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SOHA II Builders Thread - Page 109

post #1621 of 1688

So I just finished up my amp...sadly I have run into some issues which I think boil down to tube incompatibility from what I've been reading.


My TPL was bang on, 41V but my TPR was 35V. Frustrated...I thought I'd rule it out with swapping the tubes. Now I have a TPL of 46V and TPR of 33V. Everything else checks out in the amp, all the amp lines, voltage test points, everything is 100%...


Does that sound about right? My tubes are 5963's on 12.6v by the way. Just wanted to re-cap before buying some more on ebay. :/ was really looking forward to listening to this tonight.


Edit: my TP+ was 108V and 125V without with tubes in, so I wonder if that's also an indication of tube issues...

Edited by Taxihamster - 9/8/12 at 4:38pm
post #1622 of 1688
I have a pair of 5963 and they should work fine.

What is your voltage between TB+L and TPL (and the right side too). If I were to hazard a guess, there is something wrong with the either the CCS or the current mirror.
post #1623 of 1688

TB+L difference was 19v where TB+R difference was 25v even though my currents & voltages on my resistors all were perfect on P1P, PL and PR. My TB+L and TB+R were both set at 60V but the TB+ was sitting at 108 with the tubes in.


What is the CCS?

Edited by Taxihamster - 9/9/12 at 9:21am
post #1624 of 1688
Originally Posted by Taxihamster View Post


What is the CCS?


Constant Current Source. In the SOHA II, it's made up of everything between the cathode and ground. See http://www.cavalliaudio.com/diy/soha%20ii/main.php?page=design/ipdesign the last part of the page, "Finishing the Tail CCS".

post #1625 of 1688
Originally Posted by KimLaroux View Post


Constant Current Source. In the SOHA II, it's made up of everything between the cathode and ground. See http://www.cavalliaudio.com/diy/soha%20ii/main.php?page=design/ipdesign the last part of the page, "Finishing the Tail CCS".

Ah, thank you. That makes sense.


I'll go through the entire setup process once more to be 100% that every other part is bang on and see what comes of it. I'll post again if I still get a huge differential between my voltages again.

post #1626 of 1688

Just found a post mentioning tube-mismatch and to check Pin 1 on the trouble side. Turns out the voltage is bang on at Pin 1, just a bad tube.


Got more tubes on the way =D

Edited by Taxihamster - 9/10/12 at 3:34pm
post #1627 of 1688

Checked through this thread and I only found one instance where someone asked for a simplified transformer wiring diagram, but it was 240V and I need 120V.


I've never been able understand electronic schematics but I've been doing all I can to figure this out..


The transformer I found a picture of has this schematic: (should be same number of wires as "Y236103 30VA" just looks like different wire colors)



So I think I have this correct..?



Blue + Violet = Neutral

Grey + Brown = 120V


This one not so sure..



Black = 15

Red + Orange = 0

Yellow = 15



Just struggling due to the lack of schematic knowledge..

Edited by Mikael109 - 9/18/12 at 12:59pm
post #1628 of 1688

I went rooting around the thread to get you the picture to verify what you were looking for.



Though on my end...I've changed out 2 transistors Q5 & Q6R and I still have a 37V on that channel with perfect voltage on the other side. This is driving me crazy...I still can't get it to run here. Also because I don't have the case ready for testing, I wonder if I can't hear any sound because I'm grounding my RCA's straight into the load side with the ground port running straight into my ground plug/transformer setup switch.


Maybe they need to be all common ground?

Edited by Taxihamster - 9/19/12 at 3:15pm
post #1629 of 1688

Thanks so much for pulling that up!


Can see the 15-0-15 clearly and it looks like I had it right.



I'm pretty new to everything so if this is a completely incorrect thought feel free to ignore it or have me delete it.. but I noticed that in glass jar's kit "non-insulated" chassis mounted RCA connectors were specified.


If it were to built up in the normal Hammond case which is all metal I'd assume that would result in them being commonly grounded by the Star Ground standoff.


Maybe that's the issue?

Edited by Mikael109 - 9/19/12 at 4:32pm
post #1630 of 1688

I have a aluminum Hammand but I haven't mounted the RCA's yet...so I dunno if that's the issue. I should just get the holes drilled & get the star ground dropped in to at least to see if sound goes through.


Though the voltage thing is driving me friggin bonkers...

post #1631 of 1688

Just hoping someone might have some insight here...


I finished up my case, got all my grounding in place, I still have my 41v on one channel and 37v on the other channel, but I should be getting some audio output all the same though I would think right?


That's the problem now, I have no audio output at all. None. Should I post some pics? Anyone have any kind of ideas? I just want to listen to this thing already :/

post #1632 of 1688

I'm planning on upgrading the PSU and tube stage in my Starving Student based on the SOHA II design. I'm currently going trough my parts and making a list of what I'll need.


Studying the power supply, there is something I don't quite understand. I'm hoping someone here will be able to clarify things for me.


The TL783 datasheet recommends using a 82 ohm resistor between ADJ and output, to make sure to have enough current to maintain regulation. It recommends 15 mA of minimum load current. Looking at figure 12, we see that in the case of the soha II, 10 mA would be enough.


The way I see it, the tubes will use 4 mA and the setup resistors of the regulator will use just over 3 mA. So the TL783 has a load of less than 8 mA. Am I missing something here?


It seems to me as the regulator should be unstable in the SOHA II. Considering it's a proven design, I will take for granted it is stable. So is it really stable? And if so, anyone can explain to me why?

post #1633 of 1688

Dear all,


I'm using my SOHA II since severql years, with a Monica USB DAC (from DIYparadise) and a AKG K-1000. I'm happy except that the sound stops from time to time and restart some seconds later. I was convinced thqt I had an issue with the laptop and the com with the DAC. But I recently understood that it is instead the SOHA II amp that trips for some seconds from time to time (e12 board, I can hear the relay thqt trips).


I went through the thread and discuovered thqt it was somehow a knowwn issue, but did not identified solutions to, solve this issue. Would some of you have identified ways to improve the operation of the e12 in this circuit, and to suppress those trips of the protection circuit?





post #1634 of 1688

So no fix proposal for this e12 trip issue?


Best regards,



post #1635 of 1688
I had the same issue when I used my PC as source. Since I have never had this issue while using an ipod‚ a regular CD player or a MyBook Pro I think the problem came from my PC‚ not the e12,
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