Gentlemen, I need your help.
The volume controller does oscillate at certain volume levels (and always near mute) ~3...4Mhz. Happens without signal, but does not happen when power amp is disconnected.
The MAS and OpAmp (OPA1656) have ceramic and electrolytic capacitors at power lines. Below is diagram from datasheet:
I did not install C213,C214,C217,C218. But I have 47 Oms R201, R202. Will 100p in feedback fix the issue?
Thanks in advance!
The volume controller does oscillate at certain volume levels (and always near mute) ~3...4Mhz. Happens without signal, but does not happen when power amp is disconnected.
The MAS and OpAmp (OPA1656) have ceramic and electrolytic capacitors at power lines. Below is diagram from datasheet:
I did not install C213,C214,C217,C218. But I have 47 Oms R201, R202. Will 100p in feedback fix the issue?
Thanks in advance!
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The OPA1656 you quote in your text has a gain bandwidth of 53MHz while the OPA2132 shown in your diagram has gain bandwidth of 8MHz. At low (and for the OPA1656, even higher) volume levels, there won't be any phase margin so the circuit will oscillate. Fitting C213 and C214 will improve the situation significantly.
Not at all sure why you have R201 and R202 in parallel with C217 and C218. I would have expected R201 and R202 to be in series with the output capacitors.
Not at all sure why you have R201 and R202 in parallel with C217 and C218. I would have expected R201 and R202 to be in series with the output capacitors.
Opamps can't drive capacitive loads directly, like an output cable, so you must add around 100 ohms in series with the opamp outputs (usually enough for most opamps, consult datasheet for more specific information). C217 and C218 are bypassing the relevant resistors so take them out perhaps?