# SOHA Help needed



## FallenAngel

Hey guys,

 I'm thinking of building a SOHA. There is a current PCB by Digi01 at HeadWize, but I'm thinking of a bit different version. I want this one. That more or less leaves me to breadboard, which believe it or not, I actually enjoy somewhat more than PCB.

 This being my first tube project and the fact that I'm not sure whether this is consider "high voltage" (read: able to fry my ass), I thought I'd ask for help before starting.

 The parts list is really not that hard and I think I can grab all of these between (www.DigiKey.ca or canada.Newark.com) and www.PartsExpress.com, so here comes the big and scary part... I seriously don't understand some parts of this schematic.

 I took a copy of the schmetic and circled the things that are totally confusing for me.





 RED: I'm guessing this is the "J113 Cascode", uhm... do I need to match these in any way?

 GREEN: How do I connect this tube 
	

	
	
		
		

		
			





, sorry guys, first tube project, totally clueless.

 BLUE: Aaahhh! Where are the inputs and outputs? I'm hoping I labelled them right, but also, where is the ground? Does this have a virtual ground?


 Well, I think that's about it for now, thanks in advance. Oh and if you want to scream "STOP BEFORE YOU KILL YOURSELF!!!", as long as it's called for, it would definitly be appreciated.


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## a1rocketpilot

I am also about to build this as soon as the PCB's are made. Lets go in order:

 The J113 cascode does not need to be matched if I recall. Also, why not use the LND150? It's performance is only very slightly less on paper and its has a smaller part count and it has a higher voltage limit, giving more headroom in case of accident.

 The tube has 9 pins, numbered 1-9, so connect the tube socket accordingly so on the PCB. If I recall, digi01's board has the tube mounted on the opposite side from the components, so keep that in mind.

 The purple things you circled are the inputs and outputs. The two RCA inputs are on the left side of the page and the headphone jack is in the approx. center.

 As far as being high voltage goes, It is higher than many solid state designs, running at a B+ of about 60v. However this is considerably less than the normal voltages in tube amps, which is over 200v. In other words, this may sting you if you do something wrong, but it probably won't cause any real damage like real tube amps can. Hope this helps!

 Aditya


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## tomb

FallenAngel,

 I would highly recommend that you build Digi's version, first. If this is your first tube amp, you will have problem enough dealing with that. I am still confused, and I've been studying and participating in the design threads since almost the beginning of the SOHA Thread #1 (no longer in existence on Headwize).

 A couple of things -
 1. a1rocketpilot is correct: the LND150 MOSFET CCS is the superior choice. Being at least on the North American continent, you should have no trouble sourcing the MOSFET. The other CCS designs were developed because the LND150 is almost impossible to get overseas.
 2. Digi is developing a plug-in DB for the next Group Buy (#2), but most importantly, Steinchen is working on a MOSFET buffer for Digi's SOHA board. If you are familiar with the Millett Hybrid and Steinchen's DB's, then 'nuff said. The Group Buy #2 is going on as we speak - ending on Sept 30th. I have four of the boards from the 1st Round, and their quality is about as good as anything from Amb or Tangent. Highly recommended.

 Digi also has an Assembly Instructions website for the board:
SOHA V3

 Also, a1rocketpilot was incorrect on one small thing - Digi's board does not have the tube reversed. Some people build the tube boards with the caps on the bottom. That way, the tube sticks out further, making it easy to replace (and emphasizing the tube). Boutique versions of the high voltage power caps can be as tall as the tube. If you put them all on the same side of the board, you can't even see it. The typical Pana FM's or Nich UPW's don't really have that problem.


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## Blooze

Quote:


  Originally Posted by *tomb* 
_ I am still confused, and I've been studying and participating in the design threads since almost the beginning of the SOHA Thread #1 (no longer in existence on Headwize)._

 

FallenAngel - here it is if you're interested.
http://headwize.com/ubb/showpage.php?fnum=3&tid=5896


  Quote:


  Originally Posted by *tomb* 
_ 2. Digi is developing a plug-in DB for the next Group Buy (#2), but most importantly, Steinchen is working on a MOSFET buffer for Digi's SOHA board. If you are familiar with the Millett Hybrid and Steinchen's DB's, then 'nuff said._

 

I would build the amp, either breadboard (not that hard if you look through the original thread and have done a bit of soldering) or on Digi's board if you're so inclined, using the LND150 if you can get it and just the spec'd parts. I wouldn't worry about trying to tweak the thing out before you've even heard the original version. Everyone always wants to take things to the limit it seems before they've even built or heard the original. I personally don't have a problem with that, but I like to hear the difference to see if the extra expenditure was really worth it. IMO you would be better off spending money on tube rolling than diamond buffers in the beginning.

 Just be careful and follow safe practices. You would be wise to remember that you will be dealing with mains voltage coming into the PS which can surely drop you dead quick. It's always been my understanding that anything over 40V should be approached with care.

 Good luck with your build!! You'll like this little amp.


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## FallenAngel

First of all, thanks for all the feedback.

 Although I was pretty much hoping to do this on breadboard (more fun and I can use the diomond buffers), I was convinced (girlfriend really didn't want me to fry myself) to take the PCB route.

 About the CSS choice, I'm trying to get everything I need from only one source and Newark has the J113, but neither DigiKey.ca nor Newark Canada has the LND150.

 So now I have a few questions about this amp.

 1) Transformer choice, I found a cheap transformer in a surplus store near by, its a 30VCT 2Amps, I know the the suggested was like 400mA, hope the extra power woun't do anything bad.

 2) Caps... which positions would be most worth it to use boutique parts, I seriously fell in love with BlackGates since comparing them to the Nichicon UPW I had in my PINT, and they're only a few bucks more for the Standard series.

 3) Enclosure... I've got a really nice wine case I've been dying to use for an amp. It's wooden and easily big enough to fit this thing with lots of room to spare. Would I be looking at any issues with things like grounding or the transformer causing a hum?

 4) Tube socket, I'm thinking of having the tube socket on top of the case so I could switch the tubes without taking the amp apart and for simple appearance.

 5) Where do I buy the PCB? There is a link to paypal straight from http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.htm is that where I can get it? Also, how long does it take to receive it?

 Thanks again, I'm already looking forward to this amp.


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## tomb

SOHA Group Buy #2 on Headwize


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## FallenAngel

Thanks tomb, asked for 2 
	

	
	
		
		

		
		
	


	




.


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## dsavitsk

Quote:


  Originally Posted by *FallenAngel* 
_Although I was pretty much hoping to do this on breadboard (more fun and I can use the diomond buffers), I was convinced (girlfriend really didn't want me to fry myself) to take the PCB route._

 

Just don't stick your fingers in the circuit while it is on, and if you need to make adjustments while powered on, do it with one hand behind your back. 60V is enough to give you a nasty shock, but it is not in the same realm of danger as 450V. Just be careful and go slow.



  Quote:


 1) Transformer choice, I found a cheap transformer in a surplus store near by, its a 30VCT 2Amps, I know the the suggested was like 400mA, hope the extra power woun't do anything bad. 
 

Too big is not a problem. It is simply a measure of what the trafo can supply, not what it will supply. The circuit determins what is drawn.

  Quote:


 2) Caps... which positions would be most worth it to use boutique parts 
 

The most important are the cathode bypass cap (1000/16) and the coupling cap (330n.) W/r/t/ the 1000uF cap, that is way bigger than necessary. That cap sees basically the plate resistance of the tube || to the cathode bias resistor in this amp to determine frequency rolloff, so I would bet you can lower that by a factor of 10 or more. 100uF will be fine. The bigger cap does no good in this spot.


 However, especially if you are going to bread board this, buy cheap caps to get it working, and swap them out later.


  Quote:


 4) Tube socket, I'm thinking of having the tube socket on top of the case so I could switch the tubes without taking the amp apart and for simple appearance. 
 

It is fine, but the rest of the circuit should be close with the connected resistors right on the pins.


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## tomb

Quote:


  Originally Posted by *FallenAngel* 
_Thanks tomb, asked for 2 
	

	
	
		
		

		
		
	


	




._

 

Congrats! Be sure to read that link for Digi's "Walkthrough" and read the "SOHA - Thread 2" on the DIY section of Headwize - lots of good info there. Note that the BOM on Digi's Walkthrough is the correct one for his board. Not all the parts on the Headwize Library article are compatible. The Library article was for the P2P version.

 To me, the power supply is the tricky part - much different than anything we use in Solid State or the Millett. I've finally settled on a DIY-walwart approach using two duplicate leads with 15VAC + Gnd (Center Tap) on each that will terminate into two identical walwart plugs for the case. That way, the separation distance will take care of any hum, so you can use your cheap transformer without needing a toroid.

 By the way, where did you get the cheap transformer? 30VCT is not that common outside of a toroid.


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## FallenAngel

Tomb: I got the transformer from Sayal - www.sayal.com - the part number is "AM-TR-30T-2"

 Thanks dsavitsk, I was definitly thinking of doing this on breadboard, but since I ordered 2 PCBs, I'll build up that version, and if I like it, I'll breadboard my own little clone.

 I will be looking at this PCB schematic and will be ordering everything from http://canada.newark.com and www.partsconnexion.com

 Parts Choices:

 C2, C14 (dsavitsk: in my image, it's 330nF, in the PCB version it's 100nF): I've got a few of the 0.1uF and 0.47uF 715P (Orange Drops), so I'm thinking I'll throw those in there. - Newark

 C1, C13 (the ones under the Tube connection on the left of the schematic): I'm thinking "1000uF BlackGate STD" at $4.75 or if dsavitsk is right, then I can easily go with 220uF STD at $2.95, but since I don't use these caps often, I usually just get the 470uF/16V STD for $3.75. - PartsConnexion

 C3, C4, C5, C6 100uF/100V - If these aren't very important, I'm just going to find any 100uF/100V electrolytics. From manufacturers I recognize, I see Vishay BC Components "22 ASM" Series axial at $1.54.

 C7, C8, C11 47uF/16V - Again, if these aren't very important, I'll just stick some Vishay BC Components "AML 138" Series axial at $1.14 - It would actually be cheaper to go with BlackGate PK (miniature) series here, the 47uF/25V is only $0.95 and the STD series is $1.85, probably worth it for only a few cents more.

 C9, C10, C12 470uF/35V - The BOM is very strange on this one, it suggests 560uF for C12 and 1500uF for C9 & C10. I can either go with 470uF BC Components, but since these caps are basically the power supply rail caps, perhaps something better is in order?

 AC_IN - Can somebody recommend a power jack. I'm guessing I'll need it fused, so what about 92N4150 from newark? Or maybe I'll just get the CONNEX-62491 from PartsConnexion

 R4, R14 (TrimPots) - Hope this one fits 01F7709 from Newark

 Pot - PartsConnexion sells the Alps "Blue Velvet" 10K and 100K, but no 50K, the 100K should work fine, right? Or should I get the 10K?


 ---

 VERY IMPORTANT: Which Tubes do I buy? I saw quite a few in partsconnexion and I really don't know which ones to try.


 Wow, that took a really long time! Thanks for looking, any recommendations would be recommended.


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## dsavitsk

Quote:


  Originally Posted by *FallenAngel* 
_C2, C14 (dsavitsk: in my image, it's 330nF, in the PCB version it's 100nF): I've got a few of the 0.1uF and 0.47uF 715P (Orange Drops), so I'm thinking I'll throw those in there. - Newark_

 

Since you are ordering from parts connexion anyway, and since the PCB should eliminate errors, I'd pick up something for this part like a Jensen or a Mundorf or somethig snazzy. In this size they are pretty cheap and it will sound better than the 715. Even better, pick up some Vitamin Q's from ebay.

  Quote:


 C1, C13 (the ones under the Tube connection on the left of the schematic): I'm thinking "1000uF BlackGate STD" at $4.75 or if dsavitsk is right, then I can easily go with 220uF STD at $2.95, but since I don't use these caps often, I usually just get the 470uF/16V STD for $3.75. - PartsConnexion 
 

I have found the standard series to sound a little flat in this position. You might prefer a Silmic from Digikey, or a BG N series. Also, after a lot of experimentation, I now officially disagree with Rick. Bypass it with a decent 0.1uF film cap (maybe not if you spring for the N series). I have been using either Vit Q's or some russian teflon caps for this and both work great.


  Quote:


 Pot - PartsConnexion sells the Alps "Blue Velvet" 10K and 100K, but no 50K, the 100K should work fine, right? Or should I get the 10K? 
 

Tangent, Amb, and Percy sell the 50K. Percy has 50K Nobles. You can also get 50K PECs at Digikey that sound better than the Alps or the Noble. However, this amp has a ton of gain, so you need to find a pot that tracks really well at low volumes as you are not likely to turn it up much.


  Quote:


 VERY IMPORTANT: Which Tubes do I buy? I saw quite a few in partsconnexion and I really don't know which ones to try. 
 

Someone else was asking about 12au7's, but you might not like the answer: http://www.diyaudio.com/forums/showt...threadid=87219


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## FallenAngel

*C2, C14*
  Quote:


  Originally Posted by *dsavitsk* 
_Since you are ordering from parts connexion anyway, and since the PCB should eliminate errors, I'd pick up something for this part like a Jensen or a Mundorf or somethig snazzy. In this size they are pretty cheap and it will sound better than the 715. Even better, pick up some Vitamin Q's from ebay._

 

Mundorf MCap ZN 0.1uF go for $4.40, are they worth it here?
 There are also Mundoff Supreme for $10 and Jensens for $11 - $16

 Are these really worth it here, or would the MCap ZN's be fine? As for Vitamin Q's, I've found some 0.1uF and 0.22uF for around $5 each.

*C1, C13*
  Quote:


  Originally Posted by *dsavitsk* 
_I have found the standard series to sound a little flat in this position. You might prefer a Silmic from Digikey, or a BG N series. Also, after a lot of experimentation, I now officially disagree with Rick. Bypass it with a decent 0.1uF film cap (maybe not if you spring for the N series). I have been using either Vit Q's or some russian teflon caps for this and both work great._

 

Never heard somebody saying BG Standards are flag, but ok. BG N Series 470uF/16V and 1000uF/25V are same price at $12.50, would it make that much of a difference between them and the STD, I'll be getting 4 of these and when it's $50 vs $15, I gotta ask.

 Also, I can't find any Elna Silmic on DigiKey. - Ok, I just didn't know that Silmic II are RFS series, in which case, damn they're really cheap, maybe I'll go with some of these instead 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *dsavitsk* 
_Tangent, Amb, and Percy sell the 50K. Percy has 50K Nobles. You can also get 50K PECs at Digikey that sound better than the Alps or the Noble. However, this amp has a ton of gain, so you need to find a pot that tracks really well at low volumes as you are not likely to turn it up much._

 

Well, I was trying to only order from 2 places, but if I gotta get something from DigiKey, sure. If I just get the 100K from PartsConnexion, would it be worth it, or should I go with the 50K "PEC" 
	

	
	
		
		

		
		
	


	




 What's the part number for that?

  Quote:


  Originally Posted by *dsavitsk* 
_Someone else was asking about 12au7's, but you might not like the answer: http://www.diyaudio.com/forums/showt...threadid=87219_

 

[/QUOTE]
 Damn, And PartsConnexion is having their 15% off everything sale for only 3 more days, gotta place the order quick. Guess I'll be reading quite a bit.

 Ok, well that more or less settles it, I'll be ordering from DigiKey, Newark and PartsConnexion. Guess I'll be redoing the BOM for this one again.


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## tomb

*C9 and C10* are the power caps that reside between the 12V rails feeding the heaters _and_ the opamp. As such, you can pretty much view them as power caps similar to any SS amp - except even more juice is needed for the heaters. The OPA2134 used in the original design is limited to about 45ma per channel, so 470uF's used in the original design were OK. When the discussion turned to adding BUF634 or plopping a couple of OPA551's on a 2X1 adapter (200ma each!), then it was suggested that you could go as high as 3300uF each for C9 and C10. There is still a happy medium between response and capacitance, and Digi's BOM may reflect that.

*C12* is the bootstrap cap that bumps up the 30V to 50-60V for B+. It does not follow the same strategy as C9 and C10.

*For your trimmers* - don't use the ones you've shown. A standard Bourns _top adjust_ 3299W - like those used in the Millett or on the TREAD - works best.

*As for the tubes*, search through the thread on Headwize. There is an extensive review based on the original SOHA. Some great tubes (by all reports) are as follows:

 NEW Production:
 Electro-Harmonix 12AU7
 JJ ECC82
 EI 12AU7

 NOS:
 GE 5963
 GE & RCA long grey plate 12AU7's

 Some have also mentioned the Amperex Bugle Boy 12AU7, but that thing is really expensive. You can get all the ones I mentioned above for $8-$9 ea.


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## steinchen

Quote:


  Originally Posted by *FallenAngel* 
_*C2, C14*
 Mundorf MCap ZN 0.1uF go for $4.40, are they worth it here?
 There are also Mundoff Supreme for $10 and Jensens for $11 - $16

 Are these really worth it here, or would the MCap ZN's be fine? As for Vitamin Q's, I've found some 0.1uF and 0.22uF for around $5 each._

 

Mundorf MCapZN are excellent and a significant improvement over Wima MKP e.g. They are worth the investment here, it is the only cap that is directly in the signal path. The MCapZN is my personal favourite since it has a very good performance and is still affordable.

  Quote:


  Originally Posted by *tomb* 
_2. Digi is developing a plug-in DB for the next Group Buy (#2), but most importantly, Steinchen is working on a MOSFET buffer for Digi's SOHA board. If you are familiar with the Millett Hybrid and Steinchen's DB's, then 'nuff said._

 

not only a mosfet buffer, a diamond and a hybrid buffer too. None of these will be a direct drop in replacement, you'll have to air-wire the buffers to the SOHA board. Additionally you'll have to heatsink the regulators on the SOHA board due to the significantly higher current draw.

 As for Digi's plug-in DBs I doubt that they work with the SOHA because of the unbalanced psu and the lack of an output coupling cap, but we'll see.


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## tomb

Quote:


  Originally Posted by *steinchen* 
_... snip ...not only a mosfet buffer, a diamond and a hybrid buffer too. None of these will be a direct drop in replacement, you'll have to air-wire the buffers to the SOHA board. Additionally you'll have to heatsink the regulators on the SOHA board due to the significantly higher current draw._

 

I was kind of wondering - that MOSFET buffer photo you posted looked huge. 
	

	
	
		
		

		
		
	


	




 Think maybe the typical 25¢ stamped metal TO-220 heat sink will work on those regulators? There's no room otherwise.


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## steinchen

Quote:


  Originally Posted by *tomb* 
_Think maybe the typical 25¢ stamped metal TO-220 heat sink will work on those regulators? There's no room otherwise._

 

simple TO-220 heatsinks should be sufficient with the diamond or hybrid buffer when biased to a rather low level. With the mosfet buffers sucking 200mA they get pretty warm (depending on the output voltage of your transformer). Ideally the regulators would be mounted to the underside of the pcb and heatsinked through the bottom of the enclosure.


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## FallenAngel

Well guys, with all the contribution here, I got a Canadian BOM made up for 2 PCBs from Newark, DigiKey and PartsConnexion. *BOM UPDATED, new version on next page.*

 There are a couple of things there that I would like clarification on:

 C3-C6: I've used the stock Panasonic FC's here, is there something else I should be using here to go with the other "nicer" stuff, or is it just not worth it.

 C9, C10, C12: Same question as above.

 C7, C8, C11: BlackGate Stardard 47uF/16V or Elna Simic II 100uF/25V?

 T1 (Transformer): Is a toroidal really necessary here or would any old 30VCT transformer do the job well enough?

 LED: Any led recommendations?

 Thanks everyone, I'll be trying to order parts before the 15% off sale expires saturday 6pm.

 Since I found out that the boards woun't ship for A WHILE, I'll just breadboard one from the schematic posted above before the boards get in (a little different part list, but close enough).


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## dsavitsk

Quote:


  Originally Posted by *FallenAngel* 
_C3-C6: I've used the stock Panasonic FC's here, is there something else I should be using here to go with the other "nicer" stuff, or is it just not worth it._

 

I think FMs are considerably nicer, and often cheaper.


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## FallenAngel

Quote:


  Originally Posted by *dsavitsk* 
_I think FMs are considerably nicer, and often cheaper._

 

Unfortunatly FM's do go to 100V, they stop at 50V.


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## tomb

Ditto on the Pana FM's - even for those you list for C7, C8, and C11. The great thing about the SOHA design is the only cap in the signal path is C2 and C14, and that's an orange drop/box cap. So, the Pana FM might be the best non-boutique choice, period.

 According to the designers/first proto builders, T1 should be a toroid _if it's in the case._ If you mount it remotely in a different box or walwart, then whatever you want. Unfortunately, I've found the 30VCT uncommon enough that the toroid is the simplest choice anyway. 
	

	
	
		
		

		
			





 For the LED, if you're talking the tube light, be sure to use a T1 (3mm). That's different from the Millett. With a 3mm LED, though, you can push it up into the tube socket for a very direct effect.


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## FallenAngel

Quote:


  Originally Posted by *tomb* 
_Ditto on the Pana FM's - even for those you list for C7, C8, and C11. The great thing about the SOHA design is the only cap in the signal path is C2 and C14, and that's an orange drop/box cap. So, the Pana FM might be the best non-boutique choice, period.

 According to the designers/first proto builders, T1 should be a toroid if it's in the case. If you mount it remotely in a different box or walwart, then whatever you want. Unfortunately, I've found the 30VCT uncommon enough that the toroid is the simplest choice anyway. 
	

	
	
		
		

		
		
	


	




 For the LED, if you're talking the tube light, be sure to use a T1 (3mm). That's different from the Millett. With a 3mm LED, though, you can push it up into the tube socket for a very direct effect._

 

Signal path caps: cool design, for the C2 & C14, I'll go with the Mundorf MCap ZN's.

 Transofrmer: I'll probably just suck it up and buy 2 of those toroidals for the 2 board, but for my breadboarded one, which will definitly be built first, I'll use the cheap transformer inside the same case, but since this case is a 6-bottle old wine case, I'm hoping it'll be alright.

 Panasonic FM's, what's even worse is that DigiKey doesn't even have any of the FM 50V caps in stock, only lower voltage, so I can't use them for C3-C6.

 C7, C8 & C11: BlackGates are probably unnecessary, but are the FM's really better here than the Silmic II's? The price is really irrelevent since they both cost cents.


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## tomb

Hey - I'm just offering opinions on caps, nothing more. 
	

	
	
		
		

		
		
	


	




 There is a good case to be made that boutique electrolytics are also excellent power caps. I've seen BG's used for everything. Elna's were sold for the PIMETA. Nichicon ES's have been used all around on the Millett. Headwize user Neurotica used all Nichicon KZ's on his prototype SOHA PCB (Digi sent out several boards for testing before he produced the Group Buy boards.) The original P2P versions used Xicon's, which you can buy at Radio Shack (at least some sizes). So, whatever you prefer. I ordered Nichicon UPW's for the voltages not available with FM's and then FM's everywhere else - but I haven't built one, yet.


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## FallenAngel

Thanks, that about finalizes most of the BOM, we should see a finalized version tonight.

 Now onto the next 2 topics:

*1) Regulated Filament Power Supply*

 In the schematic posted in the first post, the bottom right corner right beside the transformer is the power supply for Pins 4 and 5. There isn't any LM337, C11 & C12 caps, nor R10/R11. Instead there are just a few 2W resistors and a 1N4148 diode with the LED.

 So for the breadboard version, which would you recommend?

*2) Diamond Buffer 220nF (0.22uF) cap*
 Just to verify, this should be a good quality film cap right? As in the $5/each Mundorf ZN?


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## tomb

1. I know you like the DB's, but scrap the rest of that schematic - the power supply was revised a long time ago - even for the P2P verstion. The heater filaments use an LM337 on a big heat sink and a couple of filtering caps.

 2. Yes - great quality is good here. If dsavitsk likes the Mundorf, that's a great recommendation.


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## FallenAngel

The 2 BOM's are done 
	

	
	
		
		

		
		
	


	




*Newer version below*

 It's all in one excel file, 2 sheets, first is the BOM for 2 SOHA V3.0 boards, the second is for the breadboard version in the image below. It's basically the latest (or so I hope) schematic + the diamond buffers.





 I hope I didn't miss anything very important, let me know if I did.

 Signal caps are Mundorf MCap ZN's, power supply caps are Elna Simic II where available or Nichicon PW where not.
 Resistors are Vishay Dale, except for a few in the diamond buffer version where I couldn't find 2R2 Dale resistors so I just took what I could. Unfortunately they're +/- 5%, but I hope it woun't matter much.

 One other question: Are Used/Old tubes worth buying? PartsConnexion sells them here, anything there that's worth getting used?


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## dsavitsk

Quote:


  Originally Posted by *tomb* 
_2. Yes - great quality is good here. If dsavitsk likes the Mundorf, that's a great recommendation._

 

I've not tried them yet. I was just listing names of possible things to try.


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## a1rocketpilot

One thing you may want to consider for the PSU caps and C1/C13 are the Rubycon ZA/ZL series. Sources say that they are as good/even better than the Black Gates. Those are what I am using for my SOHA. So far, Reference Audio Mods is the only place I have seen them available for purchase. RAM sells Black Gates as well and they say the ZA/ZL caps are even better, for far less. Be aware that Rubycon manufactures Black Gates as well as the ZA/ZL, however they are marketed for different markets. The ZA/ZL cap is marketed for computer use, but apparently it is great for audio. The caps aren't pretty though.)

 Aditya


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## tomb

Quote:


  Originally Posted by *dsavitsk* 
_I've not tried them yet. I was just listing names of possible things to try._

 

My mistake - it was Steinchen who said he liked them in Post #14:
  Quote:


  Originally Posted by *Steinchen* 
_Mundorf MCapZN are excellent and a significant improvement over Wima MKP e.g. They are worth the investment here, it is the only cap that is directly in the signal path. The MCapZN is my personal favourite since it has a very good performance and is still affordable._

 

Same thing, though - if either one of you said it, that would be a good recommendation.

 FallenAngel - I gave you a short list of NOS tubes. There may be some in the PartsConx that would be OK, but they don't give enough description. For instance, the black plate RCA/GE are the most sought after in other audio, but some SOHA builders are not impressed, preferring the grey plates, instead. The 5963 by GE is good, but PartsConx has Beckman? The 6189W's might be worth trying, but SOHA reviewers didn't seem to like the Phillips brand. Supposedly they are more rugged and resistant to microphoning. As stated earlier, the Amperex Bugle Boy was liked a lot, but that's a $40-$50 tube. Great reviews are given for the NEW tubes like the ElectroHarmonix, JJ, and EI.

 One of the major SOHA tube reviews originated here on Head-Fi(!) by Kippei:
http://www6.head-fi.org/forums/showp...92&postcount=7 There are other comments in that thread. Tube preferences seem to vary from P2P to PCB, and from FET opamp to BJT opamp.


----------



## FallenAngel

Quote:


  Originally Posted by *a1rocketpilot* 
_One thing you may want to consider for the PSU caps and C1/C13 are the Rubycon ZA/ZL series. Sources say that they are as good/even better than the Black Gates. Those are what I am using for my SOHA. So far, Reference Audio Mods is the only place I have seen them available for purchase. RAM sells Black Gates as well and they say the ZA/ZL caps are even better, for far less. Be aware that Rubycon manufactures Black Gates as well as the ZA/ZL, however they are marketed for different markets. The ZA/ZL cap is marketed for computer use, but apparently it is great for audio. The caps aren't pretty though.)

 Aditya_

 

Thanks, I'm going to do something wild and scrap every electrolytic cap in this design and order A LOT of these, hopefully I'm going to get good results since these are very nicely priced.

 EDIT: Ok, after adding up the bill at RAM to around $250 after including caps for an M3 I was thinking about and talying the costs for the M3 boards (Yup, my theory is if you can build 1, why not build 2) and having them populated, plus the 2 STEPS that must go with them, the proposed bill totaled over $1000 on parts for the 5 amps and 2 PSU's. Sanity finally kicks in and I've decided to not use these just yet and can't really justify the kick-in-the-ass financial hit, eh, that's the life of a 23-year-old.

 Good news though, I've found out DigiKey restocked on Panasonic FM's so I'm going to use those everywhere except for the C3-C6 100uF/100V where I have to stick in a Nichicon PW.

 New BOM attached, and ordered placed to PartsConnexion, got these tubes 
	

	
	
		
		

		
		
	


	




*Recommended*
 SKU : TUBEJJ-60246
 Name : JJ Tesla ECC82
 Qty : 2
 Price : 9.95

 SKU : TUBEEH-62013
 Name : Electro-Harmonix 12AU7
 Qty : 1
 Price : 8.95

*Randomly chose the first few on the list*
 SKU : OS-67200-155
 Name : Shuguang 12AU7
 Qty : 1
 Price : 2.50

 SKU : OS-67200-156
 Name : Fleetwood 12AU7
 Qty : 1
 Price :4.95

 SKU : OS-67200-157
 Name : Curtis-Mathers 12AU7
 Qty : 1
 Price : 6.95

 SKU : OS-67200-279
 Name : PhilipsECG JAN 6189W
 Qty : 1
 Price : 4.95


 Final check before Newark and DigiKey orders, C1 and C13: 470uF Panasonic FM or 330uF Elna Silmic II?


----------



## cetoole

Quote:


  Originally Posted by *a1rocketpilot* 
_One thing you may want to consider for the PSU caps and C1/C13 are the Rubycon ZA/ZL series. Sources say that they are as good/even better than the Black Gates. Those are what I am using for my SOHA. So far, Reference Audio Mods is the only place I have seen them available for purchase. RAM sells Black Gates as well and they say the ZA/ZL caps are even better, for far less. Be aware that Rubycon manufactures Black Gates as well as the ZA/ZL, however they are marketed for different markets. The ZA/ZL cap is marketed for computer use, but apparently it is great for audio. The caps aren't pretty though.)

 Aditya_

 

What do you mean not pretty? They look as good as the Nichicon UHE, almost as good as the Panasonic FM (and certain select FCs, I have a few FCs here with FM clothes on, but marked FC), better than Nichicon UPW and Elna RJJ, but not nearly as nice as Elna ROA. Much blacker background than the ROA's however 
	

	
	
		
		

		
		
	


	




. Proof is in the following links. IMO, they look a bit nicer than the few Blackgate NX-HIQ I have, but no pics of those. You may not believe it, but getting a bunch of capacitors to line up on a sheet of PTFE can be a real PITA.
http://img.photobucket.com/albums/v3...Yparts/ZLs.jpg
http://img.photobucket.com/albums/v3...arts/bigzl.jpg
http://img.photobucket.com/albums/v3...parts/UHEs.jpg
http://img.photobucket.com/albums/v3...Yparts/fms.jpg
http://img.photobucket.com/albums/v3...rts/lineup.jpg


----------



## FallenAngel

Hey guys, I've got all the parts and started putting this thing together. Right now I've assembled the entire power supply circuit (Filament -12.6, Bipolar +/-12V and the B+ Supply)

 After hooking it up to my transformer, I checked all the voltages to ground and here's what I got:

 The Filament supply is reading -12.4V instead of -12.6.

 The BiPolar supply is seriously out of sync which is really hard to believe since I'm using 7812 regulartors which should be equal.

 +12 is reading +11.90V, that seems fine.
 -12 is reading *-13.7V*, which seems REALLY off. I'll try using a different regulator since I ordered extras but this does seem quite strange.

 B+ Supply is reading *+66V* instead of +55 to +60. Again, really not sure why or even how for that matter, but that's because I don't even understand where this number comes from.

 A couple of quick questions before I start on the amplifier and buffer portions of the design:

 1) In the filament supply, does the voltage need to be exactly -12.6V or is -12.4V OK?

 2) Any clue why the 7912 regulator would regulate to almost -14 instead of -12?

 3) How important is it to have the B+ supply in the +55V to +60V range and what would happen if it stays at +66V?

 Thanks in advance!


----------



## tomb

There have been numerous posts about the dangers of taking readings on an incomplete SOHA - particularly if the pot or opamp is not in place. I can't explain your regulator voltages, but suspect than an incomplete build may have something to do with it. Your B+ voltage is right in line with an unloaded xfmr. I have seen posts from people with over 70V unloaded. Keep putting it together - nothing seems that bad right now.


----------



## rreynol

The +/-12v supplies being off is definately related to the OpAmp not being in.


----------



## FallenAngel

Thanks tomb and rreynol, I woun't worry myself about testing before completing the entire build.

 Just finished the diamond buffers, but unfortunatly don't PartsConnexion didn't send me the 330nF Mundorf caps so I woun't be able to finish everything until I get those.

 Asside from the waiting on those caps, process is going good, almost done assembling everything else, which also means that I'm killing my vintage wine reserve and only have 9 bottles of my favourite left Domaine Gigondan left 2000 Cuvee 
	

	
	
		
		

		
			





, should have stocked up more than a case! Oh and by the way, if anybody else is a wine person around here, drop me a line on your favourite/recommended wines.

 Quick question, I'm not positive on how to wire up the 2K trimpot, I'm guessing that I have pin 1 attached to the 1K resistor and pins 2 and 3 grounded while initially having the full 2K resistance between pin 1 and pins 2 and 3. Wow too many "ands", simply 1 -> 2,3.


----------



## mb3k

Awesome Fallen,
 I've been wondering what caps would be a collaborative preference. Originally I was lazy and ordered all SILMIC II's for the electrolytic caps, but cancelled it. 
 Thanks for the new BOM, it helps a lot. I'm going to swap out my current C14 & C2's for the Mundorf's.

 BTW, here's my build walkthrough... but obviously the electrolytic install steps still need to be written:
http://www.mb3k.com/soha.html

_Edit:_ One question, you have your fuse rated at 0.5A. Any reason to deviate from the recommended 0.25A fuse (from the Headwize article)?

_Edit 2:_ Why such the difference in capacitance:
 C1, C13: You have it spec'ed to be 470uF/25V compared to 1000uF/10V from the original article


----------



## FallenAngel

Quote:


  Originally Posted by *mb3k* 
_Awesome Fallen,
 I've been wondering what caps would be a collaborative preference. Originally I was lazy and ordered all SILMIC II's for the electrolytic caps, but cancelled it. 
 Thanks for the new BOM, it helps a lot. I'm going to swap out my current C14 & C2's for the Mundorf's.

 BTW, here's my build walkthrough... but obviously the electrolytic install steps still need to be written:
http://www.mb3k.com/soha.html

Edit: One question, you have your fuse rated at 0.5A. Any reason to deviate from the recommended 0.25A fuse (from the Headwize article)?

Edit 2: Why such the difference in capacitance:
 C1, C13: You have it spec'ed to be 470uF/25V compared to 1000uF/10V from the original article_

 

Thanks for posting the walkthrough, I read it earlier and thought it very helpful to use when making the PCB version.

 As for the fuse, the reason why I got the 0.5A instead of the headwize article recommendation of 0.25A, is I saw Digi01 recommending a 0.3A fuse and though, hell why not, I'm sure 1/2 A isn't going to kill anything any more than 1/3 Amp will. But honestly, I just didn't pay as much attention to a fuse. From what I've seen before, if it blows up, it blows up BIG, so I thought a bit of a larger fuse woun't matter.

 470uF/25V C1 and C13 were used because simply because of dsavitsk's comment on the first page, having not been sure what rating the caps should have been, I simply chose a nice in-between value in the Panasonic FM line.


----------



## FallenAngel

Hey everyone,

 I just finished putting together my breadboard SOHA with Diamond buffers and Offset Servo, and of course I'm running into problems 
	

	
	
		
		

		
		
	


	



 I checked the voltages:
 B+ : 58V
 +12 : +12.0
 -12 : -12.1
 Plate: This is where I'm getting a weird one, it's reading 55V-60V depending on how much I turn the plate resistor. The resistor I used was 1K and a 2K trimpot which gave me roughly 58V-62V, now using the stock 562Ohm resistor and 2K trimpot, I'm still seeing 55V-60V. There must be something wrong somewhere, but I'm really not sure how it would affect this value. Any suggestions?

 I'll post pics of the boards soon, but I'm not sure how much help it would be since I layed it out myself and it took ME 15 minutes to figure it out (some parts had to wait 2 weeks for).

 Also, should stick with the stock OPA2134 or maybe bump it up to something nicer?

 Thanks!


----------



## dsavitsk

Quote:


  Originally Posted by *FallenAngel* 
_I checked the voltages:
 B+ : 58V

 Plate: This is where I'm getting a weird one, it's reading 55V-60V depending on how much I turn the plate resistor._

 

If you are getting B+ on the plate, it probably means that the tube isn't conducting. Likely reasons for this are that you don't have the heater connected, or the cathode does not connect to ground.

  Quote:


 Also, should stick with the stock OPA2134 or maybe bump it up to something nicer? 
 

I'd stick with it until you get things working, then worry about tuning the sound second.


----------



## cetoole

Quote:


  Originally Posted by *FallenAngel* 
_Hey everyone,

 I just finished putting together my breadboard SOHA with Diamond buffers and Offset Servo, and of course I'm running into problems 
	

	
	
		
		

		
		
	


	




 Also, should stick with the stock OPA2134 or maybe bump it up to something nicer?

 Thanks!_

 

So, which is it, OPA2134 or Diamond Buffer, or are you using both with the DBs in a feedback loop, in which case the servo shouldnt be necessary. Or are you talking about the servo opamp, in which case, there should be no purpose to change it.


----------



## FallenAngel

dsavitsk: I'll look into that tomorrow, thanks.

 cetoole: There is a version of the schematic I'm using in Post #25 which I think should answer everything (read as: I have no idea, you lost me long time ago, I just like to build stuff and usually do it alright if schematic available 
	

	
	
		
		

		
		
	


	




 ).

 By the way, what exactly is the servo?
 Also, I didn't hook up the LED yet, could this possibly cause a problem in the heater supply?


----------



## cetoole

Quote:


  Originally Posted by *FallenAngel* 
_dsavitsk: I'll look into that tomorrow, thanks.

 cetoole: There is a version of the schematic I'm using in Post #25 which I think should answer everything (read as: I have no idea, you lost me long time ago, I just like to build stuff and usually do it alright if schematic available 
	

	
	
		
		

		
		
	


	




 ).

 By the way, what exactly is the servo?
 Also, I didn't hook up the LED yet, could this possibly cause a problem in the heater supply?_

 

I see. In that schematic, the opamp is only serving as a DC servo, whos purpose is to read the DC offset, and generate and output the inverse of it in real time to null the DC on the output of the amplifier. Say the Diamond Buffer you built was to put out 0.6vdc, the servo would inject -0.6vdc, and the output would appear to have 0vdc. It is filtered so that it only affects extremely low frequencies, those below just a couple hz. Because of this, it has no effect, or some people argue, minimal effect on audio frequencies. Its just another way for people to get rid of dc offset, without having to resort to coupling caps. Obviously this is an incomplete explanation, but I am just getting ready for bed; its been a real long day. For this servo purpose, the OPA2132 is just fine, and I wouldnt replace it.

 Speaking of coupling caps, these 0.1uf teflon foil caps I just got are huge! Much bigger than my Vitamin Q's, even the ones 10x greater capacity. Bet they would work nice in a stoopid though.

 NOTE: The DC servo is completely different than a mechanical servo, so those of you who dont like servos, and advocate replacing them with coupling caps, dont try and replace the motor in your CDP with a capacitor, it wont work.


----------



## tomb

Quote:


  Originally Posted by *cetoole* 
_NOTE: The DC servo is completely different than a mechanical servo, so those of you who dont like servos, and advocate replacing them with coupling caps, dont try and replace the motor in your CDP with a capacitor, it wont work._

 

Now you tell me! I ordered some Futaba servos's from Tower Hobbies for the SOHA, but I couldn't figure out where to put the pushrod.


----------



## FallenAngel

Quote:


  Originally Posted by *cetoole* 
_I see. In that schematic, the opamp is only serving as a DC servo, whos purpose is to read the DC offset, and generate and output the inverse of it in real time to null the DC on the output of the amplifier. Say the Diamond Buffer you built was to put out 0.6vdc, the servo would inject -0.6vdc, and the output would appear to have 0vdc. It is filtered so that it only affects extremely low frequencies, those below just a couple hz. Because of this, it has no effect, or some people argue, minimal effect on audio frequencies. Its just another way for people to get rid of dc offset, without having to resort to coupling caps. Obviously this is an incomplete explanation, but I am just getting ready for bed; its been a real long day. For this servo purpose, the OPA2132 is just fine, and I wouldnt replace it.

 Speaking of coupling caps, these 0.1uf teflon foil caps I just got are huge! Much bigger than my Vitamin Q's, even the ones 10x greater capacity. Bet they would work nice in a stoopid though.

 NOTE: The DC servo is completely different than a mechanical servo, so those of you who dont like servos, and advocate replacing them with coupling caps, dont try and replace the motor in your CDP with a capacitor, it wont work._

 

Thanks, that makes sense, but unfortunatly, in mine, it doesn't work, I'm getting like 2V offset!

 Also, could this whole plate voltage being B+ voltage be caused by the cathode being connected backwards (just a thought)?


----------



## steinchen

the 470k feedback resistor (at the output of the opamp) is probably too large, with the buffers I've build for the SOHA so far 100k has been the maximum value to give enough regulation headroom to the opamp. Try a smaller feedback resistor of aprox 50k.


----------



## FallenAngel

Quote:


  Originally Posted by *steinchen* 
_the 470k feedback resistor (at the output of the opamp) is probably too large, with the buffers I've build for the SOHA so far 100k has been the maximum value to give enough regulation headroom to the opamp. Try a smaller feedback resistor of aprox 50k._

 

Will do, thanks.

 One quick question, I'll need the OPA2134 for another project, would it matter much if I'm using an AD823?


----------



## tomb

AD823 is limited to only 15ma output current. It would not be a good choice in the SOHA, IMHO.


----------



## FallenAngel

Cool, no AD823 for the original SOHA. What about for the purpose I'm using it using it as an offset servo opamp?

 And would someone recommend a good opamp to use in the PCB version of the SOHA (boards shipping very soon).


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* 
_Cool, no AD823 for the original SOHA. What about for the purpose I'm using it using it as an offset servo opamp?_

 

the most important specs for an dc servo opamp are low input bias current and good dc specs (-> jfet input opamps). Furthermore don't pick an ultra fast opamp since it may lead into trouble, you're looking for slow dc operation here. TL071 and TL081 are just fine for this kind of job, ad823 should be fine too.

  Quote:


  Originally Posted by *FallenAngel* 
_And would someone recommend a good opamp to use in the PCB version of the SOHA (boards shipping very soon)._

 

for a standard build the recommended opa2134 is a good choice


----------



## FallenAngel

Quote:


  Originally Posted by *steinchen* 
_the most important specs for an dc servo opamp are low input bias current and good dc specs (-> jfet input opamps). Furthermore don't pick an ultra fast opamp since it may lead into trouble, you're looking for slow dc operation here. TL071 and TL081 are just fine for this kind of job, ad823 should be fine too._

 

Thanks. Quick question, would a chip like the OPA2137 work here. I see the Ib is 5pA, but I'm really not sure on what "DC Specs" mean. I've still got 2 of these lying around.

  Quote:


  Originally Posted by *steinchen* 
_for a standard build the recommended opa2134 is a good choice_

 

Would the build benefit from using a nicer chip, something like the OPA2227 or OPA2107 or would it be not really worth it?


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* 
_would a chip like the OPA2137 work here. I see the Ib is 5pA, but I'm really not sure on what "DC Specs" mean. I've still got 2 of these lying around._

 

yes, the opa137 has low input bias currents, is unity gain stable and not too fast. dc specs (e.g. offset voltage) is not that critical.

  Quote:


  Originally Posted by *FallenAngel* 
_Would the build benefit from using a nicer chip, something like the OPA2227 or OPA2107 or would it be not really worth it?_

 

not as dc servo opamp but as SOHA output opamp I assume !? Anyway, in both cases no. In current gain stages the sonical difference is much smaller than in voltage gain stages and the dc servo has (almost) no effect on sound since it only injects a little dc (no audible audio signal) to balance the offset.


----------



## FallenAngel

Great, thanks! Guess I'll be getting some more OPA2134s.


----------



## tomb

Any FET input opamp with unity gain stability and about 35-45ma current capability will work. That includes OPA2107, OPA627, and naturally, OPA2132. Even AD8620 and AD843 could be good choices (AD843 has 50ma current ouput). BJT opamps will work as well, if the CCS circuit is swapped around. The unity gain requirement still holds, though.

 The standout opamp-only appears to be the OPA551, with a basic current capability of 200ma. One user reported the OPA551 to be superior, after rolling a number of the opamps listed above.

 Beyond that, there are big advantages with incorporating buffers. One user has already combined TO-220 BUF634's with OPA627's and reported outstanding results:
  Quote:


 _"... the buf634's make a HUGE improvement over the dual opamp ..."_


----------



## Yen

Sorry to borrow the thread, but I didnt want to make a new one just for 1 simple question.

 I am not quite sure about the transformer namings, especially when I browse catalogs i.e all the transformers are named: xxVA 2*xxVAC, eg. 30VA 2*15VAC.

 So what 30VCT 400mA means like in Farnell's list of toroids.


----------



## tomb

In that list, this is the one you should probably get: 9531670.

 It's a 15VA, with 2X15V secondaries. That means it has a center tap on it with two secondary leads. "2X15V" is the same as saying "30VCT". When quoted with the "CT" designation, you use the voltage that results from the total. 15VA means Volt-Amps, so that one will have 1Amp at 15V. However, you'll be using two secondaries at 15V, so the current available will be 500ma for each 15V secondary, a perfect size for the SOHA.


----------



## Yen

Quote:


  Originally Posted by *tomb* 
_In that list, this is the one you should probably get: 9531670.

 It's a 15VA, with 2X15V secondaries. That means it has a center tap on it with two secondary leads. "2X15V" is the same as saying "30VCT". When quoted with the "CT" designation, you use the voltage that results from the total. 15VA means Volt-Amps, so that one will have 1Amp at 15V. However, you'll be using two secondaries at 15V, so the current available will be 500ma for each 15V secondary, a perfect size for the SOHA._

 

This is just what I needed to know. Thank you!


----------



## mik000000

I have finished assembly of my soha on 1 of digi's boards. I plugeed it in to test before putting tube or opamp in. (yes, i have read the posts about not worrying too much before amp and tube are in), and all seems ok more or less except the 2 40v readings are both 74.6v same as the 60v reading. And the trimpost seem to have no effect on the reading. Is this normal because the tube is not in?


----------



## FallenAngel

Quote:


  Originally Posted by *mik000000* 
_I have finished assembly of my soha on 1 of digi's boards. I plugeed it in to test before putting tube or opamp in. (yes, i have read the posts about not worrying too much before amp and tube are in), and all seems ok more or less except the 2 40v readings are both 74.6v same as the 60v reading. And the trimpost seem to have no effect on the reading. Is this normal because the tube is not in?_

 

Put the tube in! As tomb said on page 2: there have been posts (*shyly admits to reading and ignoring*) about not turning the amp on without the opamp as it WILL result in serious voltage offsets and it will not be a good idea to get 75V running through you, it'll hurt like a bitch!


----------



## mik000000

Quote:


  Originally Posted by *FallenAngel* 
_Put the tube in! As tomb said on page 2: there have been posts (*shyly admits to reading and ignoring*) about not turning the amp on without the opamp as it WILL result in serious voltage offsets and it will not be a good idea to get 75V running through you, it'll hurt like a bitch!_

 

I did read the thread re not paying too much attention to the voltage until the tube and opamp are in. But I am showing the full B+ voltage at the plates. It looks like the CCS are not doing anything at all.
 I also went back over the various threads, and noticed that digi and mb3k are showing different jumpers for the lnd150 configuration. 
 I agree that the voltage will not be exact without tube/opamp, but 75v on the plates seems to high to me.

 and btw fallenagel, are you aware of meet next weekend? i do not see your name on the list. would love to see youre soha if finished and if you make it.


----------



## FallenAngel

Buddy, try putting the tube and opamp in and make sure to wire up the POT. If you're still getting the same thing, then you'll be in the same boat as me with my breadboard version that I'm working on that is also showing B+ on the plates.


----------



## mik000000

It's alive!!!!!!!!!!!!!!


  Quote:


  Originally Posted by *FallenAngel* 
_Buddy, try putting the tube and opamp in and make sure to wire up the POT. If you're still getting the same thing, then you'll be in the same boat as me with my breadboard version that I'm working on that is also showing B+ on the plates._


----------



## mb3k

I have a question (not to thread crap)
 I will be housing a transformer for my SOHA in a different enclosure, so it will be required that I run an AC power cable from that enclosure to another enclosure with the actual SOHA board in it.
 What is the safest way to carry the AC1, AC2, as well as the center tap to the SOHA enclosure? I'm thinking of using DigiKey #CP-2184 (data sheet here) for AC1, AC2. Then using something else for the center tapped wire, but I don't know what kind of wire (thickness) for safety reasons and what type of connectors.


----------



## tomb

What I'm doing:
Jameco walwart enclosure
two separate, independent leads such as you reference (except I use 2.1mm plugs/sockets)
Each lead has AC# in the center post, and "cold" leg on the outside (reference ground)
Use two walwart sockets in the case panel to match your plug leads. The center posts go to AC1 and AC2, and the grounds from each go to the ground pads

 Just confirmed that this arrangement will work for the Cavalli-Kumisa, too - as long as you don't connect house ground to any of this. dBel reports that house ground screws up his SOHA anyway - the grounds apparently should only come from the two secondaries.

 This is also assuming you really have two secondaries, as with the typical Amveco toroids. You can also do all of this with a DIN plug/jack, but by the time you make up the cable, this will work out for a lot less $$ and trouble.


----------



## mik000000

my SOHA i running and sounds great. i am trying to tweak to match hfd580's. any suggestions as to ideal outout resistors? I put in the standard 150r, and find i am running vol ctrl nearly full. i put the output resistors in sip sockets to be able to change easily.
 any suggestions?


----------



## tomb

Quote:


  Originally Posted by *mik000000* 
_my SOHA i running and sounds great. i am trying to tweak to match hfd580's. any suggestions as to ideal outout resistors? I put in the standard 150r, and find i am running vol ctrl nearly full. i put the output resistors in sip sockets to be able to change easily.
 any suggestions?_

 

ZERO resistors. Seriously, they were put in there to help cut the gain down on low impedance phones. The HD580 is NOT one of those. Try putting some jumpers in those sockets, instead.


----------



## Yen

I am really trying to avoid Farnell, because I have to another expensive shop's services:

 My regular local shop has only 40VA 2x15V toroid and 16VA 2x15V pcb mounted transformer in their list. 

 Could I use either of these? The toroid would output 1,33Amps, does that matter? Or is it just overrated, but doesnt affect any other way?

 How about the pcb mounted transformer, which will output 0,533Amps = almost the SOHA rated. Does it give "different" volts and amps than the toroid somehow? 
	

	
	
		
		

		
			





 Another thing is the pcb costs half the price of the toroid and I would rather use it. 

 As you can see from my rather stopid and simple Qs, I am quite a newbie with transformers...


----------



## tomb

The PCB xfmr will produce hum if you locate it in the same case, or even outside nearby if it's not in a shielded box. This varies widely, but happens enough to be a concern. It can work if you build a multi-leaded walwart power supply, which keeps the xfmr at a distance.

 Toroids are not nearly as much of a problem; their design being inherently "cleaner" from interference. There is every reason to expect that you may mount a toroid in the same case as the amp without problem, assuming you exercise reasonable caution.

 Toroids are more expensive because their design costs more to fabricate. To many, however, the freedom from interference is worth the higher cost.


----------



## Yen

Quote:


  Originally Posted by *tomb* 
_Toroids are more expensive because their design costs more to fabricate. To many, however, the freedom from interference is worth the higher cost._

 

The price difference is for pcb 9euros - 18euros for toroid. I planned to build in the same case, so to purchase extra case, cables, connectors etc together will actually cost more than the toroid. I'll dump the idea. 
	

	
	
		
		

		
		
	


	




 What about the rating of the toroid I mentioned ealier? They already have stocked 40VA -> 1,33A. Is there an issue regarding the amps (SOHA regular 400-500mA vs 1,33A)?

 EDIT: btw, is there a replacement for 1N4002 diode? They do not have these stocked also... (nor the W01G)


----------



## error401

Quote:


  Originally Posted by *Yen* 
_What about the rating of the toroid I mentioned ealier? They already have stocked 40VA -> 1,33A. Is there an issue regarding the amps (SOHA regular 400-500mA vs 1,33A)?

 EDIT: btw, is there a replacement for 1N4002 diode? They do not have these stocked also... (nor the W01G) 
	

	
	
		
		

		
		
	


	


_

 

The transformer should be fine running at under its maximum capacity, however its voltage will be higher than the rated output (the output rating is usually based on full load). If a datasheet is available, it probably includes an I/V curve that will tell you what voltage you should expect with a 0.5A load.

 1N400x is pretty ubiquitous and cheap, I really can't imagine an electronics shop that wouldn't carry them, though they may not have all of the series. Any of 1N4002, 1N4003, 1N4004, 1N4005, 1N4006 etc. should be fine. The last number indicates the maximum reverse voltage. With a 40V tranny even the 1N4001 might be sufficient (with a 50V reverse voltage), but I wouldn't recommend it as the transient voltages could easily peak above this. Its purpose, as far as I can tell from the schematic, is just a snubber. When the load from the circuit is switched off, the magnetic field in the transformer will rapidly collapse, generating a voltage spike on its output that could possibly damage circuit components. The diodes shunt this voltage away from the circuit, protecting it. If you can't find the spec'd part, any silicon rectifier diode that can handle 1A and a reverse voltage of 100V or more should be fine. I wouldn't recommend a schottky diode here though as they have a poor tolerance for reverse voltage.


----------



## JLMaestro

I am also putting the toroidal trafo in a seeparate enclosure but I want an option for an LED to see if the trafo is "on" or not. How would I wire an LED to the 2ndary side of the transformer to do this? Is it even possible to hook up and LED to the AC secondary, or do I need a special AC-LED?


----------



## error401

Quote:


  Originally Posted by *JLMaestro* 
_I am also putting the toroidal trafo in a seeparate enclosure but I want an option for an LED to see if the trafo is "on" or not. How would I wire an LED to the 2ndary side of the transformer to do this? Is it even possible to hook up and LED to the AC secondary, or do I need a special AC-LED?_

 

I'd probably just half-wave rectify it with a 1N400x or similar and then run it through the normal current limiting resistor. It'll flicker at 60Hz though. If that bothers you, you'll need a full wave rectifier. Either way, just run it in parallel with whatever you connect to the output. If you connect the LED directly you might fry it, most aren't very tolerant of reverse voltage.


----------



## Yen

Thank you error and tomb. I found 1N4004, 5, 6, 7 from their list, so that's cleared. 

 I have 2 more questions before I put my order in 
	

	
	
		
		

		
		
	


	




:

 About the W01G bridge rectifier, they have only 1000V (W10G?) not the 100V. Can I use this?

 How about the css. They had J113, but not in stock now. Does it have a replacement? or replacement for 1N5297?


----------



## tomb

I believe any round bridge rectifier will work in the WOG/WOM case, as long as the current rating and voltage is sufficient. Higher values should be OK. A square rectifier might work, too. If you don't actually have the board yet, you can gauge sizes by comparing Digi's recommended rectifier with the one your store has.

 As for the CCS option, that's a discussion that's been made in detail many times. I suggest you refer to the various Headwize threads, especially:

A Simple Tube/Opamp Hybrid Headphone Amplifier (the Headwize Library Project)
The SOHA - Thread 2 (the current SOHA design thread)
Digi's SOHA PCB Walkthrough This will have specific instructions on the board's CCS options. There is a special section on configuring the jumpers.

 I am not aware of a replacement CCS besides the three options listed. The designers went to great lengths to ensure that these would work. So, other than these three: LND150, J113, 1N5297, I don't believe a substitute will work.


----------



## motherone

For connecting the multiple AC taps, I use parts like the 4-pin CB microphone connectors:

http://www.parts-express.com/webpage...hone+connector

 You could also use DIN connectors, speak-on connectors, 2.5mm or 3.5mm stereo jacks (an old DAC I had used these for a +/-15v power supply), or any number of other multi-pin connectors. I personally would stick with the CB or DIN connectors, as you run very little risk of someone mistakenly plugging them into something else.

 Personally, I don't think you should have a huge problem trying to mount a toroidal power transformer in the case with the amp, especially if its shielded. There are tons of amplifiers out there that do this, and one of the main benefits of a toroidal transformer is a reduction of stray magnetic fields. An EI-core could very well inject hum into the amplifier though. If worse comes to worse, you could always put a piece of ferrous metal between the amp pcb and the toroid if you're picking up any hum. I'm planning on mounting my SOHA in a Hammond 1455N2201 case, but I will test with the toroid before doing anything permanent.

 Also, as far as over-sizing your toroids, you're a lot safer with a toroid than an EI core. Toroids generally have pretty good regulation, and the regulation usually improves as you go up in capacity, so the voltage may be very slightly higher with an oversized transformer (within reason). EI cores have terrible regulation, which is why the voltage can skyrocket when the transformer is loaded lighter than what it's specified for. I've used EI cores that are rated at 24VAC/800ma and put out ~30-32VAC with a 300-400ma load, and I've used 1A rated toroids @ 15VAC that put out ~17VAC with an ~100ma load. Usually the datasheet of the toroid will tell you what it's regulation percentage is.

 Finally, on the W0G rectifiers, they come in various voltages, just like the 1N400X rectifier diodes. The voltage rating indicates the maximum safe voltage the rectifier can handle, and generally some percentage of that as the RMS voltage. As with capacitors, going with a higher-voltage rated part doesn't cause any issues (generally speaking). I would encourage anyone who has questions on a part to read the datasheet first. Datasheets are your friend -- they can explain a lot about the part's ratings and what they mean.


----------



## Yen

Any1 of the SOHA builders have any leftover parts?

 I need desperately the CSS (LND150, J113 or 1N5297), cos' my local source did not have any of these but everything else.


----------



## a1rocketpilot

I have a slight issue of my own. I just got my SOHA boards in, and quickly noticed that the tube socket (Azuma 9 pin ceramic from Parts Connexion) won't fit on the board. It has a central tube that goes right through the axis (I presume this is for an LED) that prohibits the pins from coming in contact with the board. Do I just have to get another tube socket that doesn't have this tube, or is there a way to fix this problem (like cutting that tube down a bit)?

 Aditya


----------



## JLMaestro

I've dove deep into the Headwize thread and found this scheme to put an LED on the 2ndary.
 Would this be feasible, and would I still get a 60Hz "flicker" with this?


----------



## error401

Quote:


  Originally Posted by *JLMaestro* 
_I've dove deep into the Headwize thread and found this scheme to put an LED on the 2ndary.
 Would this be feasible, and would I still get a 60Hz "flicker" with this?



_

 

Yes, the LED only conducts for half the cycle, and is above its threshold voltage for less time. It may not be noticable though; 60Hz is pretty fast, though you may want to up the LED current a bit over what you normally use as this is basically crude PWM. I'm not sure of the purpose of the 1N4148 in that circuit; my guess is that it's there to balance load on both sides of the waveform. It may reduce supply ripple.

 If you can't stand the flicker, set up a bridge rectifier with a rail cap, as below. Costs pennies, but is it really worth it? Use any diode that can stand the voltage. 1N4148 or 1N4001 is fine. Use whatever you use in your power supply. Around 100uF on the cap should be ample to keep the LED on all the time with a fairly stable current, voltage must be at least the rail-to-rail nominal output of the trafo. Choose your resistor as normal for LEDs since you're now running a poorly regulated, but DC system.

 Edit: Hmm I really should proofread these schematics before I post them. If you hadn't noticed, the bridge rectifier (or LED & cap) is backwards. Flip the bridge on the horizontal (or reverse all the diodes) or flip the LED & cap. The + of the rectifier is the two cathodes (marked ends) tied together, the - is the anodes.





 Overkill. Just eat the 60Hz flicker and pretend it's not there.


----------



## FallenAngel

Quick thing, that PSU schematic is a very old version which isn't used by the PCB version.

 a1rocketpilot, just cut the damn thing, you'll need to anyway, no matter how you plan to install the led just for the socket to fit the board.


----------



## FallenAngel

I'm all frustrated today! More hours spent on this breadboard SOHA with DBs and still no success! Bah!

 I've taken steinchen's suggestion and changed the feedback resistor to 50K, but I'm still getting some serious offset, but I think it's caused by a different problem.

 I double checked basically everything and I'm still getting B+ voltage on the plate with little or no adjustment from the trimpots.

 As per dsavitsk's analysis (I really never could actually say that name), I'm really not sure what's wrong. I think the cathode to grounded and heater are connected since Pin4 to ground shows -12.4V and Pin5 to Ground is a dead 0V.

 Of course, in the middle of writing this message I had a thought, could this be because of some screwup with the J113's? If they're hooked up wrong or something like that, would it cause this problem? I know B+ going into them is around 55V and plate voltage going out of them is around there as well, could it be a problem with them?


----------



## tomb

You are building Runeight's proposed design option of DB's with an opamp as a DC servo. Since no one built this and vetted his design (including him), perhaps you should post your issues on the SOHA design thread at Headwize. You are building the P2P version, so there shouldn't be any conflict with his Digi-SOHA PCB issues.


----------



## FallenAngel

Well, I had some nice success today. Fully able to adjust plate voltage to 40.0V on both plates. Stupid me installed the J113's backwards 
	

	
	
		
		

		
		
	


	




 Unfortunately though, I'm still getting a good 3V of DC offset on the output which I'm guessing is caused by some serious issues with the buffer. I'll be looking at it closely as soon as I get a chance. For now though, any advice on what kind of buffers to use if these don't work out for me would be appreciated.

 I'm also very curious at the other SOHA Class-A designs but I can't seem to find the schematics anywhere, and that's after looking through the ENTIRE 2 soha build threads


----------



## tomb

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Well, I had some nice success today. Fully able to adjust plate voltage to 40.0V on both plates. Stupid me installed the J113's backwards 
	

	
	
		
		

		
		
	


	




 Unfortunately though, I'm still getting a good 3V of DC offset on the output which I'm guessing is caused by some serious issues with the buffer. I'll be looking at it closely as soon as I get a chance. For now though, any advice on what kind of buffers to use if these don't work out for me would be appreciated.

 I'm also very curious at the other SOHA Class-A designs but I can't seem to find the schematics anywhere, and that's after looking through the ENTIRE 2 soha build threads 
	

	
	
		
		

		
		
	


	


_

 

That's why I suggested posting at Headwize and asking the questions of Runeight directly.

 The only discrete buffer ever suggested - by the original designers - is the one you're trying to build. The schematic you're working from and a simple suggestion for a BUF634 were the only buffer schemes presented by the original designers, before there was a falling out with Digi and his boards.

 Some of us are trying to add monolithics inside the feedback loop of the opamp output (as suggested), but Steinchen and Digi are the only ones that have built any sort of discrete buffer. Digi's appears to be a tiny little plug-in DB without a DC servo, so it may have huge offset with limited current capability compared to monolithics. That's my own opinion, because Runeight suggested the DC servo whenever DB's were mentioned because of the offset issues.

 Steinchen tried several different types in an attempt to improve on some of the limitations of his Millett DB's (heat, stability, etc.), but it's unclear which ones finally worked - some didn't. He seemed to "lose interest" when some of us started playing around with the monolithic buffers in frustration. We were doing this because early reports are that the basic SOHA, while pretty good, is not up to the sound quality of a Millett with DB's.

 The whole SOHA design development has been politically sensitive since Digi started selling PCB's over the protests of Runeight. That's a shame for most of us, but the atmosphere for support is supposed to be OK if you're building the P2P version. Personally, I wish you would ask - it might promote more discussion from the guys in the know about developing a more potent DB that will work for the SOHA.


----------



## steinchen

Quote:


  Originally Posted by *tomb* 
_Steinchen tried several different types in an attempt to improve on some of the limitations of his Millett DB's (heat, stability, etc.), but it's unclear which ones finally worked - some didn't._

 

basically I built 3 different pure class-A buffer types: a design suggested by AMB with a jfet input stage and a bjt output stage (I called it jisbos), a mosfet push pull and a diamond buffer. I got all 3 buffer types working. On my own SOHA I installed the jisbos buffers (pics are in the gallery of my hp) because they are compact and easy to adjust. The jisbos is the only buffer that doesn't need a dc-servo. Even with a tracking dual rail psu and perfectly matched transistors on the buffers I got huge dc offsets with mosfet and diamond buffers when the dc-servo is disconnected. 

  Quote:


  Originally Posted by *tomb* 
_He seemed to "lose interest" when some of us started playing around with the monolithic buffers in frustration._

 

there was little to zero interest in serious discrete buffers, I had a buffer working for myself and the whole discussion went to monolithic buffers like buf634 and ha5002, therefore I put my project on hold.


----------



## tomb

Quote:


  Originally Posted by *steinchen* /img/forum/go_quote.gif 
_... snip ... there was little to zero interest in serious discrete buffers, I had a buffer working for myself and the whole discussion went to monolithic buffers like buf634 and ha5002, therefore I put my project on hold._

 

With the utmost respect, Steinchen, that may have been a judgment call based on only a few posts. A few of us noobs went off on a simple tangent for some low-hanging fruit of monolithics. The Millett went the same route before DB's - the only difference being that there wasn't this bitter-feeling that seems to persist in the SOHA community.

 The result is that the group of SOHA PCB builders is pretty much left to fend for ourselves in ignorance. Someone with your level of expertise (and communication skills) is no longer involved - and that's a shame. We really need someone like yourself to help us, but most seem to be abandoning ship. The only exception to that is Runeight's declared continued support for those still building the P2P versions. That is why I suggested that FallenAngel post this issue over on Headwize.

 Here lately, when it comes to very technical modifications or revisions to the SOHA, we may be SOL.


----------



## steinchen

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_that may have been a judgment call based on only a few posts._

 

maybe I misinterpreted the existing level of interest, actually I'm in contact with exactly 1 DIYer who is going to build a jisbos buffer based on my surplus protoboards. Anyway, the bulk of the development work has been done, a GB could be started in the near future presumed that there is enough interest.

  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_A few of us noobs went off on a simple tangent for some low-hanging fruit of monolithics._

 

that's just comprehensible. Furthermore it's the only way if you want a direct drop in board. It would have been a lot easier if the SOHA pcb had been laid out with buffer options in mind (like the revMH), but let's stop this issue here, I don't want to add insult to injury.

  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_the only difference being that there wasn't this bitter-feeling that seems to persist in the SOHA community._

 

I agree, but that's a completely different story (and honestly speaking was one reason not to push my buffer project)


----------



## tomb

Quote:


  Originally Posted by *steinchen* /img/forum/go_quote.gif 
_ Quote:


  Originally Posted by *tomb* 
the only difference being that there wasn't this bitter-feeling that seems to persist in the SOHA community.

 

I agree, but that's a completely different story (and honestly speaking was one reason not to push my buffer project)_

 

I was afraid that had something to do with it. In retrospect, the board does seem awfully crowded toward the impossibly small opamp section. OTOH, the case made for a modular approach is no panacea, either. Everything seems to have combined to put the SOHA development into a dead end, effectively.

 Well, here's hoping that somebody changes their mind. Many thanks for your responses.


----------



## FallenAngel

Thanks for the clarification on the situation guys, I really didn't even know.

 I posted my problem and the schematic I'm working with on HeadWize.

 steinchen: I really hope you continue with the diamond buffers, I'm sure quite a few would be interested. Better yet, could you post you schematics so I can try them out. Thanks!


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Better yet, could you post you schematics so I can try them out._

 

np, here you are: dDB2 schematic
 this is how I would build it, the layout for a pcb is also done

 You may simplify the current mirror (axe the two base compensation transistors) when building this. Additionally you got the usual parts options:
 - OPA134 - TL071 - TL081
 - 2n5486 - BF245C
 - MJE243/253 - BD139/140 - BD137/BD138 - 2sc3421/2sa1358
 - 2R2 1W or 2W output resistors instead of two 4R7 0.5W resistors in parallel


----------



## FallenAngel

Wow steinchen, that looks really cool.

 I'm definitely going to try one of these as soon as I get the other one working.

 Just a couple of things I wanted to clarify (ok, maybe lots of things).

 First and foremost, which are the "base compensation transistors", I'm guessing Q9 and Q11, and if I remove them, I'm guessing I'll also be scrapping the resistors R9-R12.

 For the parts list, this is what I'm thinking (read as: please correct me since I know I'll get something wrong)

 Offset Servo:
 IC1: OPA2134, but will try OPA2137 (got 2 lying around from way back).

 C1: Do I really a 1uF here? I already have a pair of .22uF Mundorf ZN's that I'm using in the other servo which I will probably move to this new buffer and put some 0.1uF or 0.47uF Orange Drops in the other.

 C4/C5: 0.1uF X7R Ceramics (don't have any NP0/C0G, but I don't know if they'll be necessary)

 Power Supply addition:
 C6/C7: 1uF Tantalum
 C2/C3: 150uF Electrolytic - How much does quality matter in this position? I have a few Rat Shack 100uF electrolytics, but will probably just get some standard ones from an Sayal Electronics which is very close to my work.

 Buffer:
 BC550/BC560 - Can I replace these with BC327/BC337 - I've got lots of those and it's not easy to find the BC550/BC560 for me locally.

 BD137/BC138 - Can I replace these with BD139/BD140 - same scenario as above.

 Resistors: I'm assuming all are 1% metal film 1/4 watt - except you mentioned the 2 parallel 4R7 - any reason to have this over a single 2R2 1W? I'm assuming this is only because the only 1W MF resistors are 5% instead of 1%.

 "DCS" - Does this just connect the input of the buffer through a 50K resistor to the offset servo and to nothing else?

 Thanks!


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_First and foremost, which are the "base compensation transistors", I'm guessing Q9 and Q11..._

 

Q3 and Q6 are the base compensation transistors. If you omit them you have to wire the current mirror like it is done with the PPA or the dDB


  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_I'm guessing Q9 and Q11, and if I remove them, I'm guessing I'll also be scrapping the resistors R9-R12._

 

That's right if you want to reduce the doubled output stage to a single one 

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Offset Servo:
 IC1: OPA2134, but will try OPA2137 (got 2 lying around from way back)._

 

should be ok. You don't need a fancy opamp here, it doesn't affect the sound, the opamp only induces DC to correct the offset. Pick an opamp with a jfet input and low input bias current. You don't want / need a high speed or high bandwidth opamp here, a jellybean TL071 is just fine.

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_C1: Do I really a 1uF here? I already have a pair of .22uF Mundorf ZN's that I'm using in the other servo which I will probably move to this new buffer and put some 0.1uF or 0.47uF Orange Drops in the other._

 

Don't put exquisite and expensive McapZN's in this position, again it's only the dc servo, a boxed polyester film cap is just fine, metallized polypropylene is the highest grade I'd pick here. C1 and R18 set the corner frequency of the dc servo, that means that the values of the two matter. I must admint I went a little over the top here, 0.22uF and 500k would be more then enough.

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_C4/C5: 0.1uF X7R Ceramics (don't have any NP0/C0G, but I don't know if they'll be necessary)_

 

these two are not crucial, just pick a x7r ceramics or a film cap (polyester would be just fine)

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Power Supply addition:
 C6/C7: 1uF Tantalum
 C2/C3: 150uF Electrolytic - How much does quality matter in this position? I have a few Rat Shack 100uF electrolytics, but will probably just get some standard ones from an Sayal Electronics which is very close to my work._

 

they are just for power supply decoupling/bypassing. 
 1uF: any tantalum or polyester film cap between 1uF and 4.7uF is fine
 100uF: any electrolytic between 100uF and 220uF or so is fine

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Buffer:
 BC550/BC560 - Can I replace these with BC327/BC337 - I've got lots of those and it's not easy to find the BC550/BC560 for me locally._

 

I haven't tried them yet but they sould work too

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_BD137/BC138 - Can I replace these with BD139/BD140 - same scenario as above._

 

yes, no problem

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Resistors: I'm assuming all are 1% metal film 1/4 watt - except you mentioned the 2 parallel 4R7 - any reason to have this over a single 2R2 1W? I'm assuming this is only because the only 1W MF resistors are 5% instead of 1%._

 

correct, 0.5W resistors are 1% metal film and easy to source around the world, 1W or 2W resistors are 5% metal oxide and maybe not that easy to source

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_"DCS" - Does this just connect the input of the buffer through a 50K resistor to the offset servo and to nothing else?_

 

yes (dcs stands for dc-servo)


----------



## FallenAngel

Thanks steinchen!

 Just 2 more little questions, and I'm sure you even know what they are since it's about the only 2 parts on the schematic I didn't ask about 
	

	
	
		
		

		
			





 BF247 - I'm guessing a 2N2586 would do as a replacement here.
 180 Ohm resistors - why 180 Ohms? The original schematic shows 220 and I couldn't find 180Ohm locally. Any reason for this, or was it just the value that was required to get these stable?

 Thanks again!


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_BF247 - I'm guessing a 2N2586 would do as a replacement here._

 

yes, 2n5486 would do, BF245C too

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_180 Ohm resistors - why 180 Ohms? The original schematic shows 220 and I couldn't find 180Ohm locally._

 

that value isn't critical, anything between 160 and 220 Ohms should be fine. The buffer may become unstable when you lower it to about 120 Ohms or below.


----------



## FallenAngel

Thanks again steinchen! I'll start building this thing as soon as I've got the other one cleared up.

 Speaking of which, I'm a little stuck on that one too 
	

	
	
		
		

		
		
	


	




 After blowing up the same capacitor like 4 times and frying both voltage regulators, I've decided to try to build the regular version first to make sure everything else works and then adding the buffers.

 This of course led me to a very strange problem. I'm getting around V- on the output!

 All the other voltages are good, +12V, -12V, -12.6V, 40V on the plates.

 The only thing I'm reading that'll explain this is 4.5V and 9.5V coming from the 0.33uF Mundorf ZN caps going into into OpAmp + which I know shouldn't be right since I thought the caps are only there to get rid of this offset.

 Any ideas?


----------



## mb3k

Quote:


  Originally Posted by *JLMaestro* /img/forum/go_quote.gif 
_I've dove deep into the Headwize thread and found this scheme to put an LED on the 2ndary.
 Would this be feasible, and would I still get a 60Hz "flicker" with this?



_

 

IIRC the street lights down your street flicker at 60Hz, which you cannot see explicitly so the LED connected to the secondary shouldn't be a problem. I'd recommend connecting it from 15-0 (center tap) instead of across the entire 30VAC


----------



## FallenAngel

Yeahooo!!! It works, it works! It's AAAALIIIVEEEE!!! Muahhahaha!

 Yes, I'm very excited. Apparently, I also managed to fry the opamp in the process of building this thing so with a brand new OPA2227, I finally get virtually no offset and it even plays music 
	

	
	
		
		

		
		
	


	




! There is of course a horrid hum, but that's because I didn't even attach the input/output jacks with solder yet and the transformer is a monstrous 30VCT 2Amp used, cheap surplus store found in for a few bucks in a home-made little box of steel sheet.

 I'll attach a proper toroidal that I have and a quick listen before continuing with the buffers.

 Many thanks to Runeight@HeadWize for the help!

 Steinchen, I look forward to building your buffer very soon and already have a breadboard layout almost done and should be starting your buffer hopefully next week. 
	

	
	
		
		

		
		
	


	




 How big of a heatsink would you recommend putting on the BD137/BD138? I've got a few cheap little ones that work at I think 2W. Would this be sufficient or would you recommend a larger one?

 Thanks!


----------



## Yen

Hi!

 I have a little Q about grounding. I use the 3 pin AC inlet, where should I connect the grounding pin? Signal ground, case ground or leave it unconnected?


----------



## tomb

There have been some reports that connecting house ground to the center-tap ground of the SOHA causes _more_ hum, not less.


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* 
_How big of a heatsink would you recommend putting on the BD137/BD138? I've got a few cheap little ones that work at I think 2W. Would this be sufficient or would you recommend a larger one?_

 

Depends on how high you are going to set the bias current. A compact heat sink like DigiKey HS107 or Mouser 532-577202B00 is fine for currents up to at least 50mA per output stage.

  Quote:


  Originally Posted by *Yen* 
_I have a little Q about grounding. I use the 3 pin AC inlet, where should I connect the grounding pin? Signal ground, case ground or leave it unconnected?_

 

connecting signal ground directly to mains protective earth means calling for trouble. Connect the case to only either of these (earth is better from a safety point of view) or connect signal ground directly to the case and earth to case via a ground loop braker (e.g. a 4R7 4W resistor in parallel to a 220nF capacitor)


----------



## FallenAngel

Thanks Steinchen,

 I've got another question though. With the 50K resistor goint to OpAmp Output and 1M / 500K going to OpAmp -, wouldn't this buffer need to have a Mu-Follower CCS vs a regular CCS? As in connecting the cap leading into it above the resistor vs below it?


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_I've got another question though. With the 50K resistor goint to OpAmp Output and 1M / 500K going to OpAmp -, wouldn't this buffer need to have a Mu-Follower CCS vs a regular CCS? As in connecting the cap leading into it above the resistor vs below it?_

 

yes, you're right, good that you're asking, I forgot to mention that: with the low input impedance of 50k the buffer can be used together with the SOHA tube stage in MU-follower configuration only!


----------



## FallenAngel

Quote:


  Originally Posted by *steinchen* /img/forum/go_quote.gif 
_yes, you're right, good that you're asking, I forgot to mention that: with the low input impedance of 50k the buffer can be used together with the SOHA tube stage in MU-follower configuration only!_

 

Would that be a better idea vs making the 50K resistor something like 470K and changing the 1M resistor to 100K? That way it would work with the SOHA in a regular CCS configuration and by making the 1M resistor lower, wouldn't it get the buffer to stabilize a little faster?


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Would that be a better idea vs making the 50K resistor something like 470K and changing the 1M resistor to 100K? That way it would work with the SOHA in a regular CCS configuration and by making the 1M resistor lower, wouldn't it get the buffer to stabilize a little faster?_

 

unfortunately not. The higher the resistor the less regulation headroom for the opamp. Starting at about 150k the opamp probably falls out of regulation and you get dc offset at the output, 100k is the maximum that would work reasonably.


----------



## Yen

What about positioning trimpot? I am using these. Digi01 board's trimpot's position has one circle and two cross marked holes. Where should I put the pin 1 (pls, look the picture of trimpot)?


----------



## tomb

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_What about positioning trimpot? I am using these. Digi01 board's trimpot's position has one circle and two cross marked holes. Where should I put the pin 1 (pls, look the picture of trimpot)?_

 

The small circle on one end of the silkscreen outline signifies the shaft position of the pot.


----------



## FallenAngel

Hi Steinchen,

 I started building your buffer and quickly realized that the BD139/BD140 chips I have are TO-126 and I'll have a fun time trying to put heatsinks on them, not to mention that my idea of miniaturizing the board will be interestingly adjusted for them.

 I'm also having a really hard time finding 4.7Ohm 1/2W 1% resistors. I've got tons of 4.7Ohm 1/4W 1%, but no 1/2Watt. I've found some 1/2W 5% MF resistors at digikey for $0.61 each. Other than that, there's Metal Oxide film 5%, but no 1%.

 Would a 1/4W work here or is it necessary to use 1/2Watt?


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_I'm also having a really hard time finding 4.7Ohm 1/2W 1% resistors. I've got tons of 4.7Ohm 1/4W 1%, but no 1/2Watt. I've found some 1/2W 5% MF resistors at digikey for $0.61 each. Other than that, there's Metal Oxide film 5%, but no 1%.
 Would a 1/4W work here or is it necessary to use 1/2Watt?_

 

two 1/4W 4R7 resistors in parallel are sufficient, alternatively you may pick 1W 2R2 resistors like mouser 594-5073NW2R200J
 1% or 5% doesn't matter here


----------



## FallenAngel

Thanks. I'll try using the 1/4 Watt 1% resistors that I have.

 I'll also be getting some 2N5087/2N5088 and use those instead of BC327/BC337's as the BC550/BC560 substitutes.

 I'm also grabbing a few MJE243/MJE253 and using them as BD137/BD138.

 The transistor changes will be mainly in another version of the buffer. I'll try to get this one built with BC327/BC337 + BD139/BD140


----------



## Yen

Finally got my SOHA running! Thank you Steichen, tomb, error401, Tsappis and every1 else who has helped! 
	

	
	
		
		

		
			





Pics can be found here. Now I am burning in the ElectroHarmonix and JJ tubes. SQ wise SOHA 103 - 2 Cmoy. Didnt know my Grados got such a soundstage! 
	

	
	
		
		

		
		
	


	




 I still got one problem. I have every test points showing fine results, biased the tube to 40V, but the 60V point gives me 70V when the tube is attached. Without the tube, the reading is the correctly 60V. Is that a problem?


----------



## FallenAngel

I really wouldn't recommend taking any voltage readings without the tube in, it might be dangerous.

 If B+ is 70V instead of 60V, something is a little off, are you using the default 30VCT transformer?


 EDIT: Sanity Check question:

 What's the pintout of the 12AU7/ECC82? I've seen people use digi's board with the socket on the front of the board and on back. This can't possibly be right unless there are 2 versions of the board!

 From what I know, if I'm looking at the bottom of the tube, pin 1 is on the first pin going clock-wise after the break. Please correct me if I'm wrong. This would also mean that Yen, buddy, you might have that tube socket flipped.


----------



## rreynol

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_From what I know, if I'm looking at the bottom of the tube, pin 1 is on the first pin going clock-wise after the break. Please correct me if I'm wrong. This would also mean that Yen, buddy, you might have that tube socket flipped._

 

I'm pretty sure you're right. The pin layout of the 12AU7 isn't symmetrical at pin 5. If you are going to mount the tube exposed like that, you have to put the socket on the top side and the capacitors, regulators, etc on the bottom (rotated to get the right pins in the right holes of course).


----------



## Yen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_I really wouldn't recommend taking any voltage readings without the tube in, it might be dangerous.

 If B+ is 70V instead of 60V, something is a little off, are you using the default 30VCT transformer?


 EDIT: Sanity Check question:

 What's the pintout of the 12AU7/ECC82? I've seen people use digi's board with the socket on the front of the board and on back. This can't possibly be right unless there are 2 versions of the board!

 From what I know, if I'm looking at the bottom of the tube, pin 1 is on the first pin going clock-wise after the break. Please correct me if I'm wrong. This would also mean that Yen, buddy, you might have that tube socket flipped._

 

I am using 40VA, cos I couldn't source easily the 15VA. What changes should I make compared to digi's BOM?

  Quote:


  Originally Posted by *rreynol* /img/forum/go_quote.gif 
_I'm pretty sure you're right. The pin layout of the 12AU7 isn't symmetrical at pin 5. If you are going to mount the tube exposed like that, you have to put the socket on the top side and the capacitors, regulators, etc on the bottom (rotated to get the right pins in the right holes of course)._

 

I noticed this and mirrored the tube socket so it is correct. I dont think you will get any sound of out the amp unless you have the tube installed right.

 The amp does work perfectly and the sound is lovely. I am just wondering if the 70V will cause some problems in the long run.


----------



## tomb

The B+ voltage is unregulated, and adjusted only through the bias on the tube. Your 40VA transformer probably drops much less voltage under load than the typical transformer. Depending on the 12AU7 variant, the plate is rated for anywhere from 200 to 300 volts. So, your 70V is not going to cause an issue with the tube. All the caps are rated for 100V in that section as well.

 I'm a little confused at why your B+ voltage would be _higher_ with the tube connected than unconnected, but the SOHA has a documented history of strange readings without all of the components connected. The 60V you read without the tube in may just be a wild coincidence and not related.


----------



## Yen

#"¤¤%#¤%"#¤#¤#""#¤"!!! Sorry for my language...

 The amp, mainly the tube did get some elbow treatment when I did some maintenance on my computer today. Dunno if it was the contact or what, I started to hear regular high tempo tap sound (like some1 nervously tapping fingernails against the table) and irregularly high freqency squeeches (metal against glass). These sounds can be heard only when unsourced or paused music.

 Well, I figured, if the tube got some damage, then changing the tube will fix the problem... EH out, JJ in... Still tapping and squeeching, but not as loud as "damaged tube". The sounds are barely hearable now. It is still annoying me because I know the problem is there, and everytime there is pause in listeling or music is low I will start to listen if the tapping is there (and yes, it is there, even if wished it has miraculously dissappeared 
	

	
	
		
		

		
		
	


	




 ).

 What's the problem with my amp? It is just a thing with tubes and has to be accepted or is it something wrong with my amp? I did check the contacts of the tube sockets and the pcb. Everything is ok there...

 EDIT: "#¤¤"¤"#! Now with the new JJ tube, the tapping and sqeeching jumps up louder for some seconds and then again back to lower volume. This is happening irregularly.

 EDIT2: Note to myself: Get a decent shielded cable or get the amp away from the computer. The amp was connected straight to the mainboard's lineout with cheap mini-rca.

 Apparently the computer or other devices (printer, lcd-display, cable modem or wlan router) causes some sort of interference with the amp/signal. The noises weren't there anymore when I moved the amp downstairs on kitchen table with the laptop.


----------



## FallenAngel

Hey guys,

 I've cased up one of my SOHAs and although I get almost no hum when music is playing, I noticed a few very disturbing noise scenarios.

 1) With no source connected, there is HUGE noise, and it gets worse when I turn up the volume and more so when I touch the knob / RCA jacks.
 2) Source connected, a slight hum with / without music playing, placing my hand behind my power switch (roughly where the transformer sits) completely eliminates this noise. Moving the amp farther from my computer really improves this as well to the point that it's very hard to detect the hum with no music playing.

 Obviously, I'm much more worried about #2. This does seem like a grounding issue, any suggestions on what to do to try to resolve this?

 Thanks in advance.


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_1) With no source connected, there is HUGE noise, and it gets worse when I turn up the volume and more so when I touch the knob / RCA jacks._

 

in case you use the Alps blue velvet simply tie the pot's housing / shaft to signal ground (e.g. by the small screws at the rear)

  Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_2) Source connected, a slight hum with / without music playing, placing my hand behind my power switch (roughly where the transformer sits) completely eliminates this noise. Moving the amp farther from my computer really improves this as well to the point that it's very hard to detect the hum with no music playing._

 

sounds like the transformer and the computer's psu are introducing noise by their electromagnetic radiation. It's always a good idea to move away the amp from transformers as far as possible. Potted toroidals have a much smaller radiation field but I guess you don't want to replace it. Alternatively you may try to shield your amp with sheets of mu-metal or steel.


----------



## Yen

Hi SOHA owners and builders!

 I would like to improve my SOHA, and as you all can see from my sig, my SOHA is built with pretty mediocre components. How can I improve it?

 First, I have thought of getting better signal film caps, e.g. Mundorf ZN or Supreme, Auricap or Jensens. Going to the right direction? I am thinking spending about 10-15$ per cap. Solens are cheap and can be sourced locally, but are they worth the money compared to more expensive ones?

 As for the opamp, I am currently using regular OPA2132. I am waiting for a good diamond buffer design, but apparently SOHA is now passé and new amps have lured the diy community so that no1 is designing dbs for SOHA. Therefore only option for me is to start opamp rolling? with what opamps would you recommend?

 And what about tubes? I am currently running a JJ ECC82, which I like alot. Would the SQ improve if I start seeking for more expensive tubes, such as NOS or e.g. clear top RCAs (35$) which can be sourced from same shop with Solens 
	

	
	
		
		

		
		
	


	




?

 And what about elec caps. The ones I use is regular Jamicon-labeled. Blackgates or Muse worth the money? Or just Panasonic FM/FCs?

 Thank you for your help in advance!


----------



## steinchen

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_How can I improve it?_

 

the biggest improvements should be obtainable by a decent class-A buffer and high quality coupling caps

  Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_First, I have thought of getting better signal film caps, e.g. Mundorf ZN or Supreme, Auricap or Jensens. Going to the right direction? I am thinking spending about 10-15$ per cap. Solens are cheap and can be sourced locally, but are they worth the money compared to more expensive ones?_

 

don't spend $15 for a SOHA cap, it would be a waste of money, particulary since the 12AU7 is all but a high end tube. The Mundorf MCap is a decent cap, the Mundorf Zn is the most expensive one I'd pick (got Zn in my SOHA). The Supremes would be overkill and a waste of money.

  Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_And what about tubes? I am currently running a JJ ECC82, which I like alot. Would the SQ improve if I start seeking for more expensive tubes, such as NOS or e.g. clear top RCAs (35$) which can be sourced from same shop with Solens 
	

	
	
		
		

		
		
	


	




?_

 

The JJ is one of the best tubes (again, got them in my SOHA too). You may try a NOS tube from GE (soft and smooth) or a new Electroharmonix (more lively and bright), but don't spend more than 10 bucks for a tube. The expensive tubes are priced that high due to their shortness and not due to superior performance. Don't expect to "improve" the SQ by a large amount, you rather change the sonic signature (within certain limits).

  Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_And what about elec caps. The ones I use is regular Jamicon-labeled. Blackgates or Muse worth the money? Or just Panasonic FM/FCs?_

 

The elcos are just for psu bypassing and not in the signal path, don't waste your money for boutique caps there. Pansonic FC/FM or Nichicon UHE/HE are very nice caps and more than sufficient.


----------



## tomb

I agree with most everything that Steinchen has said. I certainly haven't had the chance to experiment with everything. However, reports are that there are some other tweaks that will help:

 It's true the electrolytics are used for power bypass - except for one pair: C1 and C13 are the cathode bypass capacitors for the tube. As such, the signal goes through them. A decent boutique cap in those positions is pretty much standard on most SOHA's that have been pictured or described. Elna's, Nichicon Muse KZ's, and I'm using Muse ES's in mine. Reportedly, Digi himself has used a couple of oil-filled caps in those positions for a noticeable improvement in sound. The uF size can be as little as 220uF, I believe (1000uF is design), and voltage is small - 16V. So, there are a lot of possibilities in that range.

 One particular tweak could be second to Steinchen's Class-A Buffer. Since he gave up early on offering a buffer to the rest of us as he did with his excellent Millett DB, we'll never know for sure. Yet, there is a big gain by rolling different opamps - AD8620, AD743, OPA2604, OPA627's, LM4562, OPA551 have all been tried in various SOHA's with improvement claims over the standard OPA2134. The OPA551 is a great choice because of it's 200ma current capability - countering the essential weakness in the SOHA output stage.

 Apparently, the biggest improvement in the output stage is achieved by adding the BUF634 within a feedback loop with the opamp. Several have experimented with it, but it puts a premium on the voltage regs on the board - heat sinks are mandatory. Reports are that the sound quality is as good or better than the Millett with the DB's. GregVDS even produced a few boards that combined the opamps and buffers on a single, small board that plugs into the opamp space on the SOHA. That's a problem with the SOHA board - the output opamp stage is painted into a corner with little room. It makes the whole thing very compact, but at a penalty in flexibility.


----------



## a1rocketpilot

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Apparently, the biggest improvement in the output stage is achieved by adding the BUF634 within a feedback loop with the opamp. Several have experimented with it, but it puts a premium on the voltage regs on the board - heat sinks are mandatory. Reports are that the sound quality is as good or better than the Millett with the DB's. GregVDS even produced a few boards that combined the opamps and buffers on a single, small board that plugs into the opamp space on the SOHA. That's a problem with the SOHA board - the output opamp stage is painted into a corner with little room. It makes the whole thing very compact, but at a penalty in flexibility._

 

Why must the BUF634 be inside the feedback loop? What would happen if you placed it outside of the loop? What about if you used just the BUF634 and no opamp, modding the circuit so you don't have a feedback loop at all?

 Aditya


----------



## mb3k

Deleted


----------



## Yen

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Yet, there is a big gain by rolling different opamps - AD8620, AD743, OPA2604, OPA627's, LM4562, OPA551 have all been tried in various SOHA's with improvement claims over the standard OPA2134. The OPA551 is a great choice because of it's 200ma current capability - countering the essential weakness in the SOHA output stage._

 

I found some OPA551 of my stash, but as they are singles, I need an (Brown dog) adaptor?

 Any1 wants to sell me some, 2SO-DIP or 2DIP-DIP? 
	

	
	
		
		

		
			





 They are (again) difficult to source here... 
	

	
	
		
		

		
		
	


	




 Or could you show me a place with good inventory of caps, pots and these adaptors, so I can order all from the same place.


----------



## steinchen

Quote:


  Originally Posted by *a1rocketpilot* /img/forum/go_quote.gif 
_Why must the BUF634 be inside the feedback loop? What would happen if you placed it outside of the loop? What about if you used just the BUF634 and no opamp, modding the circuit so you don't have a feedback loop at all?_

 

you'd get significant dc offset on the outputs

  Quote:


  Originally Posted by *tomb* 
_It's true the electrolytics are used for power bypass - except for one pair: C1 and C13 are the cathode bypass capacitors for the tube. As such, the signal goes through them._

 

correct, I overlooked those capacitors, in these positions "audio grade" electrolytics should be better

  Quote:


  Originally Posted by *tomb* 
_One particular tweak could be second to Steinchen's Class-A Buffer. Since he gave up early on offering a buffer to the rest of us as he did with his excellent Millett DB, we'll never know for sure._

 

I'll start an interest check at headwize tonight to clean up the issue (no pun taken). If there is interest we'll have a group buy. No interest no GB. I'm curious.


----------



## Yen

Quote:


  Originally Posted by *steinchen* /img/forum/go_quote.gif 
_I'll start an interest check at headwize tonight to clean up the issue (no pun taken). If there is interest we'll have a group buy. No interest no GB. I'm curious._

 

Definately in for few boards! 
	

	
	
		
		

		
		
	


	




 I have found for reasonable price Cerafines 1000uF and SilmicII 470uF for C1/C13, both costs 2,5euros / per cap. Or should I buy SilmicII 1000uF for 5e/cap, worth the double price?

 Btw, I inserted an OPA2227 to replace 2132 and noticed that my stock 770/80 isnt as boomy as it has been before. Dunno also if I passed some magical and mysterious burn-in margin with my tube or beyers. I have recently listened also quite a lot of bassless acoustic music, but when I listened old familiar records the boomyness is definately gone/less. Means that there is less bass, but with these beyers that's just a positive change! 
	

	
	
		
		

		
		
	


	




 I guess you can make a big difference with opamps.


----------



## tomb

Steinchen,

 As you are probably aware, I would definitely be interested. I don't want you to lose your interest again, but wondered if you could take another look at room on the board (don't laugh!). If you put the coupling caps on the bottom, and also C7 and C8, which are small 47uF caps, there is a pretty good rectangle space created, although offset considerably from the opamp socket position.

 Just a thought - I certainly don't want to discourage you again.

 Yen - 
 I think any Elna would do well in those positions. I have yet to find out why Runeight sized the caps at 1000uF - most amps are 220uF in this position. So, I think the 470uF's would be fine, but that's up to you.

 The OPA2227 has been previously noted in CMoy's as having less bass than the OPA2132/34, so your experience is not surprising. The OPA551's are a good bet, and will probably sound best on low impedance phones unless you go the BUF634 route (because of the higher current). Brown Dogs are at Cimarron Technology or at Tangent's Audio Shop. Tangent ships internationally, for sure.


----------



## makasin

which opamp would you guys recommend for a user of Grado sr225s and Senn HD650s? I am in the process of building my first DIY amp (SOHA v3 point to point) and I bought a OP2134PA. Is that a decent opamp for starters? Which one would be recommended with the basic SOHA setup (no buffers)? How much more work is required to pop in some buffers and would I need to change anything?


----------



## Yen

Quote:


  Originally Posted by *makasin* /img/forum/go_quote.gif 
_Which one would be recommended with the basic SOHA setup (no buffers)? How much more work is required to pop in some buffers and would I need to change anything?_

 

2134/2 is a project default and I think sounds pretty ok for starters.

 You dont need to do anything extra if you intend to use buffers in the future, unless you want to leave space for the bufferboard on top of the socket or it can be wire installed also, then you can install the buffer anywhere... And if you are building from scratch you can even integrate the buffer right to the design...

 BTW,
 I am looking a decent shop in EU, which sells "boutique" caps, and in case of electrolytics other than blackgates, with reasonable shipping charges. De audiofabriek in Netherlands has good inventory, and I were bying from there. I am bying caps for my soha and alien, but they charge heavily on shipping (12 caps cost 22euro and shipping to Finland 17e). That's more than most place from US... Any european wanna reveal their secret source?


----------



## steinchen

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_I am looking a decent shop in EU, which sells "boutique" caps, and in case of electrolytics other than blackgates, with reasonable shipping charges. De audiofabriek in Netherlands has good inventory, and I were bying from there. I am bying caps for my soha and alien, but they charge heavily on shipping (12 caps cost 22euro and shipping to Finland 17e). That's more than most place from US... Any european wanna reveal their secret source? 
	

	
	
		
		

		
		
	


	


_

 

http://www.audio-cube.nl/elna.htm shipping within Europe 9 EUR

 Schuro.de carries Elna, Panasonic, Mundorf and Intertechnik but does not ship to foreign countries


----------



## Yen

Quote:


  Originally Posted by *steinchen* /img/forum/go_quote.gif 
_http://www.audio-cube.nl/elna.htm shipping within Europe 9 EUR

 Schuro.de carries Elna, Panasonic, Mundorf and Intertechnik but does not ship to foreign countries_

 

I found that also. But they dont have any films. 
	

	
	
		
		

		
		
	


	




 Anyhow, I think I'll buy from there, if I can get another Finn joining the order with me.

 What do you think about Audyn-Caps (and more precisely Audyn-Caps Plus) by Intertechnik. They are mostly used and are famous for speakers, but how do they sound in this case?

 And is this JISBOS-buffer a finished design? I think I can get a guy here in Finland with adequate equiment to produce some protoboards.

 If I understood it correctly, I need to duplicate the schem to make it dual? How should it be connected to the opamp socket (mainly what point to what socket)?

 And what does those C1/C2 caps, and ground to ground outside the schem means?


----------



## tomb

Dsavitsk's web site is where I always look for capacitor reviews. He and I are in agreement with the caps I've used so far. 
	

	
	
		
		

		
		
	


	




 Very highly recommended:
http://www.ecp.cc/cap-notes.html. He's added a lot more stuff recently, too.

 You might notice that, in general, he finds that caps that are supposed to be great speaker caps - may not be that great in a headphone amp.

 Maybe someone's already mentioned it, but have you tried Parts Connexion? They're in Canada and ship international all the time - don't know their shipping cost, though.


----------



## steinchen

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_What do you think about Audyn-Caps (and more precisely Audyn-Caps Plus) by Intertechnik. They are mostly used and are famous for speakers, but how do they sound in this case?_

 

I haven't tried them yet, so I cannot comment their signature. From hearsay I think they are nice caps, but not as good as Mundorf.

  Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_And is this JISBOS-buffer a finished design? I think I can get a guy here in Finland with adequate equiment to produce some protoboards.

 If I understood it correctly, I need to duplicate the schem to make it dual? How should it be connected to the opamp socket (mainly what point to what socket)?_

 

The design itself is considered to be finished, the schematic you linked to is for a single channel. I already had a small run of protoboards and got one set doing it's job in my SOHA. Expect a thread at headwize next weekend, I almost finished evaluating an alternative.


----------



## Yen

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Dsavitsk's web site is where I always look for capacitor reviews. He and I are in agreement with the caps I've used so far. 
	

	
	
		
		

		
		
	


	




 Very highly recommended:
http://www.ecp.cc/cap-notes.html. He's added a lot more stuff recently, too.

 You might notice that, in general, he finds that caps that are supposed to be great speaker caps - may not be that great in a headphone amp.

 Maybe someone's already mentioned it, but have you tried Parts Connexion? They're in Canada and ship international all the time - don't know their shipping cost, though._

 

Yeah, I have read all the reviews I found so far (the 21 cap review in avguide and dsavitsk's). I even read the review by tony gee (humblehomemadehifi) for speakers... 
	

	
	
		
		

		
		
	


	




 Those Audyns has recieved good reviews for speaker x-overs.

 PCX is my last resort. I dont think their shipping is too much, but since I only need few caps and am pretty impatient, so I would like those caps asap and as low as possible. Of course, I could always wait a bit, and buy a bigger bunch later. Another option for Europeans are Acoustic Dimension, which is a dutch shop. They cary blackgates and charges significantly low shipping costs (only 5-7e), but they too dont have any films except über expensive Jensens or Jupiter... 
	

	
	
		
		

		
		
	


	




 Is there a big difference between blackgate standard and N/NX/NX-Hi-Q? By big I mean worth the double price.


----------



## tomb

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_Yeah, I have read all the reviews I found so far (the 21 cap review in avguide and dsavitsk's). I even read the review by tony gee (humblehomemadehifi) for speakers... 
	

	
	
		
		

		
		
	


	




 Those Audyns has recieved good reviews for speaker x-overs.

 PCX is my last resort. I dont think their shipping is too much, but since I only need few caps and am pretty impatient, so I would like those caps asap and as low as possible. Of course, I could always wait a bit, and buy a bigger bunch later. Another option for Europeans are Acoustic Dimension, which is a dutch shop. They cary blackgates and charges significantly low shipping costs (only 5-7e), but they too dont have any films except über expensive Jensens or Jupiter... 
	

	
	
		
		

		
		
	


	




 Is there a big difference between blackgate standard and N/NX/NX-Hi-Q? By big I mean worth the double price._

 

That Acoustic Dimension place has the Jupiter's. Very many - including Dsavitsk - think those are the best, period.

 Steinchen: that's good news about the SOHA buffers.


----------



## FallenAngel

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Steinchen: that's good news about the SOHA buffers._

 

Yup, absotely great news for the community, another reason to lose sleep for me 
	

	
	
		
		

		
		
	


	




 I didn't even get a chance finish the other 2 DB's, now there's this one too, aaah!

 Good thing that with a P2P SOHA, when something blows up (and it has many, many times in testing), I don't have to worry about killing a PCB.

 Hopefully I'll find why my other 2 buffers keep burning the opamp or blowing capacitors.


----------



## a1rocketpilot

Steinchen, please keep us updated as to whether you will formally release your diamond buffer design. My SOHA is more or less going to be maxed (for those wondering, PRP and Riken resistors (and Holco's for the values not stocked by PRP, only in the CCS), Rubycon ZA/ZL electrolytics, Mundorf ZN coupling caps, and handmade rectifier bridges using Stealth diodes). A discrete buffer is really all I'm missing to really extract max performance from this amp. Glad to see you haven't given up the pursuit of SOHA perfection!

 Aditya


----------



## tomb

Man! If you keep up with HeadWize, Steinchen's got a lot on his plate. 
	

	
	
		
		

		
		
	


	




 What with helping Runeight and Amb on the CKKIII, helping Runeight on a brand new project with the EHHA, DB boards on the Millett and now - hopefully the SOHA, and consulting on just about everything that uses a discrete output stage, Steinchen's become one of the elite resources for the DIY headphone community.


----------



## a1rocketpilot

Woah, way to go dude! I know about the CKKIII, but what is the EHHA (don't mean to thread hijack, but could someone just post a link or something)?

 Aditya


----------



## Yen

Quote:


  Originally Posted by *a1rocketpilot* /img/forum/go_quote.gif 
_Woah, way to go dude! I know about the CKKIII, but what is the EHHA (don't mean to thread hijack, but could someone just post a link or something)?

 Aditya_

 

Just roll down Headwize's DIY Workshop. About middle to the end of the topics.


----------



## Yen

This weekend, I removed the output resistors (R6/R16, 150ohms) from my SOHA boards.

 Now, I started to hear some noise, irregular snaps and taps, low volume. Is this normal? Should I put those resistors back, maybe with lower value...?


----------



## tomb

Quote:


  Originally Posted by *a1rocketpilot* /img/forum/go_quote.gif 
_Woah, way to go dude! I know about the CKKIII, but what is the EHHA (don't mean to thread hijack, but could someone just post a link or something)?

 Aditya_

 

Embedded Hybrid Headphone Amplifiers - EHHA Another one by Runeight, with major involvement by Steinchen. It looks to be the next great hybrid tube amp, with a killer SS output stage. However, saying it was still in development may be an understatement. They're way over my heads with it. When Snoopy gets involved and they start talking about phase separation, etc. it's time to sit back and wait to see what they come up with.

 BTW, those discrete SOHA buffers look like killers. An SMD stacked Jisbos buffer that will fit on the existing board with no overhang(!), a through-hole Jisbos buffer, and a through-hole DB - all with DC offset zeroing capability. Please express your interest in the Headwize Marketplace. Steinchen also has three separate threads going in the DIY section for soliciting design comments.


----------



## tomb

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_This weekend, I removed the output resistors (R6/R16, 150ohms) from my SOHA boards.

 Now, I started to hear some noise, irregular snaps and taps, low volume. Is this normal? Should I put those resistors back, maybe with lower value...?_

 

Even Solid State amps such as the CMoy and PIMETA have positions for output resistors. In those cases it's for hiss. In your SOHA, it sounds like very minute microphonic noises picked up by the tube - that are masked by the output resistors. Try starting as low as 10 ohms and increasing it until the noise goes away.


----------



## Yen

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_In your SOHA, it sounds like very minute microphonic noises picked up by the tube - that are masked by the output resistors._

 

You are right. I did experiment with (c) aluminum foil hats (tm), and yes, the noise/distortion went away... 
	

	
	
		
		

		
			





 Must try to protect the tube with something else better looking or play with those resistors. Does boutique resistors, e.g. Kiwame, have good results as output res?


----------



## Yen

My SOHA is broken apparently. I rolled the tube and switched the opamp during a tinytintytiny meet at my friends place and everything worked well there.

 Now at home, there is a terrible buzz, and the other 40V test point shows exactly the same as the 60V test point, which is about 72V. The 72V at 60V is normal, but I cant adjust the 40V and there is clearly something wrong.

 Where should I start debugging? I have checked all the connections etc., so a part might be broken?

 EDIT: Ok, I rolled another tube (JJ) and then I could adjust the bias for both channels, but the buzz is still there. Now after few rolls between EH and JJ tubes, I cant adjust the other channel at all and it shows the same 72V. Is both of my tubes gone?

 More symptom descriptions: The left channel works perfectly and sounds fine as usual, but the right channel buzz. That's where the bias sucks, right?


----------



## headphonejunkie

Maybe something is wrong with the tube socket.Check that.


----------



## headphonejunkie

Maybe you have a bad solder joint on your tube socket.


----------



## Yen

I have checked it, the connection from socket pins to PCB is fine. However, there is short between somewhere pin 5 and 6. Is that correct?


----------



## FallenAngel

Nope, no shorted pins on the SOHA, but pin 9 is not connected. 5 is grounded while 6 goes to the CCS.


----------



## headphonejunkie

check across c2 and c14. They should be an open. At least a high ohm reading. If they read 1 ohm or something like that they are bad.


----------



## tomb

Even if the CCS blew, it's unlikely that it would short to ground. Either you broke both tubes by coincidence, or HJ is correct - something came loose in the socket.

 Sometimes the pins on these NOS tubes are weak - a few rolls and they may develop a weakness and break. Or, the contact tabs in the socket have bent or broken, contacting each other.


----------



## Yen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Nope, no shorted pins on the SOHA, but pin 9 is not connected. 5 is grounded while 6 goes to the CCS._

 

OK, the problem is propably found. I had to do quite a quick fix to mirrow the socket that I forgot to do at the first time.

 I will order new sockets and enclosure and case it again.


----------



## headphonejunkie

If c2 and c14 are ok then your ccs should not be the problem.


----------



## headphonejunkie

Good. You found the problem.


----------



## Yen

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_OK, the problem is propably found. I had to do quite a quick fix to mirrow the socket that I forgot to do at the first time.

 I will order new sockets and enclosure and case it again._

 

Bah, the was no shorts, only when the tube is connected. When it is removed, there is no shorts.

 I measured the voltages, the square pin in digi's board showed 72.4 (which is the same reading as 60V and other 40V TP), and from that square pin the 6th pin showed correct biased 40V.

 I am seriously leaning to faulty tubes, cos the JJ was ok and I was able to bias it until I give it a twist and now it is broken too...


----------



## headphonejunkie

Tubes are only glass and there is a vacuum in there.


----------



## headphonejunkie

Look at your tubes under a magnifying glass and see if you see any wires broken off of the pins.


----------



## tomb

Quote:


  Originally Posted by *headphonejunkie* /img/forum/go_quote.gif 
_Look at your tubes under a magnifying glass and see if you see any wires broken off of the pins._

 

Actually, I went a week or two once with a half-broken pin. The crack was up in the glass molding - impossible to see. It would always bias really strange - sometimes not at all. I kept thinking it was the socket (was having fits with that, too) until that pin broke all the way one day. No trouble with that _socket _since - it had always been that tube.

 Yen - it may still be the socket. It's a little unusual to break two tubes like that - especially the JJ. That one may have a guarantee? In either event, it could be something with your socket that's wrenching the tube pins into premature failure.


----------



## Yen

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Yen - it may still be the socket. It's a little unusual to break two tubes like that - especially the JJ. That one may have a guarantee? In either event, it could be something with your socket that's wrenching the tube pins into premature failure._

 

I havent any problems with the socket before and I have rolled tubes many times. The socket I use is for PCB and I solderit to a piece of perfboard and connected by wires to the amp's PCB. The perfboard with the socked is kinda floating agains the case and the wire tension in between the case and PCB is keeping the socket in its place. Yeah, I know, stupidly implemented, but this case was intended for a temporary use until I find a nice one with a reasonable price tag.

 I couldn't see anything odd with my tubes, and pin's wire isnt cut or anything. The JJ warmed up just like before and I can see the two coils light up.

 It is just hard for me to believe that there is wrong with the current socket, cos I checked the connectivity from the socket's pins to PCB pads, and everything is corrects. Additionally, there isnt any shorts anymore, so I couldn't imagine anything else than broken tubes or other components.

 The trouble began this morning, when I rolled the Electro-Harmonix in, and couldn't bias other side and there was that terrible buzz. Then I unconnect the PCB, checked the socket and make a mistake while rewiring the pot. Then, I put the JJ in, _both channels were biasing correct_, but the buzz still there (couldn't remember if the buzz sounded same) because my pot wiring mess up. I thought, the problem is my floating socket and twist by grabbing from the tube, and heard a snap with the buzz, and then the same bias problem just like with the EH returned for the JJ. Then, I find out my pot wiring mistake and connect it correctly, and now only the left channel is working.

 I will order a new enclosure soon with new sockets and tube, and let's hope the problems isnt with the CSS, as I am having hell of a problem finding them J113s. See my WTB in my sig. 
	

	
	
		
		

		
			





 My regular supplier suggested J505s to replace J113, but I dont like it, cos it woulb propably alter the design and I dont understand it enought to make the required changes.

 Thank you all for the help, just continue if you come up with ideas about what's is wrong with my build. I am expecting 2005 DT990s to arrive this week, so I hope to get this person running by then. 
	

	
	
		
		

		
		
	


	




 There is a great difference between a cmoy and soha, better or worse, it depends, but at least I am liking the soha alot more than cmoy.


----------



## headphonejunkie

The buzz could be a ground issue.


----------



## Yen

Quote:


  Originally Posted by *headphonejunkie* /img/forum/go_quote.gif 
_The buzz could be a ground issue._

 

I doubt it, cos the other channel works perfectly fine. Also, I havent changed anything since it has been working for me many months now.


----------



## Yen

Any1 tried AD8620 with SOHA? Tangent loves it for battery power but what about SOHA?


----------



## ericj

No reason ad8620 wouldn't work. I've usually seen it in the gain stage behind an output buffer, but the datasheet says it should be able to sink 30ma, which would be enough for most headphones.


----------



## tomb

My AD8610/8620 datasheet says +or-45ma. That puts it in the same league as the popular OPA's. I've rolled many opamps into the SOHA, but not that one. There's no reason it wouldn't work, but since the SOHA has loads of voltage, something without that voltage-to-rail capability seems a better choice.

 Some others (besides OPA2134 design std) that work very well:
 OPA2132 (same as 2134 in sound - a bass monster, a little slurred)
 OPA627: outstanding, but not enough better than the 2107
 OPA551: boring
 AD843: needs outstanding coupling capacitors (speed/detail demon)
 AD845: same as AD843, but a little less so
 OPA2107: lusciously detailed, reasonable fast, no BrownDog to fiddle with - my favorite choice!
	

	
	
		
		

		
		
	


	




 The AD843 and OPA2107 are especially well-suited because of their battery limitations (they like lots of volts).


----------



## Blooze

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_My AD8610/8620 datasheet says +or-45ma. That puts it in the same league as the popular OPA's. I've rolled many opamps into the SOHA, but not that one. There's no reason it wouldn't work, but since the SOHA has loads of voltage, something without that voltage-to-rail capability seems a better choice.

 Some others (besides OPA2134 design std) that work very well:
 OPA2132 (same as 2134 in sound - a bass monster, a little slurred)
 OPA627: outstanding, but not enough better than the 2107
 OPA551: boring
 AD843: needs outstanding coupling capacitors (speed/detail demon)
 AD845: same as AD843, but a little less so
 OPA2107: lusciously detailed, reasonable fast, no BrownDog to fiddle with - my favorite choice!
	

	
	
		
		

		
		
	


	




 The AD843 and OPA2107 are especially well-suited because of their battery limitations (they like lots of volts)._

 

Tomb, what about the OPA551 did you find boring? I'm curious as I use low-Z cans and am looking for higher current capacity in my next build. I really liked them in my Millett (course I have a built up dDB for the next Millett when I get around to it).


----------



## tomb

Hi, Blooze! I mentioned you the other day talking about output resistors. I don't have Kiwame's like you, but I did put some carbon Stackpoles in a SOHA - made a big difference. It went from harsh to sweet in a heartbeat, with no apparent loss in detail. Anyway, thanks for your previous suggestions.

 About the OPA551 - it's sloooowww. In the Millett, it seemed to have a little more detail, a little less punch than double-BUF's. That's fine, depending on what you're looking for, but is way worse than a DB. I do not know why that fella on DIYForums suggested that the DB's were no different than the double-BUF's, but they are. If you use Steinchen's recommended 2SC/2SA transistors instead of the MJE's/BD's, then the DB's are better still.

 Back to the OPA551: specs say 3MHz and 15V/u-sec slew rate. The standard OPA2134 is 8MHz and 20V/u-sec slew rate, so much faster. Without biasing, it's probably questionable how much of the extra current is usable in the OPA551, anyway. I may change my mind again tomorrow, but those are some of the reasons I've grown tired of the OPA551.

 Actually, after rolling a number of opamps, it seems that there is a "sweet spot" of opamp bandwidth/slew rate vs. sweet sound or harshness. Right now, the OPA2107 sounds very, very good (actually slower than the OPA2134), while the speed demon AD843 and AD845 both sound a tad too harsh, picking up as much tube noise as music detail. This may be dependent on your coupling caps and output resistors, and of course, your tube (mine are all pretty cheap). Perhaps some nice Jupiters or Mundorfs would allow the use of the faster chips without it sounding too harsh.

 After all, though - you were the first with the mu-follower because you were using a BJT opamp. I though you already had enough current? I find no lack of power on any pair of phones - HD580's, Sony V6's, K81DJ's, SR80's, KSC75's, etc. - it handles them all well. I'm only using 100 ohms on those output resistors, though. Maybe that has something to do with it?


----------



## Blooze

Thanks Tomb! I've had good success with Stackpoles and if it comes down to $$$ they're a good way to go. I've got 160R'S I believe in my SOHA right now and used Kiwames throughout my whole Millett for lack of better sense at the time 
	

	
	
		
		

		
		
	


	




 My SOHA has plenty of current, but for my next one I'm gonna try something a little different and the use of single opamps was one route I was thinking of going. I'm not going to go with a DB for the SOHA because I'd rather spend the $$$ to get my Darling amp finished in this lifetime. And I've got all the parts for a line array that I need to start sometime as well as a pair of Smith Horns to build. Too many projects and NEVER enough money.

 I'll have to pick up a couple of 2107's and give then a try.


----------



## FallenAngel

Thanks for the heads up Tomb, with only my HD600's left (sold the rest of the headphones and selling off all my gear 
	

	
	
		
		

		
		
	


	




 ), I removed the output resistors and am keeping the OPA2107 in there, the combo sounds wonderful.


----------



## Yen

Now I am totally lost with this piece of *.

 Got me some new Raytheons and Sylvanias for a cheap price from ebay, but still the same problem.

 The last time right side functioned well, biased 40V and sounded lovely like usual. And the left buzz and was about 70V, which is same as the 70V TP.

 NOW, after resoldering and fixing the socket, the buzz has switched to the left side (!!!), and the music plays behind that buzz. 

 The right side is now totally silent! No buzz, no music.

 The test points shows -12V, 12V and -12,6V correct. The bottom 40V (next to -12,6V TP) shows around 8Vs and is adjustable from the trimmer. The 60V and the other 40V shows 61V, which is odd too, cos when fuctioning my 60V should be around 70V. This 40V isnt adjustable...

 OMG, I am close to build CKK3 and throw this piece of junk out of the window... 
	

	
	
		
		

		
			





 It's not the tubes, it's not the sockets, it's not the connections and groundings, it's not the opamp (tried many), so where is my problem? CSS?


----------



## Yen

Here are the readings of tube pins starting from the pad that is square in digis board and going CCW:

 1. 3,1V when R4 trimmer is at its lowest. Reacts to R4 trimmer.
 2. 0
 3. 0
 4. -12,6
 5. 0
 6. 62V (Same reading or few .x below 60V TP)
 7. 0
 8. 3,1V reacts to R4 and shows exact same reading with pin 1.
 9. -6,3V

 I hope this helped to debuging...

 EDIT: My pin order is reversed to this...


----------



## tomb

Quote:


  Originally Posted by *Yen* /img/forum/go_quote.gif 
_Here are the readings of tube pins starting from the pad that is square in digis board and going CCW:

 1. 3,1V when R4 trimmer is at its lowest. Reacts to R4 trimmer.
 2. 0
 3. 0
 4. -12,6
 5. 0
 6. 62V (Same reading or few .x below 60V TP)
 7. 0
 8. 3,1V reacts to R4 and shows exact same reading with pin 1.
 9. -6,3V
_

 

EDIT: Skip what I typed before if you saw it - my pin locations were wrong, too.

 I think you have a couple of them mixed up, though.

 copied from Wikipedia -





 It looks like your pins 4, 5, and 9 are correct (heater filaments). However, pins 1 & 6 should be at B+ (your 62V). Pins 3 and 8 should be the 40V bias (or change with the trimmer). Pins 2 and 7 should be the signal, which may read zero or very small.


----------



## FallenAngel

Yen, I don't think you should be lowering the trimpots that low with J113 CCS. They only handle like 35V so dropping from B+ 60V to 3.1V will put way too much across them and probably fry them.

 Keep your trimpots at the highest so you don't put too much voltage across the CCS. Are you sure you have everything hooked up properly in the CCS? Try to remember EXACTLY when this started.


----------



## Yen

You were right tomb.

 I installed the socket right to the PCB and this piece of * became my beloved one again! 
	

	
	
		
		

		
		
	


	




 However, I did order new sockets and will make new enclosure for my amp. 
	

	
	
		
		

		
		
	


	




 Thank again for all your help.

 Fallenangel: I think you cant adjust so much with the trimmer. I think if it is lowest, I got about 30V and max 50V or something. I doubt it will go down to 3V unless there is something wrong...


----------



## procreate

Hi Andreas,

  Quote:


  Originally Posted by *steinchen* /img/forum/go_quote.gif 
_yes, you're right, good that you're asking, I forgot to mention that: with the low input impedance of 50k the buffer can be used together with the SOHA tube stage in MU-follower configuration only!_

 

Is the v3 SOHA PCB set up for this? That's what I was going to use your buffer with.


----------



## Nordic

Yen, see if you can get a 7308 (e188cc) big quality diffirence... uses a fraction less current on the heater.. no adjustment needed.

 Tried building the SOHA 3 times, only got it to work once, but heck it was so unstable, I just gave up and build an opamp hybrid for practice.


----------



## tomb

Quote:


  Originally Posted by *procreate* /img/forum/go_quote.gif 
_Hi Andreas,

 Is the v3 SOHA PCB set up for this? That's what I was going to use your buffer with._

 

Speaking for Steinchen, but the SOHA PCB is setup for 6 different options of CCS. It's probably what causes the most confusion. In any event, the mu-follower version is supported as an option for all three choices of semiconductor - check your documentation if you aren't sure.

 No doubt, Steinchen will make this abundantly clear when he releases the boards for a Group Buy. He documeted the construction and setup very clearly for the Millett Hybrid DB's and will probably do the same for the SOHA buffers.


----------



## Yen

Quote:


  Originally Posted by *Nordic* /img/forum/go_quote.gif 
_Yen, see if you can get a 7308 (e188cc) big quality diffirence... uses a fraction less current on the heater.. no adjustment needed.

 Tried building the SOHA 3 times, only got it to work once, but heck it was so unstable, I just gave up and build an opamp hybrid for practice._

 

Thanx for the suggestion. I am currently running a Raytheon 5814 and OPA2107 and I am really satisfied with my build.

 Also, I have recased the beast, and installed the socket straight to the PCB, as you can see from my sig.

 With v3 PCB, I really havent any problems except with my socket wiring mess. At the beginning, I ordered only one socket for PCB assemble. Then I was so stupid that I didnt solder the parts on the opposite of silkscreen. Then when I had to turn the pcb upside down, then the socket order got mixed up... 
	

	
	
		
		

		
		
	


	




 Then I installed the pcb socket to a perfboard and got a lot of trouble having the socket pins soldered to perfboard pads and connections right. That's where all the problem came. 

 Now, everything works fine, except that tube (i guess) catches some noise. Dunno if the toroid in the same case causes these problems or my house's AC line is crap. I hear snaps everytime the fridge starts cooling and ends it... also, there is some noise when the oven is on...


----------



## tomb

Quote:


 Thanx for the suggestion. I am currently running a Raytheon 5814 and OPA2107 and I am really satisfied with my build. 
 

I have tried that exact combination and it is a very good one. 
	

	
	
		
		

		
		
	


	




 Yen, are those Auricaps, Hovlands, or what for your coupling film caps?


----------



## Nordic

Yen add the following to your circuit.

 1 275VAC or higher 200nf XY cap, ask specificaly for XY caps, this is a safety rateing meaning they can be used both from L to Ground as well as N. I do not take resposiblity if you don't adhere to that.
 And one 12 to 17Watt 1 ohm resistor.

 Solder one leg of the resistor to one leg of the cap.

 The free legs gets conected on the mains wire in parallel with the primary, this should filter out all clicks and switch pops.
 While buying the caps, get a second one and put it over the terminals of the switch. 

 I want to build a standalone IRF610 headphone amp, and then I will try the mosfet hybrid again. Maybe do something more elegant about the heater arangement, have some ideas but need to do some research to see if they are valid.


----------



## Yen

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Yen, are those Auricaps, Hovlands, or what for your coupling film caps?_

 

None of those, sadly. They are some random and cheap films I found from a local guitar amp / diy shop when I bought new sockets. Cant say much about their sound cos I changed at the same time with the raytheon and opa. I am pleased with the current sound. 
	

	
	
		
		

		
		
	


	




 I am still waiting for PCX to stock Elnas as they have informed during their January Sale. Then I will buy Mundorfs and 'lytics for Alien and soha to save shipping costs. Yeah, I am cheap... student. 
	

	
	
		
		

		
		
	


	




 I have some regular Panasonics (NHG, some say they are ok) and Elnas (dunno series, brown in color) in my Soha right now.


----------



## Yen

Like my attached picture?

 I did find only X2 "filtering caps" and this. Are they the same as XY?

  Quote:


  Originally Posted by *Nordic* /img/forum/go_quote.gif 
_Yen add the following to your circuit.

 1 275VAC or higher 200nf XY cap, ask specificaly for XY caps, this is a safety rateing meaning they can be used both from L to Ground as well as N. I do not take resposiblity if you don't adhere to that.
 And one 12 to 17Watt 1 ohm resistor.

 Solder one leg of the resistor to one leg of the cap.

 The free legs gets conected on the mains wire in parallel with the primary, this should filter out all clicks and switch pops.
 While buying the caps, get a second one and put it over the terminals of the switch._


----------



## tcpoint

I swapped out my OPA2134 (which sounded muddy in the bass) and put in an OPA2107 and I was impressed. I like the detail and sonic characteristics of this the OPA2107. Thanks for the suggestion Tomb


----------



## Nordic

no, its not the same, but I think its safe enough for this job.

 the first cap in you picture should go over the switch....... on the schematic it would look like a switch in parallel with the cap

 look at the bit before the transformer for the concept.


----------



## Yen

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Yen, are those Auricaps, Hovlands, or what for your coupling film caps?_

 

I did some research about those, I found out that they are Illinois Capacitor's MPW series metallized polypropylene. I did also try to find info about the manufacturer, but I think their products are mostly focused for vintage audio enthusiasts/repairers. 

Vacuumtube.com says about IC: "_Illinois Capacitor (IC) has been in business for over 50 years and has been manufacturing some of the finest capacitors in the world at a reasonable price. Each IC capacitor is inspected by trained professionals and is 100% burn-in tested to assure superior performance._"

 These caps are ment for audio, but are they any good in SOHA?


----------



## JLMaestro

Quick question,
 If I'm using the ALPS pot, do I have to ground it separately ie. unscrew the screw on the back of the ALPS and connect it to signal ground?

 EDIT: Alps "blue velvet" pot.


----------



## FallenAngel

Quote:


  Originally Posted by *JLMaestro* /img/forum/go_quote.gif 
_Quick question,
 If I'm using the ALPS pot, do I have to ground it separately ie. unscrew the screw on the back of the ALPS and connect it to signal ground?

 EDIT: Alps "blue velvet" pot._

 

Don't "have" to unless you get hum while touching the volume pot. Can't say one way or the other, that depends on whether you have metal end-panels and you connect the mains ground to case. Under that condition you don't want connect the pot to the case and then ground it to signal, all other conditions, feel free.


----------



## digi01

JLMaestro,
 the pot need not ground separately.
 I use break grounding concept layout.there are dedicated gnd point on soha v3.0 board,in the middle of C2,C7,C8.the better way is connected that gnd point to the metal chassis.

 p.s.
 that point is test reference gnd too.

 good luck,
 Zang


----------



## JLMaestro

Quote:


  Originally Posted by *digi01* /img/forum/go_quote.gif 
_JLMaestro,
 the pot need not ground separately.
 I use break grounding concept layout.there are dedicated gnd point on soha v3.0 board,in the middle of C2,C7,C8.the better way is connected that gnd point to the metal chassis.

 p.s.
 that point is test reference gnd too.

 good luck,
 Zang_

 

Thanks Digi.
 I have another question... is it okay to airwire the tube off of the PCB so the full tube can stick out of the enclosure? Is there problems with stray capacitance? I will be only moving it about an inch or two above the PCB.


----------



## digi01

an inch or two is ok.

 good luck,
 Zang


----------



## FallenAngel

I've got one that has about a foot of wiring between the PCM and tube. No issues at all.


----------



## gates_2

just built my soha

 40's are both reading + 75 volts, same as the +60 test point... with the tube and opamp in...odd...

 Any ideas?


----------



## gates_2

another interesting thing- the 337 regulator is burning hot.....and my +60 jumped up to 85 now... uh...confused

 double checked the CCS reg- it looks like i soldered it all correctly


----------



## tomb

Quote:


  Originally Posted by *gates_2* /img/forum/go_quote.gif 
_just built my soha

 40's are both reading + 75 volts, same as the +60 test point... with the tube and opamp in...odd...

 Any ideas?_

 

1. Are the heaters kicking in and do you get a glow and the 12.6V? If the tube plates are not conducting (needs heaters), then current doesn't flow through the tube and you can't bias.
 2. Bad socket/tube pins - you might try rocking the tube in its socket and see if it registers in the bias. Do this only if the tube seems loose in the socket.
 3. Bad tube.
 4. You've got the CCS messed up. Be careful - there are several versions out there. If you used the LND150, every one of those has the LND150 reversed, the resistor values are reversed, and there are two jumpers in addition to the P-C-S pins.

 P.S. It's pretty much impossible to run the heater regulator (LM337) without a heat sink.


----------



## gates_2

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_1. Are the heaters kicking in and do you get a glow and the 12.6V? If the tube plates are not conducting (needs heaters), then current doesn't flow through the tube and you can't bias._

 

Getting the heaters glowing, and geting a -12.4 volt from pin 5 of teh tube to ground

  Quote:


 2. Bad socket/tube pins - you might try rocking the tube in its socket and see if it registers in the bias. Do this only if the tube seems loose in the socket. 
 

Didn't seem loose.. checked continuity from socket to Board- all checked out...tube is very snug in there.


> 3. Bad tube.
> Quote:
> 
> 
> ...


----------



## gates_2

Some pics


----------



## Yen

Quote:


  Originally Posted by *gates_2* /img/forum/go_quote.gif 
_just built my soha

 40's are both reading + 75 volts, same as the +60 test point... with the tube and opamp in...odd...

 Any ideas?_

 

I had the same problem, and it turned out that the problem was my socket even though the continuity check went ok. Yours seems to be alright, but rerecheck or even resolder the legs just in case. Then I would also try a new tube.

 LM337 of mine is burning hot with any TO heatsing, but that's not a prob. You have to install it to the case or something big to really cool it.

 So your other TPs showed correct values?


----------



## gates_2

so... new developments
 First, I resoldered a brand new socket on- no change....

 took it over to my buddy in the other dorm. Tried out a nice telefunken + another RCA tube(good tubes, according to him).. Still had the exact same problem. Wouldn't bias. And the weird thing is, the plate voltage increases over time. It would start at like 75V. both 40V TP's show the same as the 60V TP, which corresponds to the plate voltage on the tubes. The heaters glowing, but not getting any current flowing.

 Anotehr thing I noted(may not be revelant). I was reading the voltage across the LED spot(without a LED present). It would periodically jump from 0 to like 15V and then back to 0- I can't explain that...


 Tried it again... NOw i'm getting plate voltage at pins 4 and 9..... like 6V at pin2 and -8 V at pin 7 or 8....

 Wow... very confused....

 Everywhere i do a voltage reading in the CCS section, I get plate voltage(90 or so volts), doesn't change no matter what resistor or jumper I put it on...

 This is very odd

 Thoughts?


----------



## pddjsteve

Hmm. After listening to it for a while, I've discovered the right channel seems to have a little less gain than the left. There also seems to be some "bleeding" between the channels. All the voltages measure fine, I've gone over all the solder joints again under a magnifying glass. I read about Yen's problem with the tube socket... is that where I should be looking next?

 This is more a small nagging annoyance than anything else... it sounds awesome, just a little teeny bit louder in one ear than the other


----------



## tomb

Quote:


  Originally Posted by *pddjsteve* /img/forum/go_quote.gif 
_Hmm. After listening to it for a while, I've discovered the right channel seems to have a little less gain than the left. There also seems to be some "bleeding" between the channels. All the voltages measure fine, I've gone over all the solder joints again under a magnifying glass. I read about Yen's problem with the tube socket... is that where I should be looking next?

 This is more a small nagging annoyance than anything else... it sounds awesome, just a little teeny bit louder in one ear than the other 
	

	
	
		
		

		
			



_

 

Typically, that's a pot tracking problem, or perhaps some un-matched resistors on the output.


----------



## pddjsteve

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Typically, that's a pot tracking problem, or perhaps some un-matched resistors on the output._

 

Hmm. I'll check the output resistors when I get home tonight, but I think they were pretty close to one another (they're 150 ohm 1% vishay dale). I did go through and measure all my other pairs of resistors, and they were within an ohm or two of each other. I'm using 80ohm DT770s, so I also might just jumper the output resistors to eliminate them as the culprit.

 If that looks ok, I think I'll switch out the pot. I'm using a 50k RK27 right now, would something like this ratshack pot be a decent temporary replacement? I've also got a few panasonic evj and alps rk097, but they're all 10k.


----------



## tomb

From what you describe, that's not the problem. If you are already using the RK27, and you've checked all the resistors, then that's not it.

 You may have a bad tube - perhaps the grid or plates on one side are not up to snuff. Change the tube out, re-bias, and see if that's it. BTW, have you checked the bias lately? Sometimes that can change as the tube gets broken in and could cause some channel imbalance. Of course, the high gain of the SOHA will exacerbate this problem.


----------



## sphinxllama

Hello,

 I bought a SOHA Kit 
	

	
	
		
		

		
		
	


	




 Already working on it and it went pretty good until now. 
	

	
	
		
		

		
		
	


	




 And now I have a problem and need some help from you guys. Here it comes:
 I had to desolder the LM78L12 Regulator and the LM79L12 Regulator. Now my question is if they are easy to break? Because they got pretty hot when I desoldered them. Does it matter. Would it be better to buy new ones? (I hope I can find a shop who carries them).

 I also did not do a very good job when I desoldered the parts. Have a look:



 Do I have to worry about connection problems when I solder the new part in that damaged possition? What can I do?

 greets
 kim

 P.S. hope it is OK that I post my problem in this thread seemed right to me.


----------



## gates_2

can someone confirm that I have my CCS configured correctly?

http://img297.imageshack.us/my.php?i...1010090eg3.jpg
 thanks


----------



## FallenAngel

sphinxllama : You're alright, use the same regs, they'll be fine, but personally I would prefer to use 7815 and 7915 regulators in TO220 package, if they're already out of the board, might as well 
	

	
	
		
		

		
		
	


	




 gates_2 : You should be good as well, I just can't read your resistor values.


----------



## gates_2

ahh- solved the problem

 I think I soldered the pot in wrong.... Was shorting to ground....

 Getting reasonable values now... lets try it out


----------



## sphinxllama

@FallenAngel

 thanks a lot for your quick answer! 
 I think I will use the same regs. Otherwise I would have to desolder the CCS and buy the TO220 in 12V. Hope that is right. But I heared there are some Buffers from Steinchen on its way for the soha that use 15V.

 greets kim


 Edit: Oh I see in your sig that you already have them in your soha. Where can I get them from?


----------



## FallenAngel

Quote:


  Originally Posted by *sphinxllama* /img/forum/go_quote.gif 
_@FallenAngel

 thanks a lot for your quick answer! 
 I think I will use the same regs. Otherwise I would have to desolder the CCS and buy the TO220 in 12V. Hope that is right. But I heared there are some Buffers from Steinchen on its way for the soha that use 15V.

 greets kim


 Edit: Oh I see in your sig that you already have them in your soha. Where can I get them from?_

 

Yes, Steinchen's buffers will need 15V regs, and no you don't need to change the CCS for the JisBos.

 I don't have them in my SOHA yet, I've built all the buffers I've seen for the SOHA and unfortunately couldn't get even one working yet


----------



## pddjsteve

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_From what you describe, that's not the problem. If you are already using the RK27, and you've checked all the resistors, then that's not it.

 You may have a bad tube - perhaps the grid or plates on one side are not up to snuff. Change the tube out, re-bias, and see if that's it. BTW, have you checked the bias lately? Sometimes that can change as the tube gets broken in and could cause some channel imbalance. Of course, the high gain of the SOHA will exacerbate this problem._

 

Well, this is not fun.

 The bias is ok. Jumpered the output resistors. Switched the pot out. Switched tubes. Still doing it.

 When the balance is centered, I get more output from the left channel.

 When I put the balance all the way right, I can't hear anything from the left. 

 When I put balance all the way left, I hear from both left and right, but at the same volume, as if balance was center and there was no channel difference???? 
	

	
	
		
		

		
		
	


	







 I'm about to just give up and solder the 2nd board.


----------



## tomb

Quote:


  Originally Posted by *pddjsteve* /img/forum/go_quote.gif 
_Well, this is not fun.

 The bias is ok. Jumpered the output resistors. Switched the pot out. Switched tubes. Still doing it.

 When the balance is centered, I get more output from the left channel.

 When I put the balance all the way right, I can't hear anything from the left. 

 When I put balance all the way left, I hear from both left and right, but at the same volume, as if balance was center and there was no channel difference???? 
	

	
	
		
		

		
		
	


	







 I'm about to just give up and solder the 2nd board._

 

I'm confused - how are you adjusting balance, period?

 Can you post some photos of the board? Maybe some of us can spot a problem. Honestly, this is the first problem of this type I've heard about with the SOHA boards.


----------



## pddjsteve

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_I'm confused - how are you adjusting balance, period?

 Can you post some photos of the board? Maybe some of us can spot a problem. Honestly, this is the first problem of this type I've heard about with the SOHA boards._

 

Sorry, adjusting balance on my source. Should have mentioned that. Yeah, lemme put the ALPS pot back in and then I'll snap some pics.


----------



## tomb

Quote:


  Originally Posted by *sphinxllama* /img/forum/go_quote.gif 
_Hello,

 I bought a SOHA Kit 
	

	
	
		
		

		
		
	


	




 Already working on it and it went pretty good until now. 
	

	
	
		
		

		
		
	


	




 And now I have a problem and need some help from you guys. Here it comes:
 I had to desolder the LM78L12 Regulator and the LM79L12 Regulator. Now my question is if they are easy to break? Because they got pretty hot when I desoldered them. Does it matter. Would it be better to buy new ones? (I hope I can find a shop who carries them).

 I also did not do a very good job when I desoldered the parts. Have a look:



 Do I have to worry about connection problems when I solder the new part in that damaged possition? What can I do?

 greets
 kim

 P.S. hope it is OK that I post my problem in this thread seemed right to me._

 

Sure about this? It looks to me like your photo is showing the CCS positions, not the opamp voltage regulators. Could you be confusing these?


----------



## pddjsteve

Ah, the joy of finishing the SOHA in the middle of the night a couple nights ago - I found the problem. My own stupidity. This was the first time I've used the Neutrik locking 1/4" jack, and I freaking soldered it like a 1/8" jack because I wasn't thinking. It wasn't the SOHA, it was me. 
	

	
	
		
		

		
		
	


	



















 On the other hand, I now know more about the circuit/board than before, so it isn't a complete loss 
	

	
	
		
		

		
		
	


	




 Thanks for the help, though.


----------



## gates_2

so.. problem not solved... With the pot out, i get 70 plate, and then like 51, 56 on the 2 +40 check points.....

 No matter how much i turn the trimpot either way, neither of these values change

 The second I connect the pot.... I get plate voltage at +60 and both +40 voltages, or If I turn the pot all the way one way, I get plate voltage at one +40 and a lower voltage at the other....

 Ended up breaking a RK27 pot trying to desolder it from my pimeta to try on the soha... GAH

 any ideas... With teh pot wiper all the way one way, I get a short between input left and ground... Confused.....


----------



## tomb

Quote:


  Originally Posted by *gates_2* /img/forum/go_quote.gif 
_so.. problem not solved... With the pot out, i get 70 plate, and then like 51, 56 on the 2 +40 check points.....

 No matter how much i turn the trimpot either way, neither of these values change

 The second I connect the pot.... I get plate voltage at +60 and both +40 voltages, or If I turn the pot all the way one way, I get plate voltage at one +40 and a lower voltage at the other....

 Ended up breaking a RK27 pot trying to desolder it from my pimeta to try on the soha... GAH

 any ideas... With teh pot wiper all the way one way, I get a short between input left and ground... Confused....._

 

Evaluating test points without the pot in the circuit is a long-standing issue: it doesn't work. Same for the opamp: you cannot get intelligible measurements. If everything measures OK with the pot and the opamp in the circuit, then you're fine.


----------



## matheprat

I've rebuilt my SOHA and I'm having some more problems. All the voltages are fine with the tube out, but when it's in the heater voltage drops from 12.6 to 6.3 (despite being hooked up to pin 4 (5 is connected to ground). Also, the trimmer pots have very little effect on the voltage, it stays between about 55-65 for both. The +-12V for the Opamp are fine. I have the pot installed (47K).
 Does anyone have any ideas? I have pins 1 and 6 connected to the JFETS, 8 and 3 connected to the trimmers, 2 and 7 for the input, 4 at the heater, 5 ground, and 9 not connected.
 Many thanks.


----------



## tomb

Quote:


  Originally Posted by *matheprat* /img/forum/go_quote.gif 
_I've rebuilt my SOHA and I'm having some more problems. All the voltages are fine with the tube out, but when it's in the heater voltage drops from 12.6 to 6.3 (despite being hooked up to pin 4 (5 is connected to ground). Also, the trimmer pots have very little effect on the voltage, it stays between about 55-65 for both. The +-12V for the Opamp are fine. I have the pot installed (47K).
 Does anyone have any ideas? I have pins 1 and 6 connected to the JFETS, 8 and 3 connected to the trimmers, 2 and 7 for the input, 4 at the heater, 5 ground, and 9 not connected.
 Many thanks._

 

Sounds like a P2P version. Runeight is still supporting those if you post in the "SOHA Thread 2" thread stickied in the DIY section of Headwize.


----------



## gates_2

so.. with the rk27 correctly connected, it's still not working.

 My plate voltage is reading +75 volts(at the +60 test point). Both +40 test points are reading the same plate voltage. Double/triple checked the CCS, tried several tubes...no change... Turning the trimpots doesn't change the +40 points. I can't seem to bias at all.. Tried taking out the trimpots... no change. Also, the +40 test point closest to the bottom of the board(closest to the heatsinked regulator in my pic) will read between like 62 and 75 depending on whether or not the pot is turned one way or the other.


----------



## tomb

Quote:


  Originally Posted by *gates_2* /img/forum/go_quote.gif 
_so.. with the rk27 correctly connected, it's still not working.

 My plate voltage is reading +75 volts(at the +60 test point). Both +40 test points are reading the same plate voltage. Double/triple checked the CCS, tried several tubes...no change... Turning the trimpots doesn't change the +40 points. I can't seem to bias at all.. Tried taking out the trimpots... no change. Also, the +40 test point closest to the bottom of the board(closest to the heatsinked regulator in my pic) will read between like 62 and 75 depending on whether or not the pot is turned one way or the other._

 

Pics - top and bottom, please?


----------



## headphonejunkie

Check your r7,17,r8,18 and make sure they are connected properly. I had something similar to this happen to me except I did not have them in circuit.


----------



## gates_2

mm... checked all those R's... R 7,17 are 348 ohms and r8,18 are 1K ohms, checked for continuity under the board on both... they seem good



 tons of pics..maybe this will help:
 (note the scraping on the bottom was me making sure i didn't have any bridges... I inspected the board rather thoroughly, and didnt' find any before scraped it, but I just wanted to make sure.


----------



## achina

R3 looks like it is a 562Kohm instead of 562ohm. R13 is probably the same, hard to tell from the pics.


----------



## tomb

Quote:


  Originally Posted by *achina* /img/forum/go_quote.gif 
_R3 looks like it is a 562Kohm instead of 562ohm. R13 is probably the same, hard to tell from the pics._

 

Agreed. Since those are the cathode resistors, it pretty much means little to no current flowing and the trimmers would be useless.

 Change those out and things should be a lot different.


----------



## pddjsteve

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Agreed. Since those are the cathode resistors, it pretty much means little to no current flowing and the trimmers would be useless.

 Change those out and things should be a lot different._

 

Those are easy to get wrong, I actually ALMOST did this myself, but then double checked the part values before I soldered. I actually had bought the wrong one mistakenly (searching on mouser for 562 got me the 562k as well).


----------



## tomb

Quote:


  Originally Posted by *pddjsteve* /img/forum/go_quote.gif 
_Those are easy to get wrong, I actually ALMOST did this myself, but then double checked the part values before I soldered. I actually had bought the wrong one mistakenly (searching on mouser for 562 got me the 562k as well)._

 

Hey! It must be a Mouser bug! I did the same thing, but like you - noticed it before I built one.


----------



## gates_2

ahh- works now- great

 still messed up the rk27 pot... oh well

 it kinda works....when it's turned up all the way i get balanced channels, other wise much more out of one


----------



## gates_2

one more thing... I can't seem to get the bias down on one channel below 44V. Is it just this tube or should I be concerned?


----------



## sphinxllama

Hello diyers,

 so I almost finished my SOHA. Installed all parts and now...

 The first time I applied power, the fuse in our house went out!!! 
	

	
	
		
		

		
			





 What happend??? Double checked the power cable wiring, like shown on mb3k.com homepage. Everything looked right to me. Do you have a clue what could be wrong??? I am from germany and used the 230V option shown on the homepage. Do I need to put the OPA in for testing? Do I need to connect the AudioIN and AudioOUT? Other than that everything is in place!

 I know hard to do without pictures, but I forgot my camera! Tomorrow I am going to ask my neighbour but right now it is to late. But I would like to figure it out tonight.

 EDIT: Maybe I found my mistake. Does the yellow lead go to ground? I understood it that black and red goes to ground but after reading ofer it several times I am not sure any more. Is it the mistake pleeease...


----------



## headphonejunkie

Check your transformer wiring. Something must be wrong.


----------



## sphinxllama

@headphonejunkie

 thanks a lot for your quick answer!

 Does the wiring has to look like that:

 EDIT: To SAFE my pride I have to delete this 
	

	
	
		
		

		
			





 Used the mouser IEC power entry module with fuse holder Partnumber:693-6200.4315

 EDIT: FallenAngel Thanks for your answer I think it is to late and I did not think...


----------



## FallenAngel

Definitely not! Good thing you're safe 
	

	
	
		
		

		
		
	


	




 Don't connect the red and black wires to house ground, just connect them together and isolate them from everything else. I would suggest a good mechanical connection, some solder and electrical tape over it.

 EDIT: Connect the top pin to the case for safety and make sure your input / output jacks are isolated from the case.


----------



## regal

Quote:


  Originally Posted by *sphinxllama* /img/forum/go_quote.gif 
_@headphonejunkie

 thanks a lot for your quick answer!

 Does the wiring has to look like that:

 EDIT: To SAFE my pride I have to delete this 
	

	
	
		
		

		
		
	


	




 Used the mouser IEC power entry module with fuse holder Partnumber:693-6200.4315

 EDIT: FallenAngel Thanks for your answer I think it is to late and I did not think..._

 

You must have a short


----------



## sphinxllama

Hello,

 thanks to everybody I finally finished my SOHA.
 It works now fine, but there is only one thing I am not pleased with. When I connect my mp3-player and do not play music and just touch the volume nob and turn it louder I get a rush in my headphones. Is it a ground problem? Where could it be?

 greets

 EDIT: even when I came to close to the tube I can hear some rush. Is that normal?


----------



## Yen

Quote:


  Originally Posted by *sphinxllama* /img/forum/go_quote.gif 
_When I connect my mp3-player and do not play music and just touch the volume nob and turn it louder I get a rush in my headphones. Is it a ground problem? Where could it be?_

 

If you are using a blue alps (or a copy), ground the pot by screwing the ground wire to one of the screws of the pot's casing... That could help.


----------



## sphinxllama

@Yen
 Thanks for your answer. Yes it is an AlpsPot I think a RK27. So I should wire from the potground on the pcb to a screw on the pot?
 But what confuses me is that when I come to close to the tube there is a rush too.


----------



## tomb

Quote:


  Originally Posted by *sphinxllama* /img/forum/go_quote.gif 
_@Yen
 Thanks for your answer. Yes it is an AlpsPot I think a RK27. So I should wire from the potground on the pcb to a screw on the pot?
 But what confuses me is that when I come to close to the tube there is a rush too._

 

Tangent's photo of grounding the RK27 pot (on the PPA):




 There are actually four input pads next to the pot on the SOHA. Only one Ground is needed; use the other one to wire to a screw on the RK27 as shown in the photo above.

 As for your hand, it's hard to tell. You may have a shielding issue with the tube. There is a small ground pad near pin 1 on the tube. That is sometimes used for a small snubber cap, but I haven't heard of anyone using it. Get the pot grounded first. If you still have noise issues with your hand and the tube, you might try that pad.


----------



## sphinxllama

And again thanks for your help 
	

	
	
		
		

		
		
	


	




 Sometimes a picture is worth more than a thousand words. especially in my case


----------



## sphinxllama

O.K. I used some spare time and did that job. It worked. Now the rush, when touching the pot is gone! Thanks to Yen and tomb 
	

	
	
		
		

		
		
	


	




 The problem with the tube is not gone so. I took some pictures maybe the problem can be seen easier.













 Can not see a groundpad on that tube?


----------



## achina

Have you checked out this thread?

http://www.head-fi.org/forums/showthread.php?t=228976

 It may be a grounding problem. Looks like you don't have it in a case yet though.


----------



## tomb

Sphinxllama,

 The tube "ground" is actually an internal shield. As mentioned, it's usually decoupled from Ground with a small snubber cap jumpered from pin1 to that extra pad shown in the photo:




 As I also said - I haven't seen one yet where this is necessary, though.

 Achina has a good point with his post. Did you by chance connect house ground (the third prong on a house wall outlet) to the SOHA board? The Ground on the SOHA board is for the center tap from the transformer, only. If you have tied it into house ground, you'll get a huge hum and noise. The only thing that should be connected to the SOHA "Ground" pad is the center or combined tap from the xfmr.

 If that's not it, you may have a bad tube - perhaps one overly sensitive to RF noise.

 Those are my guesses, anyway.


----------



## Yen

Quote:


  Originally Posted by *sphinxllama* /img/forum/go_quote.gif 
_The problem with the tube is not gone so. I took some pictures maybe the problem can be seen easier._

 

It is the tube catching some interference from other electronic devices. Especially if you are using it near a PC it will catch even more.

 I have also noticed, when I removed the output resistors (R6/16), that rushes are heard more often. Try casing your amp in a metallic case (which you have done already) and try some 50-100ohm quality (holco, kiwame etc. if you have $) resistors and rushes will dissapear or be less frequent and at lower volume.


----------



## headphonejunkie

I noticed your transformer wires are not twisted. I twisted mine. I am not sure if this will make a difference though.


----------



## sphinxllama

@tomb
 I soldered a wire from pin1 to that pad but it got even worse. the rush was there even without comeing to close to the tube. and music only played on one side. now I desoldered everything and it only rushes when I come to close to the tube about 5mm.

 @yen
 the amp stands away from any big electronical gear like tv or pc. so I think that point I can skip. 
 the output resistors I have exchanged with jumpers. the soha kit came with vishay dale resistors I think with a value of 150Ohms. so I did not use them because somewhere I read that resistors in that place will cause a loose in soundquality. and with beyerdynamic DT880 250Ohm impedance headphones the volume is not to loud when turned a little from zero position so both sides of the headphone are powered. 

 @headphonejunkie
 thanks, will try this option tomorrow an will post if it had some effect on the rush.

 the rush is not that bad, it can hardly be heard when music is playing and only if I come to close to the tube. but other than that it has no effect on the quality. it is just strange phenomenon to me.

 After a long day I will now enjoy the SOHA 
	

	
	
		
		

		
		
	


	













 P.S. can not stop saying thanks for all your great and tireless helping


----------



## headphonejunkie

Twisting the wires help them avoid any electrical interference from each other and should help them not give off any EMF to other components;hopefully.


----------



## sphinxllama

hi,

 just wanted to say that I found my mistake. should have read the link from achina more carefully. did not connect the case with houseground. now I did that there is NO rush when coming close to the tube! 
 and now


----------



## Sathimas

Hi there,

 I was looking for a new headphone amp and came across the SOHA.
 I've read this thread from the beginning to the end, along with some
 other threads here concerning the SOHA. I found a lot of very useful
 information, but I still got 3 Questions ... 

 My first question will hopefully easy to answer:
 I need three LEDs, not only one. I attached a picture of my case.
 (At least what it's gonna look like, ain't ready yet. Btw.: I haven't started building, nor ordered any parts yet.)
 The two knobs will be backlighted by a red LED each, but therefore I need some current for the LEDs.
 Can I simply solder some wire to the soldering spots of the socket LED ?
 If the LEDs aren't that bright anymore - no problem, I don't want the Amp to illuminate my whole room 
	

	
	
		
		

		
		
	


	




 The second question is surely almost impossible to answer 
	

	
	
		
		

		
		
	


	



 I'm gonna order the level one kit from glassjaraudio, but I want to upgrade the 
 standard caps that are in the signal path. Jeff wrote that he would order some auricaps.
 If I got that right, the caps in C1 and C13 should be exchanged.
 Has anybody any expieriences with those caps? I don't want to order the parts from several suppliers, 
 since the shipping is mostly more expansive than the parts themselves.
 Would you suggest upgrading anything else? I don't want to spend too much money.

 Also important - I'm living in Germany, so all the extra parts I need will be ordered there.

 My third question: grounding ...
 As you can see below, my case will my made out of wood and only the front and back panel will be aluminium.
 I already saw some pics of SOHAs in wooden cases, so this should be no problem,
 but is there anything special to be taken care of concerning the grounding?

 Here's the picture:




 Cheers,
 Sathimas


----------



## heatmizer

jeff will give you some upgrade options on the order form.
 c1,c13 and c2,c14

 What is the extra knob for?


----------



## Sathimas

Hmm, I already filled out the order form, but there were no upgrades choosable?
 I'll try again ... but thank you for the advice.

 The extra knob is a source selector.
 I'm tired of plugging and unplugging the CD Player, the MP3 Player and the record player.

 [EDIT]

 Just tried again, since I got no US zip code, I cannot complete the order form.
 I'm stuck at the page that tells me to choose the shipping ...
 I'll contact Jeff about that.

 Any suggestions concerning the caps anyway?
 Does anybody have a list of the things Jeff ist offering (and prices)?

 Sathimas


----------



## headphonejunkie

On the point of grounding. I use completely wooden case I made myself and have no ground problems at all. Of course if you use a metal case things are different.


----------



## heatmizer

This jeff other site:
http://www.geocities.com/jeffrossel/
 Other than that I used nichicon muse es 1000mfd in c1/c13 bypassed with panasonic ecqp and panasonic ecqp on c2/c14
 A good build guide is here:
http://www.mb3k.com/soha.html
 mb3k also has some alternative caps (boutique) on his BOM


----------



## Blooze

I built mine (p2p version) in an all wood case, but made sure I had safety ground going to all the exposed metal components (ie. tube guard, etc...) that might come in contact with any voltage. Here's a link to pics.

http://www.pedalforroses.homestead.c...phoneamps.html


----------



## Sathimas

I already head seen these sites - but I didn't really understand the BOMs.
 I don't know, maybe didn'T to see the wood for the trees 
	

	
	
		
		

		
		
	


	




 Now I got it - thank you.

 About grounding - thank you for the advice to ground all metal parts
 that might come in contact with any voltage. I'll keep an eye on that.
 @ Blooze - amazing casework - wow.

 But what about the LEDs? Is the question that stupid?


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## Sathimas

Hello guys, im back.

 My SOHA is up and running perfectly now - well, it *was *running perfectly.

 For my test- setup I only used one input, going through a turn-switch 
http://www.reichelt.de/?SID=265Sd2ha...ie%2523CUK.pdf
 Everything was perfect - what a sound, wonderful.

 Today I finally mounted my finished wooden back-side und soldered the other
 2 inputs to the switch.
 Now I somtimes got some buzzing noise in the background, like the backgroundnoise you have when your radio reception is not perfect.
 It seems to be worse on loud notes, quiet tunes do not distort. Eric Claptons Unplugged is nearly flawless,
 some Metal CDs I tested are awfully bad...

 I got no idea where the problem might be.
 Maybe its because I did not solder the ground of any single RCA Jack separately to the Signalground Spots?
 I connected the three left ones and soldered them to the left SGL, likewise the right ones.

 Hope you got some solution or hint for me.
 I was SO happy with my SOHA


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## Sathimas

Ok guys, since none of you had any idea about my problem, I had to find out myself ...

 Yesterday evening, the distortions where gone when I connected the amp to my CD Player.
 Today - they where BACK !

 I was about to go crazy... Just 10 minutes after I finally finished the case the amp started making problems again...

 Then I began to simply undo anything I did before I reconnected it.
 Only 5 minutes later I had the solution:

 I'm using a Y-adapter from my CD Player to my Onkyo Receiver and the SOHA,
 because always plugging and unplugging the cables bothers me.
 If the receiver and the amp are connected I get distortions, if the
 Onkyo is not connected - I've got perfect sound!

 Now I'm wondering how to get rid of this problem, since I'm still not willing to
 steadily change the cables - this disturbs the perfect order behind my receiver 
 ________________________________

 I still got one other problem - although I grounded the Alps, I still got a little humming.
 Not to loud, but its noticable when I listen to quiet music at a lower level.

 Any advice?


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## Blooze

Maybe build a switchbox between your sources and amps? This is what I've been thinking of doing. Seems like Nate built a nice switchbox for a headamp show once.

 Do you have resistors on the output? I got a little hum on mine without them and went ahead and put 160R resistors on the output. Took care of it.


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## Sathimas

I got the 150 Vishay/Dale Resistors on the output.

 The hum really annoys me ... I mean I don't here it on 90% of my music anyway, but I still *know* that it's there. 
	

	
	
		
		

		
		
	


	




 I don't want to build a switchbox, because of that my SOHA has a source sellector knob 
	

	
	
		
		

		
		
	


	



 My problem is that I don't have enough room here ...
 My Soha Case got rather big and it already covers like 40% of my Onkyo 674.
 Since my Receiver gets damn hot, I cannot place anything above the heat source.
 Maybe I'll build one if I'd ever posess more than one headamp


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## heatmizer

How close is the toroid to the circuit board? needs to be at least 1.5 inches away. I ended up casing the toroid in a metal enclosure to get rid of the quiet hum. My case did not allow me to move the toroid away farther.


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## Sathimas

I knew it ... the torriod ...

 The torriod is exactly zero inches away from the board,
 my case is very small (I had started building it for another amp and wasn't able to change anything anymore.)
 and because of that the torroid is kind of stuffed into the case.
 I even couldn't mount it horizontal, it has some 40degrees angle to the ground 
	

	
	
		
		

		
		
	


	




 I'll post some pictures soon.

 I'll try to get some thin metal plates and encase the torriod in them.


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## heatmizer

Try a tuna can


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## Sathimas

Here he is:




 And here the inside - as you see, I got almost no space ...
 But I'll find something, I'm sure.


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## heatmizer

As a test. Unbolt the toroid and hang it over the side. then see if you still have hum. BTW, very nice looking


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## headphonejunkie

I know this may be a pain but I would try brading all your wires. The braid should help eliminate any stray EMF which could be inducing hum. If the toroid suggestion doesn't work that is.(by braid I mean twist them tightly)


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## headphonejunkie

You should twist your wires anyway since that could eliminate the hum from the toroid too. If there is any from the toroid. The toroid shouldn't pass any hum but untwisted wires can pick up hum very easily.I would try twisting the wires on the toroid first and see what happens.Then try your input wires if that doesn't work then the output, and volume, and selector switch wires next.


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## headphonejunkie

Untwisted wires can also pass EMF which would produce hum.


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## headphonejunkie

To take a quick guess I would bet it is related to the wiring between your inputs and selector switch. They should be routed a little better and twisted. Try to keep them away from the board like your headphone out is.


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## Sathimas

Well, keeping the wires away from the board is simply impossible.
 About twisting ... the cables are too short and I would have to desolder them all to do that anyway.

 Would help shielding them with aluminium foil?
 Every shielded cable I ever opened had a layer of aluminium foil around the core.
 Wrapping the calbes would be no problem.


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## headphonejunkie

I would try twisting the wires on the toroid. You can probably do that without desoldering anything. I would also try the input connectors. Foil might work but you can short circuit something. Be careful trying that.


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## Sathimas

The problem of short circuiting something came to my mind right after I wrote that,
 but won't be a problem. I will wrap the free parts of the contacs with duct tape
 and use the aluminium foil afterwards.
 But thank you for the hint, electronics are dangerous.
 (Although I managed to be hit by an electric shock only once 
	

	
	
		
		

		
			





 )

 The problem with my case is, that some parts are hardly removable.
 The torriod is glued to the bottom of the case and the screw will turn as a whole,
 the bottom side isn't fixed in any way ... 
	

	
	
		
		

		
		
	


	




 I'll have a try later today or tomorrow, we'll see.
 Since the amp is finally finished, listening is much more fun than modifying it


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## headphonejunkie

I hope it works but be careful. You have a lot of voltage coming in from your house.


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## Sathimas

I've got exactly 230Volts coming out of the wall, and I already had these running through me 
	

	
	
		
		

		
		
	


	



 You can be sure that I'll be careful now 
	

	
	
		
		

		
		
	


	




 But my thought was to mainly shield the signal cables, from the inputs to the switch.
 Well, to be sure, I'll shield simply everything.


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## headphonejunkie

try a little at a time then test it. that way you don't have to do what is not necessary.


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## kklee

Quote:


  Originally Posted by *Sathimas* /img/forum/go_quote.gif 
_Would help shielding them with aluminium foil?
 Every shielded cable I ever opened had a layer of aluminium foil around the core.
 Wrapping the calbes would be no problem._

 

If the hum is being induced by the transformer (EMI), aluminum is useless as a magnetic shield. I can tell you from personal experience that you'll need something along the lines of magnetic shielding metal (mu metal, or the like) to quell transformer hum.

 Aluminum shielding would still be good for blocking RFI, so it may still help. It just depends on what the source of tyhe noise is.


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## konder8u

Ditto on the Pana FM's - even for those you list for C7, C8, and C11. The great thing about the SOHA design is the only cap in the signal path is C2 and C14, and that's an orange drop/box cap. So, the Pana FM might be the best non-boutique choice, period.

 According to the designers/first proto builders, T1 should be a toroid if it's in the case. If you mount it remotely in a different box or walwart, then whatever you want. Unfortunately, I've found the 30VCT uncommon enough that the toroid is the simplest choice anyway. 

 For the LED, if you're talking the tube light, be sure to use a T1 (3mm). That's different from the Millett. With a 3mm LED, though, you can push it up into the tube socket for a very direct effect.


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## tomb

Quote:


  Originally Posted by *konder8u* /img/forum/go_quote.gif 
_Ditto on the Pana FM's - even for those you list for C7, C8, and C11. The great thing about the SOHA design is the only cap in the signal path is C2 and C14, and that's an orange drop/box cap. So, the Pana FM might be the best non-boutique choice, period._

 

Agree with that completely - another Pana FM lover. 
	

	
	
		
		

		
		
	


	




  Quote:


 According to the designers/first proto builders, T1 should be a toroid if it's in the case. If you mount it remotely in a different box or walwart, then whatever you want. Unfortunately, I've found the 30VCT uncommon enough that the toroid is the simplest choice anyway. 
 

Except for a local dealer who was vacating his space and sold me about 50 FP30-400 Flat Packs at a song. 
	

	
	
		
		

		
		
	


	




 They fit the Jameco walwart case with room to spare - could even parallel two of them for more current if the Jisbos ever come along. 

  Quote:


 For the LED, if you're talking the tube light, be sure to use a T1 (3mm). That's different from the Millett. 
 

Not the MAX - it uses T1's, also. Quote:


 With a 3mm LED, though, you can push it up into the tube socket for a very direct effect.


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## Sathimas

I twisted the torriod - wires now - and it worked.
 The hum now starts to be noticable at a level that I'll never use to listen to music. 
	

	
	
		
		

		
			




 That Amp has so much power ... wow.

 Thank you again for your advice, I would have gone crazy without the good documentation here.
 ______________________________________

 Since it completely works now, it's about time to think about some modifications 
	

	
	
		
		

		
		
	


	




 Everybody here seems to be crazy about diamond buffers.
 I already found at that those transform the SOHA into a Class Amplifier (Is that correct?)
 and that this takes the sound quality to a new level - But how does it do that?
 What enhancements can I expect?

 First I'll try to get a new tube, but I haven't found any good supplier here in Germany.


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## headphonejunkie

Good to hear you got somewhere with your problem. For a tube I like a German RFT I have been using. It cost me $30 at tubedepot.com. Maybe you can find one right at the source.GE 5963's are supposed to be good too. I have a GE5814A that sound very good.


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## PJotr

Hi
 When I look on default config with LND150 http://www.mb3k.com/pics/SOHA/LND150.gif and PCB SOHA http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.pdf
 I think when we change only jumper from PC to CS we haven't change config for the source follower, because we switch C2 to pin G LND150 not to pin S.
 It's correct or I'm wrong?


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## tomb

Quote:


  Originally Posted by *PJotr* /img/forum/go_quote.gif 
_Hi
 When I look on default config with LND150 http://www.mb3k.com/pics/SOHA/LND150.gif and PCB SOHA http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.pdf
 I think when we change only jumper from PC to CS we haven't change config for the source follower, because we switch C2 to pin G LND150 not to pin S.
 It's correct or I'm wrong?_

 

The note on that pic is mis-leading. For the source follower using the LND150's, you also have to move the LND150's to the other two positions - Q1 and Q3 
	

	
	
		
		

		
		
	


	




 , and jumper from D to S in the Q2 and Q4 positions:





 Don't forget that R8 is reversed with R7, and R18 is reversed with R17. Not very confusing is it?


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## PJotr

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_ For the source follower using the LND150's, you also have to move the LND150's to the other two positions - Q1 and Q3 
	

	
	
		
		

		
		
	


	




 , and jumper from D to S in the Q2 and Q4 positions:_

 

Thanks for your answer, but I know about it.

 I want to change config between "LND150 MOSFET CCS" and "LND150 Source Follower" only with switch jumper PCS (config as writed in http://www.mb3k.com/pics/SOHA/LND150.gif)

 I think it is possible in config http://www.mb3k.com/pics/SOHA/LND150.gif.
 Only we must change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360. And now we can change config by jumper PCS.

 Look in http://headwize.com/ubb/showpost.php...52060&fpage=12


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## Blooze

Quote:


  Originally Posted by *konder8u* /img/forum/go_quote.gif 
_According to the designers/first proto builders, T1 should be a toroid if it's in the case. If you mount it remotely in a different box or walwart, then whatever you want. Unfortunately, I've found the 30VCT uncommon enough that the toroid is the simplest choice anyway. _

 

I never had any problem sourcing the flat-pack trafos. Never had an issue with any hum being loud enough to cause any problems with the music either, and I built one of the first several SOHA's, long before there were any PCB's, with the trafo right in the case.

http://www.pedalforroses.homestead.c...phoneamps.html


 Tomb is right, use a flatpack in a wall wart case if you want the least amount of PS noise.


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## tomb

Quote:


  Originally Posted by *PJotr* /img/forum/go_quote.gif 
_Thanks for your answer, but I know about it.

 I want to change config between "LND150 MOSFET CCS" and "LND150 Source Follower" only with switch jumper PCS (config as writed in http://www.mb3k.com/pics/SOHA/LND150.gif)

 I think it is possible in config http://www.mb3k.com/pics/SOHA/LND150.gif.
 Only we must change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360. And now we can change config by jumper PCS.

 Look in http://headwize.com/ubb/showpost.php...52060&fpage=12_

 

That last link has no bearing on the LND150's or the final board that Digi produced. The production boards were different from the ones supplied to several people during prototyping, anyway. If you can find a way to do it, fine, but it's not possible with the production board as implied in that note.

 EDIT: It's not even implied in the note - see the sentence about "FETs" below.

 Only the J113's are switchable _only_ by changing the P-C-S jumpers. This is explained on Digi's own website, which is where I referenced the image I posted:
http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.htm
 Scroll down to about the bottom third of the page, and you will find the different CCS configurations referenced.

 Besides, the "FETs" are only the J113's. The 1N5297's are _constant current diodes_ and the LND150's are _MOSFETs_. 

 As stated earlier in my previous post, the LND150 Source Follower has a different configuration entirely from the "regular" LND150 CCS. Good luck.


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## headphonejunkie

I am wondering if there is any difference between the sound using these two configs. I would go with source follower (which is what i am using) if there is no difference. Although, I think this config was for if you were going to use the diamond buffer bds. I think. I am planning on using the jisbos when they become available.


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## tomb

Yep. Runeight said they debated source follower vs. the "regular" config during design, but the LND150's are only available at Mouser, and the J113's have limited availability, too, I believe. So, they added the 1N5297's, but I don't think source follower is even possible with those.

 He said if you have the parts, there's no reason why you shouldn't use "source follower", period. It will work just as well with BJT _or_ FET opamps - and it is needed for Steinchen's buffers.


 EDIT - P.S. Another reason for having so many configs - the J113's have to be handled carefully. Quoting Runeight:
_"Care should be exercised when building the SOHA with the J113 JFETs. Their maximum Vdss is 35V. Under normal operating conditions they will see only about 15-20V, but if the plate voltage on the tube is too low it is possible to exceed this maximum and destroy them. To protect the JFETS, the minimum plate voltage should never be set below 20V (see below the warning about adjusting the trimpots). "_

 What that means is that unlike the convenience we have with the Millett MAX - not caring what the tube is biased at until the output stage is adjusted - if you have the tube biased incorrectly on startup in the SOHA with the J113's, you could burn them out.


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## ericj

15-0-15-0 transformers are relatively easy to find. 

 I obviate the hum issue by mounting the transformer in a wallwart case and placing it a few feet away from the amp. Use a 5-pin DIN connector for power.


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## PJotr

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_As stated earlier in my previous post, the LND150 Source Follower has a different configuration entirely from the "regular" LND150 CCS. Good luck._

 

Yes, I know.
 But 
	

	
	
		
		

		
		
	


	




 look in http://www.mb3k.com/pics/SOHA/LND150.gif on bottom writed:
 "... For the source follower configuration for the fets, just change the PCS jumper to go from C to S instead of C to P."

 But I think it is mistake because jumper PCS in position CS: switch C2 to pin G LND150 not to pin S.
 But will be work it, when we change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360..


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## tomb

Quote:


  Originally Posted by *PJotr* /img/forum/go_quote.gif 
_Yes, I know.
 But 
	

	
	
		
		

		
		
	


	




 look in http://www.mb3k.com/pics/SOHA/LND150.gif on bottom writed:
 "... For the source follower configuration for the fets, just change the PCS jumper to go from C to S instead of C to P."

 But I think it is mistake because jumper PCS in position CS: switch C2 to pin G LND150 not to pin S.
 But will be work it, when we change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360.._

 

I'll repeat this for the last time - just to be helpful - "FETs" does not mean the LND150's.


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## PJotr

OK, but when I want add eg. jisbos bufer whitch CCS option I must chose:
 1.LND150 MOSFET CCS
 2.LND150 Source Follower
 3.J113 JFET CCS
 4.1N5297 Diode CCS

 I read many info and I think I must chose 2. or 3.
 When I want eg. OPA2134 I chose 1.

 It's correct?


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## tomb

#2.

 Or #3. - by switching the P-C-S jumpers. "FETs" in the bottom note of the CCS diagrams refers to the J113's.


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## ericj

Wow. What a lot of confusion. Especially since the LND150 is most assuredly a FET. Depletion mode, which is weird, but still a FET. 

 FWIW my perfboard soha (w/ lnd150) switches between regular and mu-follower by just moving one jumper per side.


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## tomb

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Wow. What a lot of confusion. Especially since the LND150 is most assuredly a FET. Depletion mode, which is weird, but still a FET. 

 FWIW my perfboard soha (w/ lnd150) switches between regular and mu-follower by just moving one jumper per side._

 

Well, I think in Digi's part of the world there may be a practice of referring to common JFETs as FET's. Whereas a MOSFET is rarely referred to as anything other than a MOSFET.

 You are certainly correct about confusing.


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## PJotr

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_ switches between regular and mu-follower by just moving one jumper per side._

 

But (as writed before) when look in PCB ver.3 :
 in config "LND150 MOSFET CCS" when we switch jumper we switch C2 to pin G not to pin S.
 We must make changes as writed before...


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## Blooze

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_
 FWIW my perfboard soha (w/ lnd150) switches between regular and mu-follower by just moving one jumper per side._

 

Yep. Mine too.

 In fact, I'm the reason that the mu-follower configuration was developed. Had some wonky opamps I wanted to try so Runeight provided the answer after I was getting huge amounts of offset.


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## Eokboy

With the mu-follower config, can I use LM6172? Would it be too cranky for unity gain?


----------

