Hello. I realize that the topic is not new and the problems with these amplifiers are known. But I got an amplifier after an unsuccessful repair or repairs. Almost everything in this amplifier was burned out. Now there is a problem with the system of automatic quiescent current BIAS. The question on replacement of burnt operational amplifier MC35072. What is better to replace perhaps someone can tell me? I replaced it with TLE2141IP, but doubts remain.... Thanks in advance
Why you want to replace it with a different opamp?
Is it not better to fix the amp before going on a replacement adventure?
Do you have any idea what is wrong with it?
Jan
Is it not better to fix the amp before going on a replacement adventure?
Do you have any idea what is wrong with it?
Jan
I had to replace it because MC35072 and all OP27s are inoperable. 86 Volts that came to them on the power supply plus did their evil deed.
I assume you fixed that power supply first before putting in new opamps?
But if your amp still has problems, why not fix them before changing opamp types?
That looks like asking for more trouble instead of less.
Jan
But if your amp still has problems, why not fix them before changing opamp types?
That looks like asking for more trouble instead of less.
Jan
Naturally, I fixed it. What's more, I ran all the amplifier units separately. Today all power supplies work, the soft-start system works, even the amplifier starts, but the quiescent current control behaves inadequately.
Ruslan
Ruslan
OK, well that's great that you fixed those parts.
The smart thing to do next would be to diagnose the bias system but not change the opamp type.
Use the wrong opamp type with different DC characteristics and you could completely mess it up.
Get it to run with the original opamp type, that's what it was designed for.
And if you want help be clear.
When you say 'behaves inadeaquately' doesn't tell us anything. What is it?
Bias too high, too low, cannot be adjusted to correct value, etc?
Jan
The smart thing to do next would be to diagnose the bias system but not change the opamp type.
Use the wrong opamp type with different DC characteristics and you could completely mess it up.
Get it to run with the original opamp type, that's what it was designed for.
And if you want help be clear.
When you say 'behaves inadeaquately' doesn't tell us anything. What is it?
Bias too high, too low, cannot be adjusted to correct value, etc?
Jan
The situation is as follows: I could not buy an original MC35072 operational amplifier, so I tried to find a similar one. At the first startup the quiescent current was normal, but when I turned it on again the quiescent current switched to maximum. This happened because the LM339 comparator failed. So the MC35072 chip has a peak detector which controls the comparator. It is not clear to me why MC35072 was used - this operational amplifier can work with unipolar power supply, but in KRELL it receives bipolar power supply? The question is in general what to replace MC35072 with?
Ruslan
Ruslan
