[Whit]

Recently I built a "tweaking" Meta42 to test things like opamps and gain configurations. However whenever I turn the volume all the way up I get a buzzing/humming noise. I experienced this in my cmoy and corda kit and I fixed both of those problems by grounding the pot's case. This was what I thought the problem was this time. So I tied the panasonics pot casing to PG. This eliminated some of the humming but to totally eliminate the buzzing/humming I have to place my finger on any ground point including the pot's case. I checked all my solder joints and they appear ok. I'm using an Elpac WM080 power supply. The buzzing seems to get worse when using a 50K pot vs. a 10K. This amp is not currently in a case of any kind. Any help would be greatly appreciated.

 

[jeffreyj]

Quote:

Originally posted by Whit ...The buzzing seems to get worse when using a 50K pot vs. a 10K. This amp is not currently in a case of any kind. Any help would be greatly appreciated.

I bet there isn't a resistor from the Non-Inverting inputs to ground, is there? Try connecting a 10k resistor from each NI input to ground and see if that clears up the problem (or at least diminishes it with a 50k pot present).

 

[Whit]

Quote:

I bet there isn't a resistor from the Non-Inverting inputs to ground, is there? Try connecting a 10k resistor from each NI input to ground and see if that clears up the problem (or at least diminishes it with a 50k pot present).

I think I've found the problem. It is related to shielding. I took some high tech RFI shielding material (aluminum foil

), connected it to virtual ground with an alligator clip and placed the foil over the whole meta42. The result was that the buzz and hum was reduced by 98%. There is still a very slight buzz but I think this may go away when I completely shield the board in an aluminum enclosure. So I guess the problem was RFI right? I can still make the buzz worse by touching the input left and right wires. Is this because my body is acting as an antennae and injecting RFI into the circuit?