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SOHA II Builders Thread - Page 53

post #781 of 1686
Quote:
Originally Posted by runeight View Post
No. A socket is the best way to go.
Agreed - my curiosity was directly soldering an opamp to the board. I do know some folks (OCD types) who won't do anything but - and are masochistic enough to love the agony unsoldering when put in wrong or scorched.

Carry on, Shelly - you are doing great.
post #782 of 1686
Quote:
Originally Posted by runeight View Post
Egads.

The problem with the hiss problem is that not everyone has encourntered it. Because of this we haven't been able to pin down a cause. That is, to determine what is differerent about some builds compared to other builds that are using the same components.

At one time I thought it might be noise in the O/P transistors running at 100mA. But I think Ferrari measured this and it was negligible and inaudible.

Is anyone else who has a recent build also having this problem?
For me, I think the hiss is tube related. Going from a 12AU7 type to a 6DJ8/6922 type seems to have "cured" it. Within the various 12AU7s, some were noisier than others. When I first encountered it, I had a small sampling of tubes, now I have multiples of same types and brands and can pretty much say they were tube related on my end.

With my current tube, it's quiet even with Denon AH-D2000s and my more sensitive headphones (ATH-M50, M-Audio Q40). I haven't tried my IEMs, but it's way overkill for IEMs (too much gain).

YMMV.
post #783 of 1686
Quote:
Originally Posted by Computer Blue View Post
Has anyone solved the hiss yet? I just finished a glassjar kit and have some soft hiss going on. It is there with or without tubes in. Any ideas where to start looking to fix this?
No hiss here using 32 Ohm grados. Hiss problems is generally more frequent with sensitive low-Z headphones.

Hiss in both channels or in one channel only? Hissing isn't a very easy problem to solve. Could be ground issue, transformer interference or simply a part that emit more noise than usual.
post #784 of 1686
All this talk about the gain make me think I need to add resistors to the input to lower it. The only thing I've built before is a Starving Student and it has way too much gain for me. I can only use it with orthos, and not all of them. With everything else, the cheap pot is just at the point of channel imbalance. Even with the orthos, it's close.

So is adding resistors to the input the way to lower the gain, or is there another way? I'm not going to do it until I have the amp running.
post #785 of 1686
Thread Starter 
scompton, there is a lot of information on the SOHA II website at Cavalli Audio, including gain information for a few different tube types.

The gain of this amp is controlled, primarily, but the application of a small amount of negative feedback. For the 12au7 tubes the gain should be only about 9X. I suspect this is lower than your Millet. So you should try it first before making mods. Then, if you really have too much gain resistors in series with the headphones at the output are probably a better choice. Something like 100R.

Keep us posted.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #786 of 1686
Thanks, I was going to try it first. Somehow I missed the information about gain. I thought I had gone though all of the pages on Cavalli Audio.
post #787 of 1686
well, the sohaII is all soldered up, and checks out fine. One of the test tubes isnt great, only 17v dropped instead of the 19v, but i think its near enough

Just got to get it cased up and we are good to go.
post #788 of 1686
Thread Starter 
Good news.

After you break it in for a while perhaps you can tell us how it compares to your Bijou. I don't think there are too many of us with both of these amps and I would most definitely like to have your thoughts.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #789 of 1686
I have both... but balanced Bijou vs SE SOHA II isn't quite fair.
post #790 of 1686
Thread Starter 
Ah yes, I forget that you also have them both by virtue of the SOHA II coming back from operations overseas.

Perhaps that comparison is a bit unfair and you've already extensively logged your thoughts on the Bijou. So, I won't ask.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #791 of 1686
Quote:
Originally Posted by adamus View Post
well, the sohaII is all soldered up, and checks out fine. One of the test tubes isnt great, only 17v dropped instead of the 19v, but i think its near enough

Just got to get it cased up and we are good to go.
congrats adamus

Mine is moving along pretty smoothly (surprisingly) and if I put 2-3hrs more into it tonight I'm pretty confident I'll be bringing up the amp for its initial setup by tomorrow.

BTW, Jeff sent me a pair of Sylvania 5963's, when I set the heater voltage do I jump 12.6v or 6.3v? thanks.

zk
post #792 of 1686
Thread Starter 
You'll want 12.6V for the 5963 and the other variants of 12au7. Good luck.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #793 of 1686
My soha II is making music



I must've really lucked out because the voltages came up correctly from the start.
TL+14.99V
TL-14.95V
TH -12.82V
TB+ +123.2V (down to 104.6V with a pair of 5963)

Adjustments were smooth and easily set to spec as per Alex's website. Manged to set R10L/R idle currents to 100mA (220mV), TB+L/R set to 60V, then tail current set to 2mA (400mV)
Voltage difference between TB+L and TPL was fairly close to 19V with the e12 delay clicking around ~7 sec

I love my millett starving students, but I noticed right away a significant improvement in sq without any audible hiss/hum. It doesn't sound as 'tubey' like the ss and much prefer how this soha II sounds... really liking it a lot. I'll let it burnin for a while. Can't wait to do some tube rolling

Guess I can't say it enough -- thank you Alex, all the prototypers and previous builders who asked all the questions that I didn't have to. Cheers!

I'll do the casework after I complete my next amp project (CTH). I hope to have matching wooden enclosures for both with enough ventilation, which I haven't figured out how to accomplish.

zk
post #794 of 1686
Thread Starter 
Very kool zkool448. It's nice to hear that it all came up as expected with no problems. And that you like the way it sounds. I really like mine, particularly with 5963s.

Looking forward to your casework now.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #795 of 1686
Quote:
Originally Posted by zkool448 View Post
My soha II is making music



I must've really lucked out because the voltages came up correctly from the start.
TL+14.99V
TL-14.95V
TH -12.82V
TB+ +123.2V (down to 104.6V with a pair of 5963)

Adjustments were smooth and easily set to spec as per Alex's website. Manged to set R10L/R idle currents to 100mA (220mV), TB+L/R set to 60V, then tail current set to 2mA (400mV)
Voltage difference between TB+L and TPL was fairly close to 19V with the e12 delay clicking around ~7 sec

I love my millett starving students, but I noticed right away a significant improvement in sq without any audible hiss/hum. It doesn't sound as 'tubey' like the ss and much prefer how this soha II sounds... really liking it a lot. I'll let it burnin for a while. Can't wait to do some tube rolling

Guess I can't say it enough -- thank you Alex, all the prototypers and previous builders who asked all the questions that I didn't have to. Cheers!

I'll do the casework after I complete my next amp project (CTH). I hope to have matching wooden enclosures for both with enough ventilation, which I haven't figured out how to accomplish.

zk
congrats zkool! I too am eager to see how you case it. I think it's funny that you posted you would work a couple more hours and complete it tomorrow. Then, 5 hours later, we have pics of it running

I'm not surprised you like your SOHA II. My only other tube amp was the MHSS too. While that amp sounds lovely, the SOHA II is significantly better to my ears. With the 580s or the 650s it sounds great, but I do prefer the 650s. I think the MHSS might be a little warmer sounding, so it compliments the 580s better perhaps?

I'll second the thanks to Alex. I know I've said it several times, but I do appreciate you sharing this design with us. I have 2 buddies that are in love with the amp. They want me to build them one, but neither has the cash right now. Thanks again Alex
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