Quote:
Originally Posted by shaunpw
I have the Quad service data manual which shows how to make up a test din plug with 1k resistors, is that the one you mean ?
When the voltage on the outputs of ic27 is 0.0v, the volume knob is silent, and yes I was removing the shorting links before moving on.
C89 & 90 are not linked, I removed the links from all shorted caps.
I still need to trace the voltage back.
I'm kind of understanding how this thing works now and i'm sure i'll find the problem (especially with all the help you have given me !)
I'll post again when i've fitted the new op amps.
Thanks.
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I hadn't actually seen the 1k's thing in the manual but yes, that would work as 1k is low enough. Usually we just specify a 'short' as that removes 100% of any stray pickup. Just short the pins together, job done.
As you are finding out, it is the very small DC voltages on the signal lines that are the cause of the clicks. Any DC is fed to the output as a 'step change' in level as the gain (volume control) is altered and you hear that as a click. That applies even with AC coupling as it is the sudden change that is passed along the signal path.
Quote:
Originally Posted by Herald1360
That OPA381 wouldn't be a LM381 perchance?
That's a dual low noise preamplifier though it's bipolar rather than FET input. It would at least work as unity gain buffers in the circuit.
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The LM381, the 381N and the rare 381AN (ultra low noise version) are not really opamps in the sense we know today. These were really for single rail operation and would not directly slot into standard opamp configured circuitry.