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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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In Reply to: RE: Amp photos posted by Ewalaa on July 22, 2020 at 14:36:37:
The power supply is sandwiched in there. I've worked on similar, this was my approach. I disassembled it, looking first for power supply test points. If they are there, or silk screened output connections, I would measure those voltages and see if it makes sense. Since the power supply is servo'd, I would check to see if that was working, by playing music and watching the level with a scope. Sorry, I know you don't have one, here on CL scopes are inexpensive and it will be a big help on this problem. And useful for many other things.
The other thing I would do, while it was disassembled is a close visual inspection, looking for cracked or mis-colored resistors. Resistors will change color when they overheat. Check all diodes and transistors in-circuit with an ohm meter. Measuring in circuit will show some parallel paths, so in some cases you will probably unsolder some legs to determine if it is a parallel path or a bad component.
Here's some bad news, the last time I did work on a similar amplifier, I ended up tracing out some of the circuit. So you might reach out to whoever supports these and ask for a schematic.
Because of the symptom, if you have another 8" or greater speaker, preferably with a different impedance laying around, you may consider trying it. I know you said that you are sure your speaker is ok, this is a means of getting more information about the problem. What I read is that the signal to the speaker is being monitored. Depending on the thresholds for this circuit, different than expected impedance may give you some odd effects.
Another thing you can do, less info than a scope, download some wav files at different low frequencies and run the amp with it from your phone or whatever to determine if the problem is across the bandwidth or at specific frequencies. It will also give you a better idea of the nature of the distortion. Not as good as a scope, but you never know what you will hear unless you try it. Speaking of which, there are probably scope apps that use the mic as the input. Use the wav to drive and look at that, close to as good as a scope.
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- RE: Amp photos - fredtr 07/23/2008:01:14 07/23/20 (0)
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