, so may be the next items makes no sense at all or can't principally be applied to tubes like 12fk6 and the likes. Nevertheless, I want to put the following question. 

 Did you ever considered to make the board so flexible that a builder, when he/she wanted, could use separated supplies, in such a way that every eclectric function on the board has a dedicated supply in addition to the already positioned capacity-banks? Or are the electrolitic/foil-banks funtioning in such a way that in the practice of listening with this amp to music at a enjoyable level you could speak of 'separated' supplies already and therefore fully separated supplies are not of any benefit (and consequently are a waste of money)? 

 I am asking this because of an experence with modding a dynaco PAS3 some 20 years ago. When we supplied the heaters with a separated and much beefier supply (also with much more reservoir capacitance) the noisefloor of this preamp became very much lower (at that time all other things in the PAS were not yet changed exept for the couplingcaps). That modd alone contributed much to the overall musical performance and listening pleasure (the preamp was used within a quite revealing stereo system). 

 The above mentioned point of separated supplies, if technically applicable at all, is not contrary on your redesigngoals for flexibility and costcutting on the board itself, because the basic board can always be used as a board for one single supply and functioning totally sufficiently. Only when a builder in the future wants to go any further, hopefully after expierenced the basic version, there is on the basic-board already a choice to go for upgrading the supply-lines (f.e with a couple of tread supplies). This on board added flexibility could - may be - be done with the addition of a couple of extra jumpers and traces (unless this all fully disturbes too much the I suppose already given quality of the boardlay-out with bad electrical consequences, here some experts must let shine some light on the topic). For most builders this kind of onboard solution should not give too much added complexity in the buildingprocess and add at the same time some simple ensurance for future improvement. 

 May be you can comment on the above mentioned things. Wish you much succes in the further development and I am looking forward to building one in the near future.

 Greetings.


----------



## n_maher

Quote:


  Originally Posted by *skyskraper* 
_also, id like to put this to the buyers, can we add the cost of the prototype boards given away to testers and tooling to the final cost of the boards to help compensate the guys who are out of pocket developping the new boards?_

 

I won't speak for Drew but here are my thoughts on this - while I appreciate the offer, my answer is no thank you. This whole DIY thing runs on people's generosity, at least I think it does. Very intelligent, talented people (myself NOT included in that group) often volunteer great amounts of time to produce projects like the PPA, M3, MINT, PIMETA, etc. I have no concept as to what the cost of these projects were for the designers, but it certainly wasn't zero. So when this Millett project started to form I saw it as an opportunity to give a bit back to the community that has been so good to me. So while my cost in the end will have easily exceeded what I would have originally spent on boards from DIYCable I have no regrets about this choice. 

 So bring on the final round of tweaks! Also, it sounds as though one of our prototypes might be taking a trip and seeing a few other members. Hopefully we can get a little more feedback (the good kind 
	

	
	
		
		

		
		
	


	




) before the boards get ordered.

 Thanks again to all the folks involved in this project who've donated time, money, knowledge, whatever.

 Nate


----------



## art633

hi Nate

 That's generous thing to say and for me it's what I call the true spirit of DIY - it's just4fun

 Martin

 oppsss! almost forgot - the important bit - listen pleasure !

 M


----------



## drewd

I appreciate the offer to cover the proto expenses, but I'm with Nate - I don't have any problem paying for the initial proto run of boards. I've learned a few things in the process of working on the board and that more than offsets the small expense of the boards.

 Thanks guys!

 -Drew


----------



## multibit16

Quote:


  Originally Posted by *drewd* 
_I appreciate the offer to cover the proto expenses, but I'm with Nate - I don't have any problem paying for the initial proto run of boards. I've learned a few things in the process of working on the board and that more than offsets the small expense of the boards.

 Thanks guys!

 -Drew_

 

Well if it wasn't for people like you and Nate then we would have to stick with building these things on veroboard and end up with our projects looking like a rats nest 
	

	
	
		
		

		
		
	


	



 Anyway we all appreciate your time and effort and look forward to hopefully trying this thing out


----------



## skyskraper

im of the understanding that the film caps have a 15mm lead spacing, if its possible can we have pads for 5mm (most important for the non US people) and 10mm caps also?


----------



## individual6891

Quote:


  Originally Posted by *skyskraper* 
_im of the understanding that the film caps have a 15mm lead spacing, if its possible can we have pads for 5mm (most important for the non US people) and 10mm caps also?_

 

afaik this is already done.


----------



## skyskraper

cool, i must have glossed over that


----------



## JWFokker

So what's the current ETA on the final PCB design? I'm ampless and I have money burning a hole in my pocket. Should I just go with the currently available PCB and original design, or should I wait it out?


----------



## n_maher

JW,

 As I see things Drew is still working on the board a bit. What we are trying to acheive is an amp fully capable of driving higher impedance headphones like the Senn 580/6X0 series. This requires a part substitution and a little more testing. However, I think that the plan is to get that issue wrapped up by the end of next week. Provided everything is ready to roll (or at least nearly so) when I return from vacation on May 1st I'll start the group buy Monday the 2nd. The final details of the GB (ordering duration, requested man'f time, etc.) still have to be ironed out and I'm simply out of time before I leave. 

 I hope that this schedule works for you although I understand that being ampless sucks. However, you'll save around $30 waiting for this board and have a much greater degree of freedom when it comes to enclosures, parts selection and layout. Only you can decide whether or not it's worth it.

 Have a great week everyone,

 Nate


----------



## MisterX

Quote:


  Originally Posted by *drewd* 
_Also, the idea that Tyll mentioned, of providing multiple preset bias levels is very interesting and something that I'd certainly like to look into. I'll see if I can fit in a circuit to do that if there is interest._

 

If you implement this feature I would suggest that you simply add another pair of trimmers.
 That way we can still adjust the bias separately for each channel (compensates for poorly matched tubes) and you can also adjust the "high" and "low" setting to whatever bias levels you want.


----------



## drewd

I think that we're almost ready to roll! Here are some images of the board in what I hope is its final incarnation. I did not fit in the selectable bias - it's just a little too crowded in there - but that doesn't mean that it can't be air-wired by an intrepid builder!

 Also, I did some testing with the JFET cascode and I just didn't see much of an advantage to it, but definitely some potential problems. The current through the CRD is quite small and an adjustable cascode is just asking for trouble, in my opinion, because it's easy to really crank the current up. My feeling is that it would be just as easy to experiment with different CRDs to find a value that you like (if you're into that - Pete's results are in the PDF).

 The images:

Top 
Bottom
Both Layers 
Render 

 At this point, I think that it would be best to freeze the features and make changes only if somebody sees an error in the board. Please post here if you see something out of whack. Otherwise, I'm turning it over to Nate!

 -Drew


----------



## pabbi1

Has the high impedence headphone (HD 58x / 6x0) issue been addressed?


----------



## sbelyo

Quote:


  Originally Posted by *pabbi1* 
_Has the high impedence headphone (HD 58x / 6x0) issue been addressed?_

 

Yes, and no. There wasn't really any drastic changes to the original design. The issue was that the volume knob was at 3/4 to produce high volume. I have run my HD-580's on it with no issues on volume. I only noticed that if the source was low, I was forced to turn the volume up more. In my opinion I would reduce the resistor on the output to 10 Ohms. That seemed to give me a little more volume with the sennheisers.

 All in all the volume was plenty loud enough for my listening levels. I don't think the board layout would need to be changed to change the results. By changing the CRD for different values and trying different bias voltage settings it will solve the issue.


----------



## drewd

Quote:


  Originally Posted by *sbelyo* 
_Yes, and no. There wasn't really any drastic changes to the original design. The issue was that the volume knob was at 3/4 to produce high volume. I have run my HD-580's on it with no issues on volume. I only noticed that if the source was low, I was forced to turn the volume up more. In my opinion I would reduce the resistor on the output to 10 Ohms. That seemed to give me a little more volume with the sennheisers.

 All in all the volume was plenty loud enough for my listening levels. I don't think the board layout would need to be changed to change the results. By changing the CRD for different values and trying different bias voltage settings it will solve the issue._

 

I'll second that. In fact, the output resistor can be completely eliminated if you desire. Pete originally included it as a current moderator for the buffers in case there was a short circuit. But the BUF634s are internally protected against that sort of thing, so it's not necessary. The volume does go up for high impedance headphones if it's jumpered.

 -Drew


----------



## blip

Did you do any testing with a resistor instead of the CRD? That would be a lot easier to adjust than the CRD... Also it would make part ordering a lot easier.

 I know Millet decided against them, but it might be an interesting experiment.


----------



## n_maher

Quote:


  Originally Posted by *pabbi1* 
_Has the high impedence headphone (HD 58x / 6x0) issue been addressed?_

 

Yes, my prototypes had a 22*K*ohm (instead of 22ohm) output resistor which is why I had such volume problems. Jebus, I'm an idiot! 
	

	
	
		
		

		
			





 Also, as Drew mentioned, with the Buf634's these two resistors aren't needed at all. We're leaving the positions on the board so that if folks go with a different buffer configuration (diamond or otherwise) it's easily added. 

 Drew and I are hammering out the final details for the group buy so look for a new thread soon, I promise 
	

	
	
		
		

		
		
	


	




 !

 Nate


----------



## drewd

Quote:


  Originally Posted by *blip* 
_Did you do any testing with a resistor instead of the CRD? That would be a lot easier to adjust than the CRD... Also it would make part ordering a lot easier.

 I know Millet decided against them, but it might be an interesting experiment._

 

Yes, thanks for bringing that up. I tinkered around with a variety of resistors between 50K and 220K. With my Beyerdynamic DT880s, I found that the 56.2K resistor with my 30V benchtop power supply was the best alternative to the CRD. That gave a quiescent bias current of about 0.53mA (calculated). The difference between the resistor and the CRD, of course, is that the bias current will vary with the output of the tube with a resistor, but not (or not much) with a CRD. Still, the difference between the resistor and the CRD was almost inaudible - and I can't say for sure if the difference was from the resistor or just sample-to-sample variations in the amplifiers.

 The thing to keep in mind, I think, is that this amplifier is, for the money, a real slam dunk from a performance point of view, but it's not the be-all, end-all of amps. A very, very slight sonic difference between 50 cents in resistors and $3.50 in CRDs is not enough to make me take a stand against using a resistor. And I can't say that the sonic difference was bad - just ever so slightly different...but not enough that I could say exactly what that difference was.

 -Drew


----------



## guzzler

Regards class-a biasing; have you seen sijosaes mini CCS? 

http://headwize.com/ubb/showpage.php...4179&srch=CCS;

 some of the pictures have gone missing, but you get the general idea. The transistor he specs are 2N2222, and 2N2907, but you could substitute with 2N3904 and 2N3906. The schematic has gone, I'll see if I can dig it out

 g


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_I think that we're almost ready to roll! Here are some images of the board in what I hope is its final incarnation. I did not fit in the selectable bias - it's just a little too crowded in there - but that doesn't mean that it can't be air-wired by an intrepid builder!

 Also, I did some testing with the JFET cascode and I just didn't see much of an advantage to it, but definitely some potential problems. The current through the CRD is quite small and an adjustable cascode is just asking for trouble, in my opinion, because it's easy to really crank the current up. My feeling is that it would be just as easy to experiment with different CRDs to find a value that you like (if you're into that - Pete's results are in the PDF).

 The images:

Top 
Bottom
Both Layers 
Render 

 At this point, I think that it would be best to freeze the features and make changes only if somebody sees an error in the board. Please post here if you see something out of whack. Otherwise, I'm turning it over to Nate!

 -Drew_

 


 As ever an interesting lookout to the boards. I am not an expert to 'read' them in a technically sense , so I would like to let that evaluation of them over to the experts. 

 On the other hand I have tried to follow the board layout (especially the componentnumbers) at the hand of the original Pete Millet schematics. Serveral times I became confused by the newly used numers of several components. Is it possible to produce a updated schematic with updated componentnumbers and componentlist? 

 In my opininion that could be also an excersise or task by someone who is experiended to execute such a thing other then you or the organiser of the groupbuy (you both have done enough!). I think that an up to date schematic and componentlist (independent of historical examples/numbers) are useful for prospective builders.

 greetings.


----------



## guzzler

Sorted out the schematic:






 And the board






 The 2N3906 is on the right, the red LED at the top. Leave the leg of the LED dangling down to connect in place. The resistors are soldered on the top of the board directly to the TRs

 Bias with 2K resistors is ~1.2mA

 g


----------



## n_maher

Quote:


  Originally Posted by *Finch&Music* 
_On the other hand I have tried to follow the board layout (especially the componentnumbers) at the hand of the original Pete Millet schematics. Serveral times I became confused by the newly used numers of several components. Is it possible to produce a updated schematic with updated componentnumbers and componentlist? _

 

The updated parts list is already complete. I'm just putting it into excel format with hot-links to vendors so that ordering parts will be as easy as possible. We have attempted to renumber things so that the part numbers correspond between the channels, i.e. R5L serves the same function as R5R. You'll also note that Drew took the time to include the acutal component value on the board along with the part designation.

 The schematic really hasn't changed as far as I can tell, the board layout has been radically reorganized but the amplifier itself still functions exactly the same way, I think. Drew can correct me here if I'm wrong.

 I'll be trying, as much as time allows, to put together fairly detailed instructions to go along with the revised board. I'm not sure I'll get it to the level of Tangent's Cmoy pages but hopefully pretty close. It'd be wise for those who don't feel 100% comfortable to hold off ordering parts until at least the end of the ordering phase of the group buy. That'll give Drew and I the maximum amount of time tweak the documents and triple check them for errors.

 I hope that answers your questions 
	

	
	
		
		

		
		
	


	




. 

 Nate


----------



## Finch&Music

Quote:


  Originally Posted by *n_maher* 
_The updated parts list is already complete. I'm just putting it into excel format with hot-links to vendors so that ordering parts will be as easy as possible. We have attempted to renumber things so that the part numbers correspond between the channels, i.e. R5L serves the same function as R5R. You'll also note that Drew took the time to include the acutal component value on the board along with the part designation.

 The schematic really hasn't changed as far as I can tell, the board layout has been radically reorganized but the amplifier itself still functions exactly the same way, I think. Drew can correct me here if I'm wrong.

 I'll be trying, as much as time allows, to put together fairly detailed instructions to go along with the revised board. I'm not sure I'll get it to the level of Tangent's Cmoy pages but hopefully pretty close. It'd be wise for those who don't feel 100% comfortable to hold off ordering parts until at least the end of the ordering phase of the group buy. That'll give Drew and I the maximum amount of time tweak the documents and triple check them for errors.

 I hope that answers your questions 
	

	
	
		
		

		
		
	


	




. 

 Nate_

 


 Thanks for your immediate reaction! It looks that I was only a little impatient, because you and your mate adressed all I am asking for. Go on so, you deliver quality by that.

 greetings.


----------



## drewd

The schematic has not changed, only the board layout.

 Guzzler, thanks for digging up sijosae's bias circuit. He's the king of miniaturization! I don't think that it will be able to make it on the board for the group buy, but there is enough room to substitute it for the CRD as a separate component.

 By the way, I left an area 2.75" x .75" in the center of the board clear for anyone who wants to try their hand at a discrete output buffer. The sockets are separated by the space of three socket widths, so it should be easy to align the interface with the board.

 For that matter, a really clever person could also put sijosae's bias circuit on that board and run a jumper from the anode pad of the diode to the board, omitting the CRD. Just a though.

 -Drew


----------



## guzzler

No worries Drew, my pleasure. Nice to get sijosae's stuff out and about, it's always delightful! The size of the board is such that it just drops straight into a 7.5mm hole, just like that on the board.

 It's looking very nice all round, a fine job!

 g


----------



## sbelyo

Quote:


  Originally Posted by *guzzler* 
_The 2N3906 is on the right, the red LED at the top. Leave the leg of the LED dangling down to connect in place. The resistors are soldered on the top of the board directly to the TRs

 Bias with 2K resistors is ~1.2mA

 g_

 

I always forget the right way to position leds...

 Can someone refresh my mem Is it short leg of LED = In and long leg = Out or is it reversed?

 I may take a stab at these baby's


----------



## guzzler

-ve ("out" in the case, lower potential really) is the short leg, and has a flat on the body. +ve has the longer leg, and goes nearer the top the way I've drawn it

 g


----------



## sbelyo

got it...


----------



## Nisbeth

My usual rule of thumb is that minus is where something is missing... 
	

	
	
		
		

		
			







 /U.


----------



## n_maher

Word of warning, if anyone would like to throw their two cents about the "final" board design into the mix today is your last day to do so.

 Nate


----------



## drewd

At the risk of veering off track, here's an example of a discrete buffer that will fit in the ~2.5"x0.75" space on the amp. It plugs into the BUF634 sockets.






 It's taken from Sijosae's implementation of Jung's diamond buffer:






 -Drew


----------



## jerb

will those be sold along with the millet PCB (at extra cost of course)?

 or are we going to have to order/make them ourself?


----------



## pabbi1

Gerb beat me to it... yes, great risk of straying...


----------



## drewd

Quote:


  Originally Posted by *jerb* 
_will those be sold along with the millet PCB (at extra cost of course)?

 or are we going to have to order/make them ourself?_

 

Oops - I guess that's another can of worms 
	

	
	
		
		

		
		
	


	




 At this stage, I don't even know if it will work. I'll build a couple and test them. If they work and if they make a difference, then we can look into having them made.

 My main intention was just to show that a stereo diamond buffer could fit in the space that I allowed on the amp's PCB.

 -Drew


----------



## jerb

i wasnt sure what difference it made or why it was used thats why i was asking, i should probably search the fourm for some thread about them


----------



## n_maher

Okay folks, the board is done and the group buy is on - see here . Please continue to use this thread if you have any questions about the board revisions, layout, etc. However, posts in this thread related to the group buy will be ignored. 

 Thanks,

 Nate


----------



## flecom

if your going through all the trouble of making new pcb's why not replace the weakest part of the millet, that buf634... why not attach the discrete output part of something like the M3 instead of using an ic buffer?

 i have a millet and stoped using it becuase it was unable to drive my K1k's with those buf634's... but using a pair of output transistors would definately be an improvement IMHO

 good luck with the group buy, you will love the amp, i still use mine with my DT990's


----------



## vksy

Quote:


 Oops - I guess that's another can of worms 

 At this stage, I don't even know if it will work. I'll build a couple and test them. If they work and if they make a difference, then we can look into having them made.

 My main intention was just to show that a stereo diamond buffer could fit in the space that I allowed on the amp's PCB.

 -Drew 
 

Nice layout! Have you thought about regulating the current? I added diodes to sijosae's variant for my tweaked P2P Millett amp (not yet built), and the buffer area didn't change much in size even with the extra components.


----------



## n_maher

Replacing the BUF634 was discussed at length (earlier in this thread). Ultimately it was decided that in the interest of keeping this board true to the original (one of the stated goals) we'd just go with the original part. Also, you might want to take notice that we've provided enough room at the buffer locations for some enterprising builder to experiment with different buffer configurations, including diamond buffers like the PPA. I'm still not sure that this amp would adequately drive K1000s, but again, that wasn't really the goal of this particular project. 

 Thanks for your input.

 Nate


  Quote:


  Originally Posted by *flecom* 
_if your going through all the trouble of making new pcb's why not replace the weakest part of the millet, that buf634... why not attach the discrete output part of something like the M3 instead of using an ic buffer?_


----------



## drewd

Quote:


  Originally Posted by *vksy* 
_Nice layout! Have you thought about regulating the current? I added diodes to sijosae's variant for my tweaked P2P Millett amp (not yet built), and the buffer area didn't change much in size even with the extra components._

 

I'll add the parts and see how it works out. It's a worthwhile upgrade to the discrete buffer.

 I'm going to breadboard the circuit this weekend (if I get all my other work done first) and see how it all works out.

 -Drew


----------



## Buzzerbro

Alternate source for Wima Capacitors:

TAW Electronics, Inc

 I bought 24 of the following part for [size=small]$0.68 each![/size]

 MKP10 0.22uF 160VDC 10% PCM 15mm Capacitor

 Shipping was about $5. You can't order online so just shoot them an email and they will process your order. They were very helpful.


----------



## drewd

Quote:


  Originally Posted by *vksy* 
_Nice layout! Have you thought about regulating the current? I added diodes to sijosae's variant for my tweaked P2P Millett amp (not yet built), and the buffer area didn't change much in size even with the extra components._

 

Whew, that's a lot of parts in a little space:







 If the breadboarded circuit works on Sunday, I'll order some boards on Monday and see how it works out.

 -Drew


----------



## individual6891

Quote:


  Originally Posted by *drewd* 
_Whew, that's a lot of parts in a little space:






 If the breadboarded circuit works on Sunday, I'll order some boards on Monday and see how it works out.

 -Drew_

 

What about this small version?..


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_I'll add the parts and see how it works out. It's a worthwhile upgrade to the discrete buffer.

 I'm going to breadboard the circuit this weekend (if I get all my other work done first) and see how it all works out.

 -Drew_

 

some remarks:

 1. Does 'regulating' on board of the shown 'really impressive' diamond buffer also means that it is possible to feed this kind of buffer with a separate supply, if you want to? I mean 'separate' of the supplies for the tubes. Indeed, that is costlier but when it really pays, why not.

 2. Or is it that you extract the supply for the buffer from the basic board and that there is no alternative for a builder? If so, does the implementation of this kind of buffer (what I encourage) imply a different on board capacitance value in relation to this specific buffer?

 3. Are you eventually going to test the possible benefit of a separate supplying of the buffer? Looks to me a quite simple exercise. I am asking this because in my simple view a current divice is always of influence (taking severe dynamic loads because of 'playing music' !) on the existing supply configuration. 

 greetings


----------



## amb

Quote:


  Originally Posted by *individual6891* 
_What about this small version?..
 (sijosae's buffer)_

 

This one has very low input impedance and may not be a good match for being driven by tubes.


----------



## skyskraper

what are your designer's views on substituting something like j503 or j505 for the 1n5291 crd? theyre a lot easier to come across down under and im sure other places


----------



## drewd

Quote:


  Originally Posted by *skyskraper* 
_what are your designer's views on substituting something like j503 or j505 for the 1n5291 crd? theyre a lot easier to come across down under and im sure other places_

 

Yes, use the j503, it would be a direct replacement for the 1n5291. I'll look at the board and see if I can put an alternate pin location in it to allow for the TO-92 package so that you don't have to bend the pins to fit.

 -Drew


----------



## skyskraper

that would be great thanks


----------



## flecom

Quote:


  Originally Posted by *n_maher* 
_Replacing the BUF634 was discussed at length (earlier in this thread). Ultimately it was decided that in the interest of keeping this board true to the original (one of the stated goals) we'd just go with the original part. Also, you might want to take notice that we've provided enough room at the buffer locations for some enterprising builder to experiment with different buffer configurations, including diamond buffers like the PPA. I'm still not sure that this amp would adequately drive K1000s, but again, that wasn't really the goal of this particular project. 

 Thanks for your input.

 Nate_

 


 sorry i didnt read the entire thread...


----------



## n_maher

No worries, I hope that my reply didn't come off sounding like I was upset, that is certainly not the case! 
	

	
	
		
		

		
		
	


	




 Nate


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_I'll add the parts and see how it works out. It's a worthwhile upgrade to the discrete buffer.

 I'm going to breadboard the circuit this weekend (if I get all my other work done first) and see how it all works out.

 -Drew_

 

May be against all attacks on the atmosphere on this site within head-fi (imo based on quibling about some miniscule principles on building diy-headfi-amps with arguments going around among some super-ego's in this area) I want - humbly - ask if there is some progress on the point of implement a discrete buffer on the Pete Millet Hybrid? 

 If there is any technical progress with soundwize results could that lead to a specific add-on pcb? 

 Please, please I am not attending to a possibly pcb-groupbuy: I never dare to do any more!!!!! Because I do not want to be dammed from this site! On the other hand the moderators put enough fear on me to look out! 

 After some thougth, the hell with it, it is too much fun on this site ,especially at my age. 

 Well, loose from emotions, I am only interessted in a technical follow-up. 
 So, will a discrete buffer in the context of the Pete Millet Hybrid deliver a positive sonical result? That's all that count, in my opinion.

 In my opinion such a question is whithin all the rules. Or am I wrong? 

 greetings

 A view from the outside 

 I this case from the Netherlands.


----------



## drewd

Yes, progress indeed. Sorry for not keeping everyone up to date on this. The discrete buffer does make a difference, particularly for low impedance cans. I put together a rather messy-looking implementation of the "regulated" buffer as mentioned above and listened with Grado SR225s, Beyerdynamic DT880s and Sennheiser HD580s. I felt that the Grados and the Beyers improved their low end performance on very dynamic tracks (I recklessly listened to Telarc's 1812 Overture SACD), but even the Senns felt a little more like "being there". So, all in all, a good idea, I think, even lashed together on a breadboard with wires all over the place.

 I ordered a few boards to test today. If they work OK, I'll post the Eagle .brd file on the group buy web site for anybody to use as they see fit. I won't be coordinating any group buys, though. It puts me in an awkward position.

 Let me point out, though, that the BUF634 is no slouch! It performs very well in the Millett Hybrid and Pete made a very good choice when he selected it. So nobody should feel like they HAVE to go the discrete route. The change is not dramatic - it's just a bit better. I'd experiment with tube rolling before comitting to the discrete buffer.

 -Drew


----------



## drewd

Nate and I did one last spin of the board before completing the group buy. Here's a picture:






 There are two minor changes not in this board that will be on the final board. The first is some minor text changes and the second is the placement of the alternate positions for the CRDs. Otherwise, what you see is what you get!

 A disorganized parts list and some other information is on http://hybrid.fluidlight.com. Board stuffing instructions will be posted there soon - the plan is to have everything ready to go on the web page well before the boards arrive. Nate and I welcome any feedback about the web page that you have.

 By the way, the board is really rectangular - the edges are straight! I guess my camera is curved 
	

	
	
		
		

		
		
	


	




 -Drew


----------



## drewd

The parts list is revised and includes multiple sources for US amplifier builders. I'll explore non-US suppliers next.

 Please let me know if you see any problems with the parts list. Also, if anybody has other recommendations, I'd like to hear about them.

 I'm going to try to reorganize the web page so that it's easier to navigate instead of being one big, long page.

 -Drew


----------



## dr_digits

I have searched around and I can't find any information about the possiblity of stacking buf634s in this amp. Can it be done?


----------



## drewd

Quote:


  Originally Posted by *dr_digits* 
_I have searched around and I can't find any information about the possiblity of stacking buf634s in this amp. Can it be done?_

 

Yes. Bear in mind that the heaters draw 150mA. If you use the minimum recommended 400mA power supply, that leaves 250mA of current left for everything else, including the buffers, bias current and LED. That's less than 125mA per buffer.

 That's still enough to generate 800mW into a set of Grados...ouch! And without nearing the limits of the buffers' current capability.

 Anyway, what I'm getting at is that if you want to stack buffers, you may want to look into increasing the current output of the power supply. I'm using a 30V/1A regulated power supply and I find that the amplifier has plenty of power to drive headphones from 32 ohms to 300 ohms.

 My recommendation is to not stack the buffers unless you find that you're running out of current.

 -Drew


----------



## aeroes

EDIT: Wrong thread.


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_The parts list is revised and includes multiple sources for US amplifier builders. I'll explore non-US suppliers next.

 Please let me know if you see any problems with the parts list. Also, if anybody has other recommendations, I'd like to hear about them.

 I'm going to try to reorganize the web page so that it's easier to navigate instead of being one big, long page.

 -Drew_

 

I have looked at the (most recent version for the) pages for introduction, amp specs and searching components etc. 

 It looks very good and with some add on information for building in combination with navigation a builder should be able to make the project a success. 

 You requested for some recommendations. I have some. May be you can do something with them.

 1. At row one in the notes R7L/R should be C7L/R.

 2. I would suggest you to split row one and three to make a clear distinction between caps for supply and couplingcaps. In that way you can also make specific notes in relation to specific selection and/or electric functioning.

 3. Convenient to see remarks on lead space. Even so convenient is mentioning of quantity in a separate column, so there is less chance for mistakes while ordering.

 4. You mention minimum values for the caps. Are there also maximum values taken into account (apart from fysical restriction caused by the on board dimensions)? Peter Millet mentioned some percentages about that, because the real values above the minimum were not critical. I am only looking for notes that can be significant for the sonical funtioning of the amp that are base on your listening experience untill now.

 5. On my computer setup I could not reach yet the spec sheets of the 12AE6A (both brands). Only 'URL not found' is shown. All the others give a nice pdf document.

 6. Are there (really audible) differences between the tubes of different brands within the context of this amp? If so is it wise to look out for a special kind of brand? Or are there still some experiments going on by builders of the prototype boards and will there soon be some report on that on the forum? 

 7. Are you willing to give some advise on bias settings for different tubetypes, how high and/or low, some 'do's and dont's'? The spread information from the long construction thread and P.Millet article is for me still a little confusing.

 Greetings.


----------



## n_maher

I'm trying to do some research for folks on alternate enclosures (in my free time 
	

	
	
		
		

		
		
	


	




 ). Another member suggested that I look at the Lansing MicroPak C type cases. These cases can be ordered with some different options from the standard hammond cases and don't cost _that_ much more. They also still support the eurocard width. I'm trying to get my hands on a couple of these and I have a set of color samples on the way. And I'm trying to stick to "budget" cases with an eye towards keeping the overall cost of the project.

Take a look here for the C style cases.


----------



## drewd

Thanks for the great feedback!

  Quote:


  Originally Posted by *Finch&Music* 
_1. At row one in the notes R7L/R should be C7L/R._

 

Fixed

  Quote:


 2. I would suggest you to split row one and three to make a clear distinction between caps for supply and couplingcaps. In that way you can also make specific notes in relation to specific selection and/or electric functioning. 
 

Split row 1. I'll address the function and specific selection notes in a separate section that will be added this weekend. That will cover row 3 as well, but since the cap value for the film coupling caps plays virtually no role in the frequency response, it's just as well to lump them with the power supply bypass caps. In terms of quality, I'll talk about that in the build guide.

  Quote:


 3. Convenient to see remarks on lead space. Even so convenient is mentioning of quantity in a separate column, so there is less chance for mistakes while ordering. 
 

Done

  Quote:


 4. You mention minimum values for the caps. Are there also maximum values taken into account (apart from fysical restriction caused by the on board dimensions)? Peter Millet mentioned some percentages about that, because the real values above the minimum were not critical. I am only looking for notes that can be significant for the sonical funtioning of the amp that are base on your listening experience untill now. 
 

I'll address that in the parts selection section as well.

  Quote:


 5. On my computer setup I could not reach yet the spec sheets of the 12AE6A (both brands). Only 'URL not found' is shown. All the others give a nice pdf document. 
 

I have big fingers 
	

	
	
		
		

		
		
	


	




 Maybe someday my computer will realize that it's supposed to know what I mean, not what I type. Fixed.

  Quote:


 6. Are there (really audible) differences between the tubes of different brands within the context of this amp? If so is it wise to look out for a special kind of brand? Or are there still some experiments going on by builders of the prototype boards and will there soon be some report on that on the forum? 
 

It wouldn't surprise me if there were audible differences, but so far I have not been able to hear any. I'd like to know, of course. The most audible differences, as you'd probably expect, is from different tube types. I'd also be happy to hear from anybody who wants to volunteer some descriptions of the sonic qualities that they perceive from the different tubes.

  Quote:


 7. Are you willing to give some advise on bias settings for different tubetypes, how high and/or low, some 'do's and dont's'? The spread information from the long construction thread and P.Millet article is for me still a little confusing. 
 

That will definitely be included in the build guide.

 Thanks again for the great suggestions!

 -Drew


----------



## n_maher

In an effort to make sure that everyone ends up with a working PCB Drew and I went ahead and ordered up a set of "pre-production" boards. Mine arrived today and knowing my schedule for the weekend I set out to do some soldering this evening. These boards are 98% the same as the production boards, I think Drew might have added an alternate cap spacing in a couple locations and tweaked some text around.

 Step 1 - put girlfriend to bed, check.
 Step 2 - fire up the iron, check.
 Step 3 - 2-1/2 hrs of soldering and wiring, check.
 Step 4 - kick back and enjoy, check.

 I also decided that I'd try out the LED holes in the bases of the PCB. Please note that if you order your tube sockets from Tube Depot you'll have to "customize" them in order to allow light to shine through as they have a solid center. I fixed that with my drill 
	

	
	
		
		

		
		
	


	




. How's it all work you might ask? It sounds fantastic (still burning in) and looks, well you be the judge... and please pardon the hasty photography, it's 12:15am and I have to be at work in less than 8hrs so I'm trying to get to this wrapped up. 











 I'll get some better shots when my Lansing enclosures get here Tuesday and I finally get one of these cased up.

 Nate


----------



## aeroes

Magnificent!

 So gorgeous! Tube lights makes me wanna turn-off the lights while listening to music


----------



## individual6891

Very good, how does it sound? Looks a bit sparkly huh?


----------



## cetoole

Quote:


  Originally Posted by *n_maher* 
_In an effort to make sure that everyone ends up with a working PCB Drew and I went ahead and ordered up a set of "pre-production" boards. Mine arrived today and knowing my schedule for the weekend I set out to do some soldering this evening. These boards are 98% the same as the production boards, I think Drew might have added an alternate cap spacing in a couple locations and tweaked some text around.

 Step 1 - put girlfriend to bed, check.
 Step 2 - fire up the iron, check.
 Step 3 - 2-1/2 hrs of soldering and wiring, check.
 Step 4 - kick back and enjoy, check.

 I also decided that I'd try out the LED holes in the bases of the PCB. Please note that if you order your tube sockets from Tube Depot you'll have to "customize" them in order to allow light to shine through as they have a solid center. I fixed that with my drill 
	

	
	
		
		

		
		
	


	




. How's it all work you might ask? It sounds fantastic (still burning in) and looks, well you be the judge... and please pardon the hasty photography, it's 12:15am and I have to be at work in less than 8hrs so I'm trying to get to this wrapped up. 











 I'll get some better shots when my Lansing enclosures get here Tuesday and I finally get one of these cased up.

 Nate_

 

Nate, those look so sexy, especially the first shot. I really cant wait now.


----------



## n_maher

Quote:


  Originally Posted by *individual6891* 
_Very good, how does it sound? Looks a bit sparkly huh? 
	

	
	
		
		

		
		
	


	


_

 

So far it sounds great. I've got it and M3 with me at work today to do some quality listening (along with Senn 600s and Grado 225s). I'll post some impressions later in the day. And I take back everything I said about the LED holes in the bottom of the board, they rock! I'll get some better night shots tonight with my real digicam, I was hurrying last night w/ the point and shoot.

 This amp, along with my M3 will be squaring off against a PPA V2 tonight as a friend and I are getting together to have a bit of a mini-meet / review party. I think that there's a real lack of information out there about how the various DIY amps stack up against each other so we're looking to try and help that cause. I apologize in advance for being a crappy reviewer 
	

	
	
		
		

		
		
	


	




 .

 N


----------



## Finch&Music

Quote:


  Originally Posted by *n_maher* 
_So far it sounds great. I've got it and M3 with me at work today to do some quality listening (along with Senn 600s and Grado 225s). I'll post some impressions later in the day. And I take back everything I said about the LED holes in the bottom of the board, they rock! I'll get some better night shots tonight with my real digicam, I was hurrying last night w/ the point and shoot.

 This amp, along with my M3 will be squaring off against a PPA V2 tonight as a friend and I are getting together to have a bit of a mini-meet / review party. I think that there's a real lack of information out there about how the various DIY amps stack up against each other so we're looking to try and help that cause. I apologize in advance for being a crappy reviewer 
	

	
	
		
		

		
		
	


	




 .

 N_

 

Your review work will be greatly appreciated by me. Every review will be 'subjective', so do not take an too humble standpoint too soon. In the end I have to judge myself what this amps can do with quality musicreproduction, but your review can give some insight and expectation already and can motivate to build the amp as soon as possible. 

 Just out of curiosity, I want to ask with what kind of music will you perform the comparasions between the three amps. Will there be enough spreading over various kind of repertoire? Hopefully you have enough time for that. 

 I for example am especially interested in the results or impressions with various kinds of classical music and jazz. Especially in combination with the Sennheiser 6xx, because I own a senn 650/MG Head mkIII combination. 

 If it is not too much trouble I hope you and your friends can explore this musical scope to some extend.

 Greetings


----------



## n_maher

Quote:


  Originally Posted by *Finch&Music* 
_Just out of curiosity, I want to ask with what kind of music will you perform the comparasions between the three amps. Will there be enough spreading over various kind of repertoire? Hopefully you have enough time for that._

 

We're going to go as far as the catelog allows. My classical collection is woefully lacking, but I'll do what I can. I have some but we're trying to stick to tracks that we both know equally well so that we'll be better equipped to pick up on the subtle nuances of each amp. I have a feeling that the night will start out very structured and degrade quickly 
	

	
	
		
		

		
		
	


	




. We've budgeted several hours for this so here's to hoping we get to lots of different material.

 We will absolutely be running accoustic tracks during the listening session as well as pieces involving a full orchestra. From that I think you'll be able to get the general idea for how the amps would do for pure classical music. As for jazz, I'm sorry to say that my current music library is lacking entirely. Not from lack of desire, just lack of time and funds to properly explore the genre.

 Look for the full comparison by the end of the week (hopefully).

 Nate


----------



## drewd

Well, I've got loads of jazz and classical music on this end and I've been listening like a maniac for the past few weeks. Here's the latest incarnation that I'll be evaluating this week:
















 PCB is sideways in a Hammond 1455R1601BK. It fits perfectly in the rails and there's enough space front and back for the jacks, switch and volume control. I built this using the Panasonic caps in the parts list. The Panasonic FC caps are much shorter than the Elna Cerafine or Silmic caps, so they give a little bit more flexibility in case choice. Of course, as you can see, the tubes stick right on out, but that's the fun part.

 I have a couple of 7/8" rubber grommets that I'll slip into the case holes to finish things up.

 Sounds great - there are no errors in this PCB, so unless somebody comes up with a really major, killer request that just _has_ to be done, I think that the design should be considered frozen at this point.

 Thanks to everyone for the great input and suggestions. I'll post a more detailed listening review in a few days.

 -Drew


----------



## dsavitsk

Quote:


  Originally Posted by *drewd* 
_PCB is sideways in a Hammond 1455R1601BK. It fits perfectly in the rails and there's enough space front and back for the jacks, switch and volume control._

 

Is there room to cram a PS of some sort in there? Perhaps a small toroid could fit on the board where the pot usually goes?

 -d


----------



## drewd

Quote:


  Originally Posted by *dsavitsk* 
_Is there room to cram a PS of some sort in there? Perhaps a small toroid could fit on the board where the pot usually goes?_

 

I don't think so, but in the 1455R2201 there might be - there is another 2.3" of space, so it might be possible - that would give about 4"x6.3" of open space. I don't know about height, though - the case is only 1.2" tall on the outside, so it might be a tight fit!

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_I don't think so, but in the 1455R2201 there might be - there is another 2.3" of space, so it might be possible - that would give about 4"x6.3" of open space. I don't know about height, though - the case is only 1.2" tall on the outside, so it might be a tight fit!

 -Drew_

 

Your implementation looks great, also the funfactor. The choice of the case will be the difficult one in my situation. Most likely I have to import one case at substantial shippingcost, because I still can not find a case at local suppliers that suites my taste. I still regret I did not participate in the group buy for the M3 Cases, because the millet amp would also have been a good candidate for the inside of that case.

 I hope I can find in your review remarks about some of your listening experiences with classical music. Especially interested in vocals, cello, solo piano, acoustic guitar, brass and smaller ensembles. 

 Will you also put this incarnation of the Millet amp into perspective with some other amps/phones? I hope I do not asking too much!

 Looking at the latest version of the partslist I have some other remarks/suggestions:

 1. Looking at several datasheets of electrolytic caps, I have seen some specs that are may be of interest in the choiceprocess. I am taking the standpoint, that at supply points it is primarily relevant to use as low impedance caps as is possible (given size/value/voltage). I myself are going to choice between elna silmic II or panasonic fc, because they are relatively easy to obtain from where I live (otherwise I have to order abroad). 

 I have seen specs about tangens-delta/dissipation factors and impedance ratings for same voltages/values for different brands (elna silmic, elna cerafine, panasonic fc or fm, nichicon or rubicon za/zl) . What I see is that mostly these figures at the same value/voltage are different (Elna Silmic II scores a little better here than some others; assuming that the figures of industrial producers are 'objective' and comparable.). 

 When you however compare brands for the same value at different voltages then the figures grow to each other. For example in case of same value: a higher volatage panansonic fc comes technically more near to a Silmic lower voltage. My general conclusion is to go for the lowest impedance/cost relation, so it is good to use a higher voltage value in the Millet amp (sometimes 50-63V, voltage rating a little overdone, but the benefit is in the thechnical aspects and hopefully in the musical results). 

 Given this observation: is it a valid argumentation to choose a supply-cap at a higher voltage/lower impedance to technically equal a 'boutigue' cap and invest your money elsewere? In my case I spare many euro's when I go for Panasonics FC or something like that. 

 2. Another case is the coupling cap. I have read many messages on headfi and diyaudio about caps, that have to function in such a position. Much opinions, sometimes very conflicting and confusing. Now that there is no choice in this amp (no cap is the best cap) we have to look for the best compromise/price/appropiate fysical size. With the new board it is too early to have already enough expierence with several alternatives. 

 So, are there members who have experimented with different coupling caps within the context of the original Millet implementation? May be we can learn something. Did anyone ever use a polypropyleen film/foil of substantial value paralleled or instead of the now used electrolytic with small polyprop (outside of the audioband)? Did anywone ever used a non polar electrolytic (see use of that in the WNA II thread on headfi and asuming that there are np-ecaps at that voltage and they could be used in the Millet amp)?

 3. What is the leadspace for cap 6L/R?

 4. Is there any benefit to expect when you use a polyprop or polystyreen for cap 6 (I have already the correct values with little leadspace)?

 5. At row one, cell one: I would remove C7L/R, because it has already its place on row two.

 6. What is the max room for leadthickness for the electrolityc caps? I have seen that leadthicknesses varies for different brands at different capsizes.

 7. You can expect that some builders are willing to experiment with the resistors at the output. I am not familiar with that kind of resistors, but I can imagine that there is some variation in leadthickness (given the resistor sizes). So, is the board at that point 'resistor-proof'?

 8. For low Z phones it is advised you use a higher value for the output cap. Suggested value is 470 muf. Is it of any importance that you also high up this value when you expect only to use phones in the region of say 120 to 300 ohm? Or should you go simply for safe and add default a 470 muf?

 9. Further investigation has led to the observation that there are interesting electrolytic caps with the appropriate value/voltage that has a leadspace of 5 instead of the actual space of 7,5 on this version of the board (see for example Rubycon ZA, probably among others). May be it is possible to add the traces for use of electrolytics with a leadspace of 5. This makes the board even more versatile than it already is.

 I hope you can do something with my remarks or suggestions.

 Greetings


----------



## dsavitsk

A last second question about these boards that I don't believe has been asked yet ...

 What size are the holes in the boards? I have had a few PCB's recently where my hookup wire of choice (19ga TCSS) did not fit, and where leads from things like Holco resistors and Solen caps didn't fit. In fact, TCSS does not fit through in the pot position on the DIYCable boards, which, while probably not surprising, is very annoying.

 -d


----------



## drewd

Quote:


  Originally Posted by *dsavitsk* 
_What size are the holes in the boards? I have had a few PCB's recently where my hookup wire of choice (19ga TCSS) did not fit, and where leads from things like Holco resistors and Solen caps didn't fit. In fact, TCSS does not fit through in the pot position on the DIYCable boards, which, while probably not surprising, is very annoying._

 

The holes are 1.6mm - they're plenty big for your hookup wire. I've had that problem before, too, so I decided that I'd go big, just to be on the safe side.

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_I don't think so, but in the 1455R2201 there might be - there is another 2.3" of space, so it might be possible - that would give about 4"x6.3" of open space. I don't know about height, though - the case is only 1.2" tall on the outside, so it might be a tight fit!

 -Drew_

 

I have looked on the site of Hammondmfg at the full series 1455 cases. There are also versions with a height of 51.5 mm (on the outside!). That leads to the question: 

 What is the practical height of a fully stuffed millet-board with f.e. the taller elco's like Silmic II (given anough space between underside of bord and bottom of the case; with size 2201 you can use spacers I assume)? 

 Wich internal height in a case is sufficient when you do not want to cut a hole for the tubes and want only to work with a closed case? Or is it mandatory that the tubes have anough coolingspace (like the parmetal cases)?

 Greetings

 Pieter


----------



## dsavitsk

Quote:


  Originally Posted by *Finch&Music* 
_Or is it mandatory that the tubes have anough coolingspace (like the parmetal cases)?_

 

The tubes do not need to breathe. They stay cool enough that you can grab them with no danger of burns


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_The holes are 1.6mm - they're plenty big for your hookup wire. I've had that problem before, too, so I decided that I'd go big, just to be on the safe side.

 -Drew_

 

In addition to earlier questions I want to ask if on the definitive boards there will for sure be the possibility of using also electrolytics with a leadspace of 5 mm, in addition to the already possible leadspace of 7,5 mm? 

 I want to be certain of that because I have elco's on the spot that have interesting price/spec relations, but have a leadspace of 5 mm. I rather not bend the leads.

 I appreciate a reaction on that, so I can order just the right components.

 Greetings.


----------



## drewd

Quote:


  Originally Posted by *Finch&Music* 
_In addition to earlier questions I want to ask if on the definitive boards there will for sure be the possibility of using also electrolytics with a leadspace of 5 mm, in addition to the already possible leadspace of 7,5 mm? _

 

Yes, the boards will have both 5mm and 7.5mm spacing for the electrolytic caps.

 -Drew


----------



## AtomBoy

I'm looking at the parts list on http://hybrid.fluidlight.com/ as of May-19 and I'm trying to keep a sane budget for this project.

 C1, C9L/R, C10L/R - Any reason not to use the Pannasonic FC 35v, 100uF here? They're part #P10294-ND - $0.38 ea at Digi-Key.

 C3L/R-C5L/R, C8L/R - If you call TAW for WIMA option, their part number is MKP 224J250 and they're $0.72.8 ea. WIMAs part number is MKP10 .22/250/5. (I hope I got that right! They said 250VDC was the closest thing they had to the 50V that Pete's article calls for.)

 Power Suply - The part listed for Digi-Key in the table (CUI-Stack DPD240040-P6P T5020-P6P) is gonesville. It looks to me like CUI# DPD240040-P6P-TK, Digi-Key #T431-P6P-ND is the current version ($6.13).

 Tubes and sockets - Antique Electronics http://www.tubesandmore.com/ has good prices for all the tube flavors. The 12FK6 is $1.40 ea! Their socket P-ST7-814 looks like it should work, but might require some modification of the lugs to fit in the PCB. I'm willing to go at it with the grinder for a few minutes to save a buck. 
	

	
	
		
		

		
			





 Yes, I know this hoby isn't about saving money, but the spouse has only so much understanding! I checked the rules and didn't see anything about posting vendors prices, so I hope I'm not out of line. Hope this helps!


----------



## Voodoochile

Quote:


  Originally Posted by *AtomBoy* 
_Yes, I know this hoby isn't about saving money, but the spouse has only so much understanding!_

 

The eternal search for the balancing point. 
	

	
	
		
		

		
		
	


	




 The 100uF/35v FCs are a good choice, so long as the lead pitch fits. It's an excellent cap, especially for the modest cost.

 As for the PSU, while a wall-wart is okay, a decent linear makes a marked improvement. Jamont mentioned this earlier also. I found an open-frame linear (Sola or Power-One) 28v PSU for about $15. These retail for closer to $70, and they show up in surplus and on ebay fairly often.


----------



## skyskraper

1) no reason to not use them at all. although id prob go with the higher capacitance reccomendations they give for digikey/panasonic fc's.

 2) higher voltage ratings? no problemo in this case 
	

	
	
		
		

		
		
	


	




 3) the psu, id be inclined to go a nice regulated unit, whether bought (ala elpac) or built (ala steps/tread, MORE FUN 
	

	
	
		
		

		
		
	


	




 ) i think there is some discussion earlier in this thread about power supplies and their impact on the amps performance


----------



## drewd

Quote:


  Originally Posted by *AtomBoy* 
_C1, C9L/R, C10L/R - Any reason not to use the Pannasonic FC 35v, 100uF here? They're part #P10294-ND - $0.38 ea at Digi-Key._

 

The lead spacing is too narrow at 3.5mm. However, I've updated the board so that both 5mm and 7.5mm spacing caps will work. If you move up to the 180uF/35V cap, it will work, although they're about twice as expensive (still, less than $1.50 difference for 5 caps). You can also bend the leads on the 100uF/35V caps and they'll fit - they'll just look a little awkward. Sonically - probably no difference.

  Quote:


 C3L/R-C5L/R, C8L/R - If you call TAW for WIMA option, their part number is MKP 224J250 and they're $0.72.8 ea. WIMAs part number is MKP10 .22/250/5. (I hope I got that right! They said 250VDC was the closest thing they had to the 50V that Pete's article calls for.) 
 

Pete's BOM has some errors - and that was one of them. You picked the correct one, though. Also, I just checked Welborne's page and they don't list the 250V cap anymore. I don't see an appropriate substitute, either, but since TAW comes in under Welborne's prices by...well, a lot, we're probably OK there.

  Quote:


 Power Suply - The part listed for Digi-Key in the table (CUI-Stack DPD240040-P6P T5020-P6P) is gonesville. It looks to me like CUI# DPD240040-P6P-TK, Digi-Key #T431-P6P-ND is the current version ($6.13). 
 

Argh, curse me for not looking the part number up before posting it! 
	

	
	
		
		

		
		
	


	




 It does look like that adapter will do. 

  Quote:


 Tubes and sockets - Antique Electronics http://www.tubesandmore.com/ has good prices for all the tube flavors. The 12FK6 is $1.40 ea! Their socket P-ST7-814 looks like it should work, but might require some modification of the lugs to fit in the PCB. I'm willing to go at it with the grinder for a few minutes to save a buck. 
	

	
	
		
		

		
		
	


	



 

I'll add them to the list.

 Thanks for the updates!

 -Drew


----------



## drewd

I thought I'd also speak up about output cap selection.

 I've got two hybrid amps running now, one built with budget parts (Panasonic caps and pot) and the other with semi-pricy parts (Elna Silmic-II and Wima caps, ALPS Blue Velvet pot).

 There is a difference and it's noticeable. A I have to say that if it's noticeable with *my* ears, then it's probably a big difference. The second amp, with the expensive parts sounds better, with quite a bit more detail and sense of space.

 That being said, the budget amp sounds pretty darned good.

 After poking around with amp number three, I believe that the significant difference lies with the output coupling caps, which shouldn't be too surprising. The Panasonic FC and poly caps just don't perform as well as the Elna Silmic-II and Wima poly caps.

 Amp number three with Panasonic caps on the power side and the Elna/Wima combo in the audio path sounds just as good to me as the full Elna/Wima amp. That's with 12FK6 tubes and a STEPS running at 30V. Grid bias is at 13.8V.

 My off the cuff feeling is that if your aim is to get into a tube amp on the cheap and you want to go with the budget parts, you'll do just fine here. If you want to spend a few dollars extra and go for the upgraded output caps, you'll get the most bang for the buck there. If you go all out and outfit the entire amp with them, I don't know if you'll hear the difference - but I'll be the first to point out that after spending 10 years duking it out with US Navy sonar systems, my hearing isn't what it used to be!

 -Drew


----------



## skyskraper

with a well tuned discrete buffer is it possible that the offset would be low enuff that the caps could be gotten rid of entirely?


----------



## AtomBoy

I'm planning on using the spendy caps on the output section (C7L/R) and the WIMAs from TAW are actually cheaper than DK's Pannasonics. Thanks for the info on the leads. I guess one and a half clams is worth it to keep things sanitary.

 AE is currently backordered on the $1.40 12FK6, but had the 12AE6A and 12FM6. I ordered the sockets from them as well, and will see how much sledgehammer love they need to fit the board when they come in.


----------



## skyskraper

do they do tube matching at ae also?


----------



## AtomBoy

AE does do tube matching, but apparantly not on the tubes we're using. It doesn't show up as an option on the order form. They're cheap enough that I'm ordering 4 of each for spares and swapping.

 About the power supply- I'm planning on upgrading from the wall wart eventually- I've got an Ebay find on the way. The cheap option from Digi-Key will get me started and be good enough for the amp I'll give to Dad for Christmas!


----------



## drewd

Quote:


  Originally Posted by *skyskraper* 
_with a well tuned discrete buffer is it possible that the offset would be low enuff that the caps could be gotten rid of entirely? 
	

	
	
		
		

		
			



_

 

Unfortunately, no, because the plate voltage is around 12 volts and that voltage sits on the input to the buffer, so it's on the output, too. Since the amplifier operates on a single voltage power supply, the plate voltage serves sort of the same purpose as the virtual ground circuit in many transistor amps (although it's there for some other reasons, too). Pete's original article touches on this a little bit, but not with much detail.

 If you're thinking in terms of biasing an opamp and wondering why that voltage doesn't appear on the output of the buffer, the reason is because of the way that an opamp works. For example, the PIMETA or PPA cascode pulls the output of the opamp (and thus the input of the buffer) toward V- (in terms of the virtual ground). The opamp then produces whatever voltage is necessary to offset the cascode, causing the voltage on the output of the opamp (and thus the input of the buffer) to be zero (when referenced to the virtual ground). Thus, no DC offset to overcome.

 The hybrid amp is a single ended triode with no feedback, so whatever voltage sits on the plate (the output of the tube) is not nulled, so it also sits on the input to the buffer. That voltage has to be there for a couple of reasons: to provide a relatively high AC impedance on the plate for high gain and low distortion and to simulate a dual power supply for the buffer. Remember, what we call ground on something like a PIMETA is really just V+/2 - it's just a reference. But in a tube amplifier like the hybrid, ground is really zero volts. Since the buffer needs some voltage to swing around, the plate voltage serves that purpose nicely.

 Does that make sense?

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_I thought I'd also speak up about output cap selection.

 I've got two hybrid amps running now, one built with budget parts (Panasonic caps and pot) and the other with semi-pricy parts (Elna Silmic-II and Wima caps, ALPS Blue Velvet pot).

 There is a difference and it's noticeable. A I have to say that if it's noticeable with *my* ears, then it's probably a big difference. The second amp, with the expensive parts sounds better, with quite a bit more detail and sense of space.

 That being said, the budget amp sounds pretty darned good.

 After poking around with amp number three, I believe that the significant difference lies with the output coupling caps, which shouldn't be too surprising. The Panasonic FC and poly caps just don't perform as well as the Elna Silmic-II and Wima poly caps.

 Amp number three with Panasonic caps on the power side and the Elna/Wima combo in the audio path sounds just as good to me as the full Elna/Wima amp. That's with 12FK6 tubes and a STEPS running at 30V. Grid bias is at 13.8V.

 My off the cuff feeling is that if your aim is to get into a tube amp on the cheap and you want to go with the budget parts, you'll do just fine here. If you want to spend a few dollars extra and go for the upgraded output caps, you'll get the most bang for the buck there. If you go all out and outfit the entire amp with them, I don't know if you'll hear the difference - but I'll be the first to point out that after spending 10 years duking it out with US Navy sonar systems, my hearing isn't what it used to be!

 -Drew_

 


 Drew, a very interesting and enlightning post. I am glad you post it in this stadium. Most of us are still in the process of choosing and/or gathering components, so you left some choises. 

 I think you are quite right about the crucial point about the output couplingcap and as you already said it is not surprising at all. 

 However you are the only one yet to have listen in reality to its quality(-differences), but I keep in mind that much expierence on output cap quality is also applicable on the millet amp(-board).

 I have again some questions/suggestions:

 1. In the output stage there is one resistor and one combined cap functioning in the signalpath. Is it possible that also the resistor quality is of influence? Could you try already some different resistors of more than middle of the road quality?

 2. In other tube amp configurations you see also combined output cap's. In the millet amp there is the combination of one big electrolytic with one small 0.220 polyprop. The last one is a low value filmcap. I have seen combinations where they use one very substantial filmcap parallel to one even more substantial electrolytic (bipolar or non-polar), bypassed by some small filmcaps. Do you expect any benefit of that sort of combinations?

 3. If you expect benefits of other combinations is it possible to look again to the board layout, because I have observered that there are very good filmcaps (in a small box) with substantial values, but they are bigger than now can be put to the board in the outputposition. For example Evox/Rifa or Wima have beautiful polyester or polyprop box-caps at lagere values, but they have a leadspace of 27,5 mm or sometimes even a little greater (also their fysical sizes are greater). May be a little late, but another look at the board might be benefical to prospective builders.

 Greetings 

 PM: By the way (question of a non-expert): is the millet amp a output transformerless amp (OTL) in the strict sense of the theory? Or have OTL amps also no outputcaps?


----------



## dsavitsk

Quote:


  Originally Posted by *drewd* 
_After poking around with amp number three, I believe that the significant difference lies with the output coupling caps, which shouldn't be too surprising. The Panasonic FC and poly caps just don't perform as well as the Elna Silmic-II and Wima poly caps.

 Amp number three with Panasonic caps on the power side and the Elna/Wima combo in the audio path sounds just as good to me as the full Elna/Wima amp. That's with 12FK6 tubes and a STEPS running at 30V. Grid bias is at 13.8V._

 

fwiw, I exchanged the 100uF elna's for 470uF Nichicon Muse KZ's (from Percy) and it made a pretty big difference. Whether the difference is the size or the brand, or both is anyone's guess, however. The point, however, is that Drew is right that the output caps matter.


----------



## dsavitsk

Quote:


  Originally Posted by *Finch&Music* 
_1. In the output stage there is one resistor and one combined cap functioning in the signalpath. Is it possible that also the resistor quality is of influence? Could you try already some different resistors of more than middle of the road quality?_

 

The resistor quality probably matters, but it probably matters a lot less than the cap selection.


----------



## drewd

Quote:


  Originally Posted by *dsavitsk* 
_fwiw, I exchanged the 100uF elna's for 470uF Nichicon Muse KZ's (from Percy) and it made a pretty big difference. Whether the difference is the size or the brand, or both is anyone's guess, however. The point, however, is that Drew is right that the output caps matter._

 

The difference is almost certainly in the size. The output caps, in combination with the output resistor and the headphone's impedance, will set the low frequency corner, that is, the -3dB point. It's a first order high pass filter. That means that the rolloff is going to start at ten times the corner frequency. For a 300 ohm headphone, the -3dB point is around 33Hz, but the rolloff starts at ten times that, or 333Hz. For a set of Grados (at 32 ohms), the -3dB point is close to 310Hz, with the rolloff starting at 3KHz - uh oh!

 The 470uF cap moves the cutoff substantially - to 7Hz at 300 ohms and about 66Hz at 32 ohms. For low impedance cans, it wouldn't be out of line to use a 680uF cap, I suppose. I've got 470uF caps in mine for my DT880s.

 To figure the cutoff frequency on your own, the formula is just 1/RC, where R is the impedance of your headphones and C is the capacitance of the output capacitors.


----------



## amb

Quote:


  Originally Posted by *drewd* 
_To figure the cutoff frequency on your own, the formula is just 1/RC, where R is the impedance of your headphones and C is the capacitance of the output capacitors._

 

drewd, you forgot something in the denominator... the formula should be:

 f = 1 / (2 * pi * R * C)

 For a 100uF output cap, -3dB point is 5.3Hz for 300 ohm load or 49.7Hz for 32 ohm load. For 470uF, it's 1.1Hz and 10.6Hz, respectively.


----------



## drewd

Quote:


  Originally Posted by *amb* 
_drewd, you forgot something in the denominator... the formula should be:

 f = 1 / (2 * pi * R * C)

 For a 100uF output cap, -3dB point is 5.3Hz for 300 ohm load or 49.7Hz for 32 ohm load. For 470uF, it's 1.1Hz and 10.6Hz, respectively._

 

Doh! I knew that I was stretching back too many years for my signals and transforms class!

 Thanks!

 -Drew


----------



## aeroes

Will a TREAD sufficient enough to supply the Millet?


----------



## jamont

Quote:


  Originally Posted by *Voodoochile* 
_As for the PSU, while a wall-wart is okay, a decent linear makes a marked improvement. Jamont mentioned this earlier also. I found an open-frame linear (Sola or Power-One) 28v PSU for about $15. These retail for closer to $70, and they show up in surplus and on ebay fairly often._

 

An opamp based amp, like PIMETA or similar, will have a much better PSRR than a discrete amp like this one, so putting some extra bux into a good PSU makes sense. I found an audible improvement when I replaced the unregulated wall-wart with a good regulated supply. A cheap way to do this would be to get the CUI wall-wart and add a TREAD to regulate it, leaving out the rectifier.


----------



## skyskraper

thanks drew, that did make sense. i kinda worked out what was going on from his article but i didnt realise all 12v were present


----------



## Jaypetermen

Quote:


  Originally Posted by *blip* 
_... I guess I could always use the millet as a pre-amp for another gain stage... Like maybe for my pimeta or some kind of simple voltage gain stage._

 

Can the Millet-Hybrid amp be use as a pre-amp as is or does it need to be modified.

 For example, could you use it pre-M3?


----------



## Jaypetermen

Quote:


  Originally Posted by *drewd* 
_That's with 12FK6 tubes and a STEPS running at 30V. Grid bias is at 13.8V._

 

I am about to start building a STEPs & M3. I currently have the AD8610AR op-amps (which are rated up to 27VDC) and I am also thinking about building a Millit-Hybrid, since I could not resist the group buy.

 I would like to configure the STEPs to be able to power both amps (one at a time of course) without changing the voltage. Would 27VDC be a good setpoint for both of the stock amps?


----------



## skyskraper

Quote:


 as far as making the amp work as a preamp, you should not have to do anything to it. The amp should do a great job driving a high impedance load like a power amp. Output cap selection becomes pretty easy - anything over 47uF will work just fine. Pete briefly touches on that in the AudioXpress article available on his web site. 
 

with the right transformer selection you should be able to power both of them at the same time using the steps. 

 m3 < 500 ma. hybrid < 400 ma. the lm317 in the steps can push out 1.5amp (on paper) so you would have plenty of room to jiggle. 

 and maybe for safety's sake, setting the voltage at like 24 or something that isnt bordering on the max for the m3 op amp would be a good idea. fried chips =


----------



## drewd

Since the group buy is now closed, here is the final design of the board with every change that was possible to implement. The Eagle .brd file can be downloaded here and you can view it with the free version of Eagle.

Render 

Both Layers 

Top Layer 

Bottom Layer 

 I can still make small - very small - changes, but unless it's something with a big impact, I'll probably be a little resistant to change.

 I can, however, make changes if somebody has a specific request and wants to have their own boards made. I don't have enough time to do full redesigns or anything like that.

 Thanks again to everyone who contributed to this project. It's a great example of how pooling everyone's experience can turn out something very interesting and very exciting.

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_Since the group buy is now closed, here is the final design of the board with every change that was possible to implement. The Eagle .brd file can be downloaded here and you can view it with the free version of Eagle.

Render 

Both Layers 

Top Layer 

Bottom Layer 

 I can still make small - very small - changes, but unless it's something with a big impact, I'll probably be a little resistant to change.

 I can, however, make changes if somebody has a specific request and wants to have their own boards made. I don't have enough time to do full redesigns or anything like that.

 Thanks again to everyone who contributed to this project. It's a great example of how pooling everyone's experience can turn out something very interesting and very exciting.

 -Drew_

 


 Hi Drew,

 I have looked to the labeling on the board. I have only one minor point to mention. 

 The labeling of all the 'great' electrolytics show 100V. According to the partslist 35V is the minimum with no real benefit to go higher. 

 May be you could consider to change the labeling on board to 35V. 

 That's also consistent with the labeling for the other minimum voltage specs (16V and 50V respectively).

 Greetings.

 Pieter.


----------



## SHLim

Mistake, pls ignor.

 Sam


----------



## n_maher

Well, I finally got one of my prototypes cased up in a Lansing MicroPak case. I'll be looking for some sort of grommit or ring to cover the craptacular holes that I cut for the tubes 
	

	
	
		
		

		
			





, but this was my first effort with a hole saw and I was rushing. Lesson learned and with some work with the Dremel I should be able to clean it up some. The good news is the amp sounds better than it looks 
	

	
	
		
		

		
		
	


	




 .

 The lansing enclosures are available in a multitude of colors and sizes that work very nicely with integral board slots that mean you don't need PCB standoffs. And they're pretty affordable at around $20. The certainly are rugged.

 Here it is, I hope to get the black version cased up tomorrow night (right, I'll be waist deep in Paypal invoices).


----------



## AtomBoy

Looking at the parts list on http://hybrid.fluidlight.com/ as of May, 23 the p/n for the Panasonic pot is the version without threads. If you want threads, the Digi-Key p/n is P2T3503-ND.

 If you don't mind using a slighty lesser grade of resistor, here's part numbers for resistors from Digi-Key:

 RLED, R3R/L R5R/L 1.00KXBK-ND

 R4R/L 22.1XBK-ND

 R6R/L 221XBK-ND

 A panel mount 2.5mm DC Jack is CP-6-ND (there are a few other choices if you want to spend more, or don't need threads).

 D2L/R, the current regulator diode, is the only part I can't find at DK. I'm betting there's somthing that would do the job maybe in the giant table starting on page 528 of the DK catalog, but I can't figure it out.

 I don't work for DK or own stock- I'm just trying to save some pennies on the shipping charges here.

 I'm also very curious how much the parts quality really matters. I'm planning on building one amp with all the recommended spendy bits and one with cheaper bits. Then maybe one with caps made from gumwrappers and spit...


----------



## drewd

Thanks AtomBoy - the parts list has been updated.

 -Drew


----------



## dsavitsk

Quote:


  Originally Posted by *AtomBoy* 
_I'm also very curious how much the parts quality really matters. I'm planning on building one amp with all the recommended spendy bits and one with cheaper bits. Then maybe one with caps made from gumwrappers and spit..._

 

Some matter, some don't so much. The resistors at DigiKey are probably not lower quality than the ones at Mouser, and even if they are, they probably don't matter to this project. The pot probably does (though Pinky would disagree.) The output caps certainly do, the rest of the caps not so much. The tubes matter a lot.

 Oh, and if you read the original article, it is possible to replace the crd with a resistor. Pete reports mixed results. So, while I don't think DigiKey carries them, it is not absolutely essential to the project.

 -d


----------



## SHLim

Quote:


  Originally Posted by *dsavitsk* 
_Oh, and if you read the original article, it is possible to replace the crd with a resistor. Pete reports mixed results. So, while I don't think DigiKey carries them, it is not absolutely essential to the project.

 -d_

 

Don't mind I asking, what is crd? Is it the output cap?

 WNA mkII user removed their output cap and replace with resistor and this appear to improve the sound quality.
http://www6.head-fi.org/forums/showt...64#post1405364
 Can this be apply to Millet hybrid?

 TIA,
 Sam


----------



## AtomBoy

Thanks dsavitsk. I went back to Pete's article. I'm getting more out of it every time. I was thinking this part was to protect against overloading something.

 The CRD looks like it would be a neat part to experiment with. Pete mentions that different tubes would respond differently to the current on the plate which is what D2L/R regulates. Between this and setting the bias it looks like the tweaking potentials are enormous.

 Is this a weird part? I'm wondering why I can't find it at Digi-Key.


----------



## amb

Quote:


  Originally Posted by *SHLim* 
_Don't mind I asking, what is crd? Is it the output cap?_

 

No, CRD stands for "Current Regulating Diode". The name is actually a bit of misnomer because it's not a diode in the classic sense, except it is directional (has polarity). It's a current regulator (as opposed to a voltage regulator). For any given voltage applied across this device that's within the maximum rating, it only allows a fairly constant amount of current to flow through.

 Internally, it's really a JFET with the gate pin internally tied to the source pin through a resistor. CRDs come in various "steps" of rated currents. Search for the 1N5283-1N5314 series, the CR416-CR470 series, the J500 to J511 series and the E153 to E822 series for datasheets.

 Mouser carries CRDs but not Digikey.


----------



## n_maher

Quote:


  Originally Posted by *AtomBoy* 
_Is this a weird part? I'm wondering why I can't find it at Digi-Key._

 

As amb said, DigiKey = no CRDs. But just a FYI it's almost always better to order from both Mouser and DigiKey than to place one order at Newark. I hate to bash a company like that but they get you by thinking that you're saving a couple bucks on parts and the take you to the cleaners for shipping.


----------



## skyskraper

drew's been kind enough to add provisions for a j503 CRD to the board too, perhaps that is available from digikey???

 edit: a quick search doesnt seem to yield any results, i'll have a proper look when i get home from school.


----------



## drewd

Quote:


  Originally Posted by *SHLim* 
_WNA mkII user removed their output cap and replace with resistor and this appear to improve the sound quality.
http://www6.head-fi.org/forums/showt...64#post1405364
 Can this be apply to Millet hybrid?_

 

Nope - without the output caps, the DC offset will be whatever the plate voltage is set at, somewhere between 50% and 100% of the power supply voltage. That's kind of the way that it goes with tube amps. There has to be a mechanism to get rid of the DC that comes from the plate - it can be a capacitor or a transformer, but as far as I know, there aren't any DC coupled tube amps.

 That being said, I'm sure that somebody will prove me wrong 
	

	
	
		
		

		
		
	


	




 -Drew


----------



## AtomBoy

I'll get them at Mouser, then. It's just puzzling that Digi-Key has everything but this one part. Must be karma.

 I will try to get a couple of different values to play with. Pete's article mentions looking at the curve of the tube on the datasheet and figuring a value for plate current from that. Does anyone know more about what he's talking about?

 It will be interesting to try to understand the relationship between grid bias and plate current. The reading I've done so far doesn't really seem to talk about it- or it does and it just hasn't sunk in yet. 
	

	
	
		
		

		
		
	


	




 I got my order from Antique Electronic Supply today. The socket P-ST7-814 *is* going to need some snip-snip on the lugs to go in the PCB, but it doesn't look like it's going to be hard. 

 I can't get over how ancient the boxes the tubes came in look.


----------



## amb

Quote:


  Originally Posted by *drewd* 
_as far as I know, there aren't any DC coupled tube amps.
 That being said, I'm sure that somebody will prove me wrong 
	

	
	
		
		

		
		
	


	


_

 

I've seen a few DC coupled tube designs, with no capacitor or transformer at the output. They all had quasi push-pull outputs powered by a split power supply, and there are trimpots to adjust the offset. However, since these amps employ no global feedback I am not sure if the DC stability would be all that good and I'd feel a lot better if there was a capacitor in case of disaster... This is especially true for the big speaker amps where the tubes are powered by hundreds of volts. DC offset problems could be quite major!


----------



## Jaypetermen

Concerning output cap part quality.

  Quote:


  Originally Posted by *dsavitsk* 
_ The output caps certainly do, the rest of the caps not so much-d_

 

For clarification, the output caps are C7L/R and C4L/R?

 Which are considered to be the best cap for these positions? Nichicon Muze, Elna Cerafine or Elna Silmic II ?


----------



## n_maher

C7L/R are the DC coupling caps.

 Nichicon Muse or Elna Silmic caps should be just fine - Cerafines are no longer made (replaced by the Silmic line AFAIK) so you may be able to find these, you may not. I'd be very surprised if you could actually hear a difference between the two and I personally wouldn't bother with anything more expensive like Blackgates, which at 10x the price simply cannot make that big a difference.

 N


----------



## drewd

C7 and C4 are both decoupling caps. To be honest, I'm not sure that I buy into the benefit of bypassing a good quality electrolytic with a film cap for this use. My feeling is that you really end up with (effectively) is a single cap whose value is the sum of the two capacitances.

 I've built the amp with a single Panasonic FC, with a Panasonic FC bypassed with a Panasonic film, with an Elna Silmic II and with an Elna Silmic II bypassed with a Wima film. To my ears, the first two sounded the same and the last two sounded the same. The Elna cap definitely sounded better than the Panasonic. I heard more detail, particularly in the high end and more of a sense of the recording space, especially in small, live venues.

 The first amp that I built had Elna Cerafines and Wima MKP10s. It sounds identical to the Silmic-equipped amp.

 I also put a 220uF Black Gate N in there, but it didn't sound any different than the Elna - and it was a pretty pricey cap.

 Here's my recommendation: You can go flat out on this amp and build it with all Silmic II and Wima caps and get a fantastic sounding amplifier at a very reasonable price. You can also build it with Panasonic FCs and Panasonic film caps, but with a Silmic II and omit C4 on the output and have a fantastic sounding amplifier on the cheap. You can also save a few bucks by ditching the CRDs and using somewhere around a 50Kohm resistor without significantly altering the sonic quality of the amp.

 I'm working on the web pages at http://hybrid.fluidlight.com to summarize all of this stuff.

 -Drew


----------



## n_maher

Ok folks, we're officially cooking with gas now, the boards have been ordered 
	

	
	
		
		

		
			





 .


----------



## steinchen

Quote:


  Originally Posted by *drewd* 
_To be honest, I'm not sure that I buy into the benefit of bypassing a good quality electrolytic with a film cap for this use. My feeling is that you really end up with (effectively) is a single cap whose value is the sum of the two capacitances._

 

in theory it's not only a question of capacitance, also a question of distortion, impedance and linearity
http://www.tangentsoft.net/audio/input-cap.html
http://members.aol.com/sbench102/caps.html
http://www.capacitors.com/picking_ca...rs/pickcap.htm

 in one of my amps I (have to) use input coupling caps due to the DC offset of the screw* Creative Audigy2, changing the caps from Wima MKP (metallized polypropylene) to Mundorf MCapZn (polypropylene film + tin film) improved the sound considerably imo

  Quote:


  Originally Posted by *drewd* 
_I've built the amp with a single Panasonic FC, with a Panasonic FC bypassed with a Panasonic film, with an Elna Silmic II and with an Elna Silmic II bypassed with a Wima film. _

 

How much capacitance are the film caps you tried ?


----------



## drewd

Quote:


  Originally Posted by *steinchen* 
_in theory it's not only a question of capacitance, also a question of distortion, impedance and linearity

 in one of my amps I (have to) use input coupling caps due to the DC offset of the screw* Creative Audigy2, changing the caps from Wima MKP (metallized polypropylene) to Mundorf MCapZn (polypropylene film + tin film) improved the sound considerably imo_

 

Yes, I understand that, but the problem is twofold here - we need an output coupling cap because of the DC offset on the output and that output cap forms a high pass filter. So, we need a fairly large capacitance value to make sure that the corner frequency of the high pass filter is low enough that it does not affect the audible frequencies - in this amp, that's really only practical with an electrolytic cap. There's no question that an electrolytic is not the last word in any of the three characteristics that you mentioned above, but from a practical point of view, we can do pretty well with parts that are designed to be as accurate as possible.

 The input coupling caps on your amp are a different story from the output caps. You're coupling a low voltage offset into a very high impedance, so you can use quite a small cap to keep the corner low. The output coupling caps on the Millett Hybrid are combined with a very low impedance (the headphones), so they need to be quite a bit larger to make up the difference.

  Quote:


 How much capacitance are the film caps you tried ? 
 

Between .22uF and 3uF. It appears to make no difference because the capacitance of the film caps is a tiny fraction of that of the electrolytics, so the characteristics of the electrolytic caps dominate.

 It can be shown that different dielectric materials attenuate certain frequency ranges better than others. That's one of the reasons for using film caps to bypass electrolytics in the power section. It helps to reduce high frequency ripple. But that's not the problem at the output - all we want to do is block DC.

 I do agree, if you have to use a capacitor in the audio path, then a film cap is probably the best practical choice. But a 100uF film cap would be a little undwieldy, so the next best thing is a high quality electrolytic.

 Sorry for such a long post!

 -Drew


----------



## Finch&Music

drewd said:
			
		

> It can be shown that different dielectric materials attenuate certain frequency ranges better than others. That's one of the reasons for using film caps to bypass electrolytics in the power section. It helps to reduce high frequency ripple. But that's not the problem at the output - all we want to do is block DC.
> 
> Some questions:
> 
> ...


----------



## drewd

Quote:


  Originally Posted by *Finch&Music* 
_1. Does this mean that it is more essential to invest in a high quality power supply (and in combi with that quality decoupling on board) to get as low supply ripple/impedance as can be achieved? Another member already pointed out that in this amp extra attention should be payed to lowering psrr, because there are no opa's on board with internal high psrr from itself.

 2. If so, what are the best requirements for a powersupply (within reasonable costlimits)? A wallwart can always get you started, but is it rewarding enough? Is a fully filled up STEPS enough, or should you pay more attention to some supply-aspects?

 3. Or is the remaining supply-ripple of a simple linear supply of insignificant influence on the music presentation that will result when the signal is gone through a quality DC blocking electrolytic?

 4. What kind of quality supply did you use when observing the quality of the different elco combi's in the coupling position?_

 

Yes, the quality of the power supply can be sonically audible. I think that it would be appropriate to consider the quality of the power supply in terms of the quality of the amplifier when it is built - that is, if the builder's goal is to build the amplifier as inexpensively as possible, then a ~400mW wall wart is an appropriate power source. At the other end of the spectrum, for the builder who is using all high quality, expensive parts, a higher quality power supply would certainly be in order.

 I've listened to the amplifiers with the Elpac 24V desktop power supply, a Radio Shack 13.8/30V desktop power supply, a STEPS v1.0 and a TREAD clone, the latter two at 30V.

 Most of my listening has been done with two versions of the ampflier: cheap and expensive.

 The Radio Shack power supply (273-1668) is really not suited for this amp at all. It works quite nicely with opamp based amplifiers, but there is a ton of noise on its output. The Elpac was noticeably better on both amplifiers.

 On the cheap amp, I didn't hear much of a difference between the Elpac and the STEPS or TREAD power supplies. There was a difference, but I couldn't really put my finger on it and it didn't detract from the music - it was just a very slight difference in sound.

 On the expensive amp, however, there was a difference. In all of these cases where I could tell the difference, that difference was in terms of detail. Imaging, ambience and just a general feel for the music was improved between the Elpac and the STEPS and TREAD. I heard absolutely no difference between the STEPS and TREAD.

 I didn't do any lengthy listening with a cheap amp with expensive output caps, but I suspect that the power supply will also be important with that configuration because I'd estimate that that configuration gives 90% of the performance of the full-blown expensive amp.

 As far as power supply requirements go, current, obviously must be sufficient to drive the amplifier. 400mA is the minimum, more (up to a point) is better. Noise is also the enemy, so a switching power supply isn't your friend. With that said, the two power supplies recommended in the parts list are switchers, but they're pretty much as good as you'll find for the price. A linear, regulated power supply is really the clear winner, assuming that the amp is built with good quality parts.

 Noise from the power supply that makes it into the amplifier is going to be on the output - there's no getting around that - ground is absolute on this amplifier, so the power supply ripple will cause variations in the output voltage, thus the quieter the power supply, the more accurate the output.

 If I recall correctly, Tangent measured the ripple of the STEPS at less than a tenth of a millivolt - that's awfully quiet. The TREAD must be at least that quiet. When I get the time, I'll put the other two on the scope and see what their output looks like, but if I can hear a difference, then I suspect that they'll look pretty bad.

 -Drew


----------



## SHLim

Hi Drew,
 Thanks for sharing your experience. With low component count, using expensive parts look feasible for me. Looking forward to read your review on Walt Jung's diamond buffers.

 Sam


----------



## steinchen

Quote:


  Originally Posted by *drewd* 
_The input coupling caps on your amp are a different story from the output caps. You're coupling a low voltage offset into a very high impedance, so you can use quite a small cap to keep the corner low. The output coupling caps on the Millett Hybrid are combined with a very low impedance (the headphones), so they need to be quite a bit larger to make up the difference.
 ...
 I do agree, if you have to use a capacitor in the audio path, then a film cap is probably the best practical choice. But a 100uF film cap would be a little undwieldy, so the next best thing is a high quality electrolytic._

 

with 300 Ohms headphones it could be worth trying a 10uF MKP cap alone f=50Hz at -3dB, or 22uF -> f=24Hz (35mm x 46mm, 10 EUR per piece ) 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *drewd* 
_Between .22uF and 3uF. It appears to make no difference because the capacitance of the film caps is a tiny fraction of that of the electrolytics, so the characteristics of the electrolytic caps dominate._

 

agree in terms of capacitance, in terms of impedance the resulting impedance should be 1 / ( 1/R1 + 1/R2), especially at higher frequencies the film cap should make a difference (at least theoretically)


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_
 As far as power supply requirements go, current, obviously must be sufficient to drive the amplifier. 400mA is the minimum, more (up to a point) is better. Noise is also the enemy, so a switching power supply isn't your friend. With that said, the two power supplies recommended in the parts list are switchers, but they're pretty much as good as you'll find for the price. A linear, regulated power supply is really the clear winner, assuming that the amp is built with good quality parts.

 Noise from the power supply that makes it into the amplifier is going to be on the output - there's no getting around that - ground is absolute on this amplifier, so the power supply ripple will cause variations in the output voltage, thus the quieter the power supply, the more accurate the output.

 If I recall correctly, Tangent measured the ripple of the STEPS at less than a tenth of a millivolt - that's awfully quiet. The TREAD must be at least that quiet. 

 -Drew_

 

Thanks very much for this extensive answer to my questions. It really helps me in the process of choosing the components for my configuration of supply/amp chain. I think the content looks also good information for the building quide!

 Yet, another additional question: 

 You advise '400 mA as a minimum for current demand and to a point some more is better'. What do you mean with 'some more' without going into insane overspecification and unneccessary costs? 

 When I use a STEPS with a 25 VA/2*15V/832 mA transformer (type 70063) from Talema I get more than 800 mA available for (peak) current demand. That looks to me double to the minimum and I think that's more than enough supply-room (as far as the transformer is concerned) for optimal functioning of a Millet Amp stuffed with quality components. Or do I make a mistake in the calculation?

 Greetings

 Pieter


----------



## steinchen

Quote:


  Originally Posted by *Finch&Music* 
_You advise '400 mA as a minimum for current demand and to a point some more is better'. What do you mean with 'some more' without going into insane overspecification and unneccessary costs? 

 When I use a STEPS with a 25 VA/2*15V/832 mA transformer (type 70063) from Talema I get more than 800 mA available for (peak) current demand. That looks to me double to the minimum and I think that's more than enough supply-room (as far as the transformer is concerned) for optimal functioning of a Millet Amp stuffed with quality components. Or do I make a mistake in the calculation?_

 

The current that will be drawn should be no more than 80% of the transformer's rated output current. For a circuit drawing 400mA everything above 500mA is sufficient. The 25VA transformer you mentioned fits fine (for a 30V psu) and gives some headroom to you.


----------



## drewd

The quiescent current draw of the amplifier is about 160mA. That's the heaters, the buffers, the plate current and an LED. That current draw will always be present. The difference between that and the current rating of the power supply is what you have to work with for audio. With a 20% margin, that leaves 160mA of current for audio. For most headphones, that should be plenty.

 EDIT: The values above refer to the 400mA power supplies listed in the parts list at http://hybrid.fluidlight.com.

 Steinchen is right - Finch&Music's STEPS power supply will work quite nicely for this amplifier. At 800mA, the power supply can deliver all of the current that the amplifier is capable of drawing, with roughly a 17.5% margin of excess current capability. In practice, that margin is substantially higher because 250mA per channel is a lot of current!

 -Drew


----------



## Jaypetermen

I was hoping to power both the M3 and the Millet–Hybrid from the same STEPS. 

 Is this possible?

  Quote:


  Originally Posted by *skyskraper* 
_m3 < 500 ma. hybrid < 400 ma. the lm317 in the steps can push out 1.5amp (on paper) so you would have plenty of room to jiggle. 
	

	
	
		
		

		
		
	


	


_

 

or

  Quote:


  Originally Posted by *drewd* 
_The quiescent current draw of the amplifier is about 160mA. That's the heaters, the buffers, the plate current and an LED...With a 20% margin, that leaves 160mA of current for audio._

 

Maybe if they where both not powered up at the same time?


----------



## skyskraper

it would depend on the size of the transformer u choose moreso. i use a 30va toroid for my m3 tread, i intend to power both off of it. and im running my m3 with a fair slice of mosfet bias.


----------



## Jaypetermen

Does any one have a currently BOM with component quantities for the Millit-Hybrid?

 I have looked at the parts list at http://hybrid.fluidlight.com but it does not show the quantities needed for each component.


----------



## drewd

Quote:


  Originally Posted by *Jaypetermen* 
_Does any one have a currently BOM with component quantities for the Millit-Hybrid?

 I have looked at the parts list at http://hybrid.fluidlight.com but it does not show the quantities needed for each component._

 

The parts placements are shown in the first column. Add up the total number of placements and that's the number of parts that you need. For example, the first row is for C1, C9L/R, C10L/R. That's 5 caps.

 Also, it appears that Welborne does not carry the Wima film caps that are listed in the parts list, but TAW Electronics does, and for MUCH less (as has been posted earlier). I would really suggest ordering the film caps through TAW because, for the money, you won't get a better cap. You have to call them on the phone, but it's well worth it.

 Also, the Cerafines are out of production, so I guess that the Welborne parts listed there are going to be going away, too, so I'll work on updating the parts list with something else.

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_The parts placements are shown in the first column. Add up the total number of placements and that's the number of parts that you need. For example, the first row is for C1, C9L/R, C10L/R. That's 5 caps.

 Also, it appears that Welborne does not carry the Wima film caps that are listed in the parts list, but TAW Electronics does, and for MUCH less (as has been posted earlier). I would really suggest ordering the film caps through TAW because, for the money, you won't get a better cap. You have to call them on the phone, but it's well worth it.

 Also, the Cerafines are out of production, so I guess that the Welborne parts listed there are going to be going away, too, so I'll work on updating the parts list with something else.

 -Drew_

 

I have looked at the latest version of the partslist. That gives reason to make two remarks:

 1. I could not find C4 L/R (2x 0.222 mu Wima) anymore in the partslist (version 23 may). Is that on purpose or just an omission?

 2. When I try to observe the partslist it shows itself a little strange on screen. Text is spread on a much broader space than is usefull and it rolls over different cells. Older versions of the list had not that problem and could be printed out by me very easily.

 Greetings.


----------



## drewd

Quote:


  Originally Posted by *Finch&Music* 
_1. I could not find C4 L/R (2x 0.222 mu Wima) anymore in the partslist (version 23 may). Is that on purpose or just an omission?_

 

The parts are included in the range of C3L/R-C5L/R. I can see the potential for confusion, so I will edit the parts list to show each part separately.

  Quote:


 2. When I try to observe the partslist it shows itself a little strange on screen. Text is spread on a much broader space than is usefull and it rolls over different cells. Older versions of the list had not that problem and could be printed out by me very easily. 
 

I see that problem sometimes as well. I'm not sure what the cause is. It may be a combination of the HTML editor that I use and the web browser. I'll look at the HTML code and see if there is some redundant or missing code that might be causing the problem.

 Thanks for the input!

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_The parts are included in the range of C3L/R-C5L/R. I can see the potential for confusion, so I will edit the parts list to show each part separately.



 I see that problem sometimes as well. I'm not sure what the cause is. It may be a combination of the HTML editor that I use and the web browser. I'll look at the HTML code and see if there is some redundant or missing code that might be causing the problem.

 Thanks for the input!

 -Drew_

 

Thanks for your answer. 

 May be the second point is due to cell-properties of your document section. When you use (if at all) MS Excell than you have to install the correct cell-properties. 

 May be that is the cause after you have alter a new (copy-)version of the partlist? 

 If not so, than I do not have any knowledge of what could be the cause. I am just a simple reader of what is shown on screen.

 Succes with searching into the fault.

 Greetings 

 Pieter.


----------



## drewd

The parts list table should show up correctly now. The problem was from some extra code that probably came from the Excel spreadsheet.

 -Drew


----------



## n_maher

Looking good to me!


----------



## Finch&Music

Quote:


  Originally Posted by *n_maher* 
_Looking good to me!_

 

I have looked at the new version also and it looks very good now to me. 

 I strongly advise to add a second collumm to the partslist called 'qty', so there can be no cause anymore to make a fault when one is to order the number of the components. Not everyone is expierienced enough to 'read electronic specs language' immediatly in the right way. I am one of them!

 Greetings,

 Pieter


----------



## drewd

Quote:


  Originally Posted by *Finch&Music* 
_I strongly advise to add a second collumm to the partslist called 'qty', so there can be no cause anymore to make a fault when one is to order the number of the components._

 

It is so added.

 I'm working on new and improved pages that will go through the construction, a little (very little) tube theory and some ideas on parts selection and a few tweaks. I really wanted to have all of that finished a few days ago, but, alas, I find that I have a life outside of this project 
	

	
	
		
		

		
			





 Thanks again for the input!

 -Drew


----------



## kilkil

I was looking at Welborne for Wima's and noticed that there are two caps that have the size requirements:

 Wima MKP-10 and Roederstein Metallized Polypropylene Capacitors, WM210 .10uf/160V as listed in the part selection guide and

 Wima FKP-2 Polypropylene Film Capacitors, WM15 .10uf/63V

 I don't know much about caps, but would think the non-metallized cap would be better, is it better?


----------



## drewd

Quote:


  Originally Posted by *kilkil* 
_I was looking at Welborne for Wima's and noticed that there are two caps that have the size requirements:

 Wima MKP-10 and Roederstein Metallized Polypropylene Capacitors, WM210 .10uf/160V as listed in the part selection guide and

 Wima FKP-2 Polypropylene Film Capacitors, WM15 .10uf/63V

 I don't know much about caps, but would think the non-metallized cap would be better, is it better?_

 

In a perfect world, yes, the non-metallized cap would be a better performer, but in the specific case of this amplifier, the sonic difference is probably inaudible. The 0.10uF caps will definitely work - the specific value of the cap is not critical in this amplifier, but you're probably not going to hear a difference. Of course, the price difference isn't too terribly much, so if you're considering populating the other cap positions with high performance models (like the Elnas), then it's no great expenditure to go with the FKP-2 caps - it's only something like a $3.00 difference for the entire amplifier.

 Also, TAW Electronics stocks the 0.22uF Wima cap as listed in the parts sheet for something like 80 cents each. They also carry the FKP-2 caps, but they don't list a 0.10uF part on their web site.

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *amb* 
_drewd, you forgot something in the denominator... the formula should be:

 f = 1 / (2 * pi * R * C)

 For a 100uF output cap, -3dB point is 5.3Hz for 300 ohm load or 49.7Hz for 32 ohm load. For 470uF, it's 1.1Hz and 10.6Hz, respectively._

 

Some questions:

 1. What is from an audio-quality standpoint a practical -3db corner frequency for a headphone with respectively low (30-100), middle (approx >120) and high (>300) ohm caracteristic? 

 2. Is in the case of a sennheiser 650 a -3 db point of 8 a 10 Hz (more than) enough for an appropiate bandwidth? Or is it 18-20 Hz or even higher?

 3. Or is a -1 db refference point more disirable? If that is the case, what is than the formula? (The already given formula for -3 db points is workable for me; I could find the same results with the elements you give without any schooling on that point! So the other formula shall also be understandable). 

 4. When you install the outputresistor in the Milletamp should you take that little amount of ohm also into account? If yes, how? Simply adding to the ohm's of the phone?

 I am asking this because it is most likely that I mostly use a high impedance phone with the Millet. So it is to contemplate to go for a higher value filmcap instead of a quality electrolyte. I have several 30 mf available from a former speakerproject, so why not reuse those. In the case for the amp there is ample room available. 

 IMO, it is also possible to take a double route: one jack with a high value electrolytic/bypassed outputcap for low/high and one with a single filmcap only for high impedance phones. Only one phonejack will be used at the same time. The board has more than one outputposition. Or is that a dangerous route to go with too much pitfalls?

 Greetings,

 Pieter Vink


----------



## steinchen

you want to have the corner frequency as low as possible, from an audio-quality standpoint I'd say 10Hz or lower (output capacitor with headphone impedance works like a highpass filter). The higher the output capacitance the lower the corner frequency. 

 for f=10Hz @ -3dB
 300Ohm -> 50uF minimum
 120Ohm -> 130uF minimum
 75Ohm -> 220uF minimum
 32Ohm -> 470uF minimum


----------



## drewd

Quote:


  Originally Posted by *Finch&Music* 
_3. Or is a -1 db refference point more disirable? If that is the case, what is than the formula? (The already given formula for -3 db points is workable for me; I could find the same results with the elements you give without any schooling on that point! So the other formula shall also be understandable). _

 

-3dB is the standard measurement point for frequency response. The first order high pass filter that is being used falls off at 6dB per decade, so if the corner frequency is at 10Hz, the -1dB point is probably around 20Hz - that's not derived from any formula, it's just from experience.

  Quote:


 4. When you install the outputresistor in the Milletamp should you take that little amount of ohm also into account? If yes, how? Simply adding to the ohm's of the phone? 
 

The output resistor acts only as an attenuator - it has no function in the high pass filter. The 1K resistor to ground, in parallel with your headphones, though, does count. At low impedances (Grado-style low), that resistor has little effect, but at high impedances (Sennheisers), it's worth calculating the parallel resistance of the headphones and the 1K resistor if you want to be exact. However, if you just place a 470uF electrolytic cap, you'll have a corner frequency below 10Hz in all cases (for headphones that the amplifier is capable of driving).

  Quote:


 IMO, it is also possible to take a double route: one jack with a high value electrolytic/bypassed outputcap for low/high and one with a single filmcap only for high impedance phones. Only one phonejack will be used at the same time. The board has more than one outputposition. Or is that a dangerous route to go with too much pitfalls? 
 

You'll have to use a switch and a single set of outputs because even though there are two sets of outputs on the board, any capacitors that are installed will be in the circuit all the time. The caps will have to be wired after the switch. It might be easier to visualize of you draw it out on paper. When I put the second set of outputs in, I didn't think about using them for headphones of differing impedances, just as a convenience for panel wiring. 

 Another method that might work a bit better than a switch would be to use switched headphone jacks like the Re'an or Neutrik stacking jacks. You would put the paralleled 30uF caps in the normal cap positions, then a high quality electrolytic after the first jack. That way, when a set of headphones are plugged into the first jack, the caps going to the second jack are disconnected. Again, a picture on paper would make it more clear, I think.

 -Drew


----------



## Erik S.

Wondering if Mouser Part #: 505-M100.1/160/5 is the same Wima caps that are in the parts list? If so, they're alot cheaper than Welborne.


----------



## MisterX

It sure is.


----------



## Erik S.

Quote:


  Originally Posted by *MisterX* 
_It sure is. 
	

	
	
		
		

		
		
	


	


_

 

Thanks! it makes ordering parts a little easier and cheaper


----------



## steinchen

another shop carrying the tubes and sockets is http://www.thetubestore.com/ (maybe worth to be mentioned at the hybrid site)

 how to order the sockets via http://www.vacuumtubes.net/ ? They don't have a classical webshop and the pdf-pricelists contain tubes only. Does anybody got a part number ? 

 tubedepot.com is quite pricy compared to vacuumtubes.net (+$2 per tube, almost double the price) and $25 shipping for a $30 order definitely uneconomical for european customers


----------



## individual6891

I might have completely missed this but.. has anyone measured the current drain of the amp?


----------



## JWFokker

Crap. I didn't order quite enough caps from Digikey to do two amps. I totally missed the L/R thing. Its a good thing I still have to order the diodes from Mouser.

 Anyone know if either the 1N5291 or J503 is better than the other?


----------



## drewd

Quote:


  Originally Posted by *individual6891* 
_I might have completely missed this but.. has anyone measured the current drain of the amp?_

 

Not directly, but the heaters draw 150mA, the lion's share of the current. The idle current of the buffer is 2mA in low bandwidth mode, 20mA in high bandwidth mode. The LED draws a smidgen of current and the plate current is about a milliamp. So, figure between 160mA and 180mA at idle.

 -Drew


----------



## drewd

Quote:


  Originally Posted by *JWFokker* 
_Crap. I didn't order quite enough caps from Digikey to do two amps. I totally missed the L/R thing. Its a good thing I still have to order the diodes from Mouser.

 Anyone know if either the 1N5291 or J503 is better than the other?_

 

Sorry about that! The CRDs are a tossup, one is as good as the other. The 1N5291 has slightly tighter tolerances, but in this application, it's not important. I think that the 1N5291 is less expensive, so maybe that is the biggest difference.

 -Drew


----------



## slindeman

Quote:


  Originally Posted by *individual6891* 
_I might have completely missed this but.. has anyone measured the current drain of the amp?_

 

Mine draws around 190mA. It spikes to over 400mA briefly at powerup, yet I've had no problems powering it with the Elpac 24V 330mA linear wal-wart.


----------



## Jaypetermen

Does any know of a source and/or part number for panel mount tube sockets (non-baord mount sockets) for the 12FK6 or 12AE6A tubes?

 I would like to try mounting the tube sockets to the top cover of the enclosure.


----------



## n_maher

Jay,

 There literally are a ton of them on the web. If you google "7 Pin Mini Tube Socket". I think you'll see plenty.

 Nate


----------



## drewd

Quote:


  Originally Posted by *Jaypetermen* 
_Does any know of a source and/or part number for panel mount tube sockets (non-baord mount sockets) for the 12FK6 or 12AE6A tubes?

 I would like to try mounting the tube sockets to the top cover of the enclosure._

 

Here's a source: http://www.cascadesurplus.com/catalo...products_id/35. I think that I've purchased from them in the past.

 Here's another one: http://www.surplussales.com/Tubes-So...ubeSkts-2.html. I've definitely bought from them and they were fairly quick.

 Check on Google - I picked up a bunch of PCB 7 pin sockets a few weeks ago for something like 25 cents each from a surplus store.

 -Drew


----------



## SHLim

PartConnexion carry boutique 7 pin tube socket. 
http://www.partsconnexion.com/catalog/tubesockets.html
 BTW, they are having 15% sales on all caps (except BG) this month. 

 Have fun,
 Sam


----------



## JWFokker

I don't like Angela's ordering system (or lack therof) so I thought I was stuck with Tube Depot's crappy sockets. Parts Connexion has some good looking hardware for very reasonable prices. Thanks for the heads up, dude.


----------



## n_maher

Just a quick note - I've completed (finally) an excel version of the BOM w/ prices and part numbers that should be available to be downloaded within the next couple of days. I'll post a link as soon as it's up.

 For those who've been wondering, the base parts cost of this amp (what it costs to populate the board only) is around $75. You can push this down a bit more by being really picky about who you get your tubes from and so on but that's really a pretty realistic base. To that you need to add jacks, switch(es), knob(s), an enclosure and a power supply. If you keep it simple you should be able to get it all done for around $125. Maybe less, I just can't check every conceivable configuration. 

 Hope that helps some people out,

 Nate


----------



## JWFokker

Oh, wait a minute. Parts Connexion's ordering method sucks even worse than Angela's. When will resellers get around to joining everyone else in the 21st century and get online ordering? I'm not going to screw around with that crap.

 Cascade got my business. They even take Paypal.


----------



## aeroes

Im about to finish my order but I have a question.

 Can I use 25v for C7L/R position?


----------



## drewd

Quote:


  Originally Posted by *aeroes* 
_Can I use 25v for C7L/R position?_

 

Yep!


----------



## Jaypetermen

Quote:


  Originally Posted by *drewd* 
_Yep!_

 

Good news. 

 The http://hybrid.fluidlight.com/ web page mentions that the voltage rating for C1, C7L/R, 9L/R & C10L/R should be no less than 35V. 

 So a 100uf/35V electrolytic cap can be used in the C1, C7L/R, 9L/R & C10L/R positions?

 The http://hybrid.fluidlight.com/ web page also mentions that the output coupling caps determine the low frequency cutoff point. For 100uF is the lowest recommended value. For headphones with impedances <150 ohms, up to 470uF is appropriate.

 What value would be the best for a 300Ohm can like the HD-650. Would 100uf be a good fit for these cans?

 Also, can 220uf/35V caps be used in the Millit-Hybrid’s C1, C7L/R, 9L/R & C10L/R positions?

  Quote:


  Originally Posted by *amb* 
_...f = 1 / (2 * pi * R * C)..._

 

So for 300ohm 650s and a 220uf cap the -3dB point is 4.42Hz. Okay, is this a good thing?


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_Yep!_

 

This induces some incertainty for me. 

 What is the lowest possible V rating for c7L/R? 

 When a lower voltage rating in that position is really possible than there is more flexibility to choices for electrolytic output caps. Not only pricewize.

 Is there any danger when one of the tubes is going defect or disfunctioning? 35V is may be also a safety level in reference to the primarily supply voltage? 

 If so, than you can better use 35V in that output position! 

 Greetings

 Pieter Vink


----------



## n_maher

Peter and others, 

 I'm sure Drew will chime in here with more accurate advice but I think the root of the cap voltage issue has a few layers. One, there are certain caps on the board which see the full supply voltage. So for those caps, you want to make sure that you have the correct rated caps, plus a little headroom (no pun intended). Two, while a power supply may be rated for 24V oftentimes it will fluctuate up and down. Based on my own observations this can easily be a volt or so. So if it were me, I wouldn't use 25V caps for those positions, even if techinically you could. I think that's why Drew put the 35V min in the docs. 

 The bummer of it is that 25V caps seem to be more easily found in the values that we're all looking for, especially when in comes to the Elna and Nichcon caps. 

 The caps that I recommend in the BOM will be rated for 50V DC if for no other reason than to have convenient lead spacings. I don't think that folks will run into any issues choosing higher rated caps in terms of sound quality, but I'll be trying to test this for people as well.

 HTH,

 Nate


----------



## drewd

When I have my electrial engineering hat on, I would say that any caps in the amplifier should have a voltage rating of at least twice the voltage that they may be subjected to. In the case of C7L/R, the maximum voltage is V+ or 24V. That assumes a couple of things:

The power supply is delivering 24V
The bias is set at 24V
The amplifier is either broken or terribly misadjusted

 So, as an EE, I would use a 50V cap on the output.

 From a pragmatic point of view, if V+ is present on the output, you'll know that something is wrong right away. You most certainly will not be listening to anything.

 A 25V cap will block the DC at V+. And it's not going to explode or anything like that - in fact, it's not going to fail even if the voltage drifts up above 25V because you're not going to be listening to anything - you'll be turning it off because it sounds terrible! So, 25V is fine.

 There are a couple of reasons that I specified 50V caps when I made up the BOM on the website. Pete's original amplifier used them. The original amp that I built used them. And I was looking at the caps with an engineer's eye for design.

 Since there are also 5mm pin spacings on the board, lower voltage caps can be substituted. Also, please bear in mind that 100uF is not a magic value. I get the impression that Pete must have had a bunch of them on hand, so that's what he used. There's nothing wrong with using larger caps. They're bypassed with low ESR film caps, so there is no impedance issue.

 I hope that I haven't made things more confusing. The bottom line is that the power caps will see 24V all the time and the signal caps will see about half of that all the time. The specific value of the caps is not critical - well, C7L/R depends on your headphones, but, practically speaking, it's not really critical.

 -Drew


----------



## Finch&Music

Quote:


  Originally Posted by *drewd* 
_When I have my electrial engineering hat on, I would say that any caps in the amplifier should have a voltage rating of at least twice the voltage that they may be subjected to. In the case of C7L/R, the maximum voltage is V+ or 24V. That assumes a couple of things:

The power supply is delivering 24V
The bias is set at 24V
The amplifier is either broken or terribly misadjusted

 So, as an EE, I would use a 50V cap on the output.

 From a pragmatic point of view, if V+ is present on the output, you'll know that something is wrong right away. You most certainly will not be listening to anything.

 A 25V cap will block the DC at V+. And it's not going to explode or anything like that - in fact, it's not going to fail even if the voltage drifts up above 25V because you're not going to be listening to anything - you'll be turning it off because it sounds terrible! So, 25V is fine.

 There are a couple of reasons that I specified 50V caps when I made up the BOM on the website. Pete's original amplifier used them. The original amp that I built used them. And I was looking at the caps with an engineer's eye for design.

 Since there are also 5mm pin spacings on the board, lower voltage caps can be substituted. Also, please bear in mind that 100uF is not a magic value. I get the impression that Pete must have had a bunch of them on hand, so that's what he used. There's nothing wrong with using larger caps. They're bypassed with low ESR film caps, so there is no impedance issue.

 I hope that I haven't made things more confusing. The bottom line is that the power caps will see 24V all the time and the signal caps will see about half of that all the time. The specific value of the caps is not critical - well, C7L/R depends on your headphones, but, practically speaking, it's not really critical.

 -Drew_

 

1. With the above pre-requisites of a 24 v supply and a max bias at 24 V: could there be not any problem presented to your (pricey!) headphones when elco's of 25 v are executed? (Forgive me my little electronic insights, I am only looking for some insurance against stupid implementations with risk of damaging my headphones! 

 2. In general your EE approach gives me more confidence feelings than looking for the lowest possible voltages or values for a little less cents.

 3. By the way:what will be the maximum practical bias volt adjustment to expect with the different tube types that will be practised? Is'nt that maximum also to determine the max supply voltage and the practical voltage of the electrolytic's?

 4. I am planning a supply-set at 30V (STEPS based on talema 25va/2*15v; see earlier posts). In that case I assume that after regulation at 30V a 35V range (minimum) on all caps is mandatory, even in the position of C7.

 5. That strategy gives me - as far as I can imagine - the most flexibility in bias adjustment. Or is that bias-aspect fully separate of the (max) supply voltage in all other positions?

 6. In regard to the question of leadspace (and the added flexibility) I want to remark that - if funds gives you the space - do not go for the lowest level possible. I think the amp will benefit from some headroom in the supply and in the (quality) capacities on board. Than I am speaking of a balance between quantity, quality and (local) price.

 greetings. 

 Pieter Vink


----------



## drewd

Quote:


  Originally Posted by *Finch&Music* 
_1. With the above pre-requisites of a 24 v supply and a max bias at 24 V: could there be not any problem presented to your (pricey!) headphones when elco's of 25 v are executed? (Forgive me my little electronic insights, I am only looking for some insurance against stupid implementations with risk of damaging my headphones!_

 

No, the voltage rating is not a measure of how much voltage the capacitor will block, but a measure of how much voltage can be applied to the capacitor over a long period of time. When I mentioned a maximum bias of 24V, I meant that to describe a failure condition - that would indicate that the bias pot had failed and the cathode was at ground. You would quickly hear that something was wrong - but even a 25V cap will block 30V of DC, although I would recommend that you use a 50V cap in that case because it's a good design practice. Obviously you wouldn't want the cap to block 30V for any great length of time.

  Quote:


 2. In general your EE approach gives me more confidence feelings than looking for the lowest possible voltages or values for a little less cents. 
 

As an off-topic aside, when I design memory modules (my day job), I have to make a pretty good case for placing bypass caps that have even a small amount of voltage margin. For about a quarter of a cent per capacitor (and around 20 capacitors) difference between the different caps, that five cents becomes a major issue for the marketing and sales department. Fortunately, in the case of building our own amps, we get to make the decision on our own!

  Quote:


 3. By the way:what will be the maximum practical bias volt adjustment to expect with the different tube types that will be practised? Is'nt that maximum also to determine the max supply voltage and the practical voltage of the electrolytic's? 
 

The bias is up to your ears. As a practical upper limit, the tubes were designed for automotive use, so 14V is as high as you should go. The nominal value is, I think, 12.6V. Higher bias will give more gain at the cost of more distortion - this amplifier has no feedback, so the distortion is a little on the high side in comparison to a solid state amplifier. 

 The maximum supply voltage is actually a function of the heaters in this amplifier. They are nominally rated at 12V, with a maximum of 15V. Since they are wired in series, each heater drops half of the power supply voltage. Your 30V power supply is at the upper limit of the heaters' voltage. They won't last as long as they might at a lower voltage, but keep in mind that their lifetime at 12V is rated at 10,000 hours and they're pretty inexpensive.

  Quote:


 4. I am planning a supply-set at 30V (STEPS based on talema 25va/2*15v; see earlier posts). In that case I assume that after regulation at 30V a 35V range (minimum) on all caps is mandatory, even in the position of C7. 
 

Yes, that is an appropriate voltage value in your case.

  Quote:


 5. That strategy gives me - as far as I can imagine - the most flexibility in bias adjustment. Or is that bias-aspect fully separate of the (max) supply voltage in all other positions? 
 

The bias is independent of the power supply. The heaters (and the buffers) are directly affected by the power supply voltage. I would not exceed 30V. I will say that I've been running my amplifier with a 30V Radio Shack power supply (that has absolutely terrible ripple specs), a 30V STEPS and a 30V TREAD clone and everything works quite nicely.

  Quote:


 6. In regard to the question of leadspace (and the added flexibility) I want to remark that - if funds gives you the space - do not go for the lowest level possible. I think the amp will benefit from some headroom in the supply and in the (quality) capacities on board. Than I am speaking of a balance between quantity, quality and (local) price. 
 

Yes, I would say (and there has been plenty of discussion on Head-Fi to support this) that given the choice between capacitance and quality, one would do well to go for quality. A fast, low ESR cap of 100uF would be a better choice than a cheap 470uF cap. And if anybody is unsure about where to put their money on caps, the output caps are the most critical of all of the caps.

 I've built five or six of these amps by now and after some pretty careful listening with a variety of headphones and sources, I think that the parts list on the web site represents the best bang for the buck. You can go down the "Mouser" column and end up with a really sweet sounding amplifier without breaking the bank.

 Nate's Excel spreadsheet (which I'll be uploading this evening) is a slightly less expensive version that should deliver 95% of the sound.

 But don't agonize over the choice of caps. Panasonic FC's or FM's are excellent performing caps and the Wima film caps from Mouser are pretty darned cheap - and those are the critical parts, in my opinion.

 -Drew


----------



## Finch&Music

drewd said:
			
		

> Thanks for your very explicite answers! As always it gives insight and help in choosing components and making dicisions on configurations.
> 
> On the topic of different tubes :
> 
> ...


----------



## sbelyo

Quote:


  Originally Posted by *Finch&Music* 
_I have seen that a 12AE6A has another (= greater) amplificationfactor than f.e. a 12FK6. Is that factor of any significance in the sonical results? _

 

The 12AE6A to me didn't sound as detailed for vocals as the 12FK6, and the 12FM6 was in between. The bass wasn't as crisp either. However when running the Bias at 18 Vdc it was much better but lacked just a little compared to the FK
  Quote:


  Originally Posted by *Finch&Music* 
_I am in the process to choose between tube-brands. I have already chosen for a pair of each tubetype mentioned on the thread or componentlist. So I have already one pair of 12AE6E, 12FK6 and 12FM6 (all Sylvania) on my orderlist._

 

I like the RCA 12FK6 the best with Sylvania a close second. My least favorite to listen to is Westinghouse. I have also tried Tung-Sol 12FK6's I would rank those third.

 But those are just preliminary as I haven't really played too much with bias settings or chosen one recording and pair of headphones to compare the brands with.

 Hope that helps.


----------



## n_maher

Another update - after Drew's comments regarding the spreadsheet, namely that the Mouser parts might in fact be considered preferred over Digikey, I went back and added a second page to the spreadsheet with all Mouser part numbers (save for the pot, no choice there). Turns out that the Mouser version is actually cheaper by my count, even including the $5 hit you'll take unless you can come up with $25 worth of parts needed from Digikey. Hopefully my email will get to Drew before he bothers to upload the previous version of the spreadsheet as it also had the wrong value for R6, D'OH!

 And for those who might have missed it in the Group Buy thread the boards shipped today 
	

	
	
		
		

		
			











 .

 Nate


----------



## kilkil

Thanks for all the work. 

 It looks like C9 and C10 should be electrolytic caps on the excel BOM


----------



## drewd

Quote:


  Originally Posted by *kilkil* 
_It looks like C9 and C10 should be electrolytic caps on the excel BOM_

 






 Two sets of eyes and you'd think that we'd catch that - I guess that three's the charm! It's fixed.

 -Drew


----------



## kilkil

I didn't intend to validate the excel file, but one of my job at work is to make sure quality data goes out so I started validating the file without even thinking about it.


----------



## n_maher

Your validation is appreciated!


----------



## bbm3

Another set of eyes.

 Should'nt C9L/R and C10L/R be QTY 2? (Mouser Version BOM)


----------



## n_maher

yup, just caught that one this morning while placing my Mouser order. Thanks for making sure though. I've PM'd Drew to fix the version on the web!

 Nate

 P.s. I guess I know better than to do parts spreadsheets at 11pm now 
	

	
	
		
		

		
			





.


----------



## bbm3

I was going through the parts I ordered for the "original" Millett I was about to build prior to finding this thread and the group buy to see what I could salvage.

 Do I understand correctly that I can still use the 100mfd 100v caps that I bought for the "original" with my 32ohm headphones?

 BTW. Thanks for all the hard work Nate, Drew and everyone else. This is going to be a fun project.


----------



## n_maher

Yes, those caps will work fine. I've built some of my prototypes (as has Drew) based on the original parts list and you'll end up with a great sounding amp. We only modified the parts lists so that people would understand what other caps that they could use. The 100V caps are not required, but perfectly acceptable. I'll be building the Mouser version as soon as I can to compare and contrast and see if there's a difference to my ears. I'm no golden ear so I doubt I'll detect much if any difference.

 Hope that helps.

 Nate


----------



## bbm3

It sure does help. Thanks.
 Now I have to stop beating myself up for buying the $40.00 board just a couple of days before I discovered the hybrid project.


----------



## drewd

Quote:


  Originally Posted by *n_maher* 
_yup, just caught that one this morning while placing my Mouser order. Thanks for making sure though. I've PM'd Drew to fix the version on the web!_

 

It's fixed!

  Quote:


 P.s. I guess I know better than to do parts spreadsheets at 11pm now 
	

	
	
		
		

		
		
	


	




. 
 

No way! You've got to live dangerously!


----------



## bbm3

Has anyone tried installing LEDs at the bias test points to allow adjusting the L/R bias by eye? Or as a visual indicator if the bias has drifted?
 Are the tubes stable enough that once the bias is set with a meter at normal operating temperature you can forget about it?


----------



## AtomBoy

Quote:


 adjusting the L/R bias by eye? 
 

I've been looking for inexpensive voltmeters to wire to the bias points, but I'm not sure what that would do to the audio. I'd be interested if someone has any ideas here.


----------



## drewd

Quote:


  Originally Posted by *bbm3* 
_Has anyone tried installing LEDs at the bias test points to allow adjusting the L/R bias by eye? Or as a visual indicator if the bias has drifted?
 Are the tubes stable enough that once the bias is set with a meter at normal operating temperature you can forget about it?_

 

The bias has not drifted on mine after about a month. Also, at least to my ear, the bias setting is not absolutely critical - with a set of 12FK6's, I can't hear much of a difference within a couple of volts of 12V bias.

  Quote:


  Originally Posted by *AtomBoy* 
_I've been looking for inexpensive voltmeters to wire to the bias points, but I'm not sure what that would do to the audio. I'd be interested if someone has any ideas here._

 

Very little, if any. The circuit will see a voltmeter as a very large resistance to ground. Any noise that the voltmeter introduces will be insignificant in terms of the distortion in the amplifier itself. Remember, this is not a solid state device that will have virtually no distortion - count on around .5% to 1% distortion. The power supply will generate more noise than you'll hear from the voltmeter.

 Consider, though, that a voltmeter will really be an aesthetic fixture on the amplifier - the tubes have an extraordinarily long life, so the bias should not drift. Of course, there's nothing wrong with a nice looking amp and there are plenty of classy meters out there! I would recommend finding a meter that has the bias point as close to mid-range on the meter as possible, since that is the most accurate area on an analog meter.

 -Drew


----------



## bbm3

Quote:


  Originally Posted by *drewd* 
_The bias has not drifted on mine after about a month. Also, at least to my ear, the bias setting is not absolutely critical - with a set of 12FK6's, I can't hear much of a difference within a couple of volts of 12V bia_

 

Thanks for the input Drew.
 I think I'll pop a couple of LEDs in the bias test pads just for grins as long as it isn’t going to adversely affect the circuit.

 AtomBoy, 
 I was thinking cheap, as in LED, but a couple of analog meters would be way cool.

 In the next few weeks we should begin seeing some very interesting variants of the hybrid.


----------



## n_maher

Quote:


  Originally Posted by *bbm3* 
_In the next few weeks we should begin seeing some very interesting variants of the hybrid._

 

This is something I'm very much looking forward to 
	

	
	
		
		

		
		
	


	




 . That and hopefully heraing lots of people who having a great time building themselves an amp. I've got a couple of special Milletts lined up, just not sure when I'll get the time to build them. I guess there's always the winter to look forward to.

 N


----------



## dsavitsk

A note about the project website:

 Drew suggests that a Velleman PS is a good choice. At the voltages used in the Millett, some of the parts in the Velleman are slightly underspeced, particularly if you use a transformer that has a secondaries at around 30V. For instance, there are 2 electrolytics that are 35V, and there is a trim pot and a resistor that are likely at too low of a wattage rating. Replacing these four parts is probably not essential, but doing so is relatively inexpensive and adds some safety margin. 

 Here are some threads:
http://www6.head-fi.org/forums/showthread.php?t=109928
http://www6.head-fi.org/forums/showthread.php?t=114261


----------



## JWFokker

Quote:


  Originally Posted by *bbm3* 
_Thanks for the input Drew.
 I think I'll pop a couple of LEDs in the bias test pads just for grins as long as it isn’t going to adversely affect the circuit.

 AtomBoy, 
 I was thinking cheap, as in LED, but a couple of analog meters would be way cool.

 In the next few weeks we should begin seeing some very interesting variants of the hybrid._

 


 If anyone does analog meters, I want to know about it. I love 'em, but I have very minimal knowledge when it comes to electronics design so I'd have no idea how to implement them.


----------



## ble0t

Here's a couple links as long as they got brought up...

http://www.mpja.com/productview.asp?product=8718+ME

http://www.surplussales.com/Meters/MtrDCVoltsmain.html

 There's nothing too complicated about wiring them up...you just need to connect it across the load you want to keep track of.


----------



## skyskraper

there were a couple of threads on vu meters (both led and needle types) that had some cool links n stuff to pre circuits to drive them and info on using the good ones and not so good ones etc.

 not for a millet tho 
	

	
	
		
		

		
		
	


	




 dynahi mebbe.


----------



## drewd

Hey, just an update, since Nate is getting ready to send out the boards. I've updated the web site with some build instructions. Please feel free to pick 'em apart and make improvements.

 -Drew


----------



## evo_lution

Hi all,
 Looking to gather the parts together for my Millet, so i was wondering can i use WIMA MKP 0.1uf instead of the 0.22uf's. Didn't Pete mention the caps absolute values aren't critical?
 btw- i have 2 bags of these so i'm hopin' they're ok to use 
	

	
	
		
		

		
			






 evo_lution


----------



## rreynol

Quote:


  Originally Posted by *drewd* 
_Hey, just an update, since Nate is getting ready to send out the boards. I've updated the web site with some build instructions. Please feel free to pick 'em apart and make improvements.

 -Drew_

 

Drew,
 Where did you get the tube sockets you used for that build? Thanks.


----------



## drewd

Quote:


  Originally Posted by *rreynol* 
_Where did you get the tube sockets you used for that build? Thanks._

 

Hmm...good question. I got them from a surplus outfit, but I don't remember exactly which one. I don't think that they have anymore of them 
	

	
	
		
		

		
		
	


	




 [edit] Oops, I guess I lied. I got them from Electronic Surplus. 50 cents each (a bargain!)[/edit]

 [edit (again)] I guess I'm getting old. 7 pin sockets are here [edit (again)] 

 -Drew


----------



## drewd

Quote:


  Originally Posted by *evo_lution* 
_Looking to gather the parts together for my Millet, so i was wondering can i use WIMA MKP 0.1uf instead of the 0.22uf's. Didn't Pete mention the caps absolute values aren't critical?_

 

Yes, they'll work perfectly. I get the feeling that when Pete originally built his amplifier he was faced with the same situation 
	

	
	
		
		

		
		
	


	




 -Drew


----------



## rreynol

Quote:


  Originally Posted by *drewd* 
_Hmm...good question. I got them from a surplus outfit, but I don't remember exactly which one. I don't think that they have anymore of them 
	

	
	
		
		

		
		
	


	




 -Drew_

 

doh! thanks anyway. i have some of the ones from tubedepot that I modified to allow for a center hole but the ones you've got look much nicer.


----------



## evo_lution

Quote:


  Originally Posted by *drewd* 
_Yes, they'll work perfectly. I get the feeling that when Pete originally built his amplifier he was faced with the same situation 
	

	
	
		
		

		
		
	


	




 -Drew_

 

Thanks Drew


----------



## Unclewai

on the D2L/R the instruction says "Either 1N5291 or J503 must be placed, but NOT both", that means we have to keep consistency right? So we should have to put on both diodes on D2L/R right. 

 Also a small request, does anyone have extra parts for D2L/R and R2R/L? I need 4 of each. Thanks


----------



## n_maher

It just means that you want to use one type or the other and only populate one of the pairs of positions on the board. 

 So for each amp you'll either need a pair of 1N5291s or J503s. 

 Sorry I can't help with the spare parts problem, I just got what I hope to be my last DigiKey and Mouser orders for a long, long time. $500 in parts showing up is fun, but really hard on the wallet. Look for a pretty _interesting_ Millett Hybrid to be built in the near future. 
	

	
	
		
		

		
		
	


	




 Time to go home and start packing boards.

 n


----------



## drewd

Quote:


  Originally Posted by *Unclewai* 
_on the D2L/R the instruction says "Either 1N5291 or J503 must be placed, but NOT both", that means we have to keep consistency right? So we should have to put on both diodes on D2L/R right._

 

I've updated that part of the web page to make it a bit more clear:

Locations are provided on the board for the 1N5291 and the J503. *Do not* populate both diode types! Use either the 1N5291 or the J503, but not both. Also, do not mix and match - use two 1N5291s or two J503s, but not one of each. *You've been warned...*

 If you use one of each, nothing terrible will happen, but the two parts are not identical, just very close. Expect channel imbalance if you mix'n'match.

 If you populate both positions, the amplifier's gain will be too high so you won't enjoy the full use of your volume control and you'll hear plenty of distortion.

 -Drew


----------



## dsavitsk

I have been tinkering around with my Millett a bit, and have happened upon a nice, inexpensive, tweak. Pete's article suggests using 22R resistors on the output, but also suggets that their resistance should be about half of the headphones impedence. 

 I had been using the Dale resistors from Mouser suggested in the article. I replaced them with Kiwame carbon film resistors. This made the sound a bit warmer and more natural, took off a bit of upper mid glare, (I have been replacing signal path metal films with carbon films all over lately) and perhaps made the amp a bit more lush and tubey. I am sure this is not for everyone, but it is for me.

 I also lowered the resistance to 15R. I am using Grado RS-1s, and this seems to have brougt out a bit more bass. fwiw, my amp is ceraphines all around except for Nichicon muse 470uF on the output, an alps blue, and 12ae6a tubes.

 -d


----------



## comabereni

Post moved to "Group Buy" thread. Thanks.


----------



## pabbi1

Several build curiosities:

 a) What is the optimal (in your most humble opinion) voltage setting (using a STEPS) for the 12ae6a and the 12fk6 respectively? 

 b) I am using a wood front panel on a PARS metal case - is steel shielding (an easy option for me) likely to be needed? 

 c) The PARS metal case has an aluminum divider - does that need to be steel (an easy option) to shield the Millett board from the STEPS?

 d) Which tube set is likely better for Senns (HD600 or HD650)?

 e) Do I need to adjust any resistor values to boost the gain for Senns (600/650)?


----------



## n_maher

Quote:


 a) What is the optimal (in your most humble opinion) voltage setting (using a STEPS) for the 12ae6a and the 12fk6 respectively? 
 

From what I've read and what I hear the bias setting is not super critical with the exception of not going higher than say 14V. I'm sure someone can clarify this. If it were me I'd just set it at 12V and forget it.
  Quote:


 b) I am using a wood front panel on a PARS metal case - is steel shielding (an easy option for me) likely to be needed? 
 

Sheilding would only be need if you're getting interference. If the amp is going anywhere near stuff like monitors, computers or the like I'd find a way to shield it.

 c) I'll leave this to others as I'm not sure.
  Quote:


 d) Which tube set is likely better for Senns (HD600 or HD650)? 
 

With the cost of the tubes being pretty low ($3 of $4 a pop) I'd just get a set of each and try them out yourself. One man's trash is another man's treasure holds just as true for audio. Listen and decide for yourself.
  Quote:


 e) Do I need to adjust any resistor values to boost the gain for Senns (600/650)? 
 

If the amp is going to be used exclusively for Senns I'd say you could omit R4R/L and just jumper these positions. I've built all my prototypes this way and they work fine. You could also use a 10OHM value if you still wanted some resistance.

 HTH,

 Nate


----------



## mrdon

How does one connect the toggle switch to the pcb? Thanks!


----------



## drewd

Quote:


  Originally Posted by *pabbi1* 
_Several build curiosities:

 a) What is the optimal (in your most humble opinion) voltage setting (using a STEPS) for the 12ae6a and the 12fk6 respectively? _

 

24 Volts. The heaters in the tubes are designed for a 12 volt system and since they are wired in parallel, that gives them 12 volts each. The bias voltage should be set to 12V, but you can experiment a bit with that voltage. Your ear is really your best guide - and you may not hear any difference over a fairly broad range of voltages.

  Quote:


 b) I am using a wood front panel on a PARS metal case - is steel shielding (an easy option for me) likely to be needed? 
 

Probably not. My STEPS is in an aluminum Hammond case and it sits directly under my Millett in another aluminum Hammond case. I hear no hum, even at full volume. I use it at work, where I'm surrounded by fluorescent lights, computers and electronic test equipment. Oddly enough, the only noise that I ever hear is from my cell phone, but that appears to be coupled through the headphone cable.

  Quote:


 c) The PARS metal case has an aluminum divider - does that need to be steel (an easy option) to shield the Millett board from the STEPS? 
 

If you get hum from the power supply, then yes, it does need to be steel, or some other material that interacts with magnetic fields (mu metal, nickel, etc.)

  Quote:


 d) Which tube set is likely better for Senns (HD600 or HD650)? 
 

I happen to like the 12FK6 best of all of the tubes that work in the amp, but you might have a different opinion. Since the tubes are pretty inexpensive, try a couple of different sets. I'd recommend starting with the 12AE6A and 12FK6.

  Quote:


 e) Do I need to adjust any resistor values to boost the gain for Senns (600/650)? 
 

The amplifier does not use a feedback loop for gain. The gain is set by the constant current diode on the anode. You may want to reduce or even eliminate the 22.1 ohm output resistor. It was originally placed to protect the buffers from a direct short, but the BUF634s have internal protection, so it's not strictly required. The amp has plenty of gain for your Sennheisers.

 Good luck!

 -Drew


----------



## drewd

Quote:


  Originally Posted by *mrdon* 
_How does one connect the toggle switch to the pcb? Thanks!_

 

There are two pads on the board labeled S1 and S2. They are for the switch - one wire to each pad. I'll update the build instructions to address that.

 -Drew


----------



## dsavitsk

Quote:


  Originally Posted by *pabbi1* 
_c) The PARS metal case has an aluminum divider - does that need to be steel (an easy option) to shield the Millett board from the STEPS?_

 

I have a STEPS sitting about an inch to the side of my Millett. There is no shielding and no noise. I would wait until you have interference before you worry about it.


----------



## pabbi1

Thanks for the input... I have indeed purchased both sets of tubes, and see if there is a difference.

 I was just curious since the earlier posts indicated 30v, and bias of 13.5 was working very well, but possibly at the expense of tube life (which I'm fairly insensitive to).

 Mainly I'm asking questions because I'm waiting for parts...


----------



## comabereni

Quote:


  Originally Posted by *n_maher* 
_From what I've read and what I hear the bias setting is not super critical with the exception of not going higher than say 14V. I'm sure someone can clarify this. If it were me I'd just set it at 12V and forget it._

 

Many of the original Millett builders/users set their bias as high as 19V. I haven't read Pete's article in awhile, but I don't remember there being a 14V recommended ceiling. I've read most of the Millett impression posts, if not all of them, and there hasn't been a lot of comment on optimal bias settings for different model tubes--this should eventually make for some interesting discussion, i.e. we should all try different settings and find out.

 -coma


----------



## dviswa

Hi Guys,

 Did we rename the parts from the original Pete's schematic? From what I can see from his schematic there are no parts names either L or R, in contrast the PCB has plenty of parts named L/R. For somebody trying to follow Pete's schematic this is confusing.

 Regards,
 Dinesh


----------



## drewd

Quote:


  Originally Posted by *comabereni* 
_Many of the original Millett builders/users set their bias as high as 19V. I haven't read Pete's article in awhile, but I don't remember there being a 14V recommended ceiling. I've read most of the Millett impression posts, if not all of them, and there hasn't been a lot of comment on optimal bias settings for different model tubes--this should eventually make for some interesting discussion, i.e. we should all try different settings and find out.
 -coma_

 

I'll vouch for that - I accidentally set mine at 20V with no damage. The 12AE6A tubes didn't work, but they weren't hurt. Interestingly, the 12FK6's worked OK.

 As always, your ears are your best guide.

 -Drew


----------



## n_maher

Quote:


  Originally Posted by *dviswa* 
_Hi Guys,

 Did we rename the parts from the original Pete's schematic? From what I can see from his schematic there are no parts names either L or R, in contrast the PCB has plenty of parts named L/R. For somebody trying to follow Pete's schematic this is confusing.

 Regards,
 Dinesh_

 

Yup, we renamed them in the hopes of clarifying things a bit. That way you can see which part is for what channel and so on. The fluidlight sight has both a BOM and parts list that are coordinated with the production boards.

 And I can completely see how it would be hard to follow Pete's instructions with these boards, which is why we rewrote the build instructions as well 
	

	
	
		
		

		
		
	


	




.

 HTH,

 Nate


----------



## dviswa

I surely appreciate depicting symmetry where one exists, but I also prefer following schematics. Do we have a map or list of what became what. That would be really appreciated.


----------



## n_maher

Quote:


  Originally Posted by *dviswa* 
_I surely appreciate depicting symmetry where one exists, but I also prefer following schematics. Do we have a map or list of what became what. That would be really appreciated._

 

I'll get to work on it, as far as I know the answer right now is no.


----------



## drewd

Quote:


  Originally Posted by *dviswa* 
_I surely appreciate depicting symmetry where one exists, but I also prefer following schematics. Do we have a map or list of what became what. That would be really appreciated._

 

Uh oh...schematics. I will work on the schematic this week. In the interest of not screwing up Pete's original design, I worked exclusively from the board file.

 -Drew


----------



## dviswa

Quote:


  Originally Posted by *n_maher* 
_I'll get to work on it, as far as I know the answer right now is no._

 

 Quote:


  Originally Posted by *drewd* 
_Uh oh...schematics. I will work on the schematic this week. In the interest of not screwing up Pete's original design, I worked exclusively from the board file.

 -Drew_

 

Nate, Drew,

 You guys totally rock


----------



## Erik S.

In the parts list the Muse KZ 3-4030 is recommended for C2L/R, but does it fit since it is 12.5 mm in diameter while the diameter on the board is 10.5 mm?

 Is there a noticable difference by using Holco or Roederstein resistors instead of of Vishays?

 Gonna use some better parts on this Hybrid than the last one I built to see if there is a noticable difference. With that said, a Hybrid with Panasonic caps/resistors allover is pretty good 
	

	
	
		
		

		
		
	


	




 -Erik


----------



## drewd

Quote:


  Originally Posted by *Erik S.* 
_In the parts list the Muse KZ 3-4030 is recommended for C2L/R, but does it fit since it is 12.5 mm in diameter while the diameter on the board is 10.5 mm?_

 

Yes, it will fit, it's just a bit of a tight squeeze.

  Quote:


 Is there a noticable difference by using Holco or Roederstein resistors instead of of Vishays? 
 

I don't know - somebody made a comment that using carbon resistors in the audio path complemented the tube sound, but I have not tried that.

 -Drew


----------



## Emon

So...I don't suppose anyone has an extra revised PCB lying around they would mind selling?


----------



## pabbi1

Any update on the discrete buffers?


----------



## dsavitsk

Quote:


  Originally Posted by *Erik S.* 
_Is there a noticable difference by using Holco or Roederstein resistors instead of of Vishays?_

 

I think Holcos in the signal path sound harsh and brittle which does not compliment this circuit well. Rumor is that some of them have steel caps, though I don't know if this is really true. If I were using a boutique metal film I would use a PRP over the Holco (though I am not familiar with how Roedersteins sound as I've not had the opportunity to use them.) Of course, you can also leave the output resistors out completly which should be the best option.

 -d


----------



## Emon

Quote:


  Originally Posted by *pabbi1* 
_Any update on the discrete buffers?_

 

The Millet site on DIYforums said the prototype boards were ordered in May. I'm quite interested in these, as I imagine the Burr-Brown buffers are the weak point in the system.


----------



## bg4533

What is the performance difference between 24V and ~28V? 24V would allow the use of the 25V Cerafines and Silmics that are pretty easy to get.


----------



## drewd

Quote:


  Originally Posted by *bg4533* 
_What is the performance difference between 24V and ~28V? 24V would allow the use of the 25V Cerafines and Silmics that are pretty easy to get._

 

I hear no difference at all.

 -Drew


----------



## n_maher

Quote:


  Originally Posted by *pabbi1* 
_Any update on the discrete buffers?_

 

For the love of Pete, give us a moment to catch our breath will ya 
	

	
	
		
		

		
			





 . Drew and I are concurrently working on buffer options, Drew's being the far sexier of the 2. If I can get a handle on Eagle I may have something post in the next month or so. But progress is going to be slow as a lot of free time was devoted to this project and the missus is, how you say, not pleased 
	

	
	
		
		

		
		
	


	




.

  Quote:


  Originally Posted by *bg4533* 
_ What is the performance difference between 24V and ~28V? 24V would allow the use of the 25V Cerafines and Silmics that are pretty easy to get._

 

 In my opinion you do so at your own risk. The concerns of using caps that barely meet the voltage requirements of the power supply have been discussed already but the long and short of it is, if you're willing to risk an entire amps worth of caps that's up to you. Take it from someone who's blown one up the cleanup sucks.

 Nate


----------



## pabbi1

Yeah, yeah, yeah, I can listen to that (re: the missus isn't pleased) at home... 

 However, leaving that pic of the discrete buffer on the web page for everyone to scroll through every time we have to reference something is just waving the red flag at the bull... you have to anticipate a charge sometime. And, with the development status morsels (ya'll are listening to protos), well, what's a rabid DIY gonna think?


----------



## n_maher

Quote:


  Originally Posted by *pabbi1* 
_And, with the development status morsels (ya'll are listening to protos), well, what's a rabid DIY gonna think?
	

	
	
		
		

		
		
	


	


_

 

Well, to be perfectly blunt the proto blew up so we're back to revising the boards 
	

	
	
		
		

		
		
	


	




 . If you want an exploding diamond buffer just let me know!

 Nate


----------



## pabbi1

Well, thanks for the cold shower... between making a STEPS with no fuse, and exploding buffers, looks like my 4th of July is all set... 
	

	
	
		
		

		
		
	


	




 Like Tom Petty said, the waiting (for parts - Wellbourn) is the hardest part.


----------



## n_maher

Quote:


  Originally Posted by *pabbi1* 
_Like Tom Petty said, the waiting (for parts - Wellbourn) is the hardest part.



_

 

They weren't exactly "quick" w/ my delivery either so I've since found other sources for the parts they offer. Don't get me wrong, they aren't that bad, but they just don't have anything I can't get elsewhere anymore.

 And sorry for the downer on the diamond buffer, Drew's working on other options as well, but both he and I have full time jobs that have to get done in order to pay the bills 
	

	
	
		
		

		
		
	


	




.

 N


----------



## pabbi1

Not a downer at all... just thought I'd ask about it... and, started to bring up "March Madness", but, like by telepathy, the good doctor popped up.


----------



## mrdon

Almost complete. Just need a few more parts, pieces, and finishing of the wood. I'll post the finished product when complete. Enjoy!


----------



## rreynol

Been listening all day and enjoying it (Still not sure about going topless or drilling the holes for the tubes to stick through).


----------



## n_maher

Now those two posts put a serious smile on my face after a dang long day at work.


----------



## aeroes

I got all the parts already except for the tubes 
	

	
	
		
		

		
		
	


	




 Can someone tell me whats the most detailed tubes that works with millet?

 TIA!


----------



## Thaddy

Quote:


  Originally Posted by *aeroes* 
_I got all the parts already except for the tubes 
	

	
	
		
		

		
			





 Can someone tell me whats the most detailed tubes that works with millet?

 TIA!_

 

I'd say either the 12FK6's or the 12FM6's. It's all personal preference really, but stay away from the 12AE6A's, they certainly don't have the most detail. Low end? Yes. Detail? No


----------



## drewd

I think that the consensus so far has been for the 12FK6, but the 12AE6A is also well worth a try. The 12FM6 doesn't seem to get any raves.

 -Drew


----------



## dsavitsk

Quote:


  Originally Posted by *aeroes* 
_Can someone tell me whats the most detailed tubes that works with millet?_

 

I found that it depends upon the power supply. The 12ae6a's performed worse with a poor quality ps than some others, but with good clean power I prefered them.


----------



## dsavitsk

Quote:


  Originally Posted by *n_maher* 
_ Quote:


  Originally Posted by *bg4533* 
What is the performance difference between 24V and ~28V? 24V would allow the use of the 25V Cerafines and Silmics that are pretty easy to get.

 

In my opinion you do so at your own risk. The concerns of using caps that barely meet the voltage requirements of the power supply have been discussed already but the long and short of it is, if you're willing to risk an entire amps worth of caps that's up to you. Take it from someone who's blown one up the cleanup sucks._

 

I agree with Nate that with 25V caps you best use a sealed case that stinky goo can't escape from. That said, the heaters in these tubes will run on 10V, so can bring your PS down to 20V for a bit more margin of safety. Whether the fancy caps would make up in sound for running at 20V is for you to discover, however.

 -d


----------



## Secret Squirrel

Just to make sure. The parts list includes capacitors C2L/R “Voltage rating should be no less than 16V. 5mm pin spacing, 10.5mm diameter” 

 C2L/R rated at 25 Volts= No Problem?


----------



## dsavitsk

Quote:


  Originally Posted by *Secret Squirrel* 
_Just to make sure. The parts list includes capacitors C2L/R “Voltage rating should be no less than 16V. 5mm pin spacing, 10.5mm diameter” 

 C2L/R rated at 25 Volts= No Problem?_

 

Overspecing caps is not a problem.


----------



## SHLim

Quote:


  Originally Posted by *dsavitsk* 
_I found that it depends upon the power supply. The 12ae6a's performed worse with a poor quality ps than some others, but with good clean power I prefered them._

 

Hi dsavitsk,

 What is the good clean power supply you mention here?

 TIA,
 Sam


----------



## dsavitsk

Quote:


  Originally Posted by *SHLim* 
_What is the good clean power supply you mention here?_

 

With the cheap wall wart mentioned in Pete's article, the 12fm6's sounded better than the 12ae6a's. With a STEPS, the 12ae6a's were clearly better. My guess is that the 12ae6a's are more revealing and in the case of the wall wart were simply revealing the PS's noise. The 12fm6's are a bit smoother, and thus were able to smooth over the noise.

 -d


----------



## bg4533

Quote:


  Originally Posted by *n_maher* 
_ In my opinion you do so at your own risk. The concerns of using caps that barely meet the voltage requirements of the power supply have been discussed already but the long and short of it is, if you're willing to risk an entire amps worth of caps that's up to you. Take it from someone who's blown one up the cleanup sucks.

 Nate_

 

Is this amp particularly hard on caps or something? Countless people here have used used 25V caps with 24V Elpac WM080s in Pimetas and PPAs without issue. I have never read about a single exploding cap from the above example. What makes the Millet different?

 Sorry if this was covered already, but I missed it if so.


----------



## rreynol

Theres a slight difference in the PS section of the PIMETA/PPA and the Millet.

 The PIMETA takes that 24V and uses a rail splitter to end up with -12V and +12V rails. If the virtual ground collapses, the most the cap will see is 24V (theoretically).

 The millet has no such dual rail setup which is prolly why you should allow for a little bit more headroom. In the case of a steps, the power supply is configured for a range (using the 500 ohm trimpot). For instance, using the default values for the resistors in a steps allows you to use the trimpot to vary the dc output voltage between 22 and 27V. Say you have it set for 24V and the trimpot fails. What then?

 Like others have said, do what you want. You do so at your own risk.

 Edit: Its one of those things thats just better to NOT find out the hard way.


----------



## bg4533

Quote:


  Originally Posted by *rreynol* 
_Theres a slight difference in the PS section of the PIMETA/PPA and the Millet.

 The PIMETA takes that 24V and uses a rail splitter to end up with -12V and +12V rails. If the virtual ground collapses, the most the cap will see is 24V (theoretically).

 The millet has no such dual rail setup which is prolly why you should allow for a little bit more headroom. In the case of a steps, the power supply is configured for a range (using the 500 ohm trimpot). For instance, using the default values for the resistors in a steps allows you to use the trimpot to vary the dc output voltage between 22 and 27V. Say you have it set for 24V and the trimpot fails. What then?

 Like others have said, do what you want. You do so at your own risk.

 Edit: Its one of those things thats just better to NOT find out the hard way._

 

You got me on the Pimeta, but the PPA C1 is rail to rail. I understand the risks of component failure. I am asking this question from a more theoretical and educational persepective. Why is using caps up to their tolerance acceptable in one instance but not another?


----------



## rreynol

Quote:


  Originally Posted by *bg4533* 
_You got me on the Pimeta, but the PPA C1 is rail to rail. I understand the risks of component failure. I am asking this question from a more theoretical and educational persepective. Why is using caps up to their tolerance acceptable in one instance but not another?_

 


 I'd say from an educational and theoretical perspective, its not. But Murphy's Law does come to mind. :-D


----------



## skyskraper

aussie guys, the boards havent arrived yet 
	

	
	
		
		

		
		
	


	




 will keep u up to date


----------



## USER NAME:

I'm not sure where we are supposed to post our pictures so I copied this from to construction thread.

 I was just fooling around in the shop trying to think of a good chassis solution for my Millet Hybrid. It's not done yet. It's just a fully dressed chassis with no board inside. I tried to add some carbon fiber to the mix, but it just looked awkward. I'm never satisfied. Maybe I should start looking in to aluminum? Anybody have any constructive criticism?


----------



## rreynol

Here's my constructive criticism.......That case is awesome. Nice work.


----------



## DaKi][er

Quote:


  Originally Posted by *USER NAME:* 
_I'm never satisfied. Maybe I should start looking in to aluminum? Anybody have any constructive criticism?

 http://www.blueberryaudio.com/millet.jpg[img][/i]
 [/td] [/tr] [/table]


looks very nice

 if you want to go further, i'd go an alu faceplate and wooden knob on it, that'd set it off real nice_


----------



## AtomBoy

Quote:


  Originally Posted by *USER NAME:* 
_I'm not sure where we are supposed to post our pictures so I copied this from to construction thread.

 I was just fooling around in the shop trying to think of a good chassis solution for my Millet Hybrid. It's not done yet. It's just a fully dressed chassis with no board inside. I tried to add some carbon fiber to the mix, but it just looked awkward. I'm never satisfied. Maybe I should start looking in to aluminum? Anybody have any constructive criticism?





_

 

[ART STUDENT]I'd like to see it float off the table- little spike feet maybee? Also the area arround the plate is a little awkward. I would loose the arches and try a line midway between the plate and the edge. Perhaps a little chrome guardrail supported about half an inch above the surface.[/ART STUDENT] Freakin' gorgeous, man!


----------



## JWFokker

Looks good dude. It makes me rethink my decision to switch to board mount tube sockets versus my original plan to go chassis mount. Of course, your sockets do look much nicer than the ones I got. The brass especially. I'm going to have to go with AtomBoy on the tube guards. It would look better with a guard rail type of thing versus (in brass to match the sockets) rather than the arches. The amp looks somewhat monolithic and the arches are just out of place. I have no idea where you would acquire a brass guardrail type of thing though.


----------



## dviswa

Quote:


  Originally Posted by *USER NAME:* 
_Anybody have any constructive criticism?_

 

One word:
 Awesome


----------



## pabbi1

What is the relationship of voltage in to the C2 value?

 Given 24v, the C2 is recommended at no less than 16v.

 If I plan 28v, does C2 need to be higher than 16v? Conversely, if I use 16v caps in C2, what happens if I set my STEPS to 28v? Does the bias setting affect this equation (planned 14, assuming 28v incoming)?


----------



## AtomBoy

Quote:


  Originally Posted by *pabbi1* 
_What is the relationship of voltage in to the C2 value?

 Given 24v, the C2 is recommended at no less than 16v.

 If I plan 28v, does C2 need to be higher than 16v? Conversely, if I use 16v caps in C2, what happens if I set my STEPS to 28v? Does the bias setting affect this equation (planned 14, assuming 28v incoming)?_

 

C2, as the output cap, will see whatever voltage you set the bias to. You could use 28v and still set the bias to 12V for example.

 BTW is bias really the right term? You're not really setting 'grid bias' on the Millett. 'Plate voltage' is what I'm looking at in the tube theory books I'm struggling through.

http://pmillett.com/tecnical_books_online.htm


----------



## n_maher

I believe, and I'm hoping Drew will chime in here eventually, that C2 on our board is the cathode bypass cap. This cap, according to Pete, can be rated as low as 16V. I wish I new exactly what it saw but odds are if Pete was willing to use a 16V cap this has plenty of overhead built in since he recommends 50V for the other caps and we know that those can be even lower. 

 The output coupling caps (C7L/R) will see whatever you set the bias to. Be warned though and dont' be tempted to use a lower voltage cap, if you have the trimpots set wide open on startup you could easily blow a cap, it doesn't take long. If you insist on using a cap rated lower than your full power supply voltage you'd best be prepared for cleanup. The only safe way that I can see to do this is to have an adjustable supply so that you can at least get the bias set close before applying the full power supply voltage to the board. This is exactly what I did by using 25V caps on the output and testing the amp configuration with a 21V supply. Only minor fine tuning of the bias was required after hooking up the full 28V supply.

 And also, as far as I know you are in fact setting the "tube bias" when you adjust the trim pot. The "plate bias" is constant and controlled by the current regulating diodes. 

 I'd suggest that anyone considering building this amp read Pete's original article prior to construction. It's located here. 

 Great looking builds so far, I like the variety I'm seeing!

 Nate


----------



## drewd

Quote:


  Originally Posted by *AtomBoy* 
_C2, as the output cap, will see whatever voltage you set the bias to. You could use 28v and still set the bias to 12V for example._

 

C2 is the base capacitor. C7 is the output capacitor and it will see a DC voltage equal to the "bias" voltage setting. C2 will see the difference between the bias voltage and the power supply voltage.

  Quote:


 BTW is bias really the right term? You're not really setting 'grid bias' on the Millett. 'Plate voltage' is what I'm looking at in the tube theory books I'm struggling through. 
 

No, it's not bias. You're right, "bias" really refers to the voltage set on the grid to modify the natural electron flow from the cathode to the anode. The RCA Radiotron manual has an excellent and very understandable explanation of bias settings on the various types of tubes.

 When you measure what is labeled as the bias at the test points, you're really measuring the potental between the plate and the base, or, as you said, the plate voltage. But Pete called it bias, so rather than deviate too far from Pete's original design and cause confusion, I kept the terminology.

 The CRD doesn't set the voltage on the plate - it just maintains a steady current flow at whatever voltage potential is between the plate and the base. The "bias" potentiometer determines the voltage.

 -Drew


----------



## SHLim

Quote:


  Originally Posted by *USER NAME:* 
_Anybody have any constructive criticism?




_

 

I would prefer the headphone jack to locate at the front. Other than that, very nice.


----------



## pabbi1

OK, that is all very informative... and straightforward. Nate, thanks for the refresher on Pete's article.

 So, I have a STEPS which my lowest setting will give 26v. Given that, what should I expect my "bias" to be fully open? 

 Just to check: Full "bias" would be acheived with R2 fully counterclockwise?


 Finally, given MY rather low threshold between input voltage (26v minimum), C2 (16v) and C7, wouldn't the recommended Welbourne part be ROA221 (35v - which I started to get, but convinced myself otherwise)? 

 Is there an advantage to using the ROA220 over the ROA221?


----------



## rreynol

Quote:


  Originally Posted by *pabbi1* 
_OK, that is all very informative... and straightforward. Nate, thanks for the refresher on Pete's article.

 So, I have a STEPS which my lowest setting will give 26v. Given that, what should I expect my "bias" to be fully open? 

 Just to check: Full "bias" would be acheived with R2 fully counterclockwise?


 Finally, given MY rather low threshold between input voltage (26v minimum), C2 (16v) and C7, wouldn't the recommended Welbourne part be ROA221 (35v - which I started to get, but convinced myself otherwise)? 

 Is there an advantage to using the ROA220 over the ROA221?_

 

Full bias would be bad. The tubes used in this amp arent rated for 26V. Full clockwise would be biasing them to the input supply voltage (bad). The tube probably wont last too long at that voltage and the distortion will be crazy.


 Edit: also, that 35V cap wont fit in the C2 spot without some trickery.


----------



## pabbi1

As for long term settings, I'm looking at 28v, and bias of 16, well within what Pete describes, at the loss of some volume gain. 

 Avoiding burning a cap and potentially sputtering goo all over the board is my only concern at this point. For the first 60-90 seconds of this amp's life, what will the initial bias settings likely be, at the maximum (just to be sure), for me to dial something in, without burning the 16v caps was the question since midpoint puts me too close to frying C2, even at 26v.

 I am thinking this might be of help on the tip/tweak page as well, or elsewhere on the build page.


----------



## rreynol

Quote:


  Originally Posted by *pabbi1* 
_As for long term settings, I'm looking at 28v, and bias of 16, well within what Pete describes, at the loss of some volume gain. 

 Avoiding burning a cap and potentially sputtering goo all over the board is my only concern at this point. For the first 60-90 seconds of this amp's life, what will the initial bias settings likely be, at the maximum (just to be sure), for me to dial something in, without burning the 16v caps was the question since midpoint puts me too close to frying C2, even at 26v.

 I am thinking this might be of help on the tip/tweak page as well, or elsewhere on the build page._

 

The initial bias setting will be based on whatever the trimpots are at initially. If they are at 5KOhms, it will be the full power supply voltage. If you would like to not destroy your caps (and possibly tubes), you should turn each trimpot counterclockwise until you hear the faint click and then turn it a few turns clockwise (before plugging in the tubes). This will set the bias very low.


----------



## pabbi1

Please bear with me...

 Per Drew, C7 is the output capacitor and it will see a DC voltage equal to the "bias" voltage setting. C2 will see the difference between the bias voltage and the power supply voltage.

 If my incoming is 26v, and I have a "low" gain - say 10v. and C2 is the difference between incoming and "bias" for C7 (in my case, 50v caps), then I have 16v hitting C2. Is this exactly what I DO NOT want to happen.

 Having a 50v C7, wouldn't I rather have a higher gain (16-20) hitting C7, to then dial it down for a safe range for C2?

 What am I missing - other than I ought to have 25-35v caps for C2?

 I can absorb some burned tubes - I have 6 on hand.


----------



## JWFokker

The trim pots don't seem to make any difference when I adjust them. Maybe I'm not measuring the bias correctly? What should I have the multimeter set to when I measure it, and should the amp be on? I previously measured the bias when it was off and got reasonable numbers, but the trim pots don't change anything. When I tried measuring it when it was on, I didn't even get a measurement.


----------



## rreynol

Quote:


  Originally Posted by *JWFokker* 
_The trim pots don't seem to make any difference when I adjust them. Maybe I'm not measuring the bias correctly? What should I have the multimeter set to when I measure it, and should the amp be on? I previously measured the bias when it was off and got reasonable numbers, but the trim pots don't change anything. When I tried measuring it when it was on, I didn't even get a measurement._

 


 Multimeter should be on DC volts and I'd imagine that the amp should be on (why would there be current flowing with it off? if it is, you may have another problem). Do you have the tubes plugged in? When I first put mine together, I had a 'duh' moment and couldnt figure out why the trimpots had no effect on the tp voltages. Then I realized that I was dumb and plugged the tubes in. Also, I noticed that you really don't see the voltage changing much until the trim pot gets to a lower half the of the range. Hope that helps. If not, someone else will probably have some suggestions. I, too, am a tube noob.


----------



## rreynol

Quote:


  Originally Posted by *pabbi1* 
_Please bear with me...

 Per Drew, C7 is the output capacitor and it will see a DC voltage equal to the "bias" voltage setting. C2 will see the difference between the bias voltage and the power supply voltage.

 If my incoming is 26v, and I have a "low" gain - say 10v. and C2 is the difference between incoming and "bias" for C7 (in my case, 50v caps), then I have 16v hitting C2. Is this exactly what I DO NOT want to happen.

 Having a 50v C7, wouldn't I rather have a higher gain (16-20) hitting C7, to then dial it down for a safe range for C2?

 What am I missing - other than I ought to have 25-35v caps for C2?

 I can absorb some burned tubes - I have 6 on hand._

 


 I see your point. You are probably right but I'd also suggest looking at the data sheet for your trimpots and find out how many turns it is and use that to figure out what you should probably have them at when you first plug in the tubes (1/2 the number of turns, etc). Or you could just measure the resistance of the trimpots and set them for 2.5 KOhms, etc. That's probably the best suggestion. If you plan on using botique caps for C2, it might be hard finding 25V-35V caps that fit the board. Saying 10V or 16-20V isnt really the gain. Gain technically has no units. What you're speaking of is voltages being dropped across the tube, across C2/C7, etc.


 Edit: Oh and if I'm totally wrong, I apologize.


----------



## dviswa

Quote:


  Originally Posted by *JWFokker* 
_The trim pots don't seem to make any difference when I adjust them. Maybe I'm not measuring the bias correctly? What should I have the multimeter set to when I measure it, and should the amp be on? I previously measured the bias when it was off and got reasonable numbers, but the trim pots don't change anything. When I tried measuring it when it was on, I didn't even get a measurement._

 

There are 2 oblong shaped pads, one labeled as bias. I have been measuring the bias voltage across these 2 pads. Surely you are not measuring when the amp is switched on are you. BTW, the pots keep turning even after the slider has reached the end. Turn the pot back a few turns and you should see some change.


----------



## mrdon

I am soooo close to completion but....upon initially testing the unit with a PCDP conected I am getting music from the left headphone speaker but not the right. What I hear in the right side upon power up is a sound similar to a TV starting up, sort of a hum that builds, and then cuts out.

 1. Is it a matter of adjusting the bias?
 2. Is my 24VDC, 400mA wallwart powerful enough to power the 12fk6 tubes?
 3. Do my tubes need to be matched?
 4. Something else?


----------



## drewd

Quote:


  Originally Posted by *mrdon* 
_I am soooo close to completion but....upon initially testing the unit with a PCDP conected I am getting music from the left headphone speaker but not the right. What I hear in the right side upon power up is a sound similar to a TV starting up, sort of a hum that builds, and then cuts out.

 1. Is it a matter of adjusting the bias?_

 

Yep!

  Quote:


 2. Is my 24VDC, 400mA wallwart powerful enough to power the 12fk6 tubes? 
 

Yes, no problem there.

  Quote:


 3. Do my tubes need to be matched? 
 

In a perfect world, yes, that would be nice, but I don't think that you'll get any takers in the tube vendors who will want to match a couple of $3.00 tubes, so don't worry about that.

  Quote:


 4. Something else? 
	

	
	
		
		

		
		
	


	



 

I think that you covered all the bases! 
	

	
	
		
		

		
		
	


	




 -Drew


----------



## mrdon

Thanks Drew for the advice. I'll try it this afternoon. BTW, please ignore my post over at DIYForums.org. 
	

	
	
		
		

		
		
	


	



  Quote:


  Originally Posted by *drewd* 
_Yep!



 Yes, no problem there.



 In a perfect world, yes, that would be nice, but I don't think that you'll get any takers in the tube vendors who will want to match a couple of $3.00 tubes, so don't worry about that.



 I think that you covered all the bases! 
	

	
	
		
		

		
		
	


	




 -Drew_


----------



## drewd

Quote:


  Originally Posted by *drewd* 
_In a perfect world, yes, that would be nice, but I don't think that you'll get any takers in the tube vendors who will want to match a couple of $3.00 tubes, so don't worry about that._

 

I should qualify that to say that you should, at the very least, use tubes from the same manufacturer. I've got 40 or 50 12FK6 tubes here from Radio Electric Supply and I see that amongst the different brands, those of the same brand are extremely close to each other in performance. They were nice enough to write the results of the tester on the ends of the boxes.

 Mixing and matching brands is probably not a good idea, from a sonic point of view.

 -Drew


----------



## Buzzerbro

Here is my hybrid amp. It has Nichicon Muse 470uF caps on the outputs and the rest are Elna. The tubes are 12FM6. The pot is an Alps 50K. This is my maxed out version. 

 Bias is set to 14V. It sounds very good and the bass is nice with my AKG K240S headphones.  

 [size=xx-small]If the photo is not visible, its because I have exceeded GeoCities allocated Data Transfer. Sorry[/size]


----------



## MASantos

Quote:


  Originally Posted by *USER NAME:* 
_I'm not sure where we are supposed to post our pictures so I copied this from to construction thread.

 I was just fooling around in the shop trying to think of a good chassis solution for my Millet Hybrid. It's not done yet. It's just a fully dressed chassis with no board inside. I tried to add some carbon fiber to the mix, but it just looked awkward. I'm never satisfied. Maybe I should start looking in to aluminum? Anybody have any constructive criticism?




_

 

Hello,

 I would replace those arched metal things( are those kitchen door knobs?) on the sides of the tubes with wooden ones. 

 otherwise the amp looks amazing. I will also build mine in a wood enclosure, bot only in september.... 
	

	
	
		
		

		
		
	


	




 Manuel


----------



## mrdon

Still have no music coming from right channel in headphones. Tried to bias via DREWD's advice but I realized I've never biased an amp before! 
	

	
	
		
		

		
		
	


	




 Anyway, how do we noobies perform this task? Do we need voltmeter or will a multimeter do the job? Step by step instructions with pics would be very helpful! 
	

	
	
		
		

		
		
	


	



  Quote:


  Originally Posted by *rreynol* 
_Multimeter should be on DC volts and I'd imagine that the amp should be on (why would there be current flowing with it off? if it is, you may have another problem). Do you have the tubes plugged in? When I first put mine together, I had a 'duh' moment and couldnt figure out why the trimpots had no effect on the tp voltages. Then I realized that I was dumb and plugged the tubes in. Also, I noticed that you really don't see the voltage changing much until the trim pot gets to a lower half the of the range. Hope that helps. If not, someone else will probably have some suggestions. I, too, am a tube noob._


----------



## rreynol

Quote:


  Originally Posted by *mrdon* 
_Still have no music coming from right channel in headphones. Tried to bias via DREWD's advice but I realized I've never biased an amp before! 
	

	
	
		
		

		
		
	


	




 Anyway, how do we noobies perform this task? Do we need voltmeter or will a multimeter do the job? Step by step instructions with pics would be very helpful! 
	

	
	
		
		

		
		
	


	


_

 

You will need to measure dc volts across the left and right bias test points. Both a multimeter and a plain old voltmeter will work.


----------



## mrdon

Quote:


  Originally Posted by *rreynol* 
_You will need to measure dc volts across the left and right bias test points. Both a multimeter and a plain old voltmeter will work._

 

What setting do I set my multimeter on? Could you walk us through the process RREYNOL?


----------



## BlazerFRS

You'll need to set it to DC volts.


----------



## drewd

Quote:


  Originally Posted by *mrdon* 
_Anyway, how do we noobies perform this task? Do we need voltmeter or will a multimeter do the job? Step by step instructions with pics would be very helpful! 
	

	
	
		
		

		
		
	


	


_

 

I don't have my camera handy, but here is a description on what to do:

 To set the bias voltage, pick the channel that you want to adjust. Locate the two test points on the PCB. Set your voltmeter to DC volts and the scale to something over 30V. Turn the amplifier on and put one probe on each test point. If you have not adjusted the voltage yet, you'll probably find that it reads quite high. Using a flat bladed screwdriver, start turning the screw on the pot that is associated with the test points you are measuring. If I recall correctly, you'll want to turn clockwise to lower the voltage. It should take between four and six turns before the voltage starts dropping, then it will drop fairly quickly. If the voltage does not drop, turn the other direction.

 With a 24V power supply, the initial bias setting should be 12V. Match the two channels to within 0.1V and then listen!

 -Drew


----------



## shut85

i've gotten all the parts on the board except for the components like the power and inputs and outputs, i assume that s1 and s2 are for the switch but i only see a v_in pad and was wasnt sure how to connect the power exactly. wouldnt there be a v+ and a v- from the power to connect to the board, so where would the two go? also is there a certain way i have to orient the led on the pads next to d2la, like is there a + side and a - side?


----------



## drewd

Quote:


  Originally Posted by *shut85* 
_i've gotten all the parts on the board except for the components like the power and inputs and outputs, i assume that s1 and s2 are for the switch but i only see a v_in pad and was wasnt sure how to connect the power exactly. wouldnt there be a v+ and a v- from the power to connect to the board, so where would the two go? also is there a certain way i have to orient the led on the pads next to d2la, like is there a + side and a - side?_

 

S1 and S2 are for the switch.

 V+ and GND are the inputs. The amplifier runs on a single voltage, so there is no V+ and V-, only V+ and ground. You do need to orient the LED correctly - there is a flat spot on the silk screen symbol. That marks the cathode, or the "negative" side of the LED. That would correspond to the flat side of the LED and also to the short leg.

 -Drew


----------



## JWFokker

I may be the only one to forget this step, but if you're going to test the bias voltage, disconnect your headphones, because they make a loud screeching noise when testing the bias that may or may not be potentially damaging to them. At the very least, take them off your head, as it's quite loud.


----------



## n_maher

For the record, you should perform the bias adjustment before even plugging in your headphones, even worthless test phones.


----------



## pabbi1

And further for the record, 'bias' should be checked / adjusted with every tube change?


----------



## mrdon

Thanks to everyone for the instructions!

 Well, I easily adjusted the bias to 12V on the Left Channel old school analog style. 
	

	
	
		
		

		
			





 However, the right Channel is still giving me problems. 
	

	
	
		
		

		
		
	


	




 After turning the screw clockwise and couterclockwise to the "click," the bias is stuck at 24V. Could it be a
 1. Bad pot?
 2. Bad soldering point?
 3. Bad other?


----------



## n_maher

I wouln't say it's 100% necessary but if it were me I'd check it. It takes 2 seconds and could save future trouble. I've periodically checked my prototypes and the bias seems to stay pretty constant.

 Also, just one thing of note, there are still a few folks that haven't paid me for the round two shipping bills 
	

	
	
		
		

		
		
	


	




 . At least one contact me to let me know that they'd be on vacation so that's fine, the others, *don't make me come find you...*





 Nate


----------



## pabbi1

Does the bias change between tube types, say 12ae6a to 12fk6, or are all the most likely tubes fairly similarly spec'd regarding voltage / output?

 I'm setting up with the former, but will definitely also check the latter...

 And, what are the noticeable burn in breaks? 100 - 200 hours? Anyone guess what the prime useable life of these tubes?

 Last, I am using some BG on C7 (if ya got 'em, smoke 'em), so I know I have some extra burn time...


----------



## drewd

Quote:


  Originally Posted by *pabbi1* 
_Does the bias change between tube types, say 12ae6a to 12fk6, or are all the most likely tubes fairly similarly spec'd regarding voltage / output?

 I'm setting up with the former, but will definitely also check the latter...

 And, what are the noticeable burn in breaks? 100 - 200 hours? Anyone guess what the prime useable life of these tubes?

 Last, I am using some BG on C7 (if ya got 'em, smoke 'em), so I know I have some extra burn time..._

 

I didn't adjust the bias between the 12AE6As or the 12FK6s. The 12FK6s will tolerate higher bias than the 12AE6As. I don't recall off the top of my head at which point the 12AE6As start getting nasty, but it's fairly high. The 12FK6's will go up to something like 22 volts, although there's really no reason to do that.

 The tubes are rated at 10,000 hours in the data sheet. They're all NOS, of course, so it probably wouldn't be appropriate to expect that kind of life from them, but I'll bet that they'll last somewhere just short of forever.

 Break in? What I've noticed with mine (sans Black Gates, of course 
	

	
	
		
		

		
		
	


	




 ) is that after about 50 hours, the highs started to get a little recessed, just slightly attenuated. At maybe 120 hours, they came back and what I thought was a pretty bloomy midrange eased back a little - from a somewhat overenhanced presence to something still very much there, but in a much more pleasant way - just what I would expect to hear from a tube amp. The bass never changed. It's always been extremely well defined and accurate.

 Virtually all of my listening has been with 12FK6s and Beyer DT880s. I've done a tiny bit with Grado SR225s (which match up to this amp extremely well) and none with my HD580s. Well, not none - about two minutes. It just wasn't a good fit with this amplifier at all. I didn't care for the sound of the 12AE6As. I'm not sure if that says anything about my listening taste or hearing... 
	

	
	
		
		

		
		
	


	




 I suspect that your experience is going to be different - pesky BG burn in (and re-burn in). By the way, I leave my amp on 24/7. Dunno how much of a difference that makes. It's at work, so I figure if my computer and workstation can run 24 hours a day, one l'il ol' headphone amp won't make much of a difference.

 Also, you can read Erikzen's post in the Amps forum about the amp that he had for the NYC show. It's got hundreds of hours on it, so what he hears is what there is - it's definitely broken in. It's a prototype board, but all the same parts as the group buy boards.

 -Drew


----------



## pabbi1

Yeah, I plan to burn for at least a week before bothering to get too concerned with any impressions - starting tonight.

 I'll post some pics as well... and wish you hadn't said that about the 580s, though I'm sure my 600s and the soon to be acquired 650s will sound much better, even before I start the woodie experiments..


----------



## drewd

Quote:


  Originally Posted by *pabbi1* 
_I'll post some pics as well... and wish you hadn't said that about the 580s, though I'm sure my 600s and the soon to be acquired 650s will sound much better, even before I start the woodie experiments.._

 

Count on it - there's no comparison!

 -Drew


----------



## dviswa

Quote:


  Originally Posted by *n_maher* 
_I wouln't say it's 100% necessary but if it were me I'd check it. It takes 2 seconds and could save future trouble. I've periodically checked my prototypes and the bias seems to stay pretty constant._

 

Unlike your experience, I seem to have a good bit of movement in the bias levels in my amp. When I first powered it up, I had adjusted it to around 12, a day later it had drifted to 19. Even if you discount that first drift to bad initial adjustment, I found that on day 3 it had moved about 0.5 v. All this time the power supply (STEPS) has been pretty steady around 24.5V


----------



## rreynol

Quote:


  Originally Posted by *dviswa* 
_Unlike your experience, I seem to have a good bit of movement in the bias levels in my amp. When I first powered it up, I had adjusted it to around 12, a day later it had drifted to 19. Even if you discount that first drift to bad initial adjustment, I found that on day 3 it had moved about 0.5 v. All this time the power supply (STEPS) has been pretty steady around 24.5V_

 

Based on this post, I went and checked the bias on mine. It was set up at 13.5V bias last Friday. Tonight, 22V on one channel and 17 on another. bleh.


----------



## pabbi1

Ok, I've got a couple of 'Money Shots"...

Amp case 
Amp open case 
Amp board 1 
Amp board 2 


 Unfortunately, I'm getting 0 bias... on either channel. The LED doesn't power up. I have 27.5v coming out of the STEPS, and have 27.5v coming in (properly) - any ideas? What additional test point(s) can I check to narrow this down?

 Of all the things I never expected... I guess this is one way to make sure no caps melt down.


----------



## drewd

Quote:


  Originally Posted by *pabbi1* 
_Unfortunately, I'm getting 0 bias... on either channel. The LED doesn't power up. I have 27.5v coming out of the STEPS, and have 27.5v coming in (properly) - any ideas? What additional test point(s) can I check to narrow this down?

 Of all the things I never expected... I guess this is one way to make sure no caps melt down. 
	

	
	
		
		

		
		
	


	


_

 

You'll want to hook a switch up to S1 and S2 or else jumper across the two pads.

 -Drew


----------



## pabbi1

DOH! Yep, makes sense... and I thought using a switched IEC got me away from all that.

 Always the simple things...


----------



## n_maher

You should thank the amp gods when it's one of the simple things. It's the hard ones that hurt the most.


----------



## skyskraper

aussie guys, got your boards today. packed them up. will have them in the post tomorrow.


----------



## pho_boi

Quote:


  Originally Posted by *skyskraper* 
_aussie guys, got your boards today. packed them up. will have them in the post tomorrow._

 

there wouldn't be any left for me would there 
	

	
	
		
		

		
		
	


	




 ?


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## skyskraper

i dont have any spares, ive just been sent whats been paid for by others.

www.diyforums.org sells them now, but not at anywhere near the same price


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## diskostu

Some questions for nate and/or drewd regarding the parts and the associated part numbers (mouser part numbers if possible) for the amps you guys built on http://www.diyforums.org/millett.html :

 1) What RCA jacks did you use?

 2) What switch did you use on the amp that's in the Hammond 1455R2201 case?

 3) Where did you get the knob that's on the amp with the wood panels?

 Lastly, could someone post a picture of the bottom of the board showing how he/she wired and mounted the LED's.

 I've look through Mouser's website. I think I know which parts you guys used but to be safe I'm asking. I'm almost done finding all the parts. Hopefully I'll have this amp built in a few weeks.

 Thank you


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## n_maher

Quote:


  Originally Posted by *diskostu* 
_1) What RCA jacks did you use?_

 

 I personally use Cardas RCA jacks from either Moon Audio, Welbourne Labs or Handmade Audio. A quick google will find them for you. Mouser may carry RCAs but I haven't used them.
  Quote:


  Originally Posted by *diskostu* 
_2) What switch did you use on the amp that's in the Hammond 1455R2201 case?
 3) Where did you get the knob that's on the amp with the wood panels?_

 

Drew's amp, couldn't tell you. But check out the DIY "big list" on this forum. That's where I've found most of my sources for parts.

 Not every part that Drew and I (and others for that matter) used on the prototypes comes from Mouser. The idea of the Mouser BOM was to give someone an idea of what parts it would take to populate the board. If we were to try and list all the options that one would have for RCAs, jacks, knobs, etc. I'd have to quit my job. There are literally hundreds of places that you could use. I find that by using online catalogs (like Mouser and DigiKey have) I can generally get what I'm looking for.

 HTH,

 Nate


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## n_maher

Quote:


  Originally Posted by *skyskraper* 
_www.diyforums.org sells them now, but not at anywhere near the same price_

 

Just for information purposes, since that link has now been posted, those boards are sold at cost, by Drew. He orders them in batches of 10. It is just so those who'd missed the group buy would have an opportunity to still get a board for as cheap as Drew could afford to offer them. I'm not sure how long they'll be around.


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## rreynol

Quote:


  Originally Posted by *diskostu* 
_Some questions for nate and/or drewd regarding the parts and the associated part numbers (mouser part numbers if possible) for the amps you guys built on http://www.diyforums.org/millett.html :

 1) What RCA jacks did you use?

 2) What switch did you use on the amp that's in the Hammond 1455R2201 case?

 3) Where did you get the knob that's on the amp with the wood panels?

 Lastly, could someone post a picture of the bottom of the board showing how he/she wired and mounted the LED's.

 I've look through Mouser's website. I think I know which parts you guys used but to be safe I'm asking. I'm almost done finding all the parts. Hopefully I'll have this amp built in a few weeks.

 Thank you_

 

1) Mouser carrys basic RCA's. Black (161-2002), White (161-1004), and Red (161-2003). They aren't _triple iridium plated and hand assembled by the impoverished people of some south american tribe_ but they work and they don't look crappy.


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## Jaypetermen

Will the 470uf/63V, 0.7”x 1.4” ELNA Cerafine capacitor fit at C7 ? Is this the preferred value for the HD-650s? 

 What is a good boutique caps for C7 with a low profile?


  Quote:


  Originally Posted by *rreynol* 
_1) Mouser carrys basic RCA's. Black (161-2002), White (161-1004), and Red (161-2003). They aren't triple iridium plated and hand assembled by the impoverished people of some south american tribe but they work and they don't look crappy. 
	

	
	
		
		

		
		
	


	


_

 

Do you have a picture of the Mouser basic RCAs?


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## Secret Squirrel

I used 470uf/63V, 0.7”x 1.4” ELNA Cerafine capacitors for every electrolytic capacitor except C2. The fit was very tight against their neighbors, but they sat flush against the PCB.


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## Jaypetermen

Quote:


  Originally Posted by *Secret Squirrel* 
_I used 470uf/63V, 0.7”x 1.4” ELNA Cerafine capacitors for every electrolytic capacitor except C2. The fit was very tight against their neighbors, but they sat flush against the PCB._

 

I am more concerned with the 1.4" height. I am trying to put this board into a shallow 1.35" enclosure. 

 I figure with .25 standoffs, the board and some clearance I would be through the top.


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## rreynol

Quote:


  Originally Posted by *Jaypetermen* 
_Will the 470uf/63V, 0.7”x 1.4” ELNA Cerafine capacitor fit at C7 ? Is this the preferred value for the HD-650s? 

 What is a good boutique caps for C7 with a low profile?




 Do you have a picture of the Mouser basic RCAs?_

 

Here's a pic of them on a PIMETA I put together a while ago.






 I'm not a fan of gold so the nickel plating on these was right up my alley.


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## dviswa

Quote:


  Originally Posted by *Jaypetermen* 
_Will the 470uf/63V, 0.7”x 1.4” ELNA Cerafine capacitor fit at C7 ? Is this the preferred value for the HD-650s? _

 

For a 300 ohm impedance phone like 650, you can go as low as 100. I am using a 220 mfd Elna Silmic cap and am quite happy.


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## dviswa

oops, double post


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## shut85

what does it mean when my pf1 is extremely hot when i turn on the amp....also, the led doesnt turn on....is it simply i have some cold welds somewhere or something else, like would that problem be able to tell me exactly what is going wrong with the amp


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## drewd

Quote:


  Originally Posted by *shut85* 
_what does it mean when my pf1 is extremely hot when i turn on the amp....also, the led doesnt turn on....is it simply i have some cold welds somewhere or something else, like would that problem be able to tell me exactly what is going wrong with the amp_

 

There is a short somewhere. Check to be sure that you do not have any solder bridges and that D1 is installed facing the right way.

 -Drew


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## Emon

Quote:


  Originally Posted by *Jaypeterman* 
_Do you have a picture of the Mouser basic RCAs?_

 

Do you mean the Kobiconn jacks often used in PIMETAs and PPAs? bg4533 made me an adapter box of 2 RCAs to 1/4" or stereo mini when he sold me my E-MU 1212m that used, I believe, all Kobiconn components (it was free too, nice guy!). I rather like the RCAs and the mini jacks because the screw bushing is on the inside. I find screw bushings on the outside to be...ugly. Unfortunately it seems no one has designed a 1/4" jack with this in mind. There's the locking Neutrik jack, which is much nicer, but not ideal for aesthetics, in my opinion. I was almost about to buy all PCB mount jacks for my Millet and mount them using perfboard and standoffs (seperated from the main PCB) so I could have all bushing and nut-free components on the ouside. Would end up looking more like a retail stereo component. But I said screw it and went with the Neutrik jack and a knob big enough to cover the pot bushing.


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## shut85

Ok so i went back to my amp and realized my d1 was put in the wrong way. I replaced d1 and pf1 and put in d1 the correct way, however i am still having the same problem as before (the pf1 gettin really hot and the led no coming on). What damage could have been done by mounting d1 the wrong way. I am 99% sure i do not have any solder bridges unless i really did miss something checking over the board 20 times over. If it can be no other reason than a solder bridge i will try to take some pictures and post them here.


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## Voodoochile

Well guys, the last few posts have been more about construction or parts sourcing, and would be better posted in the existing construction thread for this project. Since this thread was about sourcing boards that have since been shipped, I'm going to close it.

 Please post any build or component questions in the proper thread.


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