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SOHA II Builders Thread - Page 38

post #556 of 1688
Quote:
Originally Posted by Hayduke View Post
Ferrari, do you do your own casework?

Your builds always look incredible. This one is no exception

I'd love to see some pics or guide to how you do you casework. Like what tools do you use and such.
Yes, I do my own casework… with some help from Schaeffer AG (FPE in Europe) of course.
I will post some more pics when my amp is completed.
post #557 of 1688
Quote:
Originally Posted by Uncle Bob View Post
Did some checks on my problem SOHAII today. All voltages checked out OK but I went over all the solder joints in the left channel anyway. Still got that hiss problem in the left channel. But I've found that minor flexing of the PCB makes the hiss come and go - so it seems I have a fractured connection somewhere (after I dropped the board). I've gone over the PCB with a magnifying lens but I cannot see any fault, but there must be break somewhere.
Some more info

Flexing the PCB makes the hiss come and go, but it also causes a change in volume in that channel. When there's no hiss, the left channel is noticeably quieter than the right channel

Any ideas where I start to look for the problem?
post #558 of 1688
Thread Starter 
No ideas where to start. But some ideas on where to start to start.

Put the DMM on each of the measurement points and flex the board while listening. See if any of them change when you hear the hiss come and go. This might help us to isolate what part of the circuit is croaking.
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 #559 of 1688
Quote:
Originally Posted by Uncle Bob View Post
Some more info

Flexing the PCB makes the hiss come and go, but it also causes a change in volume in that channel. When there's no hiss, the left channel is noticeably quieter than the right channel

Any ideas where I start to look for the problem?
If flexing the PCB seems to change de amplifier gain, I would look first at all the traces and solder joint around output stage to R7L/R8L and tube socket (all the feedback loop on the schematic). I would guess you have a cold solder in that part of the circuit.

But I don't think that will solve your hiss problem since reducing the ampifier gain also reduce amplifier noise.
post #560 of 1688
thanks for the suggestions, I'll keep you posted.
post #561 of 1688
Most likely it’s a mechanical issue caused by the fall.
I’m not sure if it has been asked before (I do missed posts sometimes) but… are the tubes sitting properly in the sockets? Have you tried different tubes?
post #562 of 1688
Quote:
Originally Posted by Ferrari View Post
Most likely it’s a mechanical issue caused by the fall.
I’m not sure if it has been asked before (I do missed posts sometimes) but… are the tubes sitting properly in the sockets? Have you tried different tubes?
It's depressing because the amp sounds soooooo good except for the hiss. It's a worthwhile question but I've tried different tube types and swapped them between channels with the same results

I'm still trying to hook up with someone who has a 'scope. Presumably, with a 'scope I'll be able to trace the hiss back to the point it appears in the circuit?
post #563 of 1688
Quote:
Originally Posted by Uncle Bob View Post
It's depressing because the amp sounds soooooo good except for the hiss. It's a worthwhile question but I've tried different tube types and swapped them between channels with the same results

I'm still trying to hook up with someone who has a 'scope. Presumably, with a 'scope I'll be able to trace the hiss back to the point it appears in the circuit?
If you can’t find the root cause of the problem and… at some point in the future, decide to re-build the amp on a new PCB, I will donate the output devices, all small signal BJT’s (BC550/560) and some capacitors I have on hand.
post #564 of 1688
Ferrari

Thank you for your very kind offer. I do like the amp very much and a building a new one is a definite possibility.

But I'm not going to give up on this one just yet. Besides if I do find the fault and fix it, it may give some clues as to the hiss problems reported by some IEM users.
post #565 of 1688
So the problem I had been experiencing with the amp definately follows the tubes. One is clearly bad and will need to be replaced (I will replace both). Any suggestions on which to choose? I may order a few different ones.
post #566 of 1688
My high current version is almost alive... Parts from the bin and Toshiba 2SC3422 in the buffer... All PS voltages good!
LL
post #567 of 1688
for a basic build of the soha II, how much does it come out? also, how similar is it to the soha I part-reuse wise?
post #568 of 1688
You can get a kit (including Hammond case) from glassjaraudio.com for around $200, quite a deal if you ask me.

Quote:
Originally Posted by DoomzDayz View Post
for a basic build of the soha II, how much does it come out? also, how similar is it to the soha I part-reuse wise?
post #569 of 1688
Quote:
Originally Posted by DoomzDayz View Post
for a basic build of the soha II, how much does it come out? also, how similar is it to the soha I part-reuse wise?
You could use the tube! I don't believe there are a lot of parts overlapping, but I haven't explicitly checked...
post #570 of 1688
Quote:
Originally Posted by wiatrob View Post
My high current version is almost alive... Parts from the bin and Toshiba 2SC3422 in the buffer... All PS voltages good!
Glad to see that your build is going well. In what enclosure are you going to install your SOHA II?

I've just finalized initial setup procedures on mine last evening. I also did a first and brief sound check with two set of tubes and my complete headphone inventory.

Just to say I think I found a magical sounding tube/headphone combo. More info to come later, I'll finish casing and take more time for critical listening...

I'll also post a progress picture tonight.
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