You better check for ultrasonic oscillation, with a scope, or analog VOM. Not a DVM, the cheap ones give random numbers on frequencies other than 50 or 60. The expensive RMS Fluke DVMs ignore all frequencies above 7000.
If the VOM reads AC voltage & you can't hear it, possibly ultrasonic oscillation. First reading through a .047 uf block cap on the negative lead to block the DC voltage. Take a 2nd reading through a 390 pf cap. If the voltage is still there, it is ultrasonic.
TO071 are not too bad to oscillate, they don't have a lot of slew rate. But improper compensation front to back can make about any amp oscillate.
Other possible HF noise source is a switching supply. Peavey did the CS800s switcher supply right. I own & have repaired one. Other brands and models have less stellar reputations.
Modern class D amps are another ball game, one an amateur like me with primitive test equipment does not play in.
If the VOM reads AC voltage & you can't hear it, possibly ultrasonic oscillation. First reading through a .047 uf block cap on the negative lead to block the DC voltage. Take a 2nd reading through a 390 pf cap. If the voltage is still there, it is ultrasonic.
TO071 are not too bad to oscillate, they don't have a lot of slew rate. But improper compensation front to back can make about any amp oscillate.
Other possible HF noise source is a switching supply. Peavey did the CS800s switcher supply right. I own & have repaired one. Other brands and models have less stellar reputations.
Modern class D amps are another ball game, one an amateur like me with primitive test equipment does not play in.
What makes you think the OpAmp is suspect?
In any case, we need the schematic, we have no clue about what that TL071 is doing there.
Tired electrolytic caps can make a sub plate amp just misbehave or kill itself.
They pretty much universally have no ventilation so it's a warm environment inside the recess, and manufacturers usually have no desire to fit 105 degree caps...
Couple that with most 'auto' on/off switches simply disconnecting the speaker (leaving the amp running 24/7 regardless of setting) and you have a recipe for premature failure.
Without knowing more details of the particular plate amp topology in question it's impossible to decode what else has gone on.... but odds on the op-amp is performing perfectly normally and its output is just 'reporting' what's being fed to it.
Yes to your question.
Next question🙂
Is it likely faulty if it is doing this? Answer would be 'unlikely', rather something other than the opamp is at fault.
I'm with JMFahey and Isaac Asimov: there is insufficient data for a meaningful answer.
The Last Question -- Isaac Asimov
The Last Question -- Isaac Asimov
First of all, it all depends on what the opamp does. If it is used as a replacement of a discrete input stage, and directly drives the VAS, such an opamp's failure, may result in the output clamping onto a rail causing excessing current to flow. If the opamp's internal output causes too much current due to the fault, it may disrupt the BIAS, which again causes excessive current to flow in the output. In this case, it is more like a short circuited output.
All the above does not hold if the opamp is used in signal processing (pre-amplifier stages).
All the above does not hold if the opamp is used in signal processing (pre-amplifier stages).
The TL071 was commonly used for error amps and DC servos, but almost never for a direct driver because it can’t supply more than 10 or 15mA of current (internally limited). That’s not enough to drive most high power driver/output stages directly unless it’s an output triple or mosfets (and capacitive loads make TL071’s oscillate so that’s not likely). Anyone using an output triple in a trans-nova configuration deserves their fate - and you almost never see it either. I have on occasion, and those amps were nothing but trouble (and Peavey abandoned them).