# A Super-Simple 6DJ8 Headphone Amp



## Nemo de Monet

Late last year, a Head-Fi user posted about a $95 tube amp available on eBay. This is pretty much _the_ only reference anywhere on the web to this amp, the "Xiang Rong Audio" XR01 (or XR010, take your pick). As you can see from reading that thread, the amp - as designed - needed some work to be useful.

 The folks selling that amp are _also_ selling bare PCBs on eBay (for 7 USD plus 7 USD shipping, at least at the moment); search for "6DJ8 PCB" and you should find it.

 I picked one up last year, and received it a while ago. On paper, the amp looks reasonably attractive as a _very_ entry-level design: uses 6DJ8 and similar tubes (including the Russian/Soviet varieties), runs off a single, 24VDC, 1A power supply, includes no high voltages, has a minimal parts count, and has a discrete transistor output stage - no opamps! The board is well-made, compact (the same width as Digi's old "SOHA I" board, only 2cm longer), and affordable.

 The catch, of course, is that the design itself may leave something to be desired. Still... since the PCB comes with the schematic, I'm curious what changes folks here can come up with that would make this headphone amp more usable, while still being able to use the original PCB. (There's a goodly amount of unused space on the board, and quite a few extra holes - test points, presumably - so adding a few obvious things like film bypass caps, et cetera isn't automatically out of the question.)





_(You can click on the schematic to see a larger size, FYI; I didn't want to make this page a gajillion pixels wide.)_

 FWIW, that's all the "instructions" that came with the PCB. There's room for a pair of trimpots, which I _assume_ are meant to adjust the bias... but no instructions as to what measurements to aim for. Yay, curiosity...


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## DKJones96

Well that sucks, I picked up the bare PCB from their store and apparently it was the last one. I've emailed them asking them if more will be available...

 This should make for an interesting first tube amp for me.

 Am I just going crazy here or is that schematic only for a single channel?


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## digger945

Use some kinda socket or wire "stubs" for C102 so you can experiment and try different output coupling caps, or combinations.


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## Nemo de Monet

No, you're not crazy - the schematic is just for one channel, plus the power supply bits. The other channel is identical, naturally. 
	

	
	
		
		

		
			





 I think they only list one or two boards at a time, for some reason; when I got mine last year, it was the only one listed, at the time. They have a website, and while the _finished_ headphone amp is listed for sale there, the bare PCB isn't. Maybe if we pester them nicely... 
	

	
	
		
		

		
		
	


	




 I should point out that there's ample space on the PCB for people to go nuts with all kinds of crazy, boutique components, if that floats their boat: all the resistors have 10mm lead spacing, the input (film) caps have 25mm(!) lead spacing (and enough room in general for Vitamin Q or similar PIO caps), the output (nominally electrolytic; does one _really_ need 1000uf here?) caps are 7.5mm lead spacing and will take up to 20mm diameter devices; c104/c105 are 5mm leads/up to 12mm diameter, and C103 has 10mm lead spacing and room for a 20mm diameter cap. So it's not like there are too many restraints on parts selection, with regard to size, anyway.


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## digger945

Yea it would appear that each channel uses just one of the two triodes, so just one tube is all you need.


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## holland

looks similar to the MHHA by Sijosae.


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## Nemo de Monet

Quote:


  Originally Posted by *holland* /img/forum/go_quote.gif 
_looks similar to the MHHA by Sijosae._

 

There are many similarities in the design - which, let's face it, is pretty straightforward - but I noticed a lot of the component values are different, which is one of the things I'm hoping people smarter than I will comment on. Then again, there were so many different versions and revisions of the MHHA, it's hard figuring out what was what...

 I've noticed that a lot of Sijosae's designs never seemed to garner all that much attention, here on Head-Fi or elsewhere on the English-speaking web. I suspect lack of PCB availability - and lack of promotion - accounts for it. Ah, well.


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## ludoo

Funny, I just asked DOnald (dBel) a couple of days ago if he knew about something simple using these tubes, and now this pops up. 
	

	
	
		
		

		
		
	


	




 I picked up 20 NOS 7DJ8 (half of them Philips with the A-frame getter, half of them Russian tubes probably from the Reflektor factory) and had been looking for a simple -- as I'm still a noob -- project.

 Let's hope they still have a PCB, I would not mind building one. Edit: bought a PCB. Will keep you posted once it gets here.


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## Nemo de Monet

For those in the U.S. looking at building this amp, the best source of the transistors - 2SK117 and 2SK310 - appears to be B & D. They have both parts in stock, at not terribly unreasonable prices. The downside is, they have a $15 USD minimum order, and what is basically a minimum $10 shipping fee. You'll need to order three of each device to hit the minimum order.

 There _are_ some 2SK117 available on eBay at the moment, and at good prices, but it doesn't really help much, since B & D seem to be the only decent place to get the 2SK310s. There _are_ also some 2SK310 on eBay, but they're listed by the most useless electronic vendor _ever_, at a ridiculous price. MCM have 2SK310s - at, again, a ridiculous price - and apparently stock 2SK117s, though they're on backorder at the moment. Nobody else that I've checked seems to have the 2SK310s, or the 2SK311, its higher-powered sibling.

 There _are_ *electrical* substitutes for the 2SK310, but I have no idea how they *sound*, and none of them seem to be used much (at all?) in audio designs, or are themselves obsolete or unobtanium. I suspect that there are a number of other FETs that can be substituted in this position, but have no idea what they are. Anyone?


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## ludoo

I bought the PCB from ebay and asked the seller if it was possible to buy more than one, since they have a "Pay it now" option set on the auction with a fixed quantity of 1. They replied by email, so I asked them if they can supply the transistors together with the PCB. I will let you know once they reply.


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## ludoo

The PCB seller replied they only have 2sk117, and only 5 of them. I found both at Cicon Electronics for 10$ total, plus shipping.

 Edit: do not try to get them from Cicon as they do not reply to emails and apparently don't ship either. I filed a PayPal claim and got reimbursed overnight.


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## DKJones96

I was looking at pictures of this thing and I was wondering where I should go to get the in/out jacks for this thing? I've never seen jacks that solder like these.


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## Nemo de Monet

I'm not 100% sure, but I'm fairly confident these will work. (See the datasheet.)

 If you want to use 1/4" jacks, I'm almost certain you'll have to panel-mount them and run wires to the board.

This should work for a board-mounted power jack, if I'm not mistaken; I'm just going to use a panel-mount one, so that finding a case which perfectly fits the board isn't an issue.


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## DKJones96

I didn't even think about going panel mount. Since it's an all metal case I shouldn't have the noise problems my cMoy in a plastic case gets with panel mount connectors...


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## Nemo de Monet

Going with panel-mount connections for the headphone jacks might actually be a good idea. If it turns out there's no other way to make the amp sound good besides putting resistors across the input,as Roger S did with his last year (see link in the first post), it might be worthwhile to panel-mount the jacks, and put sockets on the input pads so one can easily experiment with different resistor values. (The ground connection is 5mm from the outer solder pads for both the L and R channel, so it shouldn't be too difficult.) I'm hoping that there's another, better option - changing the value of R101, for example - but it's good to have options.

 I note that there's a PCB available at the moment, for anyone who's wanting to get in on the fun, here. (If you miss that one, there will undoubtedly be more where that came from...)


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## ludoo

Nemo, could you post a pic (or two, top/bottom) of the board? The one on ebay is almost illegible and mine will take a few days to get here.


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## Nemo de Monet

Here you go:







 I hadn't noticed before, but the top and bottom copper traces are perfectly symmetrical! How bizarre...


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## ludoo

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_Here you go_

 

Thanks!


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## ludoo

One quick question: did you find suitable heatsinks? I could not find any of sufficient dimensions with a single center pin.

 Another question: the resistors in front of the LM317 (R104/R105) don't look like 1/4W ones in the pics of the built amplifier






 but look more like 2W resistors. On the schematics, though, the only resistor with a power spec is R101, rated at 1W. 2W for R104/R105 makes sense (well maybe half of that as they are in parallel), or not? I am just a noob full of questions...


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## DKJones96

I found these, 4 pcs and they look almost exactly like what comes on the board. They have taller versions of the same thing but the enclosure I'm going to use would need holes cut in it to clear them and I'd prefer to not do that for anything but the tube itself.
4 pcs HEATSINK SILVER HS-3523 TO-220 WONDERCO TAIWAN - eBay (item 140288394246 end time Feb-08-09 22:31:04 PST)

 My questions is where do you get 2w resistors? I've got thousands of 1/2w and 1/4w resistors which I guess I could run in parallel but the lower values that this board takes I don't have.


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## Nemo de Monet

The Wonderco heatsinks are the only ones I can recall seeing with a centre pin like that, but IMO you can use anything that'll physically fit on the board - there are a number of Aavid heatsinks that should work, for example. I don't really think mechanical rigidity is a major issue for this amp... and I'm trying to keep the DIY version as Australia-proof as possible, so I don't want to just come out and say, you know, "this is the _only_ part that will work here". 
	

	
	
		
		

		
		
	


	




 The resistors in the completed amp do look pretty high-power (I think they're probably 1W, not 2W - just a different manufacturer, hence different size from the 1W, R101), but I don't know if that's really necessary; old builds of Sijosae's MHHA used, I think, 1/4W resistors in most of the positions, which is what I plan to do. If you want to play it safe, Mouser carries audiophile-approved 2W resistors from Koa that are widely agreed to be identical to Kiwame, and they're not _obscenely_ expensive. There are other 1W and 2W film resistors (carbon or metal film; you almost certainly want to avoid wirewound ones) that will work just as well.

 I for one don't see why R101 _is_ 1W, anyway. Isn't it just an attenuator, between the signal in and ground? It's basically parallel to the volume pot, which is, what, 1/4W? Am I misinterpreting that?


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## DKJones96

What's the worst that could happen? If you burn up a resistor replace that one with a higher wattage one.

 What is the tube pinout? I can't seem to find anything that's useful in my quest to determine what pins the heater runs on. I could see a power resistor if it's in series with the heater but not at the 101/201 position.


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## luvdunhill

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_One quick question: did you find suitable heatsinks? I could not find any of sufficient dimensions with a single center pin._

 

I'd check the Fischer catalog, I seem to remember heat sinks with that center pin .. of course, we cannot get those here in North America, so I've only user a few Fischer parts and usually try and find substitutes.


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## Nemo de Monet

Pins 4 and 5 are the heater per here. It's confusing, because that's apparently from the bottom. (The shield, pin 9, is the one next to R202 that isn't connected to anything.) So, the heater are the one that connects to ground, on the right side of the socket, and the pin right next to it whose trace passes under R102. R104/R105 would seem to be the ones that are on the heater circuit.

 R101/R201 (1MOhm) are between ground and the grid; R102/R202 (100 Ohm) are between ground and the cathode. What they actually _do_, I can't really say - toob theory is weak in this one. (As Donald Sutherland said in Kelly's Heroes - "I only ride 'em, I dunno what makes 'em work".)


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## ludoo

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_I found these, 4 pcs and they look almost exactly like what comes on the board._

 

Thanks, I got those too as they're cheaper for me than getting some from the US. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_My questions is where do you get 2w resistors?_

 

I get them from a local store, but they only carry a few values. The 2W I got once look exactly like those on the board used for the LM317.

  Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_The resistors in the completed amp do look pretty high-power (I think they're probably 1W, not 2W - just a different manufacturer, hence different size from the 1W, R101), but I don't know if that's really necessary; old builds of Sijosae's MHHA used, I think, 1/4W resistors in most of the positions, which is what I plan to do._

 

I will probably do the same, except for those that set the LM317 voltage.

  Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_What is the tube pinout? I can't seem to find anything that's useful in my quest to determine what pins the heater runs on. I could see a power resistor if it's in series with the heater but not at the 101/201 position._

 

ECC88 @ The National Valve Museum Edit: Nemo beat me to it. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I'd check the Fischer catalog, I seem to remember heat sinks with that center pin .. of course, we cannot get those here in North America, so I've only user a few Fischer parts and usually try and find substitutes._

 

Interesting, I will have a look as buying things from Germany is definitely cheaper for me than from the US.


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## ludoo

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_R101/R201 (1MOhm) are between ground and the grid; R102/R202 (100 Ohm) are between ground and the cathode. What they actually do, I can't really say - toob theory is weak in this one. (As Donald Sutherland said in Kelly's Heroes - "I only ride 'em, I dunno what makes 'em work".)_

 

A noob guess is the 1mohm is for the grid leak, the 100ohm biases the cathode. Been reading quite a bit lately, but digesting and understanding knowledge takes much longer.


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## DKJones96

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_Thanks, I got those too as they're cheaper for me than getting some from the US. 
	

	
	
		
		

		
		
	


	


_

 

I'm in the US and it was still cheaper than buying in the US!


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## dBel84

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_There are some 2SK117 available on eBay at the moment, and at good prices, but it doesn't really help much, since B & D seem to be the only decent place to get the 2SK310s. There are also some 2SK310 on eBay, but they're listed by the most useless electronic vendor ever, at a ridiculous price. MCM have 2SK310s - at, again, a ridiculous price - and apparently stock 2SK117s, though they're on backorder at the moment. Nobody else that I've checked seems to have the 2SK310s, or the 2SK311, its higher-powered sibling.

 There are *electrical* substitutes for the 2SK310, but I have no idea how they *sound*, and none of them seem to be used much (at all?) in audio designs, or are themselves obsolete or unobtanium. I suspect that there are a number of other FETs that can be substituted in this position, but have no idea what they are. Anyone?_

 

The input jfets I would stick to. The mosfet can be substituted for something like the IRF510. People will argue that the sound will be very different but you are running the mosfet SE either way and you are going to get that grungy mosfet sound that is ever so sweet , don't build this amp if you are looking for the lowest THD ratings. 

 ludoo has convinced me to build one with his enthusiasm 
	

	
	
		
		

		
		
	


	




 I am guessing it will perform well and it is a simple amp to build P2P. 

 ..dB


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## ludoo

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_ludoo has convinced me to build one with his enthusiasm 
	

	
	
		
		

		
		
	


	




 I am guessing it will perform well and it is a simple amp to build P2P._


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## Nemo de Monet

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_The input jfets I would stick to. The mosfet can be substituted for something like the IRF510. People will argue that the sound will be very different but you are running the mosfet SE either way and you are going to get that grungy mosfet sound that is ever so sweet , don't build this amp if you are looking for the lowest THD ratings. _

 

The IRF510 was one of the devices I was looking at as a substitute; it's cheap and available pretty much everywhere.

 I'm not looking for the lowest possible THD ratings. 
	

	
	
		
		

		
		
	


	




 I fully expect this amp to have a bit (more than a bit?) of "character", owing to its design and components. Besides, it's cheap, it's easy, and I've got most of the parts laying around, including a bunch of Russian Mystery Tubes that I think will work in this amp...


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## ludoo

Ok, since Donald is on board I'll shoot a technical question: I plan on using one of the lot of PCC88/7DJ8 NOS tubes I got. Reading the specs, I noticed that the heater works at 7V instead of 6.3V (not much of a difference according to many), but more importantly that it's designed to be connected in series instead of in parallel like the ECC88/6DJ8.

 From what I remember from the YAHA thread I read when I built mine, this should mean that the LM317 should be configured for fixed current instead of fixed voltage. Am I right?


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## dBel84

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_I plan on using one of the lot of PCC88/7DJ8 NOS tubes I got. Reading the specs, I noticed that the heater works at 7V instead of 6.3V (not much of a difference according to many), but more importantly that it's designed to be connected in series instead of in parallel like the ECC88/6DJ8.

 From what I remember from the YAHA thread I read when I built mine, this should mean that the LM317 should be configured for fixed current instead of fixed voltage. Am I right?_

 

they should work the same ECC88 PCC88 are both connected to pins 4/5 with pin 9 connected to a screen. You may be thinking of some of the 12V tubes where the heater supply can be connected between 4/5 and 9 to run the filaments in parallel and allow 6.3V operation. 

 If you wanted to adjust the voltage to 7V then exchange one of the resistors for a trimmer or use sockets to tweak the heater voltage. ( the trimmer will probably not tolerate such high current ) 

 ..dB


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## ludoo

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_they should work the same ECC88 PCC88 are both connected to pins 4/5 with pin 9 connected to a screen. You may be thinking of some of the 12V tubes where the heater supply can be connected between 4/5 and 9 to run the filaments in parallel and allow 6.3V operation._

 

In the YAHA thread on headwize fa-smith made a point a few times of making sure to configure the LM317 for fixed current iwth series heated tubes, and fixed voltage for parallel heated ones. To my limited knowledge it makes sense, and the schematics for the PCC88 report that it's wired in series. Pins are the same, yes.

  Quote:


 If you wanted to adjust the voltage to 7V then exchange one of the resistors for a trimmer or use sockets to tweak the heater voltage. ( the trimmer will probably not tolerate such high current ) 
 

I will probably do that as I'd like to try both the PCC88 and the ECC86 which I used in the YAHA.


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## Nemo de Monet

I'm assuming that R110, a 1K trimpot, is for adjusting the bias on the output stage. Is this correct? And, if so, is there any reason it couldn't be replaced with a fixed, say, 330R resistor?

 I ask because I'm playing around with a PCB layout for this amp, in the hopes of producing a design that's a little more user- and noob-friendly than the existing one. (Not that the 8audio one is _bad_, but there are a few things I think could be done better.)

 (At the same time, I hit upon an interesting idea, but I'm not familiar enough with tubes to know if it's workable: This amp design uses a dual triode, yes? What would need to be changed to make the design a mono amp - both triodes in the tube amplifying a single signal? Is it just as simple as tying the output of one section to the input of the other? I'm thinking it could be amusing to have fully-independent channels, one tube per channel, while still keeping things simple and low-voltage. Tiny-monoblock-tube-headamp, anyone?)


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## ludoo

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_I'm assuming that R110, a 1K trimpot, is for adjusting the bias on the output stage. Is this correct? And, if so, is there any reason it couldn't be replaced with a fixed, say, 330R resistor?_

 

I asked a simliar question to Donald by email a couple of days ago, here is his quick reply.

  Quote:


  Originally Posted by *dBel84* 
_A quick version is that the JFET should be ample to load the plate, the trimmer is there to try and control the CCS current - it should be in the ball park of 1.5K for 1mA so the 1K trimmer in series with the 56R resistor allows you to set the current across the resistor and hence the idle current for the plate. You will not need to change this for the ECC86._

 

Interesting idea on the mini monoblocks.

 I am planning to use ECC86 for this amp once my PCB arrives, as they low voltage tubes and might work very well here. And I have a local source of Philips NOS ones, not super cheap but decent (10 euros), I already used one in my YAHA. The MEHA used an ECC86 with 24V too, and there's a detailed explanation on how to calculate the cathode resistor, if anyone is interested.

 Edit: I love mini hybrid amps like this one, the YAHA or the SS. They are an easy build and perfect to learn some tubes theory and experiment with it.


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## Nemo de Monet

For now, I'm just sticking with the regular, double-channel amp. While I've managed to get everything in a space around 2.5 by 3.5 inches - which is not a whole lot larger than a Pimeta - I'm ambivalent whether there's any real benefit to having a smaller, somewhat more flexible design (pot and jacks offboard, meant to be panel-mounted; some of the TO-220 devices on the board edge, to allow more, larger heatsink options, et cetera).

 In the meantime, I've now got _most_ of the parts to build the amp, so should be able to start playing around with this by next weekend.


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## kansei

Does anyone have a BOM for this amp? I'm still getting up to speed amp building and it's tough to figure out what the parts list is and where to get all of them. For example, the schematic calls for a diode and I have no idea what part # that would be. I would also like to get a Hammond case (or similar) to fit this PCB, but can't exactly figure out how to size these (1455N1602BK, perhaps?).


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## Nemo de Monet

I don't think there's a _real_ BOM, as such. Part of the fun is the flexibility.

 The diode is a LED, which lights when the amp is turned on. It's designed so that you can stick it under the tube, if you like. I don't like, so I'm just using a 5mm green LED, but if you want to go that route, you'll probably want to use a 3mm high-intensity LED.

 You'll need a 6DJ8 or equivalent tube, and a nine-pin (sometimes called "noval"), PCB-mount socket. I'm using something like this; you can also go for one of these.

 There were a number of links for the Japanese transistors earlier in this thread; BG101 is a TO-220 LM317, like this one.

 You can pick up the potentiometer, and a DC power jack that will work just fine, from Amb.

 For resistors, I'm using generic 1/4W 1% metal film ones, from a $12 assortment on eBay; it's unclear whether R101/R201 really _need_ to be 1W resistors, as specified in the schematic. If so, this should work quite well. R103/R203 and R107/R207 seem to be the only resistors "in the audio path", and you could use "boutique" resistors here if you really wanted, like Mouser 660-SPR2CT521R100J for R107/R207.

 The capacitor choices probably aren't too critical; use whatever decent caps you can find for most of the positions (Panasonic FM, or whatever); C101/C201 and C102/C202 are the input and output signal coupling caps, respectively. I'd suggest some kind of nicer axial-leaded cap for the '01 position; I'll probably use some Soviet PIO caps, or maybe some smallish ERO poly caps, here. I have my doubts about the '02 cap positions; I doubt 1000uf is _really_ necessary, and will be trying some 3.3uf Wima film caps instead.


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## kansei

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_I don't think there's a real BOM, as such. Part of the fun is the flexibility.

 The diode is a LED, which lights when the amp is turned on. It's designed so that you can stick it under the tube, if you like. I don't like, so I'm just using a 5mm green LED, but if you want to go that route, you'll probably want to use a 3mm high-intensity LED._

 

20 minutes after I posted my question it occurred to me that the diode is an LED. Duh.

 Thanks for the helpful parts links, I was having trouble finding a direction on the right parts, especially the tube sockets. I will probably build this after I'm done with my Millett SS.


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## ludoo

R104/R105 (and R204/R205 ofc) will dissipate quite a lot of power as there's the heater current going through them. I will use 1W resistors (uhm, maybe I got 2W can't remember right now).


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## nikongod

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_A noob guess is the 1mohm is for the grid leak, the 100ohm biases the cathode. Been reading quite a bit lately, but digesting and understanding knowledge takes much longer._

 

Yeppo, thats right.

 Depending on your mood, you can bypass the cathode resistor with a cap which may have put the original design beyond budget 
	

	
	
		
		

		
			





 Some would argue that the CCS on the plate of the tube minimizes the need for a cathode bypass cap, but its cheap to test.
  Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_I'm assuming that R110, a 1K trimpot, is for adjusting the bias on the output stage. Is this correct? And, if so, is there any reason it couldn't be replaced with a fixed, say, 330R resistor?_

 

It controls the operating point of the tube. adjusting it will give different sounds, and accommodate variances in different tubes.

 The use of a CC(sink) to set the idle current of the output mosfet AND run the heater is pretty cool. Davistik posted this up as an idea for a high voltage alternative to the starving student.


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## DKJones96

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_The diode is a LED, which lights when the amp is turned on. It's designed so that you can stick it under the tube, if you like. I don't like, so I'm just using a 5mm green LED, but if you want to go that route, you'll probably want to use a 3mm high-intensity LED._

 

So the heaters on these tubes don't make them glow very much huh... I'll have to stick an orange LED under mine i guess 
	

	
	
		
		

		
		
	


	




 lol


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## Nemo de Monet

Most miniature tubes don't really glow all that much, if operating correctly. (I had a leaky 50EH5 in a radio once which glowed a fairly bright blue, but it wasn't _supposed_ to!) Heck, most of the older octal tubes didn't glow all that much, either.

 So, yes, if you want your tube to really glow, you'll need to light it with an LED. (I've always thought that for added fun you could turn the LED(s) into a very crude VU-meter... maybe use an RGB LED? Hmmn...)


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## DKJones96

That could be cool but with a tube amp an analog vu meter would look more at home. In my opinion anyways.

 Right now I'm working on building the power supply for this thing. I have the transformer I just need to build the regulator circuit for it which I have mostly done in Eagle. This will just be a basic 2 amp 24v regulator to get used to the transformers. I'm really interested in breaking out the center tapped 36v transformers!


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## ludoo

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_I have my doubts about the '02 cap positions; I doubt 1000uf is really necessary, and will be trying some 3.3uf Wima film caps instead._

 

I don't think you want to put 3.3uF for C102 and C202. Read one of the replies to a similar question in the Starving Student thread. 470uF are probably fine, which is what most people use in the Starving Student. And maybe R107/R207 could be dropped.


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## DKJones96

For the phones I'll be using the 1000uF and 10ohms works out perfectly, but all of the phones I'll run on this thing are low-resistance(32 ohms at the most).

 I'd complain that I still haven't gotten my PCB but I haven't gotten anything else either. This project is REALLY testing my ability to hurry up and wait.


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## digger945

^That's why I suggested making C102 socketed or something to make it easy to experiment with different caps
	

	
	
		
		

		
			





, although it isn't very difficult just to desolder/solder them.
 Maybe one week you feel like a Blackgate, then next week you might want to try a Panasonic
	

	
	
		
		

		
		
	


	




, or whatever you may have in your parts box, and don't forget bypassing.


----------



## DKJones96

Can those be socketed away from the board without introducing too much noise?


----------



## Nemo de Monet

Ah. I did the math, but thought R108/R208 factored into the equation. Bother. I did say I was going to _try_ the Wimas, for what it's worth. 
	

	
	
		
		

		
		
	


	




 Now off to order some appropriately-sized Muse... or Cerafine... or other capacitors.


----------



## digger945

If your referring to a 3.3uF Wima, yes they will work, you'll hear music, it just won't have any bass at all. It may make a very good bypass cap for a larger cap.
 The output on this amp is very much similar to the one on mine(Aikido), and I would venture to say you will be pleasantly pleased with it's performance


----------



## applevalleyjoe

Does the original ebay seller also sell pre-cut/drilled cases for this kit? If not, what are you guys planning on using?


----------



## Nemo de Monet

They have one or two cases on their website, but they're not designed for this amp, and would have to be drilled, et cetera, to fit.

 There should be an aluminum Hammond case that fits; I'll be using a plastic PacTec case, probably with custom laser-cut end panels. 
	

	
	
		
		

		
		
	


	




 For what it's worth, the PCB should fit in one of these, sideways, with beaucoup room to spare. (Actually, you could just fit _two_ of these boards in there, sideways. And still have lots of room for things like a DAC, a power supply, a crossfeed circuit, a small speaker amp, an integrated iPod LOD, _and_ other stuff, as well.) Hmmn...

 It'll fit into one of these, without a lot of room to spare.

 I used one of the latter for my SOHA, and they're quite well-made cases; they're also quite thick (I believe the top and bottom are around 3mm), so anyone planning on putting _lots_ of holes in the case with hand tools might want to consider another option. They're not the prettiest things in the world, but they get the job done... only 1/2" or so of tube will stick out, however; the larger case up top mounts the PCB differently, so you'd get to see a lot more of the tube, if that's important to you...


----------



## kansei

Thanks for the enclosure suggestions. I ordered the PCB and the tube socket yesterday, now looking to get a tube or two from the "not-too-overpriced" category. I think I have at least a week or two until the PCB shows up.


----------



## ludoo

If any of you wants a NOS 7DJ8, I have quite a few of them. I sent one pair to Donald and one to Digger, and they both liked them. I will probably have to send some stuff to the US so shipping would be very cheap, and the tubes cost me about 10$ each. I have Philips with A-frame getters from the Amperex factory, and Russian tubes probably from the Reflektor factory. The offer is good only for those building this amp, other people (except Digger who wants an extra pair) will get them only if there's any left, and will have to pay more.


----------



## digger945

Is it possible those tubes were absolutely factory brand new Ludo?
 The longer I listen to them the better and better they sound. Perhaps they needed a little time to allow all the parts to settle in.


----------



## ludoo

Quote:


  Originally Posted by *digger945* /img/forum/go_quote.gif 
_Is it possible those tubes were absolutely factory brand new Ludo?
 The longer I listen to them the better and better they sound. Perhaps they needed a little time to allow all the parts to settle in._

 

They are factory brand new. They come from the stock of a place that used to build and repair radios in the '40s-60s, and now sells electronic components. It's what's left from their old stock used for spares or repairs, I discovered they have them by accident, as they don't advertise having them.


----------



## DKJones96

This is a little off-topic, but I didn't want to start a new thread. How do you determine compatible tube part numbers and/or how do you read them? I was at a surplus store around here and they have boxes upon boxes of new old stock tubes that I want to go through but don't know what to look for lol


----------



## ludoo

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_This is a little off-topic, but I didn't want to start a new thread. How do you determine compatible tube part numbers and/or how do you read them? I was at a surplus store around here and they have boxes upon boxes of new old stock tubes that I want to go through but don't know what to look for lol_

 

I'm not an expert, but 7DJ8 are often used in place of the 6DJ8 as their main difference is the heater, which requires 7V instead of 6.3 (and posibly slightly more current, can't remember now). The ECC86 is a low voltage double triode, so in theory it should be perfect for this kind of amp/voltage. But it needs some tweaks. A good explanation on how to chose values for the ECC86 is the MEHA page.

 Other than that, I don't know.


----------



## Nemo de Monet

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_This is a little off-topic, but I didn't want to start a new thread. How do you determine compatible tube part numbers and/or how do you read them? I was at a surplus store around here and they have boxes upon boxes of new old stock tubes that I want to go through but don't know what to look for lol_

 

To be cynical, you're unlikely to come across anything in too much demand; I'd guess that 95% of NOS tubes at surplus stores these days are television tubes with few other ready applications, and the remainder are - if you're extremely lucky - very common radio tubes like the 12BE6, 12BA6, 50EH5, and so on.

 It's usually easy enough to remember what tubes will work _in an amp you own_. If you want to discover new and obscure tubes that could perhaps be made to work _in amps yet unbuilt_, I suggest picking up a copy of the RCA tube handbook, and bringing it with you. Then you can least figure out what the tubes you're looking at were _meant_ for, which is of course not always a good indicator of what they'll _do_. 
	

	
	
		
		

		
		
	


	




 If nothing else, it'll prevent you buying a bunch of tubes just because they say "Amperex" on them, only to later discover they're rectifier tubes, or something similarly un-useful for amplifier use. 
	

	
	
		
		

		
		
	


	




 For example, someone gave me a NOS Westinghouse 76 tube a while ago. A type 76? Never heard of it. A quick check, though, shows that it's a 6.3v triode meant for use as an amplifier, albeit at plate voltages over 100v. Equally quickly, one will see that, though it has a fairly usable gain (for a headphone amp, anyway) of 13.8, as a triode, you'd need _two_ to build a stereo amp with 'em...


----------



## DKJones96

I pretty much expected to see what my grandfather has at his house. A bunch of old tubes from the 30s and 40s that don't do what i need them to and, if they do, probably have stupidly high plate voltages. But you never know til you look and even ones with high voltage requirements can always make for an interesting project later on.


----------



## ludoo

Well, the 6DJ8/7DJ8 too are tubes with a half-stupidly high voltage, as their data lists a plate voltage of 90V. And I think there are othes triodes that sound good at lower voltages than those they were built for.


----------



## digger945

I agree. I am running the 7DJ8(PCC88) with just 5.9V on the heater and only 11.9V on the plate. Sounds great.
 Of course the tubes are directly connected to a Solid State output, almost exactly the same as your schematic on the first post.


----------



## DKJones96

I got the PCB today! 

 I don't think the traces on the top are actual copper traces, I think they are just a colored line, I don't see a single via and the closer I look the more I'm convinced there is only copper on the bottom layer.

 I've still got a lot of parts waiting to be received but I can at least get a jump on a few things. I can't remember if I actually ordered the fets or not... lol


----------



## Nemo de Monet

I dunno; seems pointless to print an extra layer (of what, if not copper?) on the board, but I'm sure stranger things have happened.

 Here's one incarnation of the same design, only double-sided:







 It works out to be just under 2.75 x 3.75 inches; right about _half_ the size of the eBay original. The pot and input/output jacks are left off-board, to provide more flexibility ("Australia-proofing"); the TO-220 devices are along the edge of the board, so you're less restricted with regard to heatsink choices; most resistors spots are sized for Dale RN60s or similar, except a few larger ones where space was left for the big KOA/Kiwame parts; the input caps will more easily accommodate larger box caps (10mm lead spacing); I added a second LED so you can light the tube from below, _and_ have a more conventional power-indicator light, at the same time; otherwise, basically everything is as on the "Xiang Rong" board...


----------



## DKJones96

That's brilliant! With the TO-220 devices on the edge you can just sink them directly to the aluminum enclosure!

 That'd make an easy build... There isn't enough room on this board(XR01) for the input caps I wanted to use but I should be able to use my second best choice.


----------



## DKJones96

What kind of voltages are we to expect at C102/202? Do we really need a 35v cap there? I have caps on hand here that I want to use and one set is a 470uF 50v pair and the other is a 2200uF 16v pair.

 Here are a couple of variations I've installed so far:
 -R101 is a 1/2 watt resistor, not 1w(can't find one)
 -C105/104 are 470uF 25v instead of 220uF 16v

 I'm not sure if I can get the 13 ohm and 2k ohm resistors exactly that set the 317s adj pin. I'm hoping for some out of spec 15 and 2.2k ohm resistors to come through for me. I'm also having to sub high 33 ohm resistors for R109


----------



## digger945

According to the schematic on post 1, C102(the output coupling cap) has 15V on it. It really depends on the voltage of your power supply and what kinda mosfet you use, but I'm guessing that's pretty close for a B+ of 24V.
 I wouldn't be too fussy with the 317 bias resistors, I have used anything from 5 to 30ohms in a setup almost exactly like this one. These resistors will however set the current for the mosfet above them on the schematic.
 You could also use another 317 in place of the mosfet, provided you get the pins on the 317 crossed if need be, in the correct holes. For the 317 Adjust would be used for the Gate, Input would go to the positive side(Drain on the mosfet) and Output would be towards ground(Source on the mosfet).


----------



## digger945

I just wanted to note, when I said I have used 5 to 30 ohms to set the bias for the LM317(using it as a constant current source for a mosfet or another 317), that was from the Vout(on the 317) to ground, using one resistor(in this case, it looks like you use 2 resistors parallel, which may be to allow you to use smaller rated parts).


----------



## Nemo de Monet

In other words, something like this, right? Interesting... _very_ interesting.


----------



## digger945

Yes, exactly. And my now favorite amp is this...




 ...as you can see, they are somewhat similar.
 I think you guys are gonna like this amp your building.


----------



## DKJones96

I've got most of the parts I need to complete this thing. It should be done and running by Saturday night or Sunday. I'll get some pics posted of the finished product.

 Those heat sinks we linked to look like they will be perfect for even the smaller of the two cases that were linked to. They took a while to come in but it looks like they would even work without having to cut holes in the case.

 All I'm waiting for are the fets from Cicon and the time to get the case work done.


----------



## Nemo de Monet

Nice! I'm always relieved when these sorts of things actually turn out as planned.

 I have most of the parts, but I'm still waiting for the new capacitors to arrive. I'm sure there's something else I'm missing, as well... isn't there always?


----------



## ludoo

I only got the caps and resistors, and am still waiting for the PCB, heatsinks and fets. Well, I also got the tubes and sockets but I had those already.


----------



## DKJones96

I lack C103, the lead spacing is making finding a cap for that a bit difficult if I want it to sit flush and since it's actually coming together I don't want to order something else and have to wait for yet another part to come in and radioshack's supply of radial leaded electrolytics leaves a lot to be desired.

 Oh yeah! My regulated power supply also needs finished. I've got the line filtering, rectification, and DC smoothing taken care of I just need the 317(that came in yesterday) hooked up to turn my 35vdc to 24vdc.


----------



## Nemo de Monet

Stopped at the local surplus store this afternoon, and picked up some old Wima capacitors for $0.25 apiece, as well as some Switchcraft stereo sockets, also for a quarter.

 Made the mistake of glancing through the mountain of NOS tubes, and should have heeded my advice, earlier, about such things - I remembered something in this thread earlier about a 7V tube - the 7DJ8 - but for some reason thought it was the 7AU7 instead; the store had a bunch of the latter, and I picked up a pair for $2.50 each. Alas, they're seven-volt 12AU7 subs. Oh, well... I've got a spare SOHA I board, and dropping the heater voltage to 7V shouldn't be too hard.

 Moral of the story: do as I say, not as I do.


----------



## kansei

I got my PCB after a week and a half of winning the auction. It is beautiful, and nicely sealed in plastic. Already ordered the tube and the socket, now ordering the components and enclosure. I'm very excited, this is my second amp (the first was a Starving Student).


----------



## kansei

Since I'm still a newbie at this, I decided to put together a BOM so I can get all the parts straight in my head. I used suggestions from this thread and borrowed some part #s from other DIY projects. I've attached the Excel file to this post. 

 Any suggestions are welcome, especially since I'm not 100% sure whether everything will exactly work.


----------



## Nemo de Monet

C102/C202 need to be boutique-ish electrolytics; you can _bypass_ them with other caps - PIO might not fit very easily, but anyway... the parts in your list will work, but might not fit very well - the board has holes for 15mm caps with 7.5mm lead spacing, and I think yours are 12mm caps with 5mm lead spacing.

 C103 is the power reservoir - low ESR electrolytic, bigger is probably better, all other things being equal. The board will accept a 20mm part with 10mm lead spacing; the part in your BOM is a 16mm part with 7.5mm lead spacing.

 C101/C201 are a spot where it would/could make sense to use boutique film caps, like PIOs; I can confirm that K42Y-2s will fit, though it's tight.

 Everything else, at first glance, looks like it'll probably work just fine.

 $83 USD, huh? (Really more like $103 or so once you figure in shipping, alas.) Didn't realize this was such a pricey undertaking; I guess the fact that the parts come from a lot of places, and I had a lot of the bits laying around already, made it seem cheaper than it really is.


----------



## kansei

I never even considered spacing on the PCB, thanks for the pointer. Just like my Millett SS, this is just an experiment. I plan to get the parts and fiddle with it until it works right.

 If you consider the price of the populated board and power supply from 8audio is $95 shipped, $103 is not so bad for a complete product with an enclosure and a power supply (not to mention high quality parts of your choosing and the excitement of putting it together).


----------



## DKJones96

Didn't get it together this weekend. I got some 1watt resistors and was able to gt a couple of the values I wasn't able to before. I'm just waiting for the fets STILL. Total bummer. Maybe next weekend!


----------



## ludoo

I got the heatsinks today from HK, only problem is I remember buying 4, and got 16. Must have been 4 sets of 4 each. Guess I'll have to build some more. 
	

	
	
		
		

		
			





 Only things missing now are the PCB, FETs and case.


----------



## kansei

I found a place for to buy 2sk310, 2sk117 and lmt317t. They have a very high minimum order, I guess I'm buying 10 or 15 of each....


----------



## jcc147

Hi,
 I breadboard this circuit last night, but got couple questions.

 1. I used NOS 6DJ8 tube. The filament voltage measured was 5.5v, not 6.3v
 2. The current to 2sk117 was only 0.1mA, and won't change much if I trimmed the 1kohm pot.
 It looks to me the 6DJ8 didn't drain current from 2sk117.

 Is any idea what I'm missing?

 Thanks,


----------



## digger945

I don't think your gonna see an incredible amount of current going through a 6dj8 with less than 24v on the plate, and nothing on the grid.
 5.5V will work for the filament, but more voltage and heat will mean more electrons will be flowing.


----------



## jcc147

Does the 2sk117 act as a CCS? and bias current should be around 0.5 -1mA?
 I'm new to tube amp. My knowledge is more on transistors and may not apply to tube.
 Could some one explain how the 6DJ8 diased here?
 It looks to me this is more like a self biasing:
 the current on cathode creates a negative voltage on grid, how the CCS (2sk117) used here? limiting the plate current?
 The question confusing me is if we set trim pot(R110) to have 1mA current, 1mA x 100ohm(R102) = 0.1v = -Vg, but will 6DJ8 will give 1mA plate current when Vg=-0.1v?


----------



## ludoo

It turns out the place where I ordered the fets is out of business: I never received them, they did not reply to my emails, and paypal reimbursed me as soon as I filed a claim.

 So I now need to source them from somewhere else: any of you have a set to sell me, or trade for a NOS 7dj8 tube?


----------



## digger945

B&D Enterprises has both, the K310's are $3.59 ea. and the K117's are $1.59 ea.
 There is a $15 minimum order in the states and I think a friend recently told me that it's minimum $50 international. 
 Maybe you could figure out some suitable and easily obtainable replacements. I think an LM317 would work great in place of the K310.
 You might find these on ebay(the K117/310).


----------



## ludoo

Yes, and B&D has very expensive shipping. On ebay they are 10 euro each plus shipping. For that price I'd better sell the PCB and use the parts for a different project.


----------



## digger945

Here is a link for the K117 in ebay, 3 for $1 plus $2 shipping. That's $1 ea. shipped.

 LittleDiode shows the K310's for $16 ea. and $5.99 shipping. Highway robbery


----------



## digger945

I've had 2 different results on Google suggest that replacements for the 2SK310 would be:
 BUZ60
 BUZ76A
 IRF710/720/732
 MTP3N40
 The pages state clearly that these are just suggestions. They also have links for Drop IN Replacements.
link
link


----------



## Nemo de Monet

Someone said earlier in this thread that an IRF510 should work just fine in place of the 2SK310. That's what I'd use - cheap and commonly available. That said, I _do_ have a spare set of 2SK117/2SK310, so if you've really, really got your heart set on using them, PM me.


----------



## digger945

^A very kind offer.

 And I'll make the same offer to you, should there be anything else you need that I may have. Maybe some caps or something, PM me.


----------



## DKJones96

I'm STILL waiting for my fets to arrive 
	

	
	
		
		

		
			





 A domestic company taking more than two weeks after payment cleared to get my parts to me. They are quickly getting on my bad side.


----------



## Nemo de Monet

Care to 'name and shame'? I don't remember if you posted previously who you placed the order with, but it seems they're best avoided, whoever they are.


----------



## DKJones96

I orderd from Cicon. I call during business hours and the phone just rings. I've even e-mailed them and haven't gotten a reply.


----------



## Nemo de Monet

Cicon, as in "We Rip People Off Who Unsuspectingly Believe We Are A Respectable Company" Cicon? Methinks it'll be a cold day in hell before you see anything from them... Sorry.

 FWIW, they were expensive, but I got my parts from B&D in about three days.


----------



## ludoo

I ordered them from Chicon too, and after 3 1/2 weeks and no response to my emails, I filed a Paypal complaint. In less than 12 hours I had my money back, meaning that Paypal knows about them. The only question is why they still keep their account active.

 Edit: I might have found a set, thanks to a fellow hfier (and ortho owner)


----------



## digger945

The prices at B&D Ent. aren't really all that bad. $15 minimum order for US customers and the sell other parts too. I like B&D and have used them before.

 Mouser has the NEC 2SK3105 which is listed as a drop in replacement for 47 cents each.
 Ampslab has the 2sk117BL going for 20 for $20. I have ordered from these guys before. Shipping isn't much IIRC.


----------



## kansei

I ordered 10 of each - 2sk310, 2sk117 and lmt317t. Don't have them on hand yet. I will post here once I get them if anyone is interested.


----------



## DKJones96

I will be interested since I unfortunately ordered from a BS company... Maybe we should remove the link to them on post #11. lol

 I wasn't able to pay using paypal so I've got to see what my bank can do.


----------



## kansei

I got my shipment of 2sk310, 2sk117 and lmt317t. I'm keeping two sets. One of the sets is earmarked for DKJones96, two remain up for grabs. Please send me a PM if you're interested, each set consists of 2 pieces of each type.

 Pictures, some of the 2sk117 chips are slightly different.

http://s248.photobucket.com/albums/g...e%20Amplifier/


----------



## kansei

I finished soldering most of the components to the board a few minutes ago. Had to go to Radio Shack for a few caps because I messed up my Mouser order. After some messing around with the power source I got the tube to light up. What threw me off for a while is that I forgot to jumper the power switch pads near the pot. 

 What remains is the casework and wiring up the inputs, outputs and the pot. 

 Another observation is that the mosfets get really hot. I also need to get right-size the fuse since I blew two of the fuses that I bought (unless there is a problem with the amp itself).

 Also, my BOM is incorrect in a few places. The pot doesn't fit on the board, most of the caps are incorrect in physical size, the resistors all look physically different. I will post an updated BOM when I get a chance although I don't know if I will have a solution to all of the things.

 I will work on it more either tonight or tomorrow.


----------



## ludoo

How does it sound?


----------



## kansei

Nothing yet, still haven't wired up the inputs and the outputs. I hope to do it today.


----------



## kansei

I finally finished my build. It still needs to be cased but it's otherwise working.

*Building*
 It went together very quickly. I was surprised that it was so easy. The toughest part was soldering the FETs becaue the pads are very close. I need more practice in the soldering department, a better soldering iron and an OptoVisor to see better.

*Tubes*
 I have two tubes: Philips Jan 6922 and Tung Sol Golden Dragon e88cc. The Tung Sol sounds incredibly good. I probably need to clean the contacts on the Philips. Will report on this later on.

*Sound*
 Nothing short of amazing. Female vocals sound incredible. Drums and guitars sound great. I like this amp a lot better than the Starving Student. Well worth the price and the effort.

*Parts*
 I missed a few parts ordering from Mouser so I had to get them from Radio Shack. I plan to replace two of the RS caps with Nichicon audio caps once I get the right ones. Note that the C103 I used is almost as tall as the tube. I'm using a HP inkjet printer power supply, it puts out 33 volts and 940mA (part # 0950-4466). The heatsinks specified need to be modified to fit (2 of the legs cut, and the middle leg made thinner).

*BOM*
 I'm attaching my updated BOM. Please note that the resistors in the BOM all look different from each other. If this bothers your sense of aesthetics, please do your own research.

*Pictures*
 See here for more pictures: 6dj8 Headphone Amplifier pictures by kansei13 - Photobucket


----------



## DKJones96

Yeah, I've noticed that the sizes of the caps are off a bit. When I place my mouser order for the BantamDAC I'm building I'll order the correct output caps for this thing. I'm thinking the 470uF caps I put there for now will probably sound just fine tho.

 Just a note, the output caps have 7.5mm spacing and the main power cap has 10mm. Finding values as small as the ones they want for the amp and getting those spacings isn't easy. One solution is using larger values, like the 4700uF 50V power cap kansei uses. I think I put a 35V 2200uF cap there.

 I'm almost done with the power supply; I only have a couple of wires to solder in then, if I'm brave enough, I'll plug it in and test if my hand drawn, protoboard regulator actually works. Fingers crossed!


----------



## kansei

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_One solution is using larger values, like the 4700uF 50V power cap kansei uses. I think I put a 35V 2200uF cap there._

 

That 4700uF cap dwarfs the tube, I'm thinking of mounting it horizontally.


----------



## Nemo de Monet

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_*Sound*
 Nothing short of amazing. Female vocals sound incredible. Drums and guitars sound great. I like this amp a lot better than the Starving Student. Well worth the price and the effort._

 

Congratulations on finishing the amp; I still haven't found time to add the last few bits to mine, yet. Soon, very soon. 
	

	
	
		
		

		
		
	


	




 "Better than the Starving Student"? That should pique a lot of people's interest, but are you sure you're _allowed_ to say that kind of thing around here? 
	

	
	
		
		

		
		
	


	




 Have you measured your heater voltage, et cetera, and found them to be roughly correct, even with the 33V power supply? I've cobbled together a fairly nice, regulated, 24VDC, 1A supply for this, but if it works off of 32VDC or so as well, I may just use a different supply instead.

 Also, did you run into any problems with input levels, as the guy who bought the prebuilt version did last year?


----------



## DKJones96

Input level issues? Got a link?


----------



## kansei

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_Congratulations on finishing the amp; I still haven't found time to add the last few bits to mine, yet. Soon, very soon. 
	

	
	
		
		

		
		
	


	




 "Better than the Starving Student"? That should pique a lot of people's interest, but are you sure you're allowed to say that kind of thing around here? 
	

	
	
		
		

		
		
	


	




 Have you measured your heater voltage, et cetera, and found them to be roughly correct, even with the 33V power supply? I've cobbled together a fairly nice, regulated, 24VDC, 1A supply for this, but if it works off of 32VDC or so as well, I may just use a different supply instead.

 Also, did you run into any problems with input levels, as the guy who bought the prebuilt version did last year?_

 

I like the "Super Simple" a lot. The "Starving Student" is almost as good with my coveted RCA "brown text", square getter tubes. I should note that the SS amp was my first project and was built with standard capacitors instead of audio-quality ones.

 I didn't measure any voltages, just plugged in and went. The tube lit up and I was ready to go. Good idea to measure, though, will do some measuring tonight. I tried to use a 19v power supply as well but I got a lot of distortion. This may be the reason why I was having issues with the Philips Jan 6922 tube, it may need more heater voltage than the Tung Sol e88cc. More research for me...

 No issues with input levels whatsoever, just smooth and quiet all around. My amp likes less input, I ran Foobar at 3/4 or 2/3 volume level and it worked very well. The link to the pre-built amp and issues with it is here: http://www.head-fi.org/forums/f5/95-...photos-347465/


----------



## DKJones96

Hmm, that thread is making me wonder about grounding.

 I'm guessing that it does but I'm kinda new to these kinds of amps. Educate me if I'm wrong, but this is how I understand this amp to be working. Unlike a solid state amp that runs a rail splitter and has a virtual ground that the phones can sit on at idle, this amp makes its 'virtual ground' by having a dc offset at all times from the fets/tube. Say you run 6 volts, at idle the fets supply 3v to the output caps. You get your +- output to drive the phones by varying from the 3v offset. moving to 4v gives you +1 on the other side of the cap and 2v gives you -1. 

 So, ground on the PCB and DC-in is at the same voltage potential as the inputs and outputs. Is that right?


----------



## mikeythemars

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_Another observation is that the mosfets get really hot._

 

That is correct - I purchased the pre-built version of this amp from the eBay seller and have been using it now for several weeks. What I noticed when testing it right after it arrived is that the all four mosfets and their associated heat sinks (which are large, apparently for good reason) get _very_ hot -almost to the point where they will burn a finger if contacted too long. 

 I haven't found that to hamper performance and the heat from the sinks doesn't appear to be "cooking" anything else on the board. However, it does mean I remove the top of the plastic Hammond enclosure enclosure I mounted it in when the unit is running. It also suggests that this circuit shouldn't be housed in an enclosure without adequate ventilation. 

 Regarding the "issues" another member found with the pre-built board, I did replace the input and output jacks with Neutrik 1/4 and RCAs, but kept the ALPS volume/on-off switch. I haven't had any of the noise or gain issues. The amp drives my Senn 600s easily and is dead quiet. No distortion or bass weakness/bloat, perhaps because the input is being fed directly by the tape out on my BEZ preamp (ergo, a pure low level line source, not the headphone output of a portable). I have noticed improved air when listening to tape off my Nakamichi deck (compared to running the phones directly off the Nakamichi headphone output). Things are also likely being helped by the tube I'm using - a 1963 Amperex Bugle boy. I kind of like the errie blue glow it has when it's running, a function of the blue LED the designed squeezed in under the tube socket.


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## DKJones96

I got mine together but my power source has an issue(solid 24v at idle and 6v under load, no idea wth) and it doesn't give me anything more than a thump when turned on and an eerie low hum that doesn't change with a source or anything. I'm using a 19.8v switching power supply on it but I have a hard time believing that 4v means the difference between nothing at all and full sound.

 I left it on and the 317s get warm but not the 310s. I've got some real troubleshooting to do since I noticed the LED doesn't light up either and I'm pretty sure I didn't install it backwards. Should the tube get warm to the touch? And if so, how long after it's on should it be?

 **EDIT** I was looking at the schematic and the diagram together and am wondering something, the adjustable pots I used at 110/210 have 3 legs in a tripod formation. One of the legs sits on the same line as the wiper and the 3rd leg is on the other side. Could this be causing my issue? I'm thinking no because the path of least resistance is through the wiper at anything but turned full right on the pot.


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## digger945

Your tube shouldn't get hot at all DK. I think if your dropping that much voltage you have a PS that doesn't put out enough juice or something in your amp has way lower resistance(possibly close to zero) than it should be.


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## Nemo de Monet

Huzzah, mine's alive and for the most part working as designed.

 I bought, and then misplaced, trimpots for R110/R210, so I just put a resistor (470 ohm, I think) in its place. My LM317s get fairly hot, but the 2SK310s just get warm.

 I tried powering it off a 30VDC 1A printer power supply, and this does work - you get the correct heater voltage, so yay. However, with my printer power supply, I also get a horrible hum, so I'm running it off a homebrew 24VDC, 1.5A supply. I can't imagine why yours wouldn't work off a 19V supply - you did get the polarity right, right? The tube heaters should start to visibly glow within, oh, thirty seconds or so, and the glass envelope should be warm to the touch a minute or two later. 

 With earbuds or other highly-efficient 'phones there's a slight hum on mine that doesn't increase with volume and is fairly ignorable; it isn't audible with my ATH-M30s. I have a few ideas to try to minimize this...

 I, too, used the standard Alps pot, and it's probably just my pot, but the power switch doesn't do anything! If the amp's plugged in, it's on. (At first I thought the tube - an RCA ECC88 - just took a while to dim, but after about thirty seconds standing there, I started to get suspicious...) Doh! Eh, when I case it up I'll just have to put a switch on the power line, but it's still odd.

 Oh, and also, my amplifier does something that I suspect none of yours does: picks up local 50KW AM radio station KSTP fairly clearly, if I accidentally touch any part of the input signal "upstream" of the tube. Hmmn...

 Other than that, it sounds ridiculously good.


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## digger945

Make sure your input ground is tied to pcb ground, and not just connected to HP ground. The schematic shows the pot ground not connected to pcb ground but I am sure it is supposed to be.
 So is this your first hybrid? I thought you guys would love the sound.


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## mikeythemars

Quote:


  Originally Posted by *digger945* /img/forum/go_quote.gif 
_Make sure your input ground is tied to pcb ground, and not just connected to HP ground. The schematic shows the pot ground not connected to pcb ground but I am sure it is supposed to be._

 

I assume the board on the filled (pre-built and tested version that I have) is identical to the bare PCB others are building off of. The way mine came the adustable resistor (a.k.a. volume control) is connected the PCB ground trace.

 On the subject of hum: for what it's worth, the input jacks on my setup are at the back of the enclosure, ergo at the rear of the board. They are connected to the input pads at the front via solid 24g wires inside a braided shield. I also put a small sheet of aluminum between the input jacks and the rear of the board. So the entire input line is shielded, which may be a factor in why I have absolutely no hum in my unit.


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## kansei

^ x2, digger945. I had some hum at first, then connected (-) from the power plug to the ground on the RCA plugs to the ground on the headphone jack. This fixed the hum. At first I also connected these three to the ground on the pot but this made the volume control inconsistent.


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## kansei

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_I can't imagine why yours wouldn't work off a 19V supply - you did get the polarity right, right?_

 

Mine wouldn't work right on 19v, I was getting distortion.


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## kansei

I measured the heater (pin 4) it and it says 6.2v. I also measured pin 1 and 6 (anode #1 and #2) and made them the same voltage with the trim pots (25v). Can't hear the difference with the adjustments, though. I'm still new at this so I could be completely off on both the measuring and on the pin outs.

 I got the Philips tube working as well, some contact cleaning and a thorough warm-up fixed it up.

 On an unrelated note, I am way into this as evidenced by posting to the same thread 3 times in a row.


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## Nemo de Monet

Well, for kicks, I dug out the 19VDC, 3.2A laptop power supply I've been running one of my Pimetas on, and not only does it power my 6DJ8 amp just fine... but with no hum, either. (To be fair, I'm in a different location than when I was testing earlier, but still...)

 I don't hear any noticeable distortion, but I've only been listening to it for a few minutes, and I don't have my output devices biased nearly as high as I think some folks do. 
	

	
	
		
		

		
			





 I can very much tell, though, that this amp really sings with a line-level signal, but doesn't seem to do nearly as well with the signal out of a headphone jack.

 This is my second hybrid amp, after a fairly nice 'SOHA Mk. I' I built a while back, and so far I'm mighty impressed with the sound. I don't know quite how to describe it, except to say that it's extremely musical: everything that's good about the SOHA Mk. I, and then some, without any of the SOHA's annoyances. I <3 it.


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## DKJones96

Okay, I took a couple of measurements. The amp seems to be acting like you guys are describing, the 310s are warm and the 317s are hot. I can see a slight glow within the tube and it's warm to the touch after being on for a few minutes. However, I'm reading 3.56v out of both 317s and only 2.31 at pin 4. Still nothing but a hum.

 Could the low heater voltage be making the tube not pass audio? Even after being on a while? No idea What I did wrong lol I followed the resistor values to the T!!!!


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## Nemo de Monet

It's entirely possible that it won't operate anything like correctly at 2.3V heater voltage. Why you're getting that low of a voltage, on the other hand... I dunno.

 What are you feeding it an audio signal from, and have you tried turning it all the way up? When I feed mine from an MP3 player, I need to turn it all the way up to get to a decent listening volume, and don't even begin to hear a thing until about 12 o'clock on the dial, so to speak.

 Mine's more-or-less per the schematic; the only resistors I changed were R110/R210, like I said; I've got 1200uf Elnas for C102/C202, and some 2.2uf film caps for C101/C201, only because they fit. Oh, and because I misread the schematic when I was rummaging through my parts boxes, I've got a (cough!) 12000uf Nichicon cap for C103; even by Head-Fi standards, I think that's a wee bit excessive. 
	

	
	
		
		

		
		
	


	




 I don't know how useful it'll be, but you might want to post a photo of your board; maybe someone will spot something...


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## DKJones96

I think my LED is wrong. That would explain the low voltages.

 **EDIT**

 Repalced LED with diode... still no go. still 2.x volts.


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## DKJones96

Forgive the use of flash, I don't normally use it for stuff like this but I don't have my tripod with me.









 The tube is actually a 6N1 but the only difference I've found between the 6DJ8 and the 6N1 are the heater currents... Unless this is a current feedback setup I don't see that causing it. I should probably also mention that when the amp is first started it only gets about 1.6 volts to pin 4. As the heater warms up voltage rises to 2.2.


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## kansei

If you trace what leads to pin 4, what do you measure for voltage coming out of BG201 and BG101 (pin #1 in both cases if I'm not mistaken)? Theoretically, they should both be putting out the same voltage. My thought process is that either BG101 or BG201 is not putting anything out, or something in between may be reducing the voltage (R106?).

 Also, mine runs with or without a LED (makes no difference).


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## kansei

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_Well, for kicks, I dug out the 19VDC, 3.2A laptop power supply I've been running one of my Pimetas on, and not only does it power my 6DJ8 amp just fine... but with no hum, either._

 

I'm using HD600s and can hear the low notes clipping when using a 19v supply, especially at higher volumes. The amp does not hum, just sounds bad (like there is sand in the speakers). Could the 19v supply work with lower impedance headphones? I will try tonight...


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## DKJones96

If someone could do me a quick favor. I could use in-circuit measurements of R104-5/R204-5 (ADJ on the 317 to OUT) I'm currently reading exactly 7.5 ohms on both sides(R1/R2). I'm thinking it has to be some sort of resistor value that's messing it up, maybe. I'm getting 20v to the 317s but I'm not getting 6.3v out. Since they're both getting hot I can only assume that one of them isn't actually dead. 

 Tonight I'll pull the tube and see what kind of voltage I get with no load on the heater circuit though. If it's ~6v with no tube in there I'll have to assume I got a bad batch of 317s because my power supply is doing the same thing. When the amp is off it gives me the calculated 24.5v for output but when I turn the amp on voltage drops to around 6 volts.


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## kansei

The pads for LM317s FETs are pretty close, is it possible you have a solder bridge on one of them?


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## DKJones96

That was the first thing I checked for, I might be missing one tho, I'll take a picture tonight and post it of the bottom.


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## digger945

I haven't been keeping track of everything that's been going on lately, but I wanted to mention that if someone substituted parts for the K310 or K117, then those alternate parts _may_ have a different pinout that could cause a problem.


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## Nemo de Monet

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_If someone could do me a quick favor. I could use in-circuit measurements of R104-5/R204-5 (ADJ on the 317 to OUT) I'm currently reading exactly 7.5 ohms on both sides(R1/R2)._

 

I measured mine and got around 7.2 ohms for each side, though it jumped around a bit.

 I wonder if your problem isn't, indirectly, the tube you're using; the 6N1P has a much higher heater current than the 6DJ8, and I don't know what kind of power supply you've got, but I wonder if it can't keep handle the resulting current draw.

  Quote:


  Originally Posted by *kansei* 
_I'm using HD600s and can hear the low notes clipping when using a 19v supply, especially at higher volumes. The amp does not hum, just sounds bad (like there is sand in the speakers). Could the 19v supply work with lower impedance headphones? I will try tonight..._

 

I've listened to mine at 19V for several hours now - with 40 and 60 ohm 'phones - and don't hear any signs of clipping, at all, nor any unpleasantness. Now that it's burned in a bit, it just gets better and better...


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## DKJones96

I think I solved it!!! Thanks Nemo!

 I was looking over the schematic and noticed that these 317s aren't actually setup to be constant *voltage* regulators. The increased current draw is pulling them low because they are set for a particular amount of current. At 7.5 ohms each 317 will provide 167mA which is great for the 6DJ8 at 350mA but not for the 6N1P at 600mA. I actually need 4.5 ohms.


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## Nemo de Monet

That _would_ explain it, I bet.

 If that's the case, just put another 13ohm resistor in parallel with the 15 and the other 13, and you should get right about 4.5 ohms.

 Here's hoping that works... it'd be really nice to have this design working solidly with dirt-cheap 6N1Ps. I thought I had some laying around, but they turned out to be some other sort of Soviet tube.


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## DKJones96

I got sound! It clips badly and the audio is only slightly louder than the hum but something actually comes out of the headphones now. I'm going to search for more volts and see if that clears it up.

 I've got 6.21v at the heater using 15/13/10 ohms, 13/13/10 gave me 6.6v and it clipped there too, dang tube runs as warm as the 317s!


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## kansei

Great news, DKJones96.


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## Nemo de Monet

If anyone is or was wondering, I used generic 1/4W resistors for R101/R201, rather than the 1W ones theoretically specified, and have yet to experience any issues after a dozen or so hours of use; they don't even get warm, so I'd guess the power rating there is probably a non-issue...


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## ludoo

My PCB arrived today, now I only miss the fets and I'm set.


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## DKJones96

The largest amount of power moving through the resistors is at 104-105/204-205 and from my calculations even 1/4 watt resistors would work there in stock form and my amp running 600mA should be okay with them too.


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## mikeythemars

DK, I noticed from the photo you posted that you are using 2.2uf rubycon caps as the couplers on your board. My pre-built one came with .1uf caps there and that's what the included schematic (which I assume is identical to the copy that comes with the bare boards) shows. So was the change on yours intentional or are you just employing what you had readily available? I am considering ugrading the rather basic looking caps on the pre-built board with Auris.


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## DKJones96

It was intentional. I like them quite a bit and the only other caps I've heard that I'd run are some Aerovox film caps I've got here that are too big and some polystyrene caps that weren't going to fit right either. The Rubycons fit perfectly and looked right at home so I put those on.


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## kansei

I've had my amp mounted in a Radio Shack "tub" enclosure for a few days. Not sure if the one in the link is the size I have, but it looks like the one in the link. Project Enclosure (6x4x2") - RadioShack.com

 Finally, I decided to "splurge" and get an enclosure from the eBay seller Fan_Computer (see link at the bottom). I just received the enclosure, these guys are quick - I bought it on Friday and got it on Monday. It's a very nice piece, the two parts of the shell are very solid. The end caps are metal and decent, except slightly skinny compared to the rest of it.

 The one thing that bothers me is that the PCB is a little too skinny to sit in there securely, I can dislodge the PCB by just removing the tube. Any tips on how to secure the PCB better in the channel? I thought of putting in some screws to hold the PCB down but that seems like an extreme measure. My brain hurts. Please help.

Aluminum Project Box Enclousure Case Electronic DIY_Mid - eBay (item 250331728407 end time Mar-24-09 18:55:14 PDT)


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## ludoo

I just got the FETs from Kansei (thanks *a lot*!), so I guess I have everything I need to build this amp, probably this weekend.


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## Nemo de Monet

Kansei: You could try essentially shimming the board with paper, or electrical tape, or something along those lines, to make it a more secure fit in the groove. If all else fails, you could go for a couple drops of contact cement (or even hot glue), which should be enough to hold it in place while it's being tinkered with, but still easily removed if/when you want to. It may lack a certain something, both technologically and aesthetically, but nobody's going to see it or know, so who cares?


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## kansei

Thanks for the suggestions, Nemo. I thought about the hot glue, even gluing some flat pieces of metal above the PCB groove to help keep the PCB from moving. 

 I just have to get over my casework anxiety when it comes to drilling holes and doing things like this. Practice, I suppose.


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## kansei

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_I just got the FETs from Kansei (thanks *a lot*!), so I guess I have everything I need to build this amp, probably this weekend._

 

10 days to ship from Joisey to Italy, not bad for first class mail.


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## Nemo de Monet

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_I just have to get over my casework anxiety when it comes to drilling holes and doing things like this. Practice, I suppose._

 

Practice, and luck. (What was it Yogi Berra once said? The more I practice, the luckier I get...) Also, _always_ do the front panel first. Nobody really cares what the back looks like, so if you _really_ screw the first one up, you get a second shot with the other panel. (With tube amps, you can always claim any "extra" holes in the back are for "ventilation"...)


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## ludoo

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_10 days to ship from Joisey to Italy, not bad for first class mail. 
	

	
	
		
		

		
		
	


	


_

 

Yes, really quick!


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## kansei

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_Practice, and luck. (What was it Yogi Berra once said? The more I practice, the luckier I get...) Also, always do the front panel first. Nobody really cares what the back looks like, so if you really screw the first one up, you get a second shot with the other panel. (With tube amps, you can always claim any "extra" holes in the back are for "ventilation"...)_

 

I put 3 tiny pieces of electrical tape on one side of the PCB, this is holding it in place nicely. Who would have thunk it?

 I'm going to declare my drilling last night a success. I got everything drilled out nicely except for the top. The top has a small hole in it but I did not want to push my luck with the sketchy drill bits I currently own. I'm buying a stepped bit this weekend and asking my neighbor to borrow his drill press so I can finish the top.

 My new "technique" consists of putting masking tape over the piece I'm about to drill, then drawing on it to find the right spot for drilling. Right afterwards, I stare at the piece with my OptiVisor for 5 minutes from all angles to make sure the holes will be in the right place. I lay out the volume knob and any other bits in the proposed area to see if the layout makes sense. I use a center-punch to set the holes so my drill doesn't "walk", and always drill a small pilot hole to get started. For aluminum you can use a knife to deburr the holes.


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## ludoo

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_I'm going to declare my drilling last night a success._

 

Pics!


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## DKJones96

Sounds like we'll have a few more joining the party! I still haven't acquired a larger power supply(guests in town til end of next week). I'm thinking of going with 36v(regulating it down to test) since I'm running a different tube and it may want the higher voltage anyways. As long as I don't pass 40v I should be okay. I say that because the 317s are only rated to 40v difference between in and out so with the tube starting cold having a heater voltage of ~1.5v and not wanting to worry about dead regulators I'll play it safe. The fets should be fine up there.


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## Nemo de Monet

I picked up a Phillips 6922 from an online merchant, and tried it out; low noise, and pretty decent sound - but it clips badly at 19VDC. 
	

	
	
		
		

		
			





 Happily, I also acquired a 30VDC 1A power supply that works with little to no noise with this amp, and not only does the amp _not_ clip at this voltage, but it's _significantly_ louder - something like 60db louder. (With the amp's volume control set at 10 o'clock, I have to set Foobar to -12db, and set Windows' master volume to about 75% to get a low enough volume with 40ohm 'phones that I'm not concerned for my hearing. At 19V, I had Foobar set at 0db, and the amp's volume control set to about 2 o'clock...)

 It's just as much louder with the RCA 6DJ8, BTW. I'd say if you want to run at low voltage (19-20V), an RCA 6DJ8 is a good choice, and a Phillips JAN 6922 not so much so...

 Unfortunately, at 30V the output transistors (well, their heatsinks, anyway) get _really_, somewhat alarmingly hot... like "hmmn, forced-air cooling might not be entirely out of the question once this thing gets put in an enclosure" hot.

 It still sounds ridiculously good, though.


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## digger945

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_It still sounds ridiculously good, though. 
	

	
	
		
		

		
		
	


	


_

 

This is always good to read
	

	
	
		
		

		
		
	


	



 May I also recommend the GE 6DJ8, I've been listening to a pair for a few weeks now and the mid's are out of this world good.


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## Nemo de Monet

I'll keep an eye out for one, but right now I'm trying to get or build a 24V supply that doesn't produce a hum in this amp. The 6922 sounds _great_ at 30V, but the heatsinks were hot enough to burn me (literally - got a little blister on my finger, lol), so I've switched back to the RCA 6DJ8 at 19V. The only real downside to the existing PCB is the limited space for heatsinks; if there were an easy way to bolt the transistors to a really big heatsink, I'd be perfectly happy to stick with 30V, and have an awesome-sounding amp that could double as a coffee-cup warmer...

 I've got another PCB on the way, as I've got a second set of transistors thanks to B&D's minimum order policy; I might just run a 6922 in that one at 30V, and attach a pair of VGA heatsink/fan units to the 2SK310s. 
	

	
	
		
		

		
		
	


	




 I'd be really fairly worried at 36V, to be honest. I'd be afraid it would be a bit like the solid-state amp I was prototyping yesterday: sounded butt-kickingly good for about ninety seconds, then all the magic smoke escaped, doh. (I now believe 2N5486 FETs contain more magic smoke, by volume, than any other electrical component except maybe selenium rectifiers...)


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## kansei

Mine gets hot at 33v, but hasn't overheated yet. It also runs at 19v but not with the 6922. My favorite tube so far is the Tung Sol e88cc (I also tried the Philips 6922 but it sounds a little dull, perhaps needs to be burned in?). I also bought two socket savers that I thought would be the best thing to raise the tube so it could be seen better, but they make the amp sound shrill. I will try again after I clean the socket saver contacts.

 Here are two pictures of how far I got with the amp, more pictures can be seen at 6dj8 Headphone Amplifier pictures by kansei13 - Photobucket


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## DKJones96

Looks great kansei!

 I'm looking in my 1962 RCA interchangability guide and I don't see that RCA made a 6DJ8. 

 ECC88 crosses to RCA 6J6 directly and is similar to 6BQ7-A. 

 Just a bit of info:
 6J6 - Medium-Mu Twin Triode Heater is 6.3v@300mA(may require resistor changes to keep from exceeding voltage)
 6BQ7-A - Medium-Mu Twin Triode, Heater is 6.3v@400mA(may require resistor changes to get the heater to full voltage)

 There are lots of these that will work if you want me to go through the list a bit.

 Quick question, does anybody know what the tolerances for heater voltage usually is?


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## Nemo de Monet

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_I'm looking in my 1962 RCA interchangability guide and I don't see that RCA made a 6DJ8. _

 

They might not have in '62, but they did - in Kentucky - in 19*8*2, when and where mine was made. 
	

	
	
		
		

		
		
	


	




 It seems a lot of the RCA 6DJ8s are actually Mullards, but I seem to have an actual RCA-made one. Go figure.

  Quote:


 Quick question, does anybody know what the tolerances are for the heater voltage usually is? 
 

Usually +/-10%, from what I've seen, at least for 6V/12V tubes, though I'm not positive it holds true for tubes with higher-voltage heaters, like the 117L7.


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## DKJones96

This amp is going to be the death of me...

 Actually, the tube is. I got a really nice power supply that provides very clean power but apparently not a lot of it. The .6A i need for the tube heater alone is dragging it from 24.1v down below 20. I got it because it's adjustable between +- 22v to 38v but apparently I need to get a straight 24v like the couple i saw there that will give me over 7.5 amps at 24v. Unfortunately, I'm thinking that 24v won't be enough for the tube I've got and it wants 36v.


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## kansei

Look around your house and workplace. If you have an inkjet printer you can borrow the power supply to test things out with. 

 I'm running with a 33v supply from a HP Deskjet, got it for free. I also got two free power supplies for my Starving Student amplifiers. You can also search on eBay, put in "33v power supply", then try 34, 35, 36, etc. There are some supplies listed for very cheap out there. Sometimes you will get lucky on garbage night as well.


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## Gvvt

Nemo de Monet - interesting about the RCAs. All the talk about RCA not making a 6DJ8 - instead creating their own in-house 6FW8 - seems to relate to the 1960s; as here: Tubes Asylum: Re: They MUST Be Phony Mullards ? by Sondek and the next post in that thread. Could the licensing have changed 20 years later?

 I've also got some RCA 7DJ8s that are really Mullards and Amperexes; really nice tubes. 

 I;m intrigued by the idea that at one time, somebody knew all this stuff, and now it's almost impossible to trace back.


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## DKJones96

kansei, thanks for the tip! 

 I've got clear sound but not at volume and with the 317s heat sinks reading over 180 while not in an enclosure I feel I've hit my input voltage limit without significant modification from the original heater setup.

 Here is where I'm at. I swapped out the output caps for 35v 1000uF caps like the original build specifies(tried fixing the following problem but it did nothing). Now, anything above a low listening volume begins clipping. It doesn't matter where you give the extra push(volume knob, player, or adj pots) the sound begins to clip above said volume. Under the thresh hold it sounds great though. So, I swapped tubes, since I have two of these, and it started to not only clip but almost pop in my ear when you got above the good sound and heater voltage was down to 6.08v from the 6.21v I have the first tube at. Needless to say I went back to the first tube again and will be switching out the 15/13/10 resistors for the 13/13/10 to bring the voltage up a bit on the heater.

 Right now I'm trying to figure out if the tube or the output stage is the culprit. **ADDED** I've got 6.55v at the heater and it didn't chage anything as far as sound goes(didn't think it would) but did cool the 317s down a bit and make the heater brighter. Something to note. If the player is left at a constant 1/2 volume the volume knob on the amp only adjusts volume up to 1/2 and then stays steady. If the player volume is set to full it will adjust volume and the the last half of the volume adjust seems to just adjust how much it clips.

 I could just give up on this tube and build to original specs but where is the fun in that?


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## digger945

I don't think your heater voltage is really gonna make a difference, and I haven't used the tube your using(the ones from post #156 I presume) but I don't see why it wouldn't work good in this circuit with 24V. How much current does the adjustable PS put out?


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## Nemo de Monet

Have you tried adjusting the trimpot? I really don't _completely_ understand this amp design (doh!), but it seems like the idea is to adjust for "15V" at the 2SK310s, but that's only with 24V - roughly halfway between that and the ~6.3V heater voltage, which seems like a logical place to bias the output (maybe it's just a coincidence?) 

 If I understand this correctly - which might not be the case, be warned - you might squeeze a little more headroom out of it by adjusting the trimpots until you get, say, ~12V at the 2SK310s, giving your amp a potential +/- 6ish volt output swing. (If your power supply is sagging to 19 or 20V under load, and you have the output FETs trimmed to 15V, I think you're able to swing -9V or so, but only +4 or +5V = clipping.)

 I could be really, really wrong, though. Mine has fixed resistors installed, or I'd perform some empirical experiments on my own.


----------



## kansei

******* Edit *********
 This is very interesting but you may need a tube tester to get accurate results on anything other than Uh-k. Mine won't measure accurately on anything else.
 *******************

 Here is a very interesting link on how to measure the voltages for these tubes, and what the acceptable voltages are. The table on the top of the page tells you what you should get for different types of measurements. Lower on the page they tell you how to measure on for different things (and on which pins). I'm about to measure my tubes now.

ECC88 List

 Like Nemo said, you may be able to tune in your trim pots so these voltages are in the right range (if they weren't to begin with).


----------



## DKJones96

I think I've found the problem... (on a side note, I'm using a power supply that holds 33v which it turns out is providing more than what the tube needs since it's rated at 18-30v when used as an AF amp)

 This isn't a 6N1*P*, this is in fact the 6N1. There is a HUGE difference in the gain that the two tubes have. The 6DJ8 (or ECC88) has an 'S' factor of 15 mA/V while the 6N1 (or *ECC40*) only has an 'S' factor of 6.0 mA/V. I know the ECC40 isn't directly pin compatible(8pins vs 9), but it's the closest thing I've found to the 6N1 where info is actually available. It appears to be the ECC40 with a screen to make it pin compatible with the ECC88. I've taken R109 down to 9.5 ohms and R103 to 49.6 and, while it has helped, it isn't spectacular, yet. The pop when you turn the switch on, however, has become annoying(painful). lol

 If I can figure out how the solid state half of the amp works I can probably get this tube to work by increasing its sensitivity a bit but I'd rather not.

 I've got 33v in and 26.5v at C102.


----------



## kansei

I picked up a stepped drill bit from Sears to finish my case. Although I'm not crazy spending $36 on it, I could not wait to get it from eBay. I finished the hole for the tube, and added two ventilation holes on the back panel. Still, I don't feel comfortable that the amp will run cool enough with the top on. Perhaps a few vent holes on the top? Here is a picture of the completed product. In any case, I'm finished now.










 More pics:
6dj8 Headphone Amplifier pictures by kansei13 - Photobucket


----------



## DKJones96

Very nice! The only real thing I did differently as far as the case goes is put the RCA jacks in the front. Which I'm glad I did as I'm most likely going to stick a small 12v fan in the back.

 I ordered an Electro-Harmonix 6922 overnight that should fix my lack of gain problem. I'll build another circuit around the 6J6(portable unit?) and maybe another for the 6N1s. I may buy another PCB to do experimenting on with those units but this one i want working already.

 I wonder if there is enough room in the front with it closed for the Bantam dac I got all my parts for today.... hmmm.


----------



## kansei

If you encase the Bantam in a plastic case so it doesn't short, there's plenty of room between the tube and the front panel.


----------



## DKJones96

Here is what I have so far. Thumbs up to thetubestore.com for their expedient shipping. I got the 6922 today, slapped it in, verified heater voltage, and this thing is awesome!

 Very clean sounding amp. I think it overdrives my poor HD202s tho. If something has deep bass I can hear the drivers muddying up the midrange in an attempt to create the bass being sent to it. The 317s no longer run hot either. Apparently 300mA as opposed to 600 makes a huge difference! I snapped a couple of pics. I'll get an album when I'm closer to finished(a few minor things like me wiring the volume pot backwards to fix).

 All jacks are in the front and the power switch is actually in the back by the DC jack that I'm not using in the pic. My custom mini-RCA cable works well too.





 8-second exposure showing the tube lighting up the circuit board.


----------



## kansei

That's lovely, DKJones. Looks like I'm getting a silver enclosure for my next 6dj8.


----------



## Nemo de Monet

Wow, that's going to look really nice - bright silvery tube sticking out of a bright silvery box! Very clean and modern. I might just have to jump on the silver 6DJ8 amp bandwagon. I'm glad you finally got it working, too, and are able to join in the fun. 
	

	
	
		
		

		
		
	


	




 The more I listen to this, the more impressed I am with how good such a simple design can sound. Compared to some of the amp designs out there, this thing is downright primitive, but you'd never know it from just listening to it...


----------



## kansei

I've decided to sell my first "super simple" to finance building a Bijou. It's on eBay if anyone is interested. 

 I have 90% of the parts, including the PCB, to build a second one. As soon as buy more stuff from Mouser I will get the rest of the parts and put it together.


----------



## biarritz

Hi all,

 After a disasterous build of the SOHA v3.0 I bought this amp. It came with all parts pre mounted. All looks very nice, but I am not satisfied with the sound. There is a hugh lack of bass and all sound a bit muddy. I placed a nice PIO at C101. Are there any other changes I could make to improve the sound?


----------



## kansei

Look at this post, it describes a few experiences with the pre-built amp and how to resolve.

http://www.head-fi.org/forums/f5/95-...photos-347465/


----------



## DKJones96

He uses 470ohm resistors on the input to ground. I went with 1000 ohm but I don't think there is a real difference between the two.


----------



## Nick 214

Quote:


  Originally Posted by *biarritz* /img/forum/go_quote.gif 
_Hi all,

 After a disasterous build of the SOHA v3.0 I bought this amp. It came with all parts pre mounted. All looks very nice, but I am not satisfied with the sound. There is a hugh lack of bass and all sound a bit muddy. I placed a nice PIO at C101. Are there any other changes I could make to improve the sound?_

 

What cans are you using? A good amp will expose other weaknesses in your system.

 NK


----------



## Nick 214

Guys, those both look awesome!

 @ Kansei: You could drill out the tube-hole a bid wider, to facilitate the use of some sort of cooler/damper, if you'd like.

 OItherwise, I'd just drill some small holes maybe 6-10 in a circular fashion around the base of the tube-hole. That should provide all the ventilation you need (and look classy). It's not like you're running a GM70 in there.. 
	

	
	
		
		

		
		
	


	




 NK


----------



## kansei

Thanks. I did manage to drill two more holes on the case.






 More pics:
6dj8 Headphone Amplifier pictures by kansei13 - Photobucket


----------



## Nemo de Monet

Quote:


  Originally Posted by *biarritz* /img/forum/go_quote.gif 
_Hi all,

 After a disasterous build of the SOHA v3.0 I bought this amp. It came with all parts pre mounted. All looks very nice, but I am not satisfied with the sound. There is a hugh lack of bass and all sound a bit muddy. I placed a nice PIO at C101. Are there any other changes I could make to improve the sound?_

 

What are you feeding it with? Did you buy the power supply 8Audio offer, or are you using something else? Are you using the stock Chinese tube? And, like Nick 214 asked, what headphones are you using it with?

 There should be _no_ shortage whatsoever of bass with this amp, from my experience; quite the contrary, in fact. (But remember, my power reservoir cap, C103, is - _cough!_ - 12000uf, which is undoubtedly excessive, and I think everyone else who built one here used something larger than the spec'd 1000uf, so upgrading that to a larger cap - 4700uf might be a good compromise between "too little" and "outright crazy" - might be something to look at.)

 My only other idea would be to pick up an inexpensive name-brand 6DJ8 or 6922, just on the offhand chance the Chinese one it came with is bad. If the tube's at fault, and it's really as bad as you describe, then pretty much anything ought to be a huge improvement.


----------



## DKJones96

The pre-built kit comes with the 24v supply from 8audio.

 I agree with nemo tho, there should be zero lack of bass. Quite the contrary actually, I find that it is MORE than able to drive bass to the phones. For the power res cap, I used a 2200 because it was the lowest value i could find that would directly fit.


----------



## Nemo de Monet

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_I've decided to sell my first "super simple" to finance building a Bijou. It's on eBay if anyone is interested. _

 

Finally happened to look at the auction, and - good lord! - you drove speakers with this thing? Dang, skippy. 
	

	
	
		
		

		
			





 OT, but I'm kind of surprised you didn't try selling it on Head-Fi first; I'd think someone here looking for a headamp would snap it up in an instant.


----------



## biarritz

I used the power supply from 8Audio and also my own 24v power supply. No difference.
 My cans are AKG K300, but also tried a pair of Philips inear plugs (SHE- something). The AKG's are familiar for producing a bit too much bass, but with this amp nothing much below 100 Hz.
 For tubes I used the supplied tube from 8audio, but also some NOS Philips gold pins that I use in my KT88 push pull integrated amp.
 For a source I use a DDDAC with 24 parallel TDA1543 chips and my Philips DVD 963 SA player.


----------



## kansei

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_Finally happened to look at the auction, and - good lord! - you drove speakers with this thing? Dang, skippy. 
	

	
	
		
		

		
		
	


	


_

 

They're tiny speakers. I use two of the surround speakers in my "lab" and drive them with my Millett or the "super simple". HSU Ventriloquist VT-12

  Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_OT, but I'm kind of surprised you didn't try selling it on Head-Fi first; I'd think someone here looking for a headamp would snap it up in an instant._

 

I had mixed feelings about posting it here at first because of board rules - I didn't want it to look like I am running a business (which I'm not, just trying to scrape up project $). Also, I stink at negotiating and selling on eBay usually works out well for me.


----------



## Nemo de Monet

Quote:


  Originally Posted by *biarritz* /img/forum/go_quote.gif 
_I used the power supply from 8Audio and also my own 24v power supply. No difference.
 My cans are AKG K300, but also tried a pair of Philips inear plugs (SHE- something). The AKG's are familiar for producing a bit too much bass, but with this amp nothing much below 100 Hz.
 For tubes I used the supplied tube from 8audio, but also some NOS Philips gold pins that I use in my KT88 push pull integrated amp.
 For a source I use a DDDAC with 24 parallel TDA1543 chips and my Philips DVD 963 SA player._

 

What value PIO did you replace C101/C201 with? Also, have you checked and made sure that R101/R201 are actually 1Mohm?

 The only other thing I can think of is to try adjusting R110/R210 (the trimpots) and see if they make a difference; otherwise I can honestly say I'm stumped.


----------



## ludoo

Quick question: did you use insulating pads on the heatsinks? I don't think they are necessary, but I'm probably wrong.

 Also, I almost finished soldering the parts and I just noticed my trimpots have an horizontal screw instead of a vertical one, and are not accessible. Meaning I'll have to order two vertical ones and delay completing the amp yet again, lol.


----------



## DKJones96

I didn't use them. Actually, I realized yesterday that I didn't even apply thermal grease(oops) so I've got to come up with a way to get the right 310 unscrewed without having to desolder and remove the 317 in front of it.


----------



## biarritz

Thanks for all your feedback regarding my bass problem. Today I finally had the time to purchase some new parts.
 I added the attenuated input with two 470k ohm resistor running to ground.
 I changed the input cap from 0.1uF to 0.47uF
 And changed the output caps to 470uF.
 The first change with the resisters was the best so far. Bass slightly improved as well. Changing the caps did not improve things noticable to me.
 I adjusted the trimpot to see what this improved. They were originally set to about 16 volts. Above 18 volt the soun starts to fade. I decreased to about 12v. But no hugh changes in the bass regions.
 It sounds not that bad now, but still I would like some more bass to it.


----------



## ludoo

I just turned on my Super Simple a few minutes ago and it works great! It actually sounds pretty nice, plenty of details and very nice mids, even with brand new caps that still need to settle. It might be placebo, but I think it has the potential to sound better than my boutique Starving Student, which has a fatter but less precise sound.

 I used a NOS Russian 7DJ8 tube (got plenty of those and NOS Philips/Amperex 7DJ8 too) so I tweaked the LM317 resistors to serve slightly less current (2x150ma). I used boutique parts: Silmic II electrolytics, Obbligato film caps, and an Alps Blue Velvet pot. There's zero hum or noise.

 Now I will have to concoct a case tall enough to accommodate the huge 1000uF Silmics, probably from wood and aluminum.

 Edit: forgot the pic.


----------



## kansei

Congratulations, Ludoo.

 I just tried the Philips JAN ECG 6922 tube and it's by far the best tube I've ever heard in this amp. It's very light and airy. The mids and highs are incredible.


----------



## ludoo

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_Congratulations, Ludoo.

 I just tried the Philips JAN ECG 6922 tube and it's by far the best tube I've ever heard in this amp. It's very light and airy. The mids and highs are incredible._

 

Well, I can't wait to try my 7DJ8 Philips on it. I'm listening to it now, and it sounds in a different league from my SS. I'm really glad I built it.


----------



## kansei

I'm about to build my second one. Just need some heat sinks, trim pots, a potentiometer and misc input and output connectors. Still trying to get a good deal on heat sinks, looking at eBay seller wonderco_buy79 who has some reasonably priced goodies.


----------



## DKJones96

Where do you guys have your bias set to? I've had to turn mine to where the flat spot on the trimpot is facing the 317 on their sides to get even sound from my phones. (might be an arrow on yours, depends on what pot you are using)

 Can the tube really be that imbalanced?


----------



## ludoo

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_Where do you guys have your bias set to? I've had to turn mine to where the flat spot on the trimpot is facing the 317 on their sides to get even sound from my phones. (might be an arrow on yours, depends on what pot you are using)

 Can the tube really be that imbalanced?_

 

My trimpots are turned about the same on the two channels. I have multiturn trimpots so it's hard to say, but when I set them up with the multimeter there was quite a bit of play in both directions before I found the right spot.


----------



## kansei

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_Where do you guys have your bias set to? I've had to turn mine to where the flat spot on the trimpot is facing the 317 on their sides to get even sound from my phones. (might be an arrow on yours, depends on what pot you are using)

 Can the tube really be that imbalanced?_

 

I've had some tubes turn up on a single channel only until I adjusted the trim pots. You can measure DC on tube pin #1 and #6 (connect a multimeter between the pin and ground) and adjust for the same voltage. The middle ground for my amplifier is around 20V, although I am unable to adjust some of the tubes I tried below 25v.

 However, it's tough (impossible?) to hear the difference unless you're too low on one of the channels and fading out.


----------



## Nemo de Monet

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_Can the tube really be that imbalanced?_

 

Yep, even if it's supposedly "matched". From what I recall from the old SOHA Mk. I threads, low-voltage amps like this use the tubes outside their intended design specs, so even with tubes that have been "matched" at more normal operating voltages, "your mileage may vary".

 I still haven't installed trimpots in mine yet (too busy listening to it, and trying to debug a dumb USB connector issue on another project), and am just using, I think, 470ohm resistors in each side. So far most of the tubes I've tried haven't had any audible inbalance, and the one that did - a "matched" 6DJ8, actually - was slight enough that it was correctable with a little tweak of the Windows balance slider. Maybe I'm just lucky, but all the tubes I've measured have been within 1V, section-to-section.


----------



## digger945

Looks great ludoo. Love those Obbligato's. You got a secret stash of Silmic II's?
 Good to see you guys enjoying this amp, I knew you would really like it a lot. I got some strange looks at the recent meet when I said the output on the aikido was 4 voltage regulators. Never would believe they could sound so good.


----------



## ludoo

Quote:


  Originally Posted by *digger945* /img/forum/go_quote.gif 
_Looks great ludoo. Love those Obbligato's. You got a secret stash of Silmic II's?_

 

LOL no, I just found a great and reasonable online seller in Germany who carries lots of nice stuff, including the Silmic II. And I don't get why in a simple amp like this many people go cheap on the caps: when you factor in all costs, boutique caps are maybe 2% or 3% difference on the total.

  Quote:


 Good to see you guys enjoying this amp, I knew you would really like it a lot. I got some strange looks at the recent meet when I said the output on the aikido was 4 voltage regulators. Never would believe they could sound so good. 
 

I am liking it quite a bit, it's definitely more detailed and musical than the SS and costs about the same (and is much easier to build). The only minor thing is it starts distorting at about 75%-80% volume, which is loud but still reasonable with the hard to drive HP-3 I am using. I will probably try to add bypass caps for the cathode bias resistors to try and get some more gain. If I had the money and time for a larger build, I think the Aikido would be my choice.


----------



## Nemo de Monet

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_And I don't get why in a simple amp like this many people go cheap on the caps: when you factor in all costs, boutique caps are maybe 2% or 3% difference on the total._

 

There's this tendency to think cost + complexity == quality, which I think this amp shows isn't true. But also I think you have to keep in mind that a goodly number of popular DIY amps, in particular, have been designed and marketed as "second best" versions of bigger, more expensive, more complicated, and "better" amps, and still more have ostensibly been designed to be first and foremost cheap to make; as such, _some_ people don't see the point in putting "good" components in something that doesn't "deserve" it. (I think it was over on the other forum, but someone a long time ago made some disparaging remark about putting boutique caps on an AlienDAC, saying something to the effect of 'why put high-octane gas in a Geo Metro? it's never going to go _fast_, no matter what you do to it'.)

 That said, there's a big difference between boutique and, you know, gold-plated-fairy-wings-in-unicorn-blood _boutique_. Sure, Obbligatos and Elnas are "boutique", but it's not like we're talking about Jupiter or Mundorf levels of "boutique", here. 
	

	
	
		
		

		
			





  Quote:


 I am liking it quite a bit, it's definitely more detailed and musical than the SS and costs about the same (and is much easier to build). 
 

I don't have a SS, but after a while listening to this amp with a decent power supply, I'm finding it more enjoyable than a SOHA Mk. I with JISBOS. Which saddens me quite a bit, because I have a lifetime supply of 12AU6-family tubes stashed away. 
	

	
	
		
		

		
		
	


	




 ...and, needless to say, it's a lot easier to build than a SOHA Mk. I, as well.

 Of the tubes I've tried so far - GE, Sylvania, and RCA 6AU6; JAN Philips 6922 - I'm really, really liking the Philips 6922; once it burned in a bit, it's really, _really_ nice. I haven't done any RMAA tests, and don't really plan to, but my impression is that it may be a bit more linear than the other tubes I've tried. To my ear - and this may just be me - none are lacking even the slightest in bass, and all reproduce highs quite well, but some - particularly the Sylvania - emphasize mids and vocals; I don't find this objectionable at all, as I rarely listen to instrumental music, and actually _like_ to hear what people are singing - but the Philips 6922 seems to have less emphasis here than any of the other tubes I've tried.


----------



## DKJones96

I've now got about 30 hours on my amp and I can say I'm happy with it. I've only been using my computer as a source for most of it since I kinda forgot two resistors to finish my bantam(oops), but I can say I've gotten addicted. I've been reluctant to continue use as constant as I really would like the fan installed and the cover done before I start using it daily. I'm pretty sure I'm within the safety margin for the chip but I don't like any electronics being hotter than i can hold my finger on.

 I think the success in this amp lies in its simplicity. Input cap -> tube -> fets -> output cap, that's it.


----------



## kansei

I'm halfway through building the second one. Currently missing 4 resistors, the 13 and 15 ohm ones. I'm considering putting in a 20 ohm or a 10 ohm resistor in their place to see if it will still work (I'm keeping this amp, so I may as well push the envelope). I'm also waiting on my heat sink order from overseas to come in.


----------



## ludoo

Quote:


  Originally Posted by *kansei* /img/forum/go_quote.gif 
_I'm halfway through building the second one. Currently missing 4 resistors, the 13 and 15 ohm ones. I'm considering putting in a 20 ohm or a 10 ohm resistor in their place to see if it will still work (I'm keeping this amp, so I may as well push the envelope). I'm also waiting on my heat sink order from overseas to come in._

 

Grab the resistor calculator app, determine the value you need (usually it's 1.25 / 0.33 * 2), set it in the app, you will probably find a couple of resistors you have or can easily find. That's what I did, only I used 300ma for the 7DJ8 instead of the 330 needed for the 6DJ8.


----------



## dBel84

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_ I think the Aikido would be my choice._

 

[size=xx-large]W[/size][size=x-large]H[/size][size=large]A[/size][size=medium]T[/size]![size=small]![/size][size=large]![/size][size=xx-large]![/size] - I have better plans for you me laddie 
	

	
	
		
		

		
		
	


	




 ..dB


----------



## MrSlim

So, excuse me for being lazy, but minus casing, what's the typical cost of building one of these puppies? I see the vendor has the boards for about 7$ right now on ebay, I might spring for one just for prosperity..


----------



## ludoo

Quote:


  Originally Posted by *MrSlim* /img/forum/go_quote.gif 
_So, excuse me for being lazy, but minus casing, what's the typical cost of building one of these puppies? I see the vendor has the boards for about 7$ right now on ebay, I might spring for one just for prosperity.._

 

Depends on where you are, and how far you want to go with boutique components.

 The heatsinks are a kind that's a bit hard to find, they are usually available on ebay for cheap but you'll have to add shipping costs. I bought 16 of them (2 sets of 8 instead of 2 heatsinks) so if you have problems with them I could ship you a couple.

 The LM317 are ubiquitous and should cost about 50 cents each. The other chips are harder to find, and the only reliable distributor has a minimum order I think of 20$. But then you could get a few and sell them to other people (or trade for heatsinks 
	

	
	
		
		

		
		
	


	




).

 The resistors are cheap of course, so no big problem there. The pot might be cheap as the PCB has holes foe one of the small Alps with a built in power switch (I splurged on a Blue Velvet which cost about 12 euros), and the connectors won't be a problem either.

 What you are left with are caps, ps, case and the tube. Caps might go from a few dollars to a few tens of dollars, depending on what you get. I used Obbligato film caps because I had a pair lying around but if I had wanted to stay cheap I could have used some Vishay caps which cost <1$ each, then bought some Silmic II which cost 12 euros all together.

 I have a few NOS 7DJ8 so I did not spend anything on the tube, but if you have a local dealer you should be able to get a decent one under 10$. The PS cost about 10 euros off ebay.

 All together, I think you could spend from 60-70$ up. In the EU, from 70 euros up due to higher prices and shipping costs. In my opinion it's totally worth it, it sounds very good (I prefer it to my boutique SS) and it's a really easy build.


----------



## ludoo

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_[size=xx-large]W[/size][size=x-large]H[/size][size=large]A[/size][size=medium]T[/size]![size=small]![/size][size=large]![/size][size=xx-large]![/size] - I have better plans for you me laddie 
	

	
	
		
		

		
		
	


	




 ..dB_

 

Oh lol, like what?


----------



## Nemo de Monet

Quote:


  Originally Posted by *MrSlim* /img/forum/go_quote.gif 
_So, excuse me for being lazy, but minus casing, what's the typical cost of building one of these puppies? I see the vendor has the boards for about 7$ right now on ebay, I might spring for one just for prosperity.._

 

I think you meant "for posterity", but anyway... 
	

	
	
		
		

		
		
	


	




 Like Ludoo said, it all depends on how boutique you go. 2SK117s are pretty cheap and plentiful, and it should be possible to sub a $1 IRF610 for the 2SK310s without difficulty. You'll probably need to spend $15-25 on a power supply, as well.

 Assuming you have no parts on hand, and get as much as possible from the same vendors, to cut down on shipping:

 PCB - $14, shipped.
 Tube - $15, shipped, or less.
 Socket, connectors, heatsinks - maybe $15, shipped.
 Transistors: 2Sk117s 3 for $3 shipped, on eBay; maybe $5 for everything else, so $8 total.
 Resistors: Maybe $10, if you use nice Dale parts and buy extras.
 Caps: Call it $15, shipped, for reasonably boutique parts.
 Pot: $12-20, depending on what you pick.
 Power supply: Call it $20, shipped.

 $100 USD should get you a very awesome sounding amp, less case. If you hunt around long enough, you can probably shave that down to $75 or so, and if you allow yourself $125, you should be able to use fairly boutique parts throughout. To be fair, the majority of the cost goes towards the most important parts - half the cost, more or less, is the power supply, volume control, and tube.

 Not as cheap as a Starving Student, but all of us who've built 'em seem to agree they're money well spent.


----------



## MrSlim

I don't know why I'm even thinking about this, since my CTH is sounding pretty nice.. but the fact that the Super Simple happens to use the same type of tube would mean I could share some of the same tubes as people have been playing with the CTH(using a Amperex 6dj8 in it at the mo..) and the board is cheap.. 

 Oh.. and thanks for correcting my Spelling Nemo.. 

 The Starving Student cost has gone up a lot with the demand on the tubes and the power supplies.. and the fact that the 19j6 is becoming more rare is only going to make it more expensive/unavailable..


----------



## kansei

Mine cost in the neighborhood of $80 to build, but I got the power supply for free (HP Deskjet power supply). It's easier to build than a Starving Student because it has a PC board. 

 I have an extra set of the hard-to-get transistors (2sk310 and 2sk117), let me know if you're interested. I had to buy 10 of each to meet the minimum order. I also ordered a ton of heatsinks if you need those (these have not arrived yet, but soon...)

 Take a look at one of my earlier posts which has a BOM attached to it. The BOM is not perfect, but it will set you in the right direction.


----------



## DKJones96

I finally got around to almost finishing this thing(casework that is), and I know a lot of us used the same case so I thought I'd let you all know what I did. I'll get pics up when I get it apart again to finish the case work but we have all been talking about the power fets getting hot with the regular heat sinks, and boy do they ever.

 I decided to go a different route than an acrylic case cover since it was so annoying with the PPA and decided to mount the 310s to the case itself using the insulators I bought for my starving student I haven't started yet. I've ran it for an hour and the amp itself is barely warm to the touch, the 310s are cool, the 317s are just as cool with the enclosure sealed up. I highly recommend doing this. All I did was solder patch wires between the fets and the board. However, I surface mounted my tube on the case and mounted the little sinks to the top(gave me something to screw into without an ugly nut) so that may effect how much benefit you get from this, but there is MUCH more surface area and mass on the case than those sinks offer. The tube is now the hottest running component, *by far*.


----------



## AnA1995

By looking at the schematic, notice that the capacitor C103 of 1000uF is rated only 25v. Is it enough for the input voltage of 24v? Just one volt more is not very safe I think. They should use capacitor of at least rated 35v. Please advise and appreciated. Thanks.


----------



## DKJones96

There is always some sort of margin for error built into those voltage ratings so staying 1 volt above is just fine. I have a 35v I think 3300uF cap in there because they don't make very many 25v caps with a 10mm lead spacing until you get to stupidly high capacitance ratings.


----------



## AnA1995

This afternoon, I went to the usual electronic component selling mall and found one shop selling a cap rated 80v of 1000uf which has 10mm spacing between the leads. So, once my amp arrive, I will do a measurement of the supplied power supply if it stay at 24v. If not, I may change it to higher rated voltage cap just to be on the safe side. Higher rating prolong the life span of the cap I think. Thanks..


----------



## Stevesebastianb

Here are some photos of the very same 6DJ8 amp that I am building which is almost near completion, should be finished this coming weekend!


----------



## DKJones96

You do plan on using larger heatsinks than the ones you used on the 317s for the 310s right? You'll roast those 310s in no time if you use those. 

 You cheated! You did the casework first, I think the first 100 hours of mine's life was spent on a table top lol. Nice work so far, what input caps did you go with?


----------



## Zigis

Just read this tread. Very interesting amp, however many unnecessary parts.
 R107, if you not use LED, R106, C105 too, don't now about C104.

 And most important, I wonder no one notice this before - input cap C101 - absolutely unnecessary, even harmful for sound quality.
 Amp owners, try to bypath input cap and tell us, what you hear.

 I am thinking, maybe I can try to build something similar, but with Aikido output stage with 2 x LM317, instead of 2sk310


----------



## DKJones96

Are you sure it's unnecessary? The grid has a DC offset which some direct coupled players may not like.

 I agree that R106 isn't necessary if you don't use the LED, however, if you want the LED to power up slower you can use a larger value for C105. The larger the value the slower it lights and dims when powering on. You could even get it to match the heater speed if you play with it enough.


----------



## Zigis

Yes, I am sure it's unnecessary in 99,9% cases, however I am not sure for what case reminding 0.1% are 
	

	
	
		
		

		
		
	


	



 You can see any todays tube amp schematics, headphones, preamp or integrated poweramp, you hardly find one with input cap before grid.

 Just minute ago I made a check. I measure DC offset on input of my MJ 6n1p hedamp with pot on max volume. Wen I turn amp on, there was 1 mV on 1 sec, then, wen amp is working there isn't any DC ( jumping between 0.1mV and 0)

 If LED is only for decorative purpose, not part of CCS or heater regulation, anyone is free to use or not to use it. I see folks reported amp work similar with and without LED.

 I see at this amp only as at schematic, not planing to order board. Especially I like simple and clever heater powering, no need special regulator or large hot power resistor.
 This is like in SS, only with widely available tube.

 Are 2sk310 and LM317 as hot as SS mosfets?


----------



## DKJones96

The 310s run SS hot, easy. The 317s run pretty cool when you are using a 6922/6DJ8 but I tried with a 6N1 (not enough gain at these low voltages) and it had 450mA vs 300mA heater current at 6.3 volts and the 317s ran pretty hot in that configuration. 

 I tried everything with that 6n1. 48v it sounded much better but the 317s got too hot for comfort and were running past their 40v in-out difference spec.

 Now that you mention it. I want to build a P2P version of this amp.


----------



## AnA1995

My biggest worry is the heat from those 2sk310. If it is as hot as Mosfet, I think I have to get a spacious chassis to house it with room for bigger heatsinks. But, the 2sk310 is on the PCB and thus limit the size of the heatsink we could use. Come to whose, will get additional heatsink to "join" to the existing one to increase the efficiency of heat transfer.

 Maybe de-solder the 2sk310 and clamp them on the chassis for better heat transfer if really needed. See how once I got my set...


----------



## DKJones96

I put my 310s on the aluminum chassis with isolators using wires from the pcb.


----------



## AnA1995

I got the amp yesterday. Tested and the sound is better than my CMoy amp.

 However, I have encountered two concerns here.
 1) The "pick-pop" sound during ON and OFF of the amp. Is it common for this type of output Transformerless amp?
 2) The heatsink is pretty hot for the 2SK310 MOSFET. 

 Humm...see how...


----------



## DKJones96

It does have a pop on startup. Since the tube has to warm up anyways I usually just turn the amp on when I get home and put my headphones on whenever I'm going to listen to them so it isn't a problem. Sometimes I never do listen to it and my headphones just sit there amping sound from shows or whatever I happen to be doing on the computer.


----------



## AnA1995

Thanks DKJones96, yes, the "noise" even happen by switching ON or OFF the main wall power. The noise is so powerful that it will definitely damage the headphone and our hearing. I am pretty concern. Read somehere a thermistor was use for such application. I am not sure how it is done. Anyone could advise. Thanks.


----------



## DKJones96

I've been trying to figure out a way to soft start it but can't come up with anything as of yet. The pop you hear is the output stage rushing up to bias and anything you do to slow that will cause the amp to sound different. Well, anything I've come up with anyways.


----------



## cfcubed

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_I've been trying to figure out a way to soft start it but can't come up with anything as of yet. The pop you hear is the output stage rushing up to bias and anything you do to slow that will cause the amp to sound different. Well, anything I've come up with anyways._

 

Guess you may be trying to come up with a solution short of something like amb ε12 ? Because it's much the go-to piece for this sort of thing. It's proven & transparent SQ-wise, except for those that believe they can hear the affect of relay contacts. But I guess incorporating such thing would not make this such a "super-simple" amp any longer.

 Otherwise its the pull the headphones plug bit during pwr on & pwr off for most (all?) direct/DC coupled output or capacitor coupled output headamps I would think.


----------



## AnA1995

As I am going to house this amp into a chassis, I decided to build a power supply for it. For 24v, guess I need a 18v-0-18v toriodal transformer. This is the first time building a power supply; so I decided to build a simple un-regulated PSU ( just bridge diode and capacitor). I am not sure if 120VA transformer is enough for this amp. Anyone kindly advise. Thanks.


----------



## DKJones96

I used an ammeter on this thing when it was running and while I don't remember the exact numbers it wasn't over half an amp with the heater running at 300ma. Playing it safe by doubling the power requirement and you've still only got 24VA. 

 I've got a cheap 24V x 1A (AD-270) switcher supply and it works great except for the fact that I question it actually being a switcher supply. I know it is regulated but it runs hot all the time which switching supplies don't normally do.


----------



## ludoo

I also use a cheap 24V 1A regulated switching supply I bought on ebay for like 12 euros, and it works quite well. If I were you , I would save the time needed to build the PS, get one from ebay, and build the amp in a smaller case. You also won't need to worry about safety, grounding, etc.


----------



## Stevesebastianb

Here is my completed amp, there is blog link: VR2XMQ - Steve's Blog AF through SHF: The Homebrew 6DJ8 Single Tube Headphone Project.

 Some photos:


----------



## Zigis

Finally I build p2p prototype of mixing this amp's input stage and 24V Aikido output stage. 2 x LM317 in output, no sk310 at all.
 Amp sound surprising nice, some small tweaks needed.

 DKJones96, you are right, there is large DC offset on grid, I build amp without input caps and get terrible noise wen turning pot (new Blue Velvet), with pot on max there is 240-300mV on input.
 I never had this problem before, just checked 6n1p MJ headamp with 300V powering and SS, both have 0V DC on input at any pot position.

 Why this amp work so strange? Too low voltage? 
 Is it possible to change input stage to avoid DC offset without input caps?

 Zigis.


----------



## Zigis

Strange things happening.
 I just installed input caps, now on grid is 450-500 mV, on cathode 23-35 mV, trimpot almost can't regulate output voltage - 19-22V (before it regulated from 11 to 22 V).
 One channel with trimpot on max and 21.5V on output not work at all, second channel work only with trimpot on max (19V on output)
 I connect 1K resistor in series with trimpot, get volt or two less on out with pot on max, but not enough.

 There is something wrong, I don't think larger voltage on grid than on cathode is normal situation.


----------



## Zigis

Anyone with good working amp, can you please measure and post here your voltages on cathode, grid and anode?

 Thanks, Zigis.


----------



## DKJones96

Anyone? I have mine cased where it is nearly impossible to get measurements easily.

 Are you measuring from ground to the tube? Got a schematic for the circuit you built?

 What value of resistor did you use between the grids and ground?


----------



## AnA1995

Hi Zigis, below are the readings. Hope it is helpful. 
	

	
	
		
		

		
		
	


	




 a=17.61V
 g=524mV
 k=106.4mV

 And the above readings are with 6DJ8 tube. 

  Quote:


  Originally Posted by *Zigis* /img/forum/go_quote.gif 
_Anyone with good working amp, can you please measure and post here your voltages on cathode, grid and anode?

 Thanks, Zigis._


----------



## DKJones96

Measured the amp. Including regulator losses it runs 22va with a 6922 tube. I would add another 3-5 to that if you are using the 6DJ8.

 Also, if you use a 6922 tube your R104/204 and R105/205 values should be 15 and 18 ohms. Not the original 15 and 13.


----------



## AnA1995

As I am using my mobile phone as the source for this amp; and I always heard those usual "receiving/ transmitting" noise from the mobile phone. The noise is so loud and causes the headphone diaphragm to vibrate badly to the extend that I need to take out the headphone out of my ears immediately when it happen. This problem not only will cause damage to the headphone, also cause damage to my ears in a long run. 

 Wondering anyone has the same problem with their amps? Not sure if the noise is from my phone or the phones nearby. I will use maybe a MP3 or CD player as source and see if the noise goes away. Does those tube "shield" helps?


----------



## AnA1995

Anyway, if come to worse, just switch the mobile phone to flight mode.


----------



## DKJones96

What carrier do you have? GSM(any phone with a sim card) commonly causes interference with audio equipment. CDMA(phones without sim cards) usually provides no interference at all.


----------



## AnA1995

It is GSM with sim card..... no choice I guess, only switch to flight mode when listening. 

  Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_What carrier do you have? GSM(any phone with a sim card) commonly causes interference with audio equipment. CDMA(phones without sim cards) usually provides no interference at all._


----------



## Nemo de Monet

If anyone should happen to still be interested in this design, I've tested and found that the IRF510/IRF610 work fine in lieu of the 2SK310s, and the 2N3819 can apparently sub for the 2SK117. I don't hear any difference in character versus the more exotic Japanese parts, and they're cheaper and more readily available. Also, I've become of the opinion that 1000uf for C103 may be inadequate; while 10,000uf is probably overkill 
	

	
	
		
		

		
		
	


	




 , upping that part to 1500uf or 1800uf IMO improves the performance, particularly the bass end of things, which this amp excels at.


----------



## ludoo

Time to buy a couple more PCBs then...


----------



## Nemo de Monet

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_Time to buy a couple more PCBs then... 
	

	
	
		
		

		
		
	


	


_

 

Perhaps. 
	

	
	
		
		

		
		
	


	















 We have the technology; we can make it better, and cheaper, and smaller (almost exactly half the size of the original).

 ...and then hang enormous heatsinks off the sides, completely negating the size advantage, lol. Overkill? Oh my yes! But it runs comfortably cool.


----------



## calico88

mine is smaller, I don't have the tech.
 this using cheapo component stright from the schematic.
 it sound cheapo also.

 just for fun

 cal


----------



## mikeythemars

I'm now over eight months into using this amp (a modified, upgraded version of the pre-built variant) and couldn't be happier 
	

	
	
		
		

		
		
	


	




 -- the sound from a high quality input (a.k.a. non-amplified line source directly from a CD, tuner or LP) is quite close to some _very_ high end amps I've been able to "test drive." As of this post, both the filled version and raw board are still available on eBay:

 Finished "plug and play" version ($76 + $19 shipping to U.S.):

Single End Tube Head Phone Amp Kit - Plug and Play - eBay (item 310154301644 end time Sep-07-09 10:36:07 PDT)

 Board ($7 + $7 shipping to U.S.):

6DJ8 Single End Tube Head Phone Amp Bare PCB for DIY - eBay (item 300338193470 end time Aug-19-09 08:57:41 PDT)


----------



## Nemo de Monet

Quote:


  Originally Posted by *mikeythemars* /img/forum/go_quote.gif 
_I'm now over eight months into using this amp (a modified, upgraded version of the pre-built variant) and couldn't be happier 
	

	
	
		
		

		
		
	


	




 -- the sound from a high quality input (a.k.a. non-amplified line source directly from a CD, tuner or LP) is quite close to some very high end amps I've been able to "test drive."_

 

Glad you're happy with it. 
	

	
	
		
		

		
		
	


	




 Care to share what you upgraded and modified? Volume control? Input caps? Output caps?


----------



## ludoo

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_We have the technology; we can make it better, and cheaper, and smaller (almost exactly half the size of the original).

 ...and then hang enormous heatsinks off the sides, completely negating the size advantage, lol. Overkill? Oh my yes! But it runs comfortably cool. 
	

	
	
		
		

		
		
	


	


_

 

Uhm, uhm.... I have two enormous heatsinks which have been sitting on a shelf forever. Somehow your post slipped by, what kind of PCB are you using? And is it with the original transistors or replacement parts?


----------



## DKJones96

There is only one amp I own that I would use more than this one(if it was presentable for work yet 
	

	
	
		
		

		
		
	


	




 ) and that's my OTL 6j6 headphone amp(aka The Space Heater, I actually have that on the front panel I'm ordering). However, I do find that the PPA is a better all around listener when it comes to different headphones. This amp pairs EXTREMELY well with headphones that are already reasonably balanced but with phones like the HD202s the PPAv2 sounds better strictly because of the bass boost.


----------



## mikeythemars

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_Glad you're happy with it. 
	

	
	
		
		

		
		
	


	




 Care to share what you upgraded and modified? Volume control? Input caps? Output caps?_

 

Sure:

 - Replaced both audio output capacitors with Auricaps. If anyone with the pre-built version has seen substantive improvement by upgrading the input caps or the volume control, let me know. 

 - Per recommendations from others, put the 470 ohm resistors (wire-wound) on the inputs. Probably why I have had no overdrive issues.

 - Running inputs and outputs via gold Neutricks (RCA in, 1/4 stereo out). Wiring on the input line between the RCA and the board is solid 24 gauge cat 5 wire, inside a copper braided shield. The RCA inputs are also shielded from the rest of the circuit by an aluminum shield. May be why I have no hum or noise whatsoever. 

 Also, the tube I'm using is a late 1960s Amperex. I have other CDJ8s, but after rolling them all through this I chose the Amperex (was the most sensitive and has the largest soundfield). Like any tube circuit, this thing is very sensitive to the quality and condition of the tube.


----------



## Nemo de Monet

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_Uhm, uhm.... I have two enormous heatsinks which have been sitting on a shelf forever. Somehow your post slipped by, what kind of PCB are you using? And is it with the original transistors or replacement parts?_

 

A little design I made up up that broadly follows the original we've all built, albeit with a couple of interesting changes. 
	

	
	
		
		

		
		
	


	




 It started off as a way to better heatsink the TO-220 devices, particularly the LM317s, but with the kind assistance of another fan of this design it's grown to become something rather better.

 I built the one in the photos with currently available parts (IRF610 and 2N3819), as it's just a prototype, really, but those devices just so happen to be pin-compatible with the 2SK310 and 2SK117, respectively, so if you were lucky enough to have a couple 2SK310s laying around, using them would certainly be an option.


----------



## ludoo

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_A little design I made up up that broadly follows the original we've all built, albeit with a couple of interesting changes. 
	

	
	
		
		

		
		
	


	




 It started off as a way to better heatsink the TO-220 devices, particularly the LM317s, but with the kind assistance of another fan of this design it's grown to become something rather better._

 

Can you post the schematics of the modified amp?


----------



## Nemo de Monet

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_Can you post the schematics of the modified amp?_

 

It really needs to be cleaned up a bit before it gets posted, as it's currently _very_ ugly.

 Circuit-wise, it's the same as what was posted back on page 1 of this thread, only with two slight adjustments to the LM317 heater circuitry suggested by DKJones, which should make it a lot more user-friendly in terms of tube interchangeability. (It should now accept both 6DJ8s and 6N1Ps, for example, without any changes or adjustments being required...) 

 (I guess, to be pedantic, that I also "recommend" changing the C101/C201 input caps to 1,0uf, and changing C103 to 1500uf or 1800uf... the former simply because that's what everybody seems to use anyway, and the latter because I unscientifically think it sounds better to me that way than with "only" 1000uf there.)

 Other than that, the only _really_ notable things are that it's been shrunk down to about 7x9cm, all the TO-220 devices are on the edge of the board and much easier to attach big heatsinks to, and the volume control and in/out jacks are offboard (i.e. panel-mount), so nobody feels compelled to use that little Alps pot or 1/8" jacks. 
	

	
	
		
		

		
		
	


	




 Nothing really new or exciting, sorry; for all practical purposes it's the same "super simple" amp we all know and love, only smaller and slightly easier to use.

 I hope to have all the details, Eagle and Gerber files, parts list and so on online in early September, once I've tested the (hopefully) final board design.


----------



## ludoo

Sounds really nice. 
	

	
	
		
		

		
		
	


	




 I'm not really interested in using 6N1Ps as I have a truckload of NOS Philips and Russian 7DJ8, which I really like in the "standard" version of this amp. I might build a perfboard version with your other mods though if I find the time, as I really like it.


----------



## ludoo

I spent a few minutes looking again for possible sources for the 2SK117 and 2SK310.

 I found out that the 2SK117 are pretty common everywhere, and cheap. My favourite online store in Germany carries them at about 50 cents each, so I won't need to find a substitute.

 The 2SK310 are trickier: some parts search engines list the 2SK3108 and 2SK3109 as equivalent. The specs are slightly different, but both the 3108 and 3109 are widely available, and cheap. I'm out of my depth here, anyone able to confirm they can be used as subs for the 2SK310?

 One of the parts engines also lists the IRF720 as substitute, and this too is cheap and plentyful. Again, what's the difference between the IRF510 and 720?


----------



## DKJones96

Looking at the different datasheets, I'm pretty confident that an IRF610/630 could be subbed for the 2SK310 and can still use the 2SK117(or substitute for an N-channel fet transistor of your choice).

 We aren't dealing with hardcore voltages here so what you are looking for in a substitute for the 2SK310 is a MOSFET that can handle the current you want to run. However, even at 8 ohms the optimal output power of this unit is 6 watts so the 310s that are called for are overkill.

 The 117 is there to set the bias on and be a very high impedance 'middle man' between the tube and the driver stage. As long as the replacement transistor has the same high input impedance it should work just fine.

 I may end up buying another one of these for some experimenting.


----------



## Nemo de Monet

Quote:


  Originally Posted by *ludoo* /img/forum/go_quote.gif 
_One of the parts engines also lists the IRF720 as substitute, and this too is cheap and plentyful. Again, what's the difference between the IRF510 and 720?_

 

Mainly, the maximum voltage and current handling ratings. IRF510, 100VDC, 5.6A. IRF720, 400VDC, 3.3A. Sure, on paper they don't exactly look like subs for one another, but the most they're ever going to see in this circuit is, what, 30VDC or so, at about 100ma?

 I went with the IRF610 (200V, 3.3A) in my prototype because it's cheap, common, has been used in a number of audio power amps, and I had a couple in my parts box. I ordered four IRF510s from Mouser... but accidentally got SMD versions, doh.

 If you're OCD about audiophile ju-ju, the IRF510 is apparently more desirable than the IRF610, or IRF720, or any other higher-rated parts, as it has a lower gate capacitance. At least, so say the crazy people who build enormous class-A space heaters with these devices...


----------



## ludoo

Thanks for the replies. I happen to have about 10 IRF510 and most of the other parts needed. And of course I still have about 12 heatsinks from my botched order for the first build. 
	

	
	
		
		

		
			





 So I guess I just need a few cheap 2SK117, a handful of resistors and some of the larger caps and I'm all set. Will try to fit it into a Galaxy case from Hifi2000 probably.


----------



## robertor

hi everybody,
 i open another time this 3D because i bought this headphone amp and have some problem: only 2,2v on the heater.
 someone can help me?

 thanks a lot.


----------



## nikongod

What are the other voltages around the amp?

 Can you tell from the schematic where things stop making sense?


----------



## robertor

hi nokongod,
 i use switching power supply 24v.
 not found the 2SK117 then used the 2SK170.
 not found the 2SK310 then used the BUZ90.
 the anode supply without tube is about 25v with tube 23,6v.
 betwee the LM317 and the R104/R105 i have 1,28v.

 thanks


----------



## snip

Hi there,

 I too have jumped on the bandwagon, currently have one PCB and a bag of sockets on order form 8audio.

 I have supply lines for the original specification FET's at resonable prices and have found those Wonderco sinks on eBay, so should be all set, when my PCB gets here I will see what caps I can fit on, I think I have some 1u Jensen's from way back in the day somehwere that I will go with in the input, and will likely settle on Nichicon MUSE FG for the electrolytes.
 Will likely go for .5W Allen Bradley resistors and the two 1W's also from Allen Bradley as they are resonably cheap from hificollective.

 So I can expect the valve not to glow much at all really right? In which case I probably won't bother fiddling with mounting the PCB back to top in the case and have the valve sticking up. Will just encase the whole thing and try to string together a bus powered USB DAC to plonk in there too, should be a nice little box for listening at work with a pair of SR60's or closed cups.

 Can't wait, I haven't built anything for ages.

 //Jan


----------



## Zigis

Quote:


  Originally Posted by *robertor* /img/forum/go_quote.gif 
_hi everybody,
 i open another time this 3D because i bought this headphone amp and have some problem: only 2,2v on the heater.
 someone can help me?

 thanks a lot._

 

R104,R105 and R204, R205 determine heater voltage, to be more exact, current true heater. For 6DJ8 about 7.5-8 ohms must be both resistors in parallel in each channel. 
 Check 15V on LM317 Vin first.


----------



## robertor

hi zigis, thanks for your reply.

 lm317 Vin:

 BG101 24,8v

 BG102 20,2v

 maybe there is something wrong.

 certainly i mistaked something


----------



## Zigis

Try to adjust with R110 and R210 abot 15V on both LM317 
 However with your higher voltage on "in" heater voltage must be good.

 Check R104, R105, R204,R205 resistance, they determine right current in heater.


----------



## robertor

thanks zigis, i will try to do.
 i'm inexperienced DIYer then the outcome not guaranteed.

 btw thanks a lot.


----------



## snip

Hi,

 Has anyone used the IRF610 instead of the 2SK310?

 I ask this because I have a bunch of these already and buying the 2SK310's in would cost me around £9, if the IRF610 is a go then I can go ahead and construct as soon as the PCB get here, then obviously I will need a valve but that should not prove a problem.

 Also, show me your cases! and tell me where you got'em, I am in a pretty remote area with no places around that sell that sort of stuff so am completely mail order.

 //J


----------



## snip

So I am in the process of assembling this amplifier, got the PCB from 8 audio, is it just me or is the tube socket meant to be on the solder side? As far as I can see it is.

 //Jan


----------



## jamesbobo007

No, the socket goes on the component side, Unless its changed since I built mine.
 Does the PCB look like the photo in the 2nd post on page 2 ? 
 If it does then it goes on the component side with everything else.
 If you want to post a photo ?
 This is a nice amp, you will enjoy.


----------



## snip

My board is the same yes,

 According to the tube data sheet, as seen here for example
TDSL Tube data [6DJ8]

 The grids are pin 2 and 7 right?

 Well if I look at the component side of the board, the two capacitors C101 and C201 connect to pin 3 and 8 and... Hang on, OMG I am such a dingbat, I just realised, I am ofcourse looking at the tube from underneath on that data sheet innit? Oh crumbs, now I had gone and soldered it on the underside and was getting all giddy about housing it so it would poke out the top and everything..

 Dang it, time to find the solder sucker...


 //J


----------



## fault151

Guys, does anyone have a BOM I could use for parts for the amp. I have read a few of you have tweaked parts based on the attached schematic. I was going to follow the schematic exactly as it is, but if there are a few tweaks that will improve the build, i may as well order them from the start.
   

   
  cheers
  Mark


----------



## Nemo de Monet

IRF610 should be fine, as some fairly popular commercial amps using this design use IRF630s, which have higher (i.e. worse) capacitance.
   
  Fault151: I don't have a BOM beyond what's been discussed previously in this thread; the important (IMO) changes that lots of people agree on are C101 -> 1uf or greater, and C103 -> 10000uf 35V.
   
  The input cap change is debatable, but the 1000uf power cap is way, way too small; 1000uf = anaemic bass, poor transient response, et cetera.  And 25V caps on a nominal 24V rail is bad, given that the amp will work happily (and sound good) up to 32V or so.  10000uf might be overkill (one of mine has 12000uf, which is definitely a bit crazy), but a lot of us have been happy with that, so...


----------



## fault151

Hi, I got a BOM from Kensei. I have ordered all the parts and will hopefully be putting it together as soon as I get time. Looking forward to building it.
kansei
kansei


----------



## benadski

I ordered a PCB a few days ago and will build this little amp with some modifications.
   
  -I plan not to use LM317's but TL783's. Why? Why not! 
	

	
	
		
		

		
			




  -IRF510's for the MOSFETs
  -Matched 2SK117's
  -Bigger cap on power (2700uF/50V)
  -The 13R resistor must be 18R because I'll use a JAN 6922.
  -Bigger input caps, 680N/400V fits nicely here.
  -I add power on delay to protect headphones and ears. (schematic will follow!)
   
  Now all I need is some decent headphones!


----------



## FallenAngel

Interesting choice on TL783 vs LM317, though I'm curious, ripple and noise figures are same if not better on LM317, why?  Especially since this is a CCS anyway.  I'd toss in a 1uF tantalum cap to lower noise as well, might make more sense.
  I don't think you need to match the 2SK117, they'll be adjusted via trimpot anyway.
  Certainly no need for a 400V rating input cap, and considering the 1M resistor, 0.1uF is plenty.


----------



## benadski

I read that the TL783 has better transient response and better in- and output voltage regulation. Since the current will be stable in this setup, the (input) voltage specs are important I think. Am I wrong? Also if I want to go for much higher supply voltage it's no problem! 
	

	
	
		
		

		
		
	


	



   
  Where would you like to add a tantalum cap? Not between the input of the regulator and ground I hope? I use 220uF low-ESR's at the output of the regulators. The power cap is a low-ESR type as well.
   
  EDIT: After reviewing the datasheets I think the TL783 has much better ripple rejection figures at rated current (with caps currently used). Maybe a cap between Vadj and ground will improve the figures of the LM317. The TL783 will not work very well wit a cap between Vadj and ground.


----------



## FallenAngel

I'm confused, are you building a power supply and want to use the TL783 or are you using this instead of the LM317 that's used as a current source in the amp?  I was thinking of the latter.


----------



## benadski

The latter. Sorry for the confusion! I want to experiment with different tubes, that's why I need some more juice. A normal LM317 might not be enough. The TL783 also is built for optimal performance without a capacitor on the adjustment terminal, a LM317 is not. That were my original criteria. I think that's why it will outperform a LM317. I overlooked the fact that in the schematic, the adjust pin is connected directly to the capacitors. The TL783 might work without the 220uF capacitors at about the same specs as the LM317 with the caps.
   
  But I think I have to listen for a long time to both setups to hear (or not hear) the difference.
   
  EDIT: Another thing is, there is a carefully hidden problem with the TL783. It needs more than 10 Volts between input and output! So that means about 17V is the minimum. It is in the datasheet, only once in the small print. This is another reason why it will not work with the original setup I think... 
   
  I'm back to the LM317 again! Maybe I'll order some HV ones.


----------



## yellowjeep

Can somebody post up a BOM? I have a pretty good idea of what is needed but having it all in one place would be good. This looks like a better alternative than the SSMH for me a this will be my first diy (well other than a impedance adapter). 
   
  I am planning to air wire the tube socket and FETs (I'm not even sure if I am saying the right thing, whatever is heat sinked) to the top of the yet to be determined enclosure, this should be alright correct?


----------



## Fred_fred2004

PM me your email address (I can't see how to attach an excell file) and I can send you one
   
  cheers
  FRED


----------



## yellowjeep

What dimensions am I look for for C104 and C105?
   
  EDIT: up to 12mm dia. with 5mm leads. I have read this thread thought like 3 times now and some how missed it on the first page.


----------



## yellowjeep

So my parts list is coming together, this is my first time doing anything like this at all so its been pretty slow going. I have a few questions about my cap selection. 
   
  For c101/201 I have 1uf 100v these were mentioned earlier on in the thread. 
   
  For c102/202 I have Nichicon KW 470uF 63v. I picked these because it was discussed early in the thread that 1000uF was was probably over kill. 
   
  For c103 I have a Nichicon KW 6800uF 35v. This is rated for audio I think KW might be part of the Muse series not sure.
   
  For c104/105 I have Nichicon FW 220uf 16v. These are 12.5mm in diameter I think these will should work even with the size difference.
   
  Can anybody tell me if these are decent choices?  I was looking for stuff rated for audio but I really have no idea what I am doing. 
  The rest of my BOM is Kensai's by way of Fred. There are notes on the BOM that r103/203 and r107/207 should be replaced with some thing of better quality since they are in the audio path but I don't know what to look for.
   
  Any help or comments would be appreciated.


----------



## jamesbobo007

Seems like good cap choices to me. If you want to get crazy, C102/202 are the ones to benefit most from "boutique" parts.
  I would check the size for C104/105, its tighter on the board than it looks but I dont remember the size exactly !
  Good luck, have fun !


----------



## yellowjeep

Any recommendations for the resistors? Or is that something I should just leave as is? Just to show how green I am I was thinking the Muse KW was a boutique cap. I think I am good with my choices based you what Beezar had to say about the, As far as the c104/5 goes the spec I found said 12mm with 5mm ls. I couldn't find anything on Mouser with the spec'ed rating at that exact size. The one I listed is 12.5mm with 5mm lead spacing so that is an extra .25mm all the way around, which to my mind seems pretty workable. I could be dead wrong though. Thanks for your reassurance jamesbobo007.


----------



## jamesbobo007

For the resistors I used what I had. Mostly carbon film but I did use carbon composite fro R103/203 and R107/207 because I had them.
  I did go open it up and check, I did use 12.2mm caps are they were too tight, I simply drilled another hole for the C104 a little further down the trace towards R106.
  You could also simply leave the caps up off the board some so they go over the resistors.
  In the pic you can see how tight it gets with the resistors right there.



   
 more pics here if your interested.


----------



## yellowjeep

That picture really helped. I think doing what you suggest for c104/5 either mounting it off the board or drilling. The pictures you linked to are exactly how I wanted to set mine up with the heat sinks out side of the case. I was planning on air wiring the FETs and the tube socket but I like how clean yours looks mounted on different sides of the board.
   
  I am wondering though how the tube socket is mounted? Does mounting it on the other side of the board simply change which channel goes to each triode? Also I am assuming the FETs are flipped 180 degrees to get the pins in the right place. Seems simple enough. I am also seeing that your FETs are socketed, I'll have too look for those. 
   
  Sorry for all the noob questions. I have no experience building electronics at all and these responses have been really really helpful and I can't tell you how much I appreciate it!


----------



## jamesbobo007

No problem, everyone here was new once !  and,,,sorry about your wallet.
  The tube socket is mounted to the case as are the mosfets. I "air wired" them as you say. I used jumpers, I just ran them in the back side of the board instead of the top.
  I used old floppy drive power cables for the Fet's, thats the sockets you see


----------



## Nemo de Monet

Oy, is this thread still alive? Amazing!
  Quote: 





yellowjeep said:


> For c102/202 I have Nichicon KW 470uF 63v. I picked these because it was discussed early in the thread that 1000uF was was probably over kill.


   
  It was convincingly (i.e. math was involved) argued somewhere that C102/C202 should be 1000uF, I think. It's not too hard to find suitable caps, so I tend to err on the side of caution there, per (dBel's?) advice.
   
  The discussions of overkill usually involved C103, the main power reservoir cap. I am absolutely convinced that the 1000uF specified there on the schematic is inadequate. Some of us have used caps as large as... 16000uF? there (I've got 12000uF in one of mine) to good effect, but I'm pretty sure everyone agrees this is overkill. 4700uF is probably a relatively safe and sane size that will sound good. (The most immediately noticeable benefit to increasing C103 above the "recommended" 1000uF is, erm, 'significantly improved low-frequency response', i.e. the bass goes from fairly weak and flabby to... _not_. 
	

	
	
		
		

		
			





 ) It should be noted that the cheap (in every sense of the word...) Bravo/Indeed 6DJ8 headamps that were all the rage a year or so ago used a (very very cheap) 6800uF cap here, while otherwise following the rest of the schematic as published, more or less (no input caps), and I'm pretty confident that their having done so is one of the reasons those little amps sound so good and were so popular, however briefly.
   


> There are notes on the BOM that r103/203 and r107/207 should be replaced with some thing of better quality since they are in the audio path but I don't know what to look for.


   
  I used some quasi-exotic resistors from Digi-Key, alleged to be identical to some pricey European boutique brand, but at a fraction of the cost. Alas, it's been almost two years, and I can no longer immediately remember either brand name. 
	

	
	
		
		

		
		
	


	



   
  They're green in color, but that's about all I know. Maybe someone else knows which ones I'm talking about.
   
_(God, this new post-editor-for-dribbling-idiots is annoying. If some moderator with the patience to understand this abomination wants to fix the formatting of this post... have at it, and more power to you. And to think, I'd forgotten why I rarely post here anymore...)_
 [/quote]


----------



## GT20v

Here is mine still in casing up progress..just waiting to get me out of the couch 
	

	
	
		
		

		
		
	


	




 does anyone tried the Indeed amp with our amp?
   
  which sound nicer?


----------



## yellowjeep

I am committed now! I ordered the PCB, 2SK117s and an NOS Russian 6N23P from eBay today. I am hoping that I didn't get the wrong tube but from my research I think they are direct equivalents. I realized that it might take up to 30 days for the tube to get here so I might wind up getting something else anyway... and I will start rolling tubes.
  
  Quote: 





nemo de monet said:


> _And to think, I'd forgotten why I rarely post here anymore...)_


 

 Well I'm really glad you did. I was actually just starting to wonder if the smaller input caps were going to be a problem since I hadn't found any picture with people using them.
   
  I followed James' advice and picked out some carbon composite resistors for r103/203 and r107/207 for a few cents more I figured why not. 
   
  I am trying to get my Mouser order finished up. I have switched c101/201 to 1000uf Panasonic FCs I read that these sound pretty good and there are a bunch in stock so that's a plus even though it breaks my all Nichicon scheme. On that note does the quality of c103 effect the sound or is it simply the capacitance  that is helping out the bass?
   
  I am going to sub the 2SK310s out for IRF510s because they are more readily available. 
   
  Now I just need to pick out the panel mount stuff. Any advice on a pot that is also a switch?
   
  PS. sorry about my stream of consciences posts. I get to typing out a reply and think of about 10 other things I want to say.


----------



## Nemo de Monet

I suspect that the "quality" of C103 (i.e. low ESR) has a certain effect, but no amount of "quality" will compensate, as far as I can tell, for too-low capacitance.
   
  Can't help you on a switched pot, as I never use 'em. As far as I'm concerned, the fact that the amp runs (by default) on 24VDC, and those illuminated vandal-proof pushbutton switches run on 24VDC, is a beautifully synergistic pairing just waiting to happen, like steamed rice and Japanese curry. 
	

	
	
		
		

		
		
	


	



   
  GT20V: I have one of the "Bravo" amps, which were identical to the Indeed, except for the engraving. I've discussed the commercial amp at the links below:
   
  http://www.slugsite.com/archives/1289
   
  and
   
  http://www.slugsite.com/archives/1357
   
  The short version is that the DIY "Super Simple" is superior in just about every way. The main differences - all shortcomings, IMO - in the Bravo/Indeed amp are:
   
  1, no input coupling caps
  2, unspectacular 25VDC output caps
  3, very very unspectacular 25VDC C103 reservoir cap with little space for a quality replacement
  4, IRF630s
  5, no fuse
  6, questionable heatsinking
   
  With regards #6, I've had my Bravo amp running 24/7 for around ten months now, and it's failed to blow up, melt down, fall over, or sink into the swamp. I may just be lucky, however. 
	

	
	
		
		

		
		
	


	



   
  In terms of sound quality, I'd say the "Super Simple", if built with reasonable quality components and sensible component values, has lower noise, better bass response, a generally livelier and more enjoyable sound, and better bass response, and can be safely run at somewhat higher voltages. The Bravo isn't *bad*, per se; a lot of people really like it, after all. It's just hampered by some fairly ignorant and short-sighted cost-cutting measures which prevent it from living up to its full potential.


----------



## yellowjeep

Alright I am still confused about about what pot I need and looking at the board isn't helping me much. All the pots I'm finding have 3 pins the board shows 6 holes. Well 5 because two of them share a trace, I am assuming this is just to reinforce the stability of a board mounted pot. I am also assuming that the rear most pot holes in the board are are a switch as I read that it is originally designed to take a board mounted pot/switch. 
   
  I also am confused by all the different types of LEDs and their ratings. I understand that this amp will operate with out but I would like to use an orange one to light the tube. 
   
  /noob


----------



## jamesbobo007

OK, well for the LED, pick your LED then use a calculator to figure the resistor value, like this one http://led.linear1.org/1led.wiz
  About the pot, you need a stereo pot, it will have 2 gangs each with 3 terminals. The board is setup for a pot with a switch like this one but at 100k not 10k


----------



## yellowjeep

Perfect thanks James! So the r106 is based off of what the value of r106, makes sense now I was thinking it was odd that there was only one for that position. Thanks for the advice on the pot too. When (if) I finish this amp will it be in no small part because of your help and everybody else in this thread.
   
  Am I correct in thinking that the rear most holes/pin for the pot are for a switch mechanism?


----------



## GT20v

Yeelowjeep,
  Yes you are correct. That is the switch. Mine came with alps pot that have the on-off switch built in. it occupy the whole 8pin.


----------



## yellowjeep

Thanks GT20v! I guess its what I am looking for doesn't exist so I suppose I will mount a rocker switch on the back and call it a day. 
   
  I used the link that James provided so my soft orange LED is a go. Just need to pick out a pot a switch and a power supply. I will worry about an enclosure after I know it works. Thanks again everybody.


----------



## yellowjeep

Alright. Everything is ordered but the PS and PS jack I still have to figure out what I am going to do there.
   
  This should be interesting.


----------



## GT20v

emo,
   
  Sorry I failed to read your reply earlier 
   
  Anyway thanks rot he summary of SSimple vs Indeed amp.....u just save me the money 
	

	
	
		
		

		
		
	


	



   
  but...i have some question here..
   
  1, no input coupling caps<<Isnt to be a better design not to have input caps? less stuff in signal path is better?
   
  2, unspectacular 25VDC output caps<<< This can be change to a better one I guess?
   
  3, very very unspectacular 25VDC C103 reservoir cap with little space for a quality replacement<<same as above unless space issue...
   
   
  just to see the diff btw Ssimple n bravo/Indeed amp.


----------



## Nemo de Monet

GT20V:
   
  1. In theory, maybe. In reality, it's not quite that simple, as, among other things, DC offset can become an issue. As far as I can tell they were omitted to save space and money, not for any dubious sonic improvement.
   
  2. You certainly can change the output caps (I've done so), but what were there were kind of laughable for an "audiophile" product. (Mine began leaking electrolyte within about six months.)
   
  3. You're extremely constrained as far as what will fit here, in terms of voltage + lead spacing + overall diameter. If you want a reasonably quality low-ESR 35V cap here, you'll almost certainly have to drop down to 3600uF, which may or may not be... suboptimal. My biggest complaint here is really that they used a 25V part on a 24V rail, a very noobish no-no, IMO.
   
  You certainly can replace all the elecrolytic caps, and the tube. Even the resistors in the signal path, if you're feeling really ambitious. At the end of the day you'd wind up with a cramped amp with a questionable layout, marginal heatsinking, no fuse, and no easy way to be mounted in an enclosure...


----------



## GT20v

yeah agreed..done my research abt indeed amp...I conclude our amp is better!yeah!


----------



## Zigis

I built this amp without board, p2p. Of course first upgrade, I made, was remove input cap (1 cap in signal path is better than 2). Then start scratching noise, wen turning pot, DC come from tube to pot.
  I can't eliminate Dc offset from tube grid/pot with so low 24V power. Wen I connect 48V PS from Starving Student amp, DC on pot disappear.
   
  So, in this schematic input cap is essential.
   
  Nemo de Monet, can you check DC offset on your Bravo amp pot? Are schematic slightly different?
   
  This Super Simple amp is not Sijosea amp copy, same principle , but different


----------



## Nemo de Monet

The circuit, as far as I can tell (I haven't checked every resistor...), is identical, save for the lack of input caps, and the addition of a tiny tantalum cap on each channel between the drain of BG201/BG202 and ground. On mine they aren't marked. What purpose they serve, I'm not 100% sure. Given the cost-cutting involved in making the things, I figure they're there for a reason, though.
   
  I'm not sure an actual accurate schematic was ever published for the Bravo or Indeed amps. On eBay, one of the two sellers, I forget which, was using Sijosae's old schematic, taken directly from HeadWize or wherever.
   
  I'll try to pop the bottom off mine tonight and see what DC is present at the pot, if any.


----------



## GT20v

guys...is there any significant improvement if i add tantalum caps btw output and adj pin of LM317?
  As per the datasheet?


----------



## yellowjeep

These are wrong part to replace the 2SK310, huh?
   
http://www.mouser.com/Search/ProductDetail.aspx?R=IRF510SPBFvirtualkey61370000virtualkey844-IRF510SPBF
   
  Fail on my part. I should have paid closer attention. EDIT ratshack had them go figure. 
   
  And while I am at it. I just want to double check that this is right 
   
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220630118644&ssPageName=STRK:MEWNX:IT#ht_1425wt_905


----------



## Nemo de Monet

Yeah, you want the through-hole TO-220 IRF510, not the SMD version. Don't worry, we've all done that. 
	

	
	
		
		

		
			




   
  And yes, those 2SK117s will do just fine.


----------



## GT20v

err any insight for my question guys??
   
  thanks


----------



## Fred_fred2004

Have a look at the TREAD supply
   
http://tangentsoft.net/elec/tread/
   
  Tangent expains the use of that capacitor in the text
   
  cheers
  FRED


----------



## GT20v

hi Fred,
   
  in TREAD Lm317 is used for voltage regulator,
  while here LM317 is used for current source.
   
  Im not sure if there is a benefit to it....


----------



## Nemo de Monet

Odds are they will have no meaningful effect, given that the LM317s are little more than constant-current sources for the tube heaters, a not-terribly-demanding application by almost anyone's standards. But, in the spirit of pseudoscientific inquiry, given that tantalum caps are only around $1 each, and you only need two, you could go ahead and add them, and see if you discern any appreciable difference...
   
  ...and then, because this *is* Head-Fi, sadly, you can then be accused of suffering from either the placebo or reverse-placebo effect, get flamed, perform a crude double-blind test, get flamed again, go and buy a high-end oscilloscope, make measurements suggesting the effect is for all purposes meaningless, have your equipment and methodology called into question, buy a *really* high-end oscilloscope, take a couple of college classes on analog-circuit design and statistics, perform new scientifically-valid tests which only confirm the first, inconclusive measurements, and come back to eventually publish your findings... only to be accused of hijacking the thread and get flamed. 
	

	
	
		
		

		
		
	


	



   
  Just saying...


----------



## yellowjeep

That's one of the funniest things I've ever read.


----------



## GT20v

Nemo, well said! I was laughing my lung out to the honest but scary truth from you.I can then sleep in peace..thanks


----------



## yellowjeep

So I am thinking of getting something like this for my power supply as 24v 1a is what I saw mentioned most often. But I have reread this thread (for like the 5th time) and I am curious as to what effect a 33v PS would have. I found a reference here stating that 36v works well but my power cap is 35v so I can't go that high.  


 I just wish my board/tube/heat sinks would get here so I can get to work on this thing so I don't have time to think up so many questions.


----------



## Nemo de Monet

That should work fine, though the Legion Of Very Anal Linear PSU Fanbois have some dogma-filled tracts they'll probably be sharing with you shortly on the many sinful and wicked moral and psycho-electrical shortcomings of a SMPS like that. I suggest you tell them where to stick their $75 toroids, but it's up to you. 
	

	
	
		
		

		
		
	


	



   
  You can go up to around 40VDC, if your capacitors are rated sufficiently. The most immediate effect you'll notice will be the output transistors getting even hotter. 
	

	
	
		
		

		
		
	


	




 As to whether you'll hear any difference... see comments above regarding placebo and reverse placebo effects, double-blind tests, flamewars, et cetera. 
	

	
	
		
		

		
		
	


	




 (In theory, more voltage = better, because it gets the tube closer to its intended operating point, which is something the many detractors of this amp like to whine about, despite not having built or heard one. In practice I'm unconvinced this is actually true, having tried PSUs up to 35VDC and not noticed an appreciable difference in sound or character. The extra power dissipated by the groovy space heater, on the other hand, is quite noticable...)
   
  Note that if you deviate from 24V supply, the bias point for the output transistors changes. As far as I can tell, the marked aimpoint of 15V is chosen because it's midway between the ~6V heater voltage and the supply voltage, so at 30V you want to aim for 18V, at 32V you want to aim for 19V or so, et cetera. Failure to do so might lead to gentle clipping when driving fairly large and inefficient loudspeakers at moderately high volume.


----------



## nikongod

Quote: 





nemo de monet said:


> That should work fine, though the Legion Of Very Anal Linear PSU Fanbois have some dogma-filled tracts they'll probably be sharing with you shortly on the many sinful and wicked moral and psycho-electrical shortcomings of a SMPS like that. I suggest you tell them where to stick their $75 toroids, but it's up to you.


 

  100% win


----------



## jamesbobo007

Quote: 





nikongod said:


> 100% win


 


  +1
  OT I know, but Nemo is on a roll !


----------



## yellowjeep

Its all coming together. Just waiting on the PCB and heat-sinks from HK/China.
   
  I got my tube today from eBay seller sneg_pnd78. I'm sure you guys already know about him but I just wanted to give him a thumbs up. I got the tube much quicker than I was expecting. Navships wire also arrived today. 
   
  Just because I am paranoid and know very little about tube I want to verify that this will work. From what I've read it should but I wanted to check with the experts. 
   
http://cgi.ebay.com/E88CC-6DJ8-6N23P-Russian-Tubes-ONE-More-NOS-/160465532983#ht_1884wt_1139


----------



## Nemo de Monet

Yep, the 6N23P will work just fine; I have a couple in amid my "hopefully lifetime supply of relatively inexpensive tubes".


----------



## yellowjeep

Sweet, thanks Nemo. I just ordered the PS I posted earlier, I sort of forgot about it. I wish I would have remembered as I will be stuck waiting for it now.


----------



## yellowjeep

Something interesting. I just got my board today started going though my box of components. For C104 and C105 I ordered these. The data sheet states that they are 12.5mm dia. but I just measured about 5mm dia. they are labeled 220uf 16v so I am assuming they will work its just odd that they would be that far off in size. 
   
  Edit. The data sheet says 6.3x11 so the product page is off. This should still work though correct?


----------



## Nemo de Monet

They'll still work. You can (almost) always make physically-smaller parts work; the opposite is usually not the case.


----------



## yellowjeep

They are on the board!
   
  Another snag, the trim pots I got are the ones listed on kansei's BOM. If I orient them the way he did in this picture using all three pins won't I be losing the adjust-ability and negating the point of the trim pot?  Do I need to clip the pin furthest from the adjustment screw? Sorry if this is a stupid question, I am way out of my element. These are the trim pots BTW


----------



## Pseudonyms

What kind of cans have you guys tested this headphone amp on, and at what impedance?
   
  I just picked up a pair of DT 880's @ 250 ohms, and I am curious if this would be a good amp project to work on


----------



## yellowjeep

Here is where I sit now. I did a lot of reading about pot and figured out how I needed to mount them.  I was expecting my heat sinks to be here today but no joy. The build has gone a lot smoother than I expected. I only misplaced one set of resistors but that got sorted quickly. Now I just need to figure out how to wire the input and output, time to do more reading. Here is  a link to an obnoxiously large version.
   

   
  Pseudonyms, I won't be much help as I haven't finished yet but I plan on using it with HD555s (that I am modding), HD280s and my KCS75s (also modded). I built a small 75 ohm  impedance adapter and I will try all of the said cans out with that too. Eventually I am going to build my self some Thunderpants, I have heard those synergize really well with hybrid amps.


----------



## ludoo

Quote: 





pseudonyms said:


> What kind of cans have you guys tested this headphone amp on, and at what impedance?
> 
> I just picked up a pair of DT 880's @ 250 ohms, and I am curious if this would be a good amp project to work on


 

 I use it with old Yamaha orthodynamic phones (HP-50A and HP-3), 150ohm, and it works beautifully.


----------



## kansei

I used Sennheiser HD600 and they worked very well.


----------



## Fred_fred2004

I've used mine with K702's and 600ohm K240's and it seemed to drive them very well
   
  cheers
  FRED


----------



## Nemo de Monet

I've used mine extensively with ATH-M30s (65ohms), and to a much lesser extent with RP-HTX7s (40ohms), some severely ancient ATH-5s (??ohms) and even some cheap old Koss UR-19s (32ohms), and have encountered no problems. Sorry, just not cool enough for high-impedance 'phones, I guess.
   
  They also drive 8ohm speakers really well, too.


----------



## yellowjeep

Delayed again. I finally got my heatsinks form HK yesterday only to find out that they are a way to small using the photos from this thread as a reference. I was going to just buy some from radio shack but their exceedingly crappy customer service made me leave before buying them. I went ahead and ordered the Wonderco heatsinks talked about early in this thread. I got an email form Wonderco about 10 min after I paid saying that they had already shipped, but it looks like I have another 2 weeks before I will finally get to listen to this amp.


----------



## Nemo de Monet

Just remember, if it was easy, anyone could do it. 
	

	
	
		
		

		
		
	


	




 Don't worry, though - it's definitely worth the wait.


----------



## yellowjeep

Still waiting on the power supply, Wonderco heat sinks worked beautify. I should have got those in the first place. Does anybody have a couple of random tube they wouldn't mind parting with, maybe something that didn't suit your tastes or just sounded bad. I am mostly interested in experimenting rather than finding a perfect tube at the moment so cheap would be good.


----------



## yellowjeep

MUSIC!
   
  So it works about 95%. I have some weird hum issues that I don't really know where to start with. I have a feeling that a lot of it stems from not being cased yet. The hum is minimized when I touch the power jack, and sometimes when I touch the pot at the same time minimizes it more. I also have the issue that others have described with the "bzzzzthemp" sound when the amp it turned on with headphones plugged in. 
   
  I also feel like there might be a channel imbalance but that could be that the soundstage is so much wider than the Fiio E5 I had been using. It could also be that everything has to work has to have some burn in time as well.  I haven't tried it out with anything other that my pair of Koss KCS75s but so far it sounds fantastic, just need to take care of the hum issues.
   
   
  Edit Sounds good with HD555 too


----------



## Nemo de Monet

The hum sounds like a grounding issue, but troubleshooting that can be "fun".  As to imbalance - this can often be due to the tube used, though djusting the trimpots may or may not help. This is where it helps to have multiple tubes to play with - the odds of two tubes being identically imbalanced are relatively slim.
   
  What kind of power supply are you using, and what's the output voltage? I've had some horrible problems with noise and hum with non-isolated supplies. I eventually settled on one of those 24V Meanwell SMPSes that are like $15, crammed into a plastic enclosure. Dead silent, which surprised me greatly.
   
  I'm not sure where you're at, but if you're really extremely desperate for cheap tubes to play around with in this, I've got and am happy to part with a new 6N23P that's only been used for an hour or so. Really very nice-sounding, just very very microphonic, which is subpar on a desk with two computers, in a house with four people and three cats. 
	

	
	
		
		

		
		
	


	




 I've also got a 1979-vintage Chinese military 6N11, that was "OEM" with one of those cheap Bravo Audio amps, which I'd be happy to get rid of. Don't really recall anything about it, to be honest. Probably not as good as the Electro-Harmonix 6922s, but probably better than the current-production 6N11s.
   
  There are some probably-quite-decent 6DJ8s and subs on eBay right now, quite cheap - including some 6N23Ps at a bargain price that are probably worth pouncing on. Otherwise if you hunt around a bit, you can usually come across NOS JAN 6922s for reasonable amounts, and all the ones I've tried (Phillips/Sylvania) have been extremely good. Ditto the Electro-Harmonix 6922, at least in the cheaper, non-gold-plated version.


----------



## yellowjeep

[size=medium]I am using cheap PSU I asked about earlier, this. I am also using this tube. 
   
  I think the imbalance issue is in my head rather than in the amp. I have been listening to the amp on and off all night and I feel like its switch from the right to the left now. I was sick a few weeks ago and ever since I have felt like I hear better on the left, its weird and I think I am just paranoid.  
   
  I am also having a terrible hum when the the source is unplugged. I am wondering if how I have the RCAs wired is a problem, I have them tied together and then one single wire running to the ground hole of the input on the PCB. 
  Like I said earlier the hum all but goes away when I touch hold the PS jack or I just discovered if I touch the headphone jack, it might be that I am using wires that are way longer than ideal for the PS. I'm pretty much stumped  
   
  Funny thing, I originally had the RCAs grounded to the extra hole for the PS and I was picking up NPR when the volume was turned all the way down.
   
   
  I'd be happy to take those tubes off your hands just interested in trying others. I'm in KS. ​[/size]


----------



## yellowjeep

I am in the process of casing my amp up. I still have to drill a hole for a switch, I already drilled a huge one thinking I could get it large enough for my switch but no dice, so I am committed to my big switch. Lesson learned I suppose. I also need to find somebody with a stepped drill bit and a drill press to do the hole for the tube and possibly some vent holes. I am thinking about a craigslist ad with a 6 pack in return for 3-4 holes drilled. The rest of my case work is acceptable I suppose but I will do somethings differently next time. 
   
  That said, I still have hum coming from somewhere. Most of it is gone after grounding the pot but there is still quite a bit when there is no source plugged in and even where there is there is still a low level hum that is independent of volume.


----------



## yellowjeep

I think I have the hum issue solved. I am just waiting on a plastic DC jack and a stepped bit to finish this thing up.  I scored an Amperex Bugle Boy that sounds amazing but is slightly microphonic compared to the 6N23P which also seem over built.


----------



## ppklok

Hi. Could someone share "the" BOM? As my pcb is still in post I don't want to wait another week for rest of the parts..
   
  Btw which factory is your 6N23P from, yellowjeep ?


----------



## yellowjeep

The tube is from the Reflector factory according to the eBay auction.
   
  There is no "the BOM" as far as I could tell. Here is a link to the original BOM Kansei put together. FWIW for my build I used most of the resistors listed in the BOM but substituted all of the caps and a few resistors in the audio path, the BOM is a good starting point but half the fun, for me anyway, getting to be really picky about what components I was using. For instance using a larger than specified cap for C103, there are tons of recommendations in this thread.  
   
  Edit: C103 is the main power cap and the schematic calls for a 25v 1000uf electrolytic. I think its been universally agreed upon that 25v probably doesn't leave enough margin for error when using a 24v power supply. I personally used a 35v 6800uf Nichicon Muse and I know others have sometimes been using caps north of 10000uf . Food for thought.
   
  Read though this thread for other substitute ideas. Some of the MOSFETs are hard to source. I replaced the 2SK310 with IRF510s from Radioshack. I'm done rambling. If you have any other questions I will try to help, I owe it to the community to pay it forward.


----------



## ppklok

Great, Kansei's bom looks almost the same as what I have figured out from the photos. Is that correct that only R101/R201, R104/R204, R105/R205 and R109/R209 needs to be 1W, rest 1/4W.
   
  I have a Panasonic EVJ volume pot which is only 50k so is possible to use it instead of 100k pot?
   
  I agreed, the MOSFETs are quite hard to get especially if you don't want to order from many vendors. I think I will use IRF510s and 2N3819s.
   
  For tube I went for Voskhod 6N23P because some people claim that it's "better" than Amperex PQ's. Even if it's only a opinion for under five bucks I think it's worth of trying.
   
  Thanks.


----------



## yellowjeep

From what I've read the value of the pot determines two things, noise floor and how easy it is for your source to drive the amp. So the higher the value of the pot the the easier the amp is to drive but the trade off is that you also have a higher noise floor. In most of the threads I have read people seem to favor 50k pots a good compromise, I think you will be alright with the Panny.


----------



## Pseudonyms

Would this capacitor be suitable for use in the C101/C201 spot?
   
http://www.futurlec.com/Capacitors/C100UPF.shtml


----------



## FallenAngel

Yes, Wima MKS4 is quite nice.


----------



## Pseudonyms

Very cool. I'm almost done assembling my list.  The whole electrolytic capacitor business has got me in a jumble though. So many choices.  What are the spacings on them again?


----------



## GT20v

Quick question.....
   
  is the fuse really needed here? is it ok if I omit it?


----------



## yellowjeep

You could but why? If you have a spike in power or you short something when adjusting bias you will fry transistors and all kinds of stuff rather than just a cheap fuse.


----------



## GT20v

well..it just that im using a regulator....unnecassary stuff in the signal path....i dont see a power spike as issue...


----------



## yellowjeep

Go for it then


----------



## MrSlim

Quote: 





gt20v said:


> Quick question.....
> 
> is the fuse really needed here? is it ok if I omit it?


 


  So, you are going to rely on the house circuit breaker that your amp is plugged into to protect you from an error in wiring in the amp from destroying expensive components in the amplifier. That means that 15 amps of current will be flowing through the mistake before the breaker trips.  That can do a lot of damage.
   
  Unless I missed something, there are no fuses in the signal path in this design(no one does that anymore), they are strictly in the power supply.


----------



## lehtinel

Bump goes the thread. I was wondering if someone could help me with picking resistors for this amp. I'm unable to find single or assorted places to find 13ohm or 35ohm resistors. I live in Finland so if anyone can point to a ebay seller I would be thankful.
   
  I've decided to go with this amp after my Cmoy trials, should be interesting, Im in no hurry though, I'll get the PCB in the upcoming weeks and start picking up the rest of the parts.


----------



## lehtinel

Still looking for an assortment of suitable resistors, i've seen a few on eBay that contain most of the ones I need, although not the ones I mentioned earlier. I've put up a part list which is about 70€ for me, with Elna Silmic II electrolytic caps and Dijon / ICEL polypropylen caps. Othervise maybe a JJ / Elextro Harmonics tube and a Hammond box to put the stuff in.


----------



## ludoo

Quote:


lehtinel said:


> Still looking for an assortment of suitable resistors, i've seen a few on eBay that contain most of the ones I need, although not the ones I mentioned earlier. I've put up a part list which is about 70€ for me, with Elna Silmic II electrolytic caps and Dijon / ICEL polypropylen caps. Othervise maybe a JJ / Elextro Harmonics tube and a Hammond box to put the stuff in.


 


  I'm compiling a BOM with European sources, will have it ready today or tomorrow if you are still interested.


----------



## nanaud

Hi Lehtinel, I'm starting this project too.
   
  I can see, as a lot of dudes here, I have the "XR01" board bought on 8Audio ; the same can be found on eBay.
  After purchasing a miserably chinease low quality "Indeed/Muse/Bravo style" headphone amp, I started to upgrade it ; but finally, the lack of space for components pushed me to start a new one from scratch, with audio quality parts only.
   
  I have my parts list, with a reseller in France and a few abroad.
  Both 13 and 15 Ohms are available in quality equiv. to Allen Bradley :
  http://cgi.ebay.fr/5-resistance-carbone-13R-1-4W-5-carbon-comp-resistor-/280610280678
 http://cgi.ebay.fr/5-resistance-carbone-15R-0-5W-10-carbon-comp-resistor-/270693226513
  TIP : you can change the 13 & 15 Ohms // resistors by 1 only resistor = 6.9 ~ 7.0 Ohms @ 1/2 W (it will only dissipate 1/4 W)
  The LM317 is used as a current regulator (not a voltage) : see http://diyaudioprojects.com/Technical/Voltage-Regulator/
   
  I've found 6R8 resistors 0.6 W that could fit (provide 184 mA instead of 180 mA).
  http://cgi.ebay.fr/25-resistance-couche-metal-6R8-0-6W-1-Philips-MRS25-/270680801009
  As they're not on signal path, a metallic layer resistor is good enough.
   
  If you want so, I could buy the hole list (usually 5 to 25 components per "item") and send you what you need in 1 only enveloppe in Finland.
  I'll check if he can have the hole list, even not on eBay, he sold me different parts several times, he's sending only to France.
   
  Also I have a plan for 2 6922/6DJ8 tubes (either from ITT or Jan Philips).
  What do you think about that ?
   
  Arnaud


----------



## nanaud

I completed the list.
  I share here the spreadsheet ; it's public so you can add comments (in red with your name).
  Of course all the parts are available in France and I can send you elsewhere (with the real postal fees, no margins from me).
   
  https://spreadsheets.google.com/ccc?key=0AtupC_2cbmp3dE1jVmdQODkwY0xRZHA0aHR1U1JCUEE&hl=fr&authkey=CNiB584C


----------



## nanaud

BTW, in France we have SCR / Solen MKP caps (you may know the PB-MKP -FA / -FB / -FC series for XO filters).
  They are a good value for a low cost ; of course, the higher quality the higher price. Up to 110 µF or 200 µF.
   
  Ex.
  0,1 µF Polypropylene (630 V) @ 1,50 Eur
  0,1 µF Polypropylene / Tin foil @ 3,80 Eur
  0,1 µF Teflon / Tin foil (1000 V) @ 32,50 Eur


----------



## lehtinel

Quote: 





> If you want so, I could buy the hole list (usually 5 to 25 components per "item") and send you what you need in 1 only enveloppe in Finland.
> I'll check if he can have the hole list, even not on eBay, he sold me different parts several times, he's sending only to France.
> 
> Also I have a plan for 2 6922/6DJ8 tubes (either from ITT or Jan Philips).
> ...


 


  Hi Arnaud, this sounds interesting indeed, it would help me in getting the resistors. Im not concerned about the rest of the part list, I can get everything from casing to the tubes and in between here in Finland. We could continue going trough details in private messaging.
   
  Regards,
   
  Lasse


----------



## ludoo

Most of what you need can be found from banzaieffects in Germany. You only need to
   
  * get the proper heatsinks from ebay (the link is in my list)
   
  * get the 2sk117 from ebay (they are pretty cheap)
   
  * swap the IRF-510 for the Hitachi transistors
   
  * add to-220 mounting kits or use locally sourced screws and thermal paste (you can get it from banzaieffects too, or any decent pc store will carry it)
   
  In my list, I used resistor values for the 7DJ8 tube, which needs less current. And a few items are optional, like the voulme pot (I use locally sourced Alps blue velvets), but it should give you most you need from Banzai. With nice Cerafines for the output caps, good but cheap Wima for the input caps, etc.
   
Link to spreadsheet here


----------



## nanaud

Yes, we could replace rare & expansive 2SK310 by simple IRF510 ... but I've read that IRL510 (or IRL530) gives better results with expanded banwidth.
   
  I've bought both and tried IRL510 then replaced 1000µF poor output caps by 2200µF Elna Silmic II and the 2 upgrades expand the higher bandwidth, gives more spacial image and clarity ; my caps were new and they will give better after more than few hours. Notice that you have to find good/thick heatsinks for the IRL ones !
   
  But maybe it have been already talked thru these 25 thread pages ...?


----------



## nanaud

I hope I could reply to this soon !
   
  I've bought the "Indeed/Bravo" amp style, and I've been (not a little) disapointed.
 After a few upgrades - but it would need a lot - I'm starting a new, clean and quality drived project.
  I've recently found this forum where, apparently, a lot of folks bought the same ''XR01'' PCB
   





  
  Quote: 





gt20v said:


> does anyone tried the Indeed amp with our amp?
> 
> which sound nicer?


----------



## haz101

You think this would do the job?
   
http://cgi.ebay.co.uk/FC1237-Headphone-amplifier-protection-kit-DIY-C59-/120656345258?pt=LH_DefaultDomain_0&hash=item1c17adb8aa
   
  This would give the time for the amplifier to power up before the relays kick in hence no pop sound.
  Well this is what the relay's do on my TK2050 amp.
   
  I'm very interested in this headphone amp project I will have to definitely build my own!!
   
  The amount of advice on knowledge on is great will help me to build my own, keep up the good work!!


----------



## haz101

Has anyone tried using an 1000uf capacitor for C103 like on the schematic? 
  Reading through the forum people have commented that 1000uf its not big enough.
   
  I ask has I have a 1000uf black gate which I won off ebay dead cheap
	

	
	
		
		

		
		
	


	




 and would like to use it, I know that it would make the 
  biggest difference in C102/C202 but don't want to pay £40 for another one.


----------



## ludoo

Quote: 





haz101 said:


> Has anyone tried using an 1000uf capacitor for C103 like on the schematic?
> Reading through the forum people have commented that 1000uf its not big enough.
> 
> I ask has I have a 1000uf black gate which I won off ebay dead cheap
> ...


 


  I have 1000uf on mine and it works great. I suspect that unless you have a good DAC and excellent headphones, you won't notice much difference.


----------



## haz101

Well I will just see if I like it only being 1000uf.
  I've almost finished  just waiting for the 1k pots and tube socket its very frustrating as they were ordered a week ago!!
   
  I'm using Elna silmic II, K40Y-9 capacitors with IR510 mosfet and a Mullard ECC82 should be good.


----------



## haz101

Well I completed my build today fired it up for the first time and nothing
	

	
	
		
		

		
		
	


	



  Not even the heaters in the tube light up. I try to adjust the 1k pots but it makes no difference to the voltage, its always 24v exactly the same as the main input voltage.
   
  I think that the K117's may be damaged.
  ​


----------



## Nemo de Monet

Hmmn, I used to get updates when people posted to this ancient thread, but not any more.
   
  I'm not sure where you're measuring 24VDC at, so it's hard to guess what's wrong. You don't have the LM317s in backwards or something, do you? Did you include the LED? Are you measuring with the tube in the socket? Also, what variety of 2SK117 did you go with? I think you might run into problems if you're using the -Y or -GR versions.
   
  I'm one of those who tried a 1000uf cap for C103, the power reservoir, and one of those who maintains that's undersized. That said, there have been so many variations made of this design, with so many different components, that it's easily possible for pretty much any definitive statement to be disproved...


----------



## lehtinel

I started building mine today. Still missing heatsinks, a couple of resistors and such, but should have all parts by next week.
   
  This will be interesting to build and use after the Cmoy that was my first (been happy with that at work for little over half a year now). My configuration will be Elna Silmic II 1000uf caps on C103 and C102/202, I have 220uf/50v Silmic II:s for the C104/C105 spot too, but they won't fit in there, guess I will go for basic low-ESR caps here, any comments on the C104/105 cap choice?
   
  For C101/C201 I've got Wima 0.1uf, Solen Fast 1.0uf and Icel 1.0uf caps, guess I'll tinker about and see what sounds best (once i've got the thing running). My current tube is a cheap 12AX7 tube from my guitar amp, will probably change this once I've confirmed I have a working amp.


----------



## jamesbobo007

I had the same issue with C104/105. In my case, I was able to put in new holes for the pads of C104 a bit closer to R106. Worked for me, Here is a pic of my C104/105 http://i592.photobucket.com/albums/tt8/jamesbobo/6DJ8%20amp/JD8caps.jpg
  My other plan was to add a thru hole in the void area to the left of R203 and R209,for the Negative lead, bring it under the board back to the (-) pad and use the (+) pad as is. If you look at the pic of the board on page 2, 2nd post, it should make sense.
  3rd plan was to just leave it up in the air and bend the leads, there is plenty of vertical room !
   
  Enjoy !


----------



## lehtinel

Quote: 





jamesbobo007 said:


> I had the same issue with C104/105. In my case, I was able to put in new holes for the pads of C104 a bit closer to R106. Worked for me, Here is a pic of my C104/105 http://i592.photobucket.com/albums/tt8/jamesbobo/6DJ8%20amp/JD8caps.jpg
> My other plan was to add a thru hole in the void area to the left of R203 and R209,for the Negative lead, bring it under the board back to the (-) pad and use the (+) pad as is. If you look at the pic of the board on page 2, 2nd post, it should make sense.
> 3rd plan was to just leave it up in the air and bend the leads, there is plenty of vertical room !
> 
> Enjoy !


 


  Hmm...wouldn't it be possible to use the R106 + hole for the C104 cap. They are in the same line and if I am correct R106 is for the led only (which Im planning to skip anyhow). Would this work?


----------



## jamesbobo007

I see what your thinking but I dont think it will solve it, you wouldnt be increasing the space between the (-) legs of C104/105, which is where I had my size issue.
  But dude,,,no led ??  what good is a tube if you cant see it glow ? LOL
  Really, just get it running, clean it up later if you want.


----------



## lehtinel

Quote: 





jamesbobo007 said:


> I see what your thinking but I dont think it will solve it, you wouldnt be increasing the space between the (-) legs of C104/105, which is where I had my size issue.
> But dude,,,no led ??  what good is a tube if you cant see it glow ? LOL
> Really, just get it running, clean it up later if you want.


 


  Haha, I know, Im crazy, maybe I'll just stick in the small low-esr caps I'll get next week for C104/105 and put a BRIGHT led under the tube instead. We'll see, thanks for the input!


----------



## lehtinel

They do sit on the board by sacrificing the led resistor. R109 should just fit in there, it being a 1/4w resistor.


----------



## jamesbobo007

Awesome fix !


----------



## lehtinel

Quote: 





jamesbobo007 said:


> Awesome fix !


 


  Well, you got me into it so...the thanks go to you 
	

	
	
		
		

		
			




   
  Coupling caps arrived today, Solen Fast 1.0uf just snugly fitted in place. Minor soldering done today (aaah, holiday), waiting for heatsinks and the rest of the resistors, here tomorrow maybe.


----------



## lehtinel

Got the last parts on Tuesday, smaller heatsinks than I was expecting, I have some more, larger, coming in later, so I'll change them out. Other than that everything seems okay.  I didn't have time to connect input, output and volume pot before leaving on holiday. I connected my 24v 2.5A power supply to the board, but couldn't get any reading when measured from the PCB. The power supply itself gave out 23.8V measured from the input socket. 
   
  Any ideas? Should the board power up or does it have something to do with the pot missing maybe? 
   
  Well, no panic, ran out of time and will get back to the project next week when I get home again.


----------



## Nemo de Monet

Were you trying to measure voltages without a tube in place? That generally doesn't work on this design.


----------



## lehtinel

Quote: 





nemo de monet said:


> Were you trying to measure voltages without a tube in place? That generally doesn't work on this design.


 
   
  I've got the tube in place but still my measurements are at 0v all over the place. The PS gives out the correct voltage when not connected to the board. As soon as I hook it up Im at 0v. I should have time to solder the pot + input and output in place today, maybe that will change things.
   
  I can't see direct flaws in my build, other than leaving R106 + the LED out of the equation. You never know though


----------



## lehtinel

There seems to be an issue with my power supply. I can't get a reading from it now, it's brand new with short circuit and overload protection so I don't now what is up with it. Dont have any other 24v PS hanging around, tried an 12v / 1A PS and that gave a reading at the power input and behind the fuse.


----------



## jamesbobo007

This wont explain your wacky voltage readings, but where is your power switch for the amp?


----------



## lehtinel

Quote: 





jamesbobo007 said:


> This wont explain your wacky voltage readings, but where is your power switch for the amp?


 


  Not installed yet as Im not sure with the casing (the eddystone / hammond crule aluminium casing is teporary or a shell for someting nicer), I have one handy though. The jack is now directly wired to the board.


----------



## jamesbobo007

I asked because I dont see a jumper in the pads for the switch part of the pot ? With out a jumper in there you will read voltage at the jack and fuse, but not sure about any other points ??


----------



## lehtinel

Quote: 





jamesbobo007 said:


> I asked because I dont see a jumper in the pads for the switch part of the pot ? With out a jumper in there you will read voltage at the jack and fuse, but not sure about any other points ??


 


  You're absolutely right, will have to fix that, thanks!


----------



## lehtinel

Picked up a Compaq 19v / 3A PS at a local fleamarket, can only get 14v out of it though. This gets the amp running, but the sound is unbalanced and muddy.


----------



## lehtinel

Voilá, it works. Tried the PS I bought and it works perfectly now. Only thing i notice is minor buzzing in the background, it becomes louder when I adjust the volume from the pot. There's also a louder hum at the as i adjust the volume down. Guess this is some sort of grounding issue.


----------



## jamesbobo007

Glad its working !   Wait till you have it in its final enclosure before sorting out the hum.


----------



## jdkJake

Is it only when you are actually touching the pot?
   
  What kind of pot are you using? Generally, you need to ground the body of the pot otherwise you will form a ground loop every time you touch it.


----------



## lehtinel

Quote: 





jdkjake said:


> Is it only when you are actually touching the pot?
> 
> What kind of pot are you using? Generally, you need to ground the body of the pot otherwise you will form a ground loop every time you touch it.


 

  
  I've got the 100k Alps RK27 pot. I'd say there is a very slight hum even when Im not touching the pot and also a variation in the hum / distortion in the middle stages when I turn the pot. As a rule the humming gets louder when I grab the pot. 
   
  It will be touhing the aluminium casing in the end, so that might sort it out.


----------



## jdkJake

lehtinel said:


> I've got the 100k Alps RK27 pot. I'd say there is a very slight hum even when Im not touching the pot and also a variation in the hum / distortion in the middle stages when I turn the pot. As a rule the humming gets louder when I grab the pot.
> 
> It will be touhing the aluminium casing in the end, so that might sort it out.




Depends on how you attach the pot to the casework.

In any case, a quick test (and one resolution to the problem) is straightforward. On the back of the alps, there are little screws. Back one out ever so slightly and attach a wire behind it. Then run that wire to a ground point on your board. See if it cures the problem.


----------



## lehtinel

Quote: 





jdkjake said:


> Depends on how you attach the pot to the casework.
> 
> In any case, a quick test (and one resolution to the problem) is straightforward. On the back of the alps, there are little screws. Back one out ever so slightly and attach a wire behind it. Then run that wire to a ground point on your board. See if it cures the problem.


 

 Thanks for the tip. Did a quick fix and connected a alligator clip from the pot to ground. All the buzz is gone, I can turn the pot all the way and nothing appears. So as far as I can tell, it works as it should now. Very airy sound, good resolution, no distortion at normal or higher volumes.
   
  Yet to do any measurements from different spots, little unsure where to poke and I don't wan't to poke wrong - although the fuse should prevent big disasters. For now, some musical enyoniment...


----------



## lehtinel

The amp seems to be working solidly, waiting for some casing parts to finalize it. I have a slight background noise, could it maybe be fixed with the attentuted input that is referred to in the beginning of this thread?


----------



## lehtinel

Finally completely boxed up in the aluminim case, don't know if I will do a better case for it. Put 470k resistors for attentuated input and the last of the noise is gone. A good experiense after the Cmoy trials. Boxing it up has been the hardest part, it really takes hours on hours cutting cabels and preparing the case.


----------



## jdkJake

Pictures?


----------



## lehtinel

Quote: 





jdkjake said:


> Pictures?


 


  As you wish:
   

   

   

   

   
  Was real irritated at myself as I din't give the paint enough time to dry and also didn't leave the casing in a clean enough space while it was drying. But you learn...I guess. Good sound, next up is the GrubDAC, this amp will get some tubes to swap out and maybe a higher capacity power cap - well see.


----------



## jdkJake

Very nice! Thanks for sharing. I really like the knob.

Does it get very hot when running?

BTW, You should consider posting it in the build thread as well.


----------



## lehtinel

Quote: 





jdkjake said:


> Very nice! Thanks for sharing. I really like the knob.
> 
> Does it get very hot when running?
> 
> BTW, You should consider posting it in the build thread as well.


 

 Thanks! The knob really gives it a 70's feel  It stays relativly cool when turned on, I measured 47c inside the case. On the outside in doesint really get that warm.
   
  Thanks on the tip for the build thread, will post it there for sure.


----------



## sashaw

Just soldered up my board. I replaced 2sk310 with IRL510, and use CV5358 instead of 6DJ8. However, the output gives around 100mv AC and it does not work. Anyone can help? PS: I was buying resistors in a combo, so all of them are 1W rating, will that be the problem?


----------



## sashaw

I have tried the 1K trim pot so that pin3 on LM317 is 15v, however, after 13ohm and 15ohm, it gives 8v instead of 6.3v which is the tube required. can anyone suggest a solution?


----------



## berserkir

Finished mine, just waiting for friend of mine to do some drilling for box.
  Used Panasonic FC caps 1 x 3900uF, 2 x 1800uF, 2x 470uF and Roederstein MKT1813 1uF with EH 6922 tube
  Did few minutes test driving with some really old headphones and seemed to work well and the sound was awesome


----------



## audiowize

Has anybody cut the trace feeding B+ to the 6DJ8 and fed it with higher voltage?  With a 24v supply feeding the 6DJ8, how much plate voltage is there even (10-15v max??)
   
  Incidentally, with the voltage regulator sitting under the fet, you could probably jack the voltage up on both stages.


----------



## nikongod

The 6dj8 is DC coupled to the output FET. you cant really bump the plate voltage on the tube without increasing the voltage supply to the FET too. 
   
  Im not sure if the heat-sinks are large enough to handle the extra heat, or if the various caps are rated adequately, but it would probably be a fun project for someone who wanted to go a little wild with it.


----------



## vmedchagr

What happens if instead of a 100k you use a 50k or a 10k one ?


----------



## curiousmuffin

anybody tried using this as a preamp? can i wire rca outs parallel to the headphone jack without worrying about hum?
   
  and do all resistors get hot? i'd like to sneak in carbon comp resistors wherever i can if i can avoid the value drift.


----------



## Zigis

I design my own PCB variation of this amp
   

   
   
  Tube's socket is on top side, all other parts on other side. PCB are double sided, designed for Alps Blue Velvet pot, 6.3mm headphone socket, large power and output caps, bias trim pot.
   

   
  In my prototype amp FETs and LM317 are mounted to enclosure, however vertical heat sink can be used.


----------



## sashaw

Quote: 





zigis said:


> I design my own PCB variation of this amp
> 
> 
> 
> ...


 
  WOW, nice case.


----------



## ludoo

Quote: 





zigis said:


> I design my own PCB variation of this amp


 
   
  Great job! Have you got a couple of PCBs to spare?


----------



## Zigis

Boards are double sided, with ground plan, fixed with 2 screws near tube socket and pot's and headphones jack's nuts to front
   

   
   
  I have few board left, if anyone wants to try it.
  1 PCB shipped are 10 Euro


----------



## Zigis

Thanks ludoo, yes I have few


----------



## Zigis

Quote: 





sashaw said:


> WOW, nice case.


 
  Thanks, actually it is fast prototype, made from piece of aluminum U profile, lot of scratches, some drilling errors. 
  Idea is - black anodizing finish and side panels from good wood, walnut or bubinga. 
  I made it about year ago, project stopped because of lack of time and I can't find good anodizing service locally. Maybe I go to powdercoating route.


----------



## Zigis

As promised, here are schematic with parts numbers and values for those of you, who building amps with my boards.
   
   

   
  There is small differences. At power input I use CRC filter, partly independent for each channel. C4 is shared for both channels, then R8a, C3a go to right channel, R8b, C3b go to left channel.
   
  I find with some NOS Russian 6N23P tubes I can't get 15V at input with original 1K trimpot, changing to 2K pot solve problem. Use 2k multiturn trimpot, this is more universal.
   
  For power filtering and output I use low ESR 1000uf 35V PanasonicFM caps.
  Instead of original 2 parallel R104/R105 I use single 8.2 ohm resistor in each channel. (R7a,R7b on my board)
   
  Amp's gain is about 10, too much for my needs. I use at input series resistors x2 - x3 of pot value. This make input signal attenuation and increase amps input impedance. In photo you can see - RCAs are connected to boards input with 100k resistors, instead of usually wires.


----------



## KimLaroux

Clean design, I like it. I've got a few questions though regarding it, mind to educate me? 
	

	
	
		
		

		
			




   
  Is there an audible difference with using a CRC filter? Is the background noticeably quieter?
   
  How do you go about calculating the appropriate values of capacitors and resistors in such a filter? Do you use an equation or a simple rule of thumb?
   
  Why did you add a 10 ohm resistor to the output of the amplifier? There seems to be a general myth here on head-fi that lower output impedance is best. It's interesting to see someone adding a resistor to the output...
   
  Thanks for taking the time to share your experience, it's appreciated.


----------



## ludoo

Quote: 





zigis said:


> As promised, here are schematic with parts numbers and values for those of you, who building amps with my boards.


 
   
  I got the board a couple of days ago, and it's very well made, thanks a lot for the schematics!
   
  If you make another batch, would it be possible to design it with larger capacitors? In my old build I used the Elna Silmic II, but they are too large for your board.


----------



## Zigis

Thanks, KimLaroux.
  I have not made A/B tests with and without additional RC filter, however I believe PS filtering and cleaning never can be too much.
  What exactly we hear in phones or speakers? We hear PS, slightly modulated with audio signal
	

	
	
		
		

		
			





, think about it this way.
  Even if PS dirt is not listenable as background noise, it can reduce music clarity and transparency.
  To be honest, I did not made special calculations, just take large enough low ESR caps and 1 ohm was what lying in my part box and what I usually see in others low voltage CRC PS filters.
  Schematic I posted is mostly for part numbers, related with my PCB, they are different from schematic in the page 1 in this thread. Part values is just what I  use in my build, anyone can recalculate and use something slightly different.
   
  10 ohm resistor in output is from original schematic (page 1 in this thread), I believe it is for protecting FET from short circuiting wen plugging phone jack on working amp.
  If you believe, you can always plug and unplug phones with amp off, newer with amp on, you can short this 10 ohm resistor, probably gain in sound quality.


----------



## Zigis

Nice to hear, you got the board, ludoo.
   
  If I made changes on board (in fact going to order completely different board) expenses are larger. Only if there are interest for at least 15-20 boards, price will stay reasonable (about 10 euro). The same PCB, without changes, I can reorder in smallest quantity and same price.
   
  If there would be large enough interest, we can discuss changes and make new board design.
  One handy extra, I can imagine - additional contact pad with small hole for DMM probe, for 15V point on each channel. After each tube changing small 15V correction required.
   
  One thing, I forgot to say before. PCB maker forgot to make 2 x 3mm mounting holes for screws near tube socket, however i make them in file. For my amp I drilled holes myself.


----------



## curiousmuffin

i must have the worst luck, my amp not even working on the first try and the only place to to turn to is a thread that's no longer active... but here goes 
   
   all my transistors r from dubious sources. irf510 could be fake, lm317 also. and then i got 2sk30 instead of 117 because that's the only suitable one the shop owner could offer.
  the amp doesn't work. 
  at first i realized i installed the 2sk30 with wrong pinouts. (they need to be turned 180 degrees) and then after fixin that, the amp still doesn't turn on. no tube glow, heatsink heat, sound, nothing 
   
  voltage reads 24v across every pin. resistors, tubes, caps. i did use 220uf caps in c102,103 instead of 470uf, and 230ohm instead of 220ohms where specified. i don't think they matter as much, do they?
   
  i really hope to hear that it's probably the nfet transistor.
   
  PLEASE HELP!


----------



## curiousmuffin

it works now after changing the fuse. i had 1a slow blow fuse when my psu was 1.8a.  i put 2a fuse in, did the star grounding mod, and now the sound is simply gorgeous. for the price it's a steal, and it's actually the best headphone amp i've heard in my limited experience.


----------



## KimLaroux

Quote: 





curiousmuffin said:


> it works now after changing the fuse. i had 1a slow blow fuse when my psu was 1.8a.  i put 2a fuse in, did the star grounding mod, and now the sound is simply gorgeous. for the price it's a steal, and it's actually the best headphone amp i've heard in my limited experience.


 
   
  This logic is wrong. It's not the power rating of the PSU that dictates how much current flows trough the fuse, it's the power the amplifier actually uses. Look at it this way: the AC power socket in your room are rated for 15A, does everything you connect to them uses 15A? An electric trimmer pulling 15A would be powerful enough to cut down a tree. So no, a wall socket is rated 15A because it will melt (actually, the breaker should trigger) and catch fire if you load it with more than 15A. And that's why your fuse should never be higher than the current rating of your PSU. The point of a fuse is to protect the power supply against overload and short circuits. Using a 2A fuse on a PSU rated for 1.8A is useless, you might as well have no fuse. The PSU will die before the fuse blows. And if you're using a switching PSU, then the fuse really IS useless, since switching PSU have overload and short circuit protections built in.
   
  The starving student amplifier uses around 350 milliamps, or 0.35 Amps. These amplifiers being very similar, I would venture in saying they use about the same amount of power. Actually, this one could be more efficient than the SSMH since you can limit the current bias using the LM317. A 0.5 Amps fuse would be a lot more appropriate.
   
  Which makes me think, was the original fuse blown when you put it in, or did the amplifier blow it? Because if the amplifier actually blew the 1A slow blow fuse, there might be something wrong in your circuit. Aren't the heat sinks getting overly hot? No wires melted yet?


----------



## curiousmuffin

well i wouldn't call this a logic. more like a foolish assumption out of not knowing what the heck i was doing. x) 

logic calls for fundamental reasoning- electrical knowledge is hardly a requirement for that. 

everythings working soundly as far as i can tell. and the amp actually runs much cooler than i expected.

i do have a 24v 5a psu tho. i think i wanna try this out with the same fuse.


edit: I hooked it up to the said psu and the sound is much more powerful and sweeter. lm317 sinks are now almost too hot to touch.

here's the sorry state my amp's in atm. the 'casing', for the lack of a better description, was done in hurry with a handsaw with some scrapwood, just to elevate the amp of the ground. in the future it will be housed in a proper chassis with the tubes and caps sticking out on the top.

i tried to use boutique components throughout as this unit was also going to serve as a preamp in my main rig. panasonic thsa 10000uf smoothing cap with a pair of blackgate 220ufs. outputs are silmic ii 1000uf bypassed with mundorf supreme. the red ones are .33uf jantzen supreme, and carbon film resistors in most locations. 

sound is simply gorgeous. rich, powerful and very tubey with that inevitable mosfet 'sheen' that i actually like.


----------



## Zigis

All my PCBs are sold out.
  If someone are still interested in boards, please let me know. I can order new bunch, if there are interests in at least 7-10 boards. They made ordered PCBs in one week, usually.
  Zigis


----------



## ludoo

Zigis, I really like your PCB. One suggestion though: if you make a next revision, could you leave more space for larger caps? In my build I use the Elna Silmic II but they are too large to fit on your board. It makes sense to leave space for good components, since you already designed the board with a good pot in mind.


----------



## Zigis

Hi ludoo, yes I remember about caps. As I say before, I can make changes if there is enough interest in boards. Any change in layout manufacturer understand like "new design" and this is more expensive than just repeat existing board (they use old templates).
  b.t.w., what diam. is your Elnas? 17mm? PanasonicFM 1000uf 35V are 13mm.
   
  On board are missing 2 wholes, 3mm diam. for mounting board to enclosure. I drilled wholes myself.
   
   

   
  Here is board layout wit marked with yellow missing wholes. This is manufacturers fault, I hope in next bunch this will be fixed.


----------



## ludoo

The Elna Silmic II 470uF 35V are 16x31.5 mm, the 1000uF 35V 18x35.5 mm. Large caps, but they do sound good.


----------



## jsandin

Zigis I wrote to you about the PCBs, but I caught up on the thread and see you're looking for more interest.
   
  I can order 3x boards myself, and also request space for bigger caps please!
   
  Lets see if some other members are also interested.


----------



## Zigis

Hi jsanddin, I just read your PM.
  If you are willing to present board design, I can order PCB's tomorrow and they may be ready after week or so.
  If you prefer larger space for caps or any other change, new design PCB cost me about 150 euro. This mean, I can do it if there is interest for at least 15 boards for 10 euro each. Or less boards for higher price.
   
  In the mean time we can discuss changes and draw new board.


----------



## mkusan

Quote: 





jsandin said:


> Lets see if some other members are also interested.


 
  After already built one zigis board , I am interested in one more.
  Too say that I was impressed with the sound would be an understatement.
  However, I do not need more space for bigger caps, but if majority here decide on the new layout I will obey
	

	
	
		
		

		
		
	


	




.


----------



## Evshrug

Sorry if this a DIY only thread, but are these amps available as already assembled? I have a lot of interest in a nice tube amp, but I already have too many hobbies & time demands to train a new skill  So, I appreciate what all of you have invested in yourselves


----------



## Zigis

Evshrug, I can build one for you, if you like. Prototype, based on my own PCB, you can see in post 398.
  Details we can discus in PM.
   Zigis


----------



## Evshrug

I'll reply to your PM, but I'd just like to say (again?) to all the DIY'ers who are tweaking and experimenting, I am continually impressed by your enthusiasm, desire for knowledge and eeking out just a bit more performance, and community spirit.
A little random? Maybe. But where do discoveries come from, and how do we get new product configurations?


----------



## Zigis

I ordered new bunch of PCBs again, without changes. 
  3 boards will be left over, so if anyone are interested, let me know.
  Boards will be ready at the  end of next week.


----------



## Evshrug

mkusan said:


> After already built one zigis board , I am interested in one more.
> Too say that I was impressed with the sound would be an understatement.
> However, I do not need more space for bigger caps, but if majority here decide on the new layout I will obey .



Lol same here, and I am excited that the new order is underway!
I've been slowly reading this thread, read the last few pages before my first post, and since then about a page a day starting at the beginning. I think it's fascinating that Zigis built his first version of this amp over 3 years ago! I've been learning a lot just reading this thread and the Bravo tube amp thread, but Zigis must've learned a whole lot since then! Ludoo too, but... I'm not sure I'd hear the difference in the even bigger caps, lol.


----------



## jpaul64

Hi, two questions: what is the max. output power for 32R and 300R headphones? Thanks


----------



## jpaul64

I hope its successfull? ALT COPY and CTRL V! Schematics and Layout for new PCB.


----------



## jpaul64

I hope its successfull? ALT COPY and CTRL V! Schematics and Layout for new PCB.


----------



## jpaul64

nothing to see! Lets try jpeg...


----------



## ludoo

Pasting images in the editor does not work: images are only viewable in the edit window. Here are your images as proper attachments (image icon, then upload)


----------



## jpaul64

thanks Ludoo! Bizarre, my problem with the "insert image" icon is solve?!
   
  Hammond 1444-24CWW chassis.
   
  TKD CP-2500 or ALPS RK27112.
   
  MKS4, Mundorf MCAP or ZN coupling capacitors.
   
  The output capacitors are MKS4 220µF/50VDC/30VAC from WIMA, or electrolyt capacitor.
   
  Iset resistor can be MRA5 (5W), PR02 (2W) or MP930 (TO220).
   
  Tube, MOSFET and regulator on the top of the PCB.
   
  Board is 200x150mm.


----------



## Evshrug

Jpaul,
"Quote" ludoo's post to see the HTML code to post a picture.
If your image is already on the web, you can copy it and post it this way:
[ IMG ALT=""]_paste URL of pic here_[/ IMG]
Delete the spaces before IMG. There should still be a space between IMG and ALT.

Is this your version of the design? Have you built it yet? How much did it cost with those Mundorfs?

I think the PCB layout pic looks like a brain, with left and right hemispheres.


----------



## jpaul64

The grey outlined parts on the BOT; the brown outlined on the TOP. Heatsink should be a big custom one (simple alu bloc) thermally contacted to the metal cover of the case (Hammond or other).
   
  Low cost version: first start with the PCB. WIMA or any cheap MKT/MKP RM7,5mm. Electrolyt capacitor ELNA, PANASONIC and ALPS. No Mundorf or big output WIMA coupling capacitors.
   
  Waiting for christmas then upgrade: MUNDORF (coupling input capacitor for 2.6€ or 7€ and fast decoupling capacitors for 2,5€); WIMA MKS4 220µF/50V (don´t know the price? perhaps 10€/piece); Caddock MP930 8R0 (or other TO220 thermally coupled with the Mosfets). Forget the ALPS and choose TKD CP-2500 or better my coming standalone volume control.
   
  Two in serie VISION LiFePO4 +12VDC batteries (charging like gel batteries but with higher current) with Meanwell charger.
   
  The board is big enough for some experimentation. 30€/piece for 50 pieces ordering at PCB-POOL. Cheap amplifier if grouped ordering!


----------



## Evshrug

What is the output impedance that the headphone "sees" with this amp?


----------



## KimLaroux

Quote: 





evshrug said:


> What is the output impedance that the headphone "sees" with this amp?


 
   
  From the schematic, I'd guess 10 ohms. Anyone can confirm?


----------



## Evshrug

kimlaroux said:


> From the schematic, I'd guess 10 ohms. Anyone can confirm?



Yeah, I saw that, but admittedly my knowledge on amp component effects is minimal. Zigis theorized that the 10 Ohm resistor is there to keep from blowing out headphones as you connect them while the amp is powered on, yet amps like the FiiO E11 somehow manage with measured output Ohms of > 1 Ohm. And who knows if that the _measured_ ohms would match the rating of that one resistor?

How do other amps compensate for the headphone insertion event, and would a resistor of a smaller value be adequate (like 5 ohms)?


----------



## nikongod

The 10 ohm resistor is there to protect the AMP when you plug in headphones with the volume way up high. 
  A 10ohm resistor will not protect the headphones from much of a fault in the amp. 
   
  You could PROBABLY use a smaller resistor, but why? Lots of headphones sound great with a bit of source impedance and compared to what a high voltage tube operated at low voltage and current does to the signal a 10ohm resistor is nothing. 
   
  Keep a bit of safety factor, leave it in.


----------



## Evshrug

nikongod said:


> The 10 ohm resistor is there to protect the AMP when you plug in headphones with the volume way up high.
> A 10ohm resistor will not protect the headphones from much of a fault in the amp.
> 
> You could PROBABLY use a smaller resistor, but why? Lots of headphones sound great with a bit of source impedance and compared to what a high voltage tube operated at low voltage and current does to the signal a 10ohm resistor is nothing.
> ...




Safety is definitely important, don't want to ruin your equipment or, worse, hearing!

I have read that impedance matching headphones to 1/8 the output ohms is one more thing to help drive headphones to their full dynamic potential... I think that many people who see the 10 Ohm output and then may immediately write the amp off without even hearing it. A lot of the most affordable headphones are rated at 32 Ohms. But then, this is the Internet, full of conflicting reports and misinformation. Some people actively seek out things to raise impedance between the amp and headphone, like the Etymotic adapter to "convert" the ER-4p into the ER-4s. They say that it helps to dampen the background noise, which obviously would be great for tube amps (and vinyl LP record albums). Now you, Nikongod (reference to the camera brand? Love Nikons, almost got one instead of my Olympus), are saying that tubes for headphone amps (low voltage & current) add so much of their own distortion, that the output ohms doesn't even make a noticeable difference in comparison.

So, is there a grain of truth in all three perspectives, or what? How are we defining the effect of this distortion, anyway? When I would use the word "distortion" to describe a sound, I would say something like "The overdriven bass in that bad Kanye West song called 'Gold Digger' usually produces really bad distortion in low-fidelity headphones." Am I actually thinking of "clipping" instead of "distortion?"

Thanks very much for the information so far - I think I would have to take classes to learn all this for myself.

Also, my curiosity about possibly lower output ohms is purely selfish... I have a pair of 62Ohm AKG Q701 headphones, if the output was within that target of 1/8 the ohms of the headphone, I would have both the benefits of lower distortion AND amp protection. As they say, "have your cake, and eat it too."


----------



## nikongod

The 10ohm resistor wont do anything to protect your hearing, and probably wont do much to protect the headphones either. The 10ohm resistor is just there for the amp. 
   
  The objectively correct way to drive headphones implies that there is an objectively corect headphone. Ask the objectivists to identify the objectively correct headphone some time, its amusing if you like making fun of people. 
   
  The fact of the matter is that the largest difference between any 2 amps with any aspiration of "quality" is smaller than the difference between almost any 2 headphones... So until there is an objectively correct headphone (there will never be - measures flat VS sounds flat VS diffuse field) building an objectively correct amplifier is an interesting academic exercise but ultimately an exercise in futility. 
   
  Where does the damping factor rule come from? Certainly not from the IEC standard for driving headphones that specifies a 120ohm output impedance - which gives only a damping factor of ~3 with HD650 or 2 with any 250ohm beyer headphone... The damping factor rule comes from multi-way speakers where it only makes any sense because there NEEDS to be a standard so that things work across brands. When multi-way speakers started to become the norm in the 60/70s the companies that explained it best happened to be the ones that were very good at building ~0ohm output impedance amps. The companies that built VERY nice systems with everything designed as a system got left in the dust. 
   
  In headphone land where there are no crossovers (except in multi-way IEM's, which realllllllly need 0ohms, which just proves the need for 0ohm amps for things with crossovers...) the importance of achieving an arbitrary damping factor could even be counter productive. Quite a few headphones sound subjectively better with a decent bit of output impedance... 
   
  In the end the only way you will find the right answer is to experiment. Well, at least until the objectivists can identify an objectively correct headphone*. Heh, considering that there are half a dozen ways to measure a headphone (In onter words they cant even agree how to measure) you still have plenty of time on your own. 
   
  *How ironic would it be if the objectively correct headphone only measured correctly if it was driven by a 120ohm source impedance?


----------



## Zigis

Yes, 10 ohm resistor at output is to protect FETs, if output is shorted by plugging and unplugging phones on working amp.
  On the other hand, I just see Millett SS amp schematic, similar output stage (OK, different CCS, twice voltage, same IRF510) no output resistor. At least my SS amp work flawless several years now, and I often change phones on working amp.
   
  B.t.w., I got PCBs today, 3 are spares, if someone is interested.


----------



## Evshrug

NikonGod,
Just wanted to thank you for your highly instructive post. I have many posts where I write a lengthy analysis and response to what I've just read or been asked... But this won't be one of them. Do you mind if I link to your post in a thread I'm thinking about starting? I want to pull together interesting and useful information I read into a kind of blog that I can use as a reference, and share with others who ask the same questions.

Zigis,
Updates? You got the PCBs on the 16th...


----------



## Zigis

Yesterday I made test about 10 ohm output protection resistor necessity.
  I short amp's output to ground *before *output resistor on working amp, while music playing. First I try ground output on short moment, imitating TRS connection, then I shorted playing amp on 10 seconds. I try it with both channels in a row. Output FETs survival, nothing are damaged in the amp.
  So, my conclusion is - output resistors are not required for safety reason, at least with IRF510 at output (original China amp use different output FETs)
   
  If someone use my PCB, just solder piece of wire in R9a and R9b position.


----------



## Evshrug

zigis said:


> Yesterday I made test about 10 ohm output protection resistor necessity.
> I short amp's output to ground *before *output resistor on working amp, while music playing. First I try ground output on short moment, imitating TRS connection, then I shorted playing amp on 10 seconds. I try it with both channels in a row. Output FETs survival, nothing are damaged in the amp.
> So, my conclusion is - output resistors are not required for safety reason, at least with IRF510 at output (original China amp use different output FETs)
> 
> If someone use my PCB, just solder piece of wire in R9a and R9b position.




Interesting. Is there a way to use a fuse (either a self-sacrificing burn out fuse or a mechanical circuit breaker) in place of the resistor without sacrificing sound quality, thus gaining protection and low output resistance? Personally, I already am in the habit of turning my volume down before turning off my audio equipment and putting things away, because I hated the pop from the powered desktop speakers I used to have when I turned them off.

Btw I do have some experience building things. I learned several different construction techniques in my 3D design class, I took a class on metal smithing, and I put together my own computer. I just don't know much about circuit design and soldering that doesn't go with a blow torch


----------



## KimLaroux

Honestly, if you're gonna claim the resistor is there to protect against short circuit, the MOSFET will be the last thing I'd worry about. The IRF510 can easily push 20 Amps on a pulse. So everything before the MOSFET is more likely to fail before the MOSFET does. And even then, with the amount of capacitance on the power rails, the capacitors will not even have the time to discharge before you're done plugging your headphones in.
   
  I am more willing to believe that adding a resistor at the output will lower the overall gain of the amplifier, which may give you better S/N ratio.


----------



## KimLaroux

I just randomly thought about something. Since the resistor is after the output decoupling capacitor, it adds to the impedance of the RC network. This translates into less bass roll-off if you use the amp with low impedance headphones.
   
  Though a resistor as low as 10R will not change much if the output capacitors are over 500µf.


----------



## Evshrug

Quote: 





kimlaroux said:


> I just randomly thought about something. Since the resistor is after the output decoupling capacitor, it adds to the impedance of the RC network. This translates into less bass roll-off if you use the amp with low impedance headphones.
> 
> Though a resistor as low as 10R will not change much if the output capacitors are over 500µf.


 
  Did you think of this after reading TKdockweller's (sp) ODAC review? I'd like to actually see measurements and hear it for myself, but I'll probably never work up the ambition to clear the myth for myself.


----------



## KimLaroux

Well, no, I haven't read his review. I'm steering away from reviews nowadays, since I don't need to buy more stuff. Though now that you seem to make a link between what I said and his review, I think I'll have to go read it just to see how what I said matches what he said.
   
  I actually thought about it during my shower. I always get the most random Eureka moments in my showers...


----------



## Evshrug

kimlaroux said:


> Well, no, I haven't read his review. I'm steering away from reviews nowadays, since I don't need to buy more stuff. Though now that you seem to make a link between what I said and his review, I think I'll have to go read it just to see how what I said matches what he said.
> 
> I actually thought about it during my shower. I always get the most random Eureka moments in my showers...



Lol, indeed reading reviews are wallet-dangerous. Just so you know, I tend to make obscure links between things... I actually see the link in a comment posted on the last paragraph of the review. Here is the comment, so you don't have to read a review/temptation:
-------
doktorsteve 9/28/12 at 3:22am
Science guy here - re the last paragraph. The output of the ODAC has a fairly large capacitor to ground right on the output. Most of the difference between cables is due to capacitance (IMHO). This interacts with the output impedance of the DAC (or whatever) and can upset the output buffer to some extent. In the ODAC the capacitor swamps the cable capacitance in most cases so the cables all sound the same.
-------

So... Basically I don't think what I read has much to do with what you though of. For someone like me, with former engineering aspirations before a major change in focus, it is interesting to juggle these concepts around in my head.

P.S. I also have eureka moments in the bathroom, though usually while on the porcelain throne/ thinking stool.


----------



## nikongod

Quote: 





evshrug said:


> P.S. I also have eureka moments in the bathroom, though usually while on the porcelain throne/ thinking stool.


 
   
  My best ideas come to me while dropping a deuce.


----------



## Evshrug

nikongod said:


> My best ideas come to me while dropping a deuce.




And my best singing is done in the shower! However, I keep my audio gear (and any microphones!!!) away from such a humid environment.

I should be able to enjoy this amp sometime next week!


----------



## Evshrug

Well, amp received. The craftsmanship is beautiful and luxurious. The damping on the volume knob reminds me of the damping on the zoom rings of high-grade camera lenses. I love the fit and finish of the unique and charming enclosure. But unfortunately, the tube didn't survive the mail. Anyone seen good 6DJ8 tubes for sale recently?


----------



## ludoo

Quote: 





evshrug said:


> Well, amp received. The craftsmanship is beautiful and luxurious. The damping on the volume knob reminds me of the damping on the zoom rings of high-grade camera lenses. I love the fit and finish of the unique and charming enclosure. But unfortunately, the tube didn't survive the mail. Anyone seen good 6DJ8 tubes for sale recently?


 
   
  I have a few NOS 7DJ8, they are practically identical to the 6DJ8 and sound great in this amp. But it would be uneconomical to ship them to the US... Check on ebay, a single tube won't cost much.


----------



## Evshrug

Yeah, not too expensive, I just wanted to show off my rig to the only other audiophile in my family (my dad) when I drive 11 hours tomorrow to go see him. It's just bad luck.

Would this pair (so I have a spare) be a good value?
http://www.ebay.com/itm/2-Vintage-JAN-Sylvania-6DJ8-ECC88-Stereo-Tubes-/181023926212?_trksid=p3284.m263&_trkparms=algo%3DSIC%26its%3DI%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D21%26pmod%3D400340551355%26ps%3D54

How about this one?
http://www.ebay.com/itm/1956-FOIL-RCA-5963-12AU7-12AU7A-BLACK-PLATE-Vintage-Amp-Audio-Radio-Tube-Valve-/160926216892?pt=Vintage_Electronics_R2&hash=item2577f332bc

Woah!
http://www.ebay.com/itm/12AU7A-Sylvania-vacuum-tubes-38-tested-strong-made-in-the-USA-/190754532129?pt=Vintage_Electronics_R2&hash=item2c69db2b21


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## KimLaroux

Are you certain the 12AU7 can be used as a replacement for the 6DJ8? Retailers seem to sort these as two different types of tubes. I'd verify this amp can use a 12AU7 before buying a new tube.


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## Evshrug

kimlaroux said:


> Are you certain the 12AU7 can be used as a replacement for the 6DJ8? Retailers seem to sort these as two different types of tubes. I'd verify this amp can use a 12AU7 before buying a new tube.




You know, I think you're right. I must've gotten the tube families mixed up from researching the bravo/indeed amps. After my last post, I found this resource... A good one?

http://www.audiotubes.com/6dj8.htm


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## Evshrug

Zigis' amp has been maintaining itself as my favorite, really enjoying it with my Sylvania and Bugle Boy tubes; I have some Vokshods now too, but I haven't had the time or compulsion to roll them in yet, the ones I have tried sound so good! Stuck on the Bugle Boy right now. Zigis sent me some new side plates, but I'm trying to find the right kind of screwdriver head to put them on.


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## Zigis

Evshrug, you need Hex key or hexagon L key, something like this
   
   

  They are available in any hardware or building material store. 
  For screws in amp you need only 2 mm bit, buy smallest and cheapest set. I hope metric hex keys are available in US.


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## liquidzoo

Quote: 





zigis said:


> Evshrug, you need Hex key or hexagon L key, something like this
> 
> 
> 
> ...


 
   
  Something like this:  http://www.harborfreight.com/fold-up-hex-key-set-94589.html
   
  I'd be surprised if you could find cheaper than Harbor Freight (though it's definitely possible).


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## Zigis

Quote: 





liquidzoo said:


> Something like this:  http://www.harborfreight.com/fold-up-hex-key-set-94589.html
> 
> I'd be surprised if you could find cheaper than Harbor Freight (though it's definitely possible).


 
   
  I find cheaper in the same place 
   
  http://www.harborfreight.com/10-piece-hex-key-set-94597.html


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## ludoo

Zigis, did you by any chance manage to alter the design of your board so that larger capacitors like the Elna Silmic II can be used? If so I'd be interested in getting a board...


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## Evshrug

Quote: 





zigis said:


> I find cheaper in the same place
> 
> http://www.harborfreight.com/10-piece-hex-key-set-94597.html


 
  I finally located my tool case, has a bunch of sprockets and tools, including a large variety of drivers, but no allen wrench small enough for the 2mm screws. There's a local hardware store... I probably would not be able to find a set for $2, but it might be cheaper after the $9 total price from harborfreight if you consider shipping. And maybe, I could just take the amp with me and I could borrow one for 5 minutes, they let people borrow tools at the auto parts stores.
   
  Can't help but notice the irony... the set you found, called the Pittsburgh... I live in the city of Pittsburgh. LOL.
   
 Ludoo, It's up to you, but I am already very impressed with the amp built to it's current spec. What do you expect the larger caps to do, increase bass extension? The bass extension already matches (mostly) my FiiO solid state amp (without boost), with my Amperex 6DJ8 "Bugle Boy" and Vokshod 6N23P tubes I don't feel like anything is being "held back" on this amp. Maybe you know something I don't, but the sound is already "enthusiast grade."


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## ludoo

Quote: 





evshrug said:


> Ludoo,It's up to you, but I am already very impressed with the amp built to it's current spec. What do you expect the larger caps to do, increase bass extension? The bass extension already matches (mostly) my FiiO solid state amp (without boost), with my Amperex 6DJ8 "Bugle Boy" and Vokshod 6N23P tubes I don't feel like anything is being "held back" on this amp. Maybe you know something I don't, but the sound is already "enthusiast grade."


 
  I already built one with the original board and "audiophile-grade" components, look at the start of this thread.  I simply want to make another with the same components, and Ziggy's board design would allow me to use a smaller enclosure.
   
  Excellent caps cost only a few euros/dollars more than good ones, I think in this case it's a good investment. The difference is slight but audible, it makes no sense to skimp on five capacitors when the difference is maybe 5% of the total cost of the build. The problem though is that audiophile grade caps are much larger than regular ones, they fit on the original Chinese board but not on the redesigned one.


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## Evshrug

Quote: 





ludoo said:


> I already built one with the original board and "audiophile-grade" components, look at the start of this thread.  I simply want to make another with the same components, and Ziggy's board design would allow me to use a smaller enclosure.
> 
> Excellent caps cost only a few euros/dollars more than good ones, I think in this case it's a good investment. The difference is slight but audible, it makes no sense to skimp on five capacitors when the difference is maybe 5% of the total cost of the build. The problem though is that audiophile grade caps are much larger than regular ones, they fit on the original Chinese board but not on the redesigned one.


 
  Oh, I read through the whole thread before I first posted last year. But what, exactly, do the larger capacitors do?


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## ludoo

Quote: 





evshrug said:


> Oh, I read through the whole thread before I first posted last year. But what, exactly, do the larger capacitors do?


 
   
  They are larger only in the physical sense. The difference is in the capacitor quality, and the fact they are made specifically for audio (eg Elna Silmic II).


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## Zigis

Quote: 





evshrug said:


> I finally located my tool case, has a bunch of sprockets and tools, including a large variety of drivers, but no allen wrench small enough for the 2mm screws. There's a local hardware store... I probably would not be able to find a set for $2, but it might be cheaper after the $9 total price from harborfreight if you consider shipping. And maybe, I could just take the amp with me and I could borrow one for 5 minutes, they let people borrow tools at the auto parts stores.
> 
> Can't help but notice the irony... the set you found, called the Pittsburgh... I live in the city of Pittsburgh. LOL.


 
  I did not notice Pittsburgh name before 
   
  If I had known that it is so complicated, I would have added to package one 2mm hex.


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## Zigis

ludoo, sorry, only old good design PCBs available  
  New design cost much and I myself don't need larger caps so much.
   
  If I where you, I make it creative way. With little legs bending 16mm caps (470uf Elna) will fit, I think. You may change C2 output caps and maybe C3 second stage power caps too.
  C4, first stage power cap is not so sensitive.
   
  Output caps you can solder slightly above surrounding small resistors, or solder resistors on boards other side. I am sure, similar creative way you can push in C too.


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## Zigis

Here is finished version of my amp, with oak side panels, linseed oil finishing.
   
  Now amp have its own name -* Rock'n Glass* headphone amp.
  Name come from amp's powerful sound and hybrid nature.
   

   

   
   
  This one exemplar are with lin outputs.


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## Evshrug

Lol, I was just going to tell you tonight that I bought some hex wrenches, and got the sides on... Mostly. Two of the holes didn't line up, but I thought I could copy the screws from the side that did fit using Photoshop. Looks like you changed other external parts of the amp as well... Did you fix the bias reading leads to be available in an attractive way like you wanted?

Nice photos. A little reddish and the bottom photo was slightly dark, but that kind of thing can be fixed in a few seconds inside photoshop.


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## Zigis

Are anyone of Super-Simple 6DJ8 Headphone Amp builder or owner trying this amp with [size=11.818181991577148px] Beyerdynamic DT 990 250 ?[/size]


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## stupidmop

I have the dt990 250s 
	

	
	
		
		

		
			





. Can a board(s)/kit be purchased? Very elegant amp design, I like it! Thanks!


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## Zigis

Thanks, stupidmop!
  At the moment I haven't any boards left, only 2 ready built amps.
  Few forum asked about boards too, so I think I am going to order next bunch. May be available in 2 weeks or so.
   
  I ask about DT990, because someone wanted ordering amp for his phones.


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## stupidmop

Cool. I'll look forward to building this bad boy. 
	

	
	
		
		

		
		
	


	




 Thanks Zigis, can't wait!


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## Zigis

Finally boards are ready.
  If someone are interested, I have 4 or 5 PCBs spare.


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## stupidmop

You have PM. Thanks Zigis


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## Zigis

[color=#000000]stupidmop and MonkeyD.Luffy, your boards are sent.[/color]
   
  Zigis


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## stupidmop

Got mine! Thanks Zigis


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## samwell7

Just started mine! Although now I have to wait for the bulk of the parts because no stores in Australia seem to carry nice caps or any transistors. Going to use a nichicon 4700uF cap for C103 and Vought some rifa caps for c101 and c201, the tube is gonna be a JAN spec Philips 6922 and I'm gonna use a Hammond case with the top cut off to let it all breathe. Also had to order an IRF510 instead of the other one. I'm getting very excited for all this stuff to come so I can finish it off


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## UKToecutter

Are there any boards left?
   
  I fancy building this!!


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## Zigis

I have few boards at the moment. 
  PM  if you are interested.


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## samwell7

Just finished mine! sounds really good! I get a 'whiney' high pitched noise through mine all the time though.  It starts out loud and slowly gets quieter, I'm wondering if it's my power supply, or something to do with the tube heating up?
   
*EDIT*: after leaving it run for maybe 5-10 minutes with music through it the sound has turned into more of a light static.  It keeps disappearing for a little while, and then coming back


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## holland

Quote: 





samwell7 said:


> Just finished mine! sounds really good! I get a 'whiney' high pitched noise through mine all the time though.  It starts out loud and slowly gets quieter, I'm wondering if it's my power supply, or something to do with the tube heating up?
> 
> *EDIT*: after leaving it run for maybe 5-10 minutes with music through it the sound has turned into more of a light static.  It keeps disappearing for a little while, and then coming back


 
   
  tubes...it's a love hate relationship.  yours might be going, can you swap?


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## samwell7

Quote: 





holland said:


> tubes...it's a love hate relationship.  yours might be going, can you swap?


 
   
  On the plus side this sounds amazing, definitely got that ballsy tube sound I've been looking for, it overdrives nicely as well.  I will swap and try soon, the sound is gone when I just use it as a preamp before some powered speakers.  It was pretty much gone when I was using my headphones as well.  I'm using a JAN spec Phillips 6922
   
  here's a photo also


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## ludoo

I had a similar issue, and fixed it by thouroughly cleaning with some fine sandpaper the tube and tube socket contacts, which were slightly oxidized. It might also be due to a grounding problem, check if the sound changes when you touch the sockets or metal case with your hand.
   
  It's a great little amp, isn't it?


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## samwell7

ludoo said:


> I had a similar issue, and fixed it by thouroughly cleaning with some fine sandpaper the tube and tube socket contacts, which were slightly oxidized. It might also be due to a grounding problem, check if the sound changes when you touch the sockets or metal case with your hand.
> 
> It's a great little amp, isn't it?



Well the socket I have at the moment is really hard to get the tube into and doesn't quite fit in properly, I've ordered a new socket which should fit the tube more snug. Pretty sure I considered it not a grounding problem because it didn't change when I touched stuff. I think it might be the ground problem because it didn't go in properly and when I moved the amp on its side the noise came back a little louder. Will report back with the new socket, and also bought a switched potentiometer for it so those wires and running through, I reckon they will melt on the heatsink of the MOSFET. It is an amazing amp for the money, it sounds awesome. How I thought a tube would sound before I started listening to them.


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## Zigis

Anyone know replacement part for 2sk117, preferably available in Farnell?
 I am waiting for package from Thailand, but it is too long time.
  
 What parameters I need to look for similar working in CCS? Similar gate current (14mA) ? anything else?


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## Zigis

Can BF254A work?
  
 Or NTE312 maybe, datasheet:
  
http://www.nteinc.com/specs/300to399/pdf/nte312.pdf


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## duncan1

The BF254  isnt a fet but an NPN transistor. The   2SK117 is an N channel fet that works to  50V. A 2SK68 would  do/2SK106/2SK163/2SK184 would all work.


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## Zigis

Typo, I mean BF245 N channel fet, of course.
  
 Actually I ordered NTE312 from Farnell and it work great in amp, so if anyone have parts problem, this is good and easy to get replacement part, only pins are different.
  
 I buy some BF245A locally, not tested yet. Yes, and package with 2SK117 arrived yesterday


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## duncan1

The BF245 is only good for  30V I wouldnt use it . But glad to hear your amp is now working great.


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## DKJones96

kimlaroux said:


> Are you certain the 12AU7 can be used as a replacement for the 6DJ8? Retailers seem to sort these as two different types of tubes. I'd verify this amp can use a 12AU7 before buying a new tube.


 

 You know, with a little bit of circuit modding a 12A*7 series tube could work.
  
 The standard circuit is setup for 6.3V across pins 4 and 5, if you were to re-calculate the constant current supply resistors and snip the shield connector at pin 9 you'd not only have the option of any of the 9A based dual triodes but your regulators would work MUCH cooler. A 12AY7 would be a good tube for matching gain but an AU7, AT7, or AX7 should all work and since they all have the same heater current rolling is a simple swap.
  
 Great, now you have me wanting to build another one of these!


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## DKJones96

Simple mod actually works!
  
 I used a 12AY7 for my quick test but haven't tested the others yet(exams). Swap in a 8.2 ohm resistor on each LM317 for a CC of 150mA. They end up both going to the same pin(3 I believe) and if you leave one of them alone but send the other one to pin 4(should be to ground so cut that) the shield should already be grounded on pin 9 which completes the heater/output circuit. With that setup you should only need to re-bias between tube swaps(it might not even need that really) from 12AU7, 12AY7, 12AT7, 12AX7, and a multitude of other dual triodes if you aren't afraid of air wiring(I have my tube air wired to make the tube stick out of my chassis more).
  
 I want to play with it a little bit more because there is no reason why an LM317LZ(to-92 packaged LM317) couldn't be used in place of the 2SK117(pinout might be different). It's just a simple plate CCS with a depletion mode jfet. If this is the case it might be possible to also make this a super cheap build seeing as it would just use 4x LM317s and a couple of output MOSFETs.
  
 Unfortunately, I might not be able to test the LM317 idea since I don't want to mess up my original. If anybody has some boards they could sell I could play a bit more.


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