Kingston
Well-known member
Hello,
I have a tube preamp with a mains switch on the front panel. Without going further into details, the situation is such that the switch resides very close to wiring that is VERY subject to the 220/240VAC signal, DI input and interstage gain pot for example. The switch obviously has the mains signal going to and forth the switch, thus doubling the problem. No matter how I move the wire around, I measure about +40dB of added 50hz mains hum (FFT display). If I move the wire (with switch) completely away from the troubled spot the hum completely disappears, no longer measurable.
1. The easiest solution would be to move the switch to the back of the panel. But the souffle is already eaten, the hole is drilled. And I do prefer the switch on the front side.
For academic reasons lets look for alternatives:
2. obvious solution to the problem is shielding the wire. I managed to remove about 30dB of the hum by shielding with this heavy duty transformer sheet I have. I fashioned it so that it completely covers the wire and the switch. Unfortunately this also creates weird occasional clicks in the signal. Not loud, but I can't ignore these either.
What is the best way to shield mains wires? Clearly I didn't do it correctly. What is the best shielding material for this?
3. The last brute force solution I thought of is remote relay based switch. I guess I could create a special 12VDC signal for the relays which would have no effect of the front panel wiring. This means constant standby current draw of course, which is not not ideal.
Tips and tricks appreciated. Any easy "slap-on" solutions?
Thanks,
Mike
I have a tube preamp with a mains switch on the front panel. Without going further into details, the situation is such that the switch resides very close to wiring that is VERY subject to the 220/240VAC signal, DI input and interstage gain pot for example. The switch obviously has the mains signal going to and forth the switch, thus doubling the problem. No matter how I move the wire around, I measure about +40dB of added 50hz mains hum (FFT display). If I move the wire (with switch) completely away from the troubled spot the hum completely disappears, no longer measurable.
1. The easiest solution would be to move the switch to the back of the panel. But the souffle is already eaten, the hole is drilled. And I do prefer the switch on the front side.
For academic reasons lets look for alternatives:
2. obvious solution to the problem is shielding the wire. I managed to remove about 30dB of the hum by shielding with this heavy duty transformer sheet I have. I fashioned it so that it completely covers the wire and the switch. Unfortunately this also creates weird occasional clicks in the signal. Not loud, but I can't ignore these either.
What is the best way to shield mains wires? Clearly I didn't do it correctly. What is the best shielding material for this?
3. The last brute force solution I thought of is remote relay based switch. I guess I could create a special 12VDC signal for the relays which would have no effect of the front panel wiring. This means constant standby current draw of course, which is not not ideal.
Tips and tricks appreciated. Any easy "slap-on" solutions?
Thanks,
Mike