ADCOM GTP-400 Channel cuts out

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Hello all. I have a friends ADCOM GTP-400 on my desk. One of the channels cuts out/static.

I traced a good signal all the way back to the ADCOM 6A Opamp (IC551) The output pin 6 will be fine, until i turn the volume knob past 1/2, then sound stops/static, and I get the full negative rail (-18VDC) on output pin 6 of the OPAMP. OPAMP Pin 2 and 3 are inputs, and Pin 3 is fine when this happens, but pin 2 will shoot all the way up a -3 volts when output goes to neg rail - pin 2 has the feedback return input...

I turn unit off and restart and all ok, until I turn up volume again...

Don't know if the -3vdc is from the output going to -18vdc (feedback to pin 2), or if the -3vdc causes the -18vdc at output.

Anyway, I think it may be the opamp itself (ADCOM 6A = LT1026?) but wanted to throw this out in case someone has a smarter opinion...
 

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Member
Joined 2005
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Whoops, it is a LT1056, not LT1026...a new one is on its way!

I have to see if I have a single Opamp - all the others are dual opamps (OPA2134, 5532, TL072, 4562, etc)

Actually I found a single TL062 and a pair of LM318P, both of which are singles?



EDIT - ok, the TL062 is also a dual (duh)...so only single I have are the LM318, and I also have a few OPA627, and OPA637, but not risking those on my friends equipment!!
 
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