Sorry for the delay.
1.2 is about what I'd expect. I've seen about 1.25, generally.
I don't understand the muting circuit as you've described it. N-channel jfets need negative gate voltage to switch off.
I also don't understand why you have positive voltage on pin 4 of the optocoupler. Is it still positive after the end of the mute delay?
The outputs could be an issue. I know that you can't go from the TIP to the FJA without problems. The MJE to the FJA could cause some issues, especially the bias stability.
I'd expect a driver problem but the problem could be any component back to the muting transistor. I'm assuming that you have confirmed that you have clean audio at the muting transistor.
1.2 is about what I'd expect. I've seen about 1.25, generally.
I don't understand the muting circuit as you've described it. N-channel jfets need negative gate voltage to switch off.
I also don't understand why you have positive voltage on pin 4 of the optocoupler. Is it still positive after the end of the mute delay?
The outputs could be an issue. I know that you can't go from the TIP to the FJA without problems. The MJE to the FJA could cause some issues, especially the bias stability.
I'd expect a driver problem but the problem could be any component back to the muting transistor. I'm assuming that you have confirmed that you have clean audio at the muting transistor.
Hello Perry,
as described before, the Optocoupler was the cause, that i havent any output. I changed the optocoupler, now i have a signal at bouth banks.
The jfet is pulling the input signal to ground, at the beginning of the first input stage. See the last diagram. I rechecked the voltages at the optocoupler. Ground is sec. center. At Pin 6 i have now -15VDC, the same as on Pin 4. It stays on all the time.
Now iam troubleshooting the repaired channel with this sawtooth problem.
It seems, that there is a new transitor leaking in the second stage from the negative side..
Also sometimes i have dc offset... so there is still an intermittend problem.
as described before, the Optocoupler was the cause, that i havent any output. I changed the optocoupler, now i have a signal at bouth banks.
The jfet is pulling the input signal to ground, at the beginning of the first input stage. See the last diagram. I rechecked the voltages at the optocoupler. Ground is sec. center. At Pin 6 i have now -15VDC, the same as on Pin 4. It stays on all the time.
Now iam troubleshooting the repaired channel with this sawtooth problem.
It seems, that there is a new transitor leaking in the second stage from the negative side..
Also sometimes i have dc offset... so there is still an intermittend problem.
I don't know right now. But iam not sure if this is causing my problem.
See attached picture. The left transistors signal is OK, the right one bad and pulled down. At the schematic the good side is 1,the bad side 2..
If I remove q105, the signal is good... But the transistors are OK. The 15 v is also present.
See attached picture. The left transistors signal is OK, the right one bad and pulled down. At the schematic the good side is 1,the bad side 2..
If I remove q105, the signal is good... But the transistors are OK. The 15 v is also present.
Attachments
If you're serious about glasses, the drug store cheater glasses can help greatly. Here, you can get 3 pairs for $8 and they're decent quality.
As a side note, bridges are easy to make. Some of the most dreaded tech support threads start with... I resoldered all of the connections and now I have another problem.
If you use the FJA transistors, run the amp through its entire thermal range and confirm that the bias holds. The On-semi type transistors require different biasing than the FJA types. The difference may or may not cause you any problems.
As a side note, bridges are easy to make. Some of the most dreaded tech support threads start with... I resoldered all of the connections and now I have another problem.
If you use the FJA transistors, run the amp through its entire thermal range and confirm that the bias holds. The On-semi type transistors require different biasing than the FJA types. The difference may or may not cause you any problems.
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