So, after replacing the Cx13 and Cx15 capacitors in a Punch 400a4 that would not bias correctly, the bias issue is solved.
When doing a frequency sweep to check if the amplifier is still functioning as intended 20Hz to 20kHz, the signal on the output drops to zero on the oscilloscope at 17.5 kHZ. At 17.4 kHz it reappears.
Is this what I am looking for to determine functionality of the amplifier?
I did not know, if the amplifier was not functioning properly, if the signal would be distorted at a certain frequency, drop out or if it is a triggering issue with the scope.
What am I looking for when running a frequency sweep form say, 20 Hz to 20 kHz?
Another reason I am asking is because I have a 360a2 I repaired, (no capacitor changes), that drops out at ~18 kHz on the same scope.
When doing a frequency sweep to check if the amplifier is still functioning as intended 20Hz to 20kHz, the signal on the output drops to zero on the oscilloscope at 17.5 kHZ. At 17.4 kHz it reappears.
Is this what I am looking for to determine functionality of the amplifier?
I did not know, if the amplifier was not functioning properly, if the signal would be distorted at a certain frequency, drop out or if it is a triggering issue with the scope.
What am I looking for when running a frequency sweep form say, 20 Hz to 20 kHz?
Another reason I am asking is because I have a 360a2 I repaired, (no capacitor changes), that drops out at ~18 kHz on the same scope.
At what level (volts across the speaker terminals) are you testing?
With or without a load?
What shuts down in the amp?
The bias voltage from the comparator?
When one channel shuts down, does the other channel shut down as well? Drive one channel with music while testing the other with the signal generator.
Are you still getting signal at the input to the differential amplifiers when the amp shuts down?
Do you lose rail voltage when the amp shuts down?
With or without a load?
What shuts down in the amp?
The bias voltage from the comparator?
When one channel shuts down, does the other channel shut down as well? Drive one channel with music while testing the other with the signal generator.
Are you still getting signal at the input to the differential amplifiers when the amp shuts down?
Do you lose rail voltage when the amp shuts down?
Are you doinbg a manual sweep while watching the scope?
Or a different method? Can you explain what exactly you do?
There can be any of a number of effects that cause this while the amp is perfectly fine.
Jan
~19 V just before clipping
No load
I will have to do some more testing to get answers to the other questions, but the problem may have been the signal source.
I was using a head unit as a signal source with bluetooth from a function generator app. When I changed last night to a bench function generator, I was able to maintain a good signal through all the frequencies.
Also tested at ~1.5 V across the speaker terminals and could tell much easier on the amp.
In general, when doing this type of test what are the preferred parameters/setup?
@jan.didden,
Yes, doing a manual sweep while watching the scope.
Please see the above post #4 for my approach.
Thanks
Yes, doing a manual sweep while watching the scope.
Please see the above post #4 for my approach.
Thanks
There are a LOT of amps that don't do well at high frequencies at more than a low level. They can't drive the outputs off quickly enough and will have cross-conduction (basically, over-biasing).
You will generally test like this to confirm that biasing is OK at about 1v of signal.
In many amps, higher levels will mask crossover/notch distortion.
You will generally test like this to confirm that biasing is OK at about 1v of signal.
In many amps, higher levels will mask crossover/notch distortion.
