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FallenAngel  
#1 Posted : Wednesday, January 1, 2014 11:15:09 PM(UTC)
FallenAngel

Rank: Member

Groups: Member
Joined: 3/2/2011(UTC)
Posts: 7
Location: Toronto, Ontario, Canada

Hi guys,

I've recently discovered that one channel has a DC offset problem. I've went over the components and everything looks fine. I had to replace VR4 as it got damaged during debugging. Since the balanced/SE stage only has passive components except for IC1, I'm having a hard time tracking down the problem.

I'm seeing that the DC offset on the left channel is about 4mV on startup and it slowly drifts down to close to under 1mV within a few minutes, while the DC offset on the right channel starts off around 140mV and drifts to about 5mV within 15 minutes (as I adjusted VR4 when the output stage was warm).

I'm thinking the only thing left to do is replace IC1 with another opamp, then I'm completely out of ideas.

Any thoughts?
FallenAngel  
#2 Posted : Thursday, January 2, 2014 2:14:51 AM(UTC)
FallenAngel

Rank: Member

Groups: Member
Joined: 3/2/2011(UTC)
Posts: 7
Location: Toronto, Ontario, Canada

Problem solved by replacing the opamp with an LT1057 I had around.

Guess I somehow fried a single channel of the opamp (likely by plugging it into a new power amp I've built and tested, must have back-fired).

Now on to buying another LM4562 and replacing the stacking socket I ripped off while taking the stack apart.
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