It's most likely a grounding issue. Does it hum with only one channel powered?
Reassemble paying close attention to keeping signal and return lines as closely coupled as possible (twist leads together to minimize the loop area). Same with power and return. Make a star each of the signal grounds and power grounds. Connect those stars together at the common ground. Is the common ground connected directly to the chassis or lifted?
Reassemble paying close attention to keeping signal and return lines as closely coupled as possible (twist leads together to minimize the loop area). Same with power and return. Make a star each of the signal grounds and power grounds. Connect those stars together at the common ground. Is the common ground connected directly to the chassis or lifted?
Between chassis and ground there is the NTC.
Yes single channel also hums.
It also hums with no signal cables at all
Yes single channel also hums.
It also hums with no signal cables at all
Take it all apart and start again without the Chassis.
Build up the PSU and test it.
Build up the amplifier, attach it to the PSU and test it.
Remove the Input dummy plug and remeasure the output noise and hum. It should be a lot higher maybe 10dB to 30dB higher than with the shorting plug in place.
Report your test results.
DO NOT attach any speaker !!!!!!
I tried my first test transformer, which is too small but works, 2 x 15V, 120 VA and I get music and no hum.
So could the transformer have been damaged in a way that makes it hum now?
I measure 18.6 V AC at one secondary winding and 18.2 V at the other. If the isolation burned at one point, it has one winding less, that will make it hum by moving the center away from ground - reasonable?
If the difference of 0.4 V is one winding, it would have about 2 x 45 windings, a normal number? Primary ~275 windings?
So could the transformer have been damaged in a way that makes it hum now?
I measure 18.6 V AC at one secondary winding and 18.2 V at the other. If the isolation burned at one point, it has one winding less, that will make it hum by moving the center away from ground - reasonable?
If the difference of 0.4 V is one winding, it would have about 2 x 45 windings, a normal number? Primary ~275 windings?
You got me? I'm wondering how the transformer would have failed? Maybe it failed mechanically over time and developed a shorted winding? Did you have it mounted without a rubber pad?
I wonder too. No rubber pad. On the picture you see that it's encapsulated 😕
Maybe the metal sheet is too weak.
How many amps do you need to make a 0.47 ohm resistor glow in 3 seconds? Double that value for 2 channels ...
Maybe the metal sheet is too weak.
How many amps do you need to make a 0.47 ohm resistor glow in 3 seconds? Double that value for 2 channels ...
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Identify the problem and solve the problem.
If you can't identify it, then what hope do you have of solving it?
If you can't identify it, then what hope do you have of solving it?
Are you planning to replace the bad/undersized transformer or are you attempting to repair it?
Also, I think folks are encouraging you to rebuild the amp and clean up the wiring as a bonus in the process. I went through the same procedure on one of mine just last week. Well worth the time and effort IMHO.😉
