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Strange hum in SOHA II (getting louder, turning into hiss and disappearing in about 3min)

post #1 of 6
Thread Starter 

I have a strange problem with my SOHA II.

 

When I turn the amp on there's a relatively quiet hum in the background.

That hum does not change with the volume - it stays constant.

 

Over several minutes ( two or three ...) it becomes louder, then a quiet hiss joins in.

Then this hiss gets louder while the hum becomes quieter.

Both fade out together - then the amp is dead quiet.

 

The amp runs without problems apart from that - sounds wonderful!

 

I hope somebody has a clue...

 

Thx

Sathimas

post #2 of 6

pull the tubes out, with the power off, then power it on.  is the noise still there?  it might be from the tube/input stage.  It sounds like a combination of electrical and transistor noise.  Check your solder joints, particularly on the input side, if there is no hiss with the tubes out.

post #3 of 6
Thread Starter 

Thanks for the advice.

 

I just tested it without tubes - there's no noise then.

 

I'll try to reflow the solder joints as next step.

post #4 of 6

Hi Sathimas, did you reflow the solderings? did it solve the problem? I'm asking because I'm having the same issue with my soha.

 

Thanks!!!

post #5 of 6

I had this problem with my SOHA II when it was running a pair of 12AU7s, but I recently switched to the 6DJ8s and there is no hiss at start up anymore...

Also as a side note my amp seems to run cooler with the 6DJ8s but has lesser gain than the 12AU7s.

 

Edit: Weird I just rolled my 12AU7s in and it's different from before, I can now max the pot with out going deaf. They now have about the same gain as my 6DJ8s...

Maybe running the amp at 6.3v did something?

 

Edit2: Turns out one of the 12v inputs came loose *doh* everything back to normal now, I didn't think it would work with just one 12v input into it...interesting...


Edited by Jaivan - 12/12/10 at 10:23pm
post #6 of 6
Thread Starter 

I did not have the time to resolder the soha yet, hopefully I'll do that this week.

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