Originally Posted by jmf
I'm the happy owner of a SOHA II amp (kit bought at www.glassjaraudio.com). I decided last week to print and archive all information about my amp, from http://www.cavalliaudio.com. And I was too late... Disaster ! There is still a web page, but there are not anymore the schematics, BOM, initial start-up sequence, the board drawings... All those precious information needed for the maintenance of the amp.
I sent a message on the website to know if it was possible to get those information for maintenance purpose, but I had no answer.
Would somebody have archived those precious information and agree to share them ?
I especially need them to tune some bias. My amp seems to drift, and it seems to be the reason for e12 spurious triggers.
I really hope someone will be able to help.
What do you tune to deal with the drift?
I'm having similar yet different issues with e12 spuriously triggering, but did not build this amp. I've got some basic knowledge of electronics (studied a bit of EE back in the day). I bought this amp a long time ago from another user here (who separated the power supply into another box).
R8 does have some DC voltage with a multimeter during those times. I thought I had seen it on both channels, but now it's definitely just the R channel
I did tweak the tail currents to be exactly 200mA, but that did not solve the issue. Now, curiously, it got in a state where if I have my basic DMM between ground and either R8L or R8R, the DC offset goes away and it plays sound. And the instant I release it, the sound cuts off instantly. Some time later, depending on how warmed up the tubes are, it comes back on its own.
Any tips for what to investigate? What's the deal with the DMM fixing the sound: is it a grounding issue? All the test points from the website look good, though my drop from TPL and TB+L is only 15V (same for the right channel).
Source is a E-MU 0404 USB DAC off of a laptop.
Edited by DoomzDayz - 12/14/16 at 4:57pm