05-17-2013, 09:54 PM
Well, after spending another 3hrs with it...
It is in a way a GND loop, but little of it. I rerouted everything to the star GND-ing scheme and the result was just a bit better than before....and even that might've been some of wishful thinking.
I could swear that it started after I put it in the box and I started recalling events.
The recollection resulted in ""You used the variac and nnowe you just use the isolation transformer".
Once I plugged it in the Variac the hum went down about an order of magnitude. That is it is still there but it is quite bearable.
Than I measured the voltage in the Mains, 125V AC, and set the Variac to it. The hum immediately went up.
It goes up almost by a step about 117-120V AC. Bring it back under 115V and it is reasonably quiet.
Mistery solved for practical purposes.
If I were bold enough I'd rerouted the whole GND scheme, but...not worth it.
PS. Probably need a bucking transformer, eventually.
It is in a way a GND loop, but little of it. I rerouted everything to the star GND-ing scheme and the result was just a bit better than before....and even that might've been some of wishful thinking.
I could swear that it started after I put it in the box and I started recalling events.
The recollection resulted in ""You used the variac and nnowe you just use the isolation transformer".
Once I plugged it in the Variac the hum went down about an order of magnitude. That is it is still there but it is quite bearable.
Than I measured the voltage in the Mains, 125V AC, and set the Variac to it. The hum immediately went up.
It goes up almost by a step about 117-120V AC. Bring it back under 115V and it is reasonably quiet.
Mistery solved for practical purposes.
If I were bold enough I'd rerouted the whole GND scheme, but...not worth it.
PS. Probably need a bucking transformer, eventually.
