[MdRex]

It was mentioned on Tangent's troubleshooting guide that if the AC voltage on the + and - pads of the OPAMP is very different, there is a problem with the feedback loop, my PPA has a different voltage. But all the resistors in the feedback loop are of correct value, double checked.

My question is if the buffer circuit is part of the feed loop? Because if it is, the buffers may be the problem. Someone please help me...

And am I suppose to get AC on the + pad on the ground channel?

 

[HIPPOhifi]

Quote:

Originally Posted by MdRex /img/forum/go_quote.gif It was mentioned on Tangent's troubleshooting guide that if the AC voltage on the + and - pads of the OPAMP is very different, there is a problem with the feedback loop, my PPA has a different voltage. But all the resistors in the feedback loop are of correct value, double checked.

How different is the voltage? (remove the opamps/buffers first so you don't cause further damage)


Quote:

Originally Posted by MdRex /img/forum/go_quote.gif My question is if the buffer circuit is part of the feed loop? Because if it is, the buffers may be the problem. Someone please help me...

Yes they are. The feedback loop goes from the opamp out -> R11 -> buffer -> R4 -> R5 -> opamp -in.

I don't think the buffers are the problem.

Quote:

Originally Posted by MdRex /img/forum/go_quote.gif And am I suppose to get AC on the + pad on the ground channel?

On the + power pad on the ground channel you should have +DC. I think you might have a short on your board somewhere. Remove buffers and opamps, follow this debugging process and recheck the voltage after each step:

a. check voltages without op amp/buffers in
b. check for shorts
c. resolder all parts
d. check the resistance of each resistor and ensure it matches the specificed resistance.
e. if you are using Q1 and Q2 replace them.
f. replace the transistors in the power supply section, all the Q** parts.

Once the voltages are normal replace buffers and opamps. Just a note use the term DC instead of AC.