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SOHA II Builders Thread - Page 113

post #1681 of 1688
Quote:
Originally Posted by headphonejunkie View Post

From quick research I wonder if it would be possible to add JISBOS to slots where the op amps are on the SOHA II.
Would it not add that much more fidelity to the amp?

There's no need for the Jisbos on the SOHA II. The output is already a discrete topology. The opamps serve as servo circuits to zero out the voltage offset without having to use output coupling caps.
post #1682 of 1688

Oh,Then I stand corrected.

 

Thanks TOMB

post #1683 of 1688
Quote:
Originally Posted by headphonejunkie View Post

From quick research I wonder if it would be possible to add JISBOS to slots where the op amps are on the SOHA II.
Would it not add that much more fidelity to the amp?

Nope, the opamp is only there for feedback, not the signal itself.
post #1684 of 1688

Hello,

 

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.

 

Best regards,

 

JM

post #1685 of 1688

Hi,

 

Up... Nobody has archived the elements related to the SOHA II ? I asolutly need them for maintenance.

 

Help !    :-)

 

JMF

post #1686 of 1688

Oups, it is back on http://www.cavalliaudio.com/pages/soha-ii

 

Thanks a lot !!!

 

JMF

post #1687 of 1688
Quote:
Originally Posted by jmf View Post
 

Hello,

 

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.

 

Best regards,

 

JM

 

 

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
post #1688 of 1688

Looking closer and at the instructions, it appears my amp is missing the star ground stand-off screw between the two heatsinks? I'm a bit surprised I don't have bigger issues if that's the case. The only ground is through the power supply connection (a separate box which is grounded to the chasis) and the output pot / headphone-out's connection to the front plate (from what I can tell, the box and plates are all separately annodized and thus aren't connected)?

 

Nevertheless, the DC offset is just the R channel, so would that indicate that it isn't a grounding issue? Test points on both sides all look good.  Issue does not follow the tube.

 


Edited by DoomzDayz - 12/14/16 at 4:58pm
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