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25vp-p, 60 HZ is on the outputs. I measured the electrolytic s and visual-ed the solder joints. The hum is not affected by volume settings. I disconnected the pre-amp section, no help.
Next step????
Next step????
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Sure it isn;t 120Hz?
Is this output a sawtooth, a sine, a distorted wave? It there DC offset too?
LOUD hum is usually either DC on the output causing extreme ripple into the load. AFter that, loss of main rail filter. It is one thing to measure a cap, but another thing completely to make sure it is in circuit. Resolder all the main filter caps.
Be careful disconnecting preamps from power amps. MANY amps use that connection for the ground reference at the PA input.
I don't know what your main rail voltages are, but they should both be present at the output stage and approximately equal. Then all the op amps and other low level stuff runs on 15v rails. Are they both present, clean, and up to voltage?Education is what you're left with after you have forgotten what you have learned. -
Hi Enzo,
I was a pure, 60 Hz sine wave but it is now gone. I put the amp back together and got a lot of loud "pops" and static which blew a speaker. The rails are still there. +/- 78v, +/- 38v, but I have not looked at the 15v rail yet. But, hey...at least the hum is gone because there is no output. I'l gett back to you with more info. Thanks.Comment
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Took it back apart and checked the +/- 15v lines. There was an cold solder joint on the +15v regulator. I re-soldered it and also found the toroid power transformer was loose and had been leaning on one of the bridge rectifiers and edge of the ckt board. The insulation was worn through from vibration but the wires were OK.
Could be the 15v gone was causing the hum and the 60 cycle all over the place was from the transformer. It works great now. Thanks for your help Enzo.
I'm a championship bbq cook. If you ever need any advice, just shoot me a message.Comment
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