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In Reply to: RE: Granite audio ground zero posted by jhrlrd on August 26, 2016 at 21:01:25
Might be helpful to distinguish between "buzz" which is most often 120Hz ripple (the output from the PS rectifiers which is "spikey", looks like a sawtooth waveform) and "hum" at 60Hz which is more sinusoidal (mains frequency coupling in). Ground loop problems result in "hum". Hiss and "buzz" are related to issues in the amp.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Follow Ups:
I don't know how to describe it exactly...a buzz out of the woofer, mid and tweeter are higher pitch, but it is also saw-tooth sounding, so I guess hiss would be the wrong way to describe it.
One of the first things I tried was a cheater plug. did nothing.
They are new KT150 tubes, don't have a second pair of 12AT7's to try.
How do you isolate signal ground from chassis ground, and still have them both grounded?
Jolida 3502rc, can't seem to find the schematic
Edits: 08/29/16 08/29/16 08/29/16
"How do you isolate signal ground from chassis ground, and still have them both grounded?"
There are various schemes out there. One uses back-to-back diodes. The forward voltage drop of the devices act as a barrier to ground loop currents. With my DIY power amps I use a thermistor in parallel with a 1uF film cap. The cold resistance of the thermistor acts as a barrier (resistance goes toward zero gif there is a fault and real current) and the cap AC grounds the circuit.
You should make sure the ground connection in your amp isn't compromised. I had similar issues with one of my amps. I needed to scape (sand) the chassis under the ground lug to achieve a solid connection. A circuit that is not properly grounded will certainly "buzz".
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
I found the paint under the grounding post, cleaned that.
I found the power cord feeding the power condition was wired backward,
ie hot and neutral reversed, fixed that...
still the same buzz.
I think upon close comparison, the left channel is buzzing a bit more than the right, so I swapped tubes...still the same.
It buzzes less in integrated mode.
Do you have a scope? A DMM? If you do, see if you can trace back from the output and find where the noise enters the signal path. Also check to see if you have excessive ripple on the PS rails. If that is the case you could have a defective PS filter cap. An in circuit cap ESR meter works well for testing these. Good luck, these issues can be very frustrating. I know!
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Thanks for the tips JKT, I don't have a scope, but maybe I can borrow or buy a used one. It's frustrating to find what you think must be the problem and it turns out not to be...
or maybe I'll have to bite the bullet and send it somewhere for repair.
Shipping kills
You might try posting this issue you are having on the DIY tubes forum here. Lots of inmates have more experience trouble shooting than I do.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
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