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Crate PA-B8350 Op Amp question

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  • Crate PA-B8350 Op Amp question

    I have a puzzling op amp problem. I am attaching the relevant schematic. I put in a signal of 8mV P-P at pin 3 of the IC1A op amp At pin 1 TP1 I get the same amplitude signal out. I changed to another op amp with the same results. I can get that signal to the input sides of R7 and R14 but nothing out of them. I suspect that is because it was supposed to get 85mV not 8mV. Can anyone offer any suggestions?

    Thanks in advance.
    Attached Files

  • #2
    It is often difficult to see a signal at the input pins of op amps - look up "virtual ground" in the op amp context. You have a signal at the input resistors of IC2a and IC3a. You cannot see the signal at the input pins, but what does it look like at the output pins of those ICs? if the signal is there, then the inputs were working.

    The input to IC1a is balanced. if you only put a signal into pin 2 of the input XLR connector, you need to at least ground pin 3 of it. Note that while the 1/4" input jack is a TRS for balanced, if you plug an unbalanced TS plug into it, the sleeve grounds the ring contact. That specified 12mv input was for a balanced signal, not one side of it.

    What are we trying to fix?
    Education is what you're left with after you have forgotten what you have learned.

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