Quite so . . . in actuality the grounding looks like a wire jungle. Perhaps, I've overdone it.Can you get PE gnd to shield your signals and shunt line ingress perhaps due to high Z or lack of balanced differential instrument amp use?
It's up to you to show layout, schematic and cabling.
Yes for PE gnd. The chassis is acting as a capacitor to stray e-fields from house wiring. You are not using balanced diff. amps.First, are you suggesting that I run a wire from the chasis to the "house" ground, thus effecting a physical "earthing?"
Second (and I've attached a schematic), the hum becomes prominent when rotating the LEFT volume control. (The left side of the stereo signal is the one being inverted by the LM386.)
Tony, are you saying DO NOT REMOVE the 4.7uF caps between the balance pot and inputs 2 and 3?View attachment 192358View attachment 192359
Sorry disregard that. I missed the 50k bias when I glanced at the schematic.
But you can measure to see if any DC drop is on the caps. These may be redundant.
I would start to use my finger to inject hum in the circuit and find out how it is getting in. The ground design is not self-evident from the schematic alone and the structure of the cables, PCB and chassis connections for common mode rejection need to be examined.
Tell us how the L pot affects the hum. Is it proportional or does it maximize near the 50% range?
Another test is to replace the +/-15 with external floating DC like a linear lab supply or two 9V batteries to test if the hum goes away.
That will reduce the number of paths hum can get in or identify the problem.
Also reverse the AC input polarity so if it is C coupling XFMR feedthru hum it may affect the result.
I don't think you can jump to that conclusion. If the layout sucks OP could be picking up radiated 60 HZ.When you remove the input the hum is unaltered - so psu then - see above for fixes.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?