Hello again. I have yet another problem with a circuit feature I don't quite understand...
Below is a schematic of the Trace Elliot V-type preamp (sorry about poor quality). As you can see it has an AC ground, coupled to the chassis via three caps.
The complaint is that the amp hums and buzzes and picks up atmospheric noise, but when you touch the metal toggle switches the noise goes away. These are connected to the circuit ground. It's not the usual 'grounding-yourself' thing, as the switches are connected to circuit ground not chassis ground, and a jumper between the two grounds solves the problem regardless of where you stand and what you touch. When you connect the circuit ground to chassis ground the noise all goes away. So touching the switches simply provides them with enough grounding to sort the problem.
Could someone explain the rationale of cap-coupled grounding to me? The caps are 0.1uF and test ok; hard to believe all three might have failed and there's continuity between all circuit grounds and a good ground on the chassis.
Would it be Very Wrong to just connect circuit ground to chassis ground? Worth trying new grounding caps?
Below is a schematic of the Trace Elliot V-type preamp (sorry about poor quality). As you can see it has an AC ground, coupled to the chassis via three caps.
The complaint is that the amp hums and buzzes and picks up atmospheric noise, but when you touch the metal toggle switches the noise goes away. These are connected to the circuit ground. It's not the usual 'grounding-yourself' thing, as the switches are connected to circuit ground not chassis ground, and a jumper between the two grounds solves the problem regardless of where you stand and what you touch. When you connect the circuit ground to chassis ground the noise all goes away. So touching the switches simply provides them with enough grounding to sort the problem.
Could someone explain the rationale of cap-coupled grounding to me? The caps are 0.1uF and test ok; hard to believe all three might have failed and there's continuity between all circuit grounds and a good ground on the chassis.
Would it be Very Wrong to just connect circuit ground to chassis ground? Worth trying new grounding caps?
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