RadioNoise? VVR? Standby Switch Lead

[surfsup]

Okay, I need some opinions on this one. I've been battling this for a while now and today have been experimenting.

I have an issue where the VVR knob controls radio "feedback", or something. When the VVR is positioned between 3 and 4 I get this buzzing like my cell phone is next to the amp and starts roaming. It is a constant buzzy sound. Moving the VVR knob above 4 or below 3 and the amp is quiet.

In the pic below, the black wire comes up around the caps, to standby, then standby goes to the VVR via the white wire, then it goes to two diodes where on one side the orange goes to the OT. Initially I twisted the whites near the VVR and that helped, and then I re routed the black (untwisted but ziptied) to the orange and white figuring opposite currents would cancel. This helped more but there is still just a touch of this buzzing.

So I unzipped it, then turned on the amp and started moving it around and noticed any time I touch the black wire, buzz immediately dissapears! Great! a solution! but I can't keep my finger on that wire with it in the cabinet. So...what can I do to "simulate" that? Shielded wire? Twist them?

[surfsup]

Well i put a shielded run in place of the black wire. Same buzzing between 3-4 on the vvr. Now, if i tough the vvr 5w resistor, buzz goes away. I'm thinking it is the vvr. Touching the orange lead doesn't affect things.

Could a ceramic resistor pick up radio interference?

[UR12]

Buzzing is almost cause by wire routing allowing noise to be picked up by a wire or inducing it in another wire. You might try putting a cap from one end of the wire to ground. May try either ends. A .01 or .001 should do the trick.

[surfsup]

Put a .01uF to ground and its worse. Now the range is from 4-6 or 4-7 and buzzing is worse. Anyone have another idea? I gotta pack up anyway but would appreciate any suggestions.

Or maybe this amp just won't get the vvr. Maybe i can use the hole for a presence control or something...

[Richie]

I'd say keep playing with the lead dress, to see what changes it or makes it stop. Sometimes you have to have wires close to the chassis,and some wires away from the chassis. Also one thing, do you have a bottom shield plate? try laying a piece of thin metal across the chassis and see if it changes. An amp open like that can pick up noise and things without a shield plate.

[Structo]

You could try the Silver Face trick by wrapping a wire around the wire in question and grounding one end.

[surfsup]

I ran shielded to the standby switch and did try to put an oven tray over the amp. Didn't help. In the car now heading to family but will keep trying lead dress this wknd maybe. I'll try twisting allb the leads or maybe move the vvr to the rear. Drilling....i love drilling!

Happy thanksgiving to TAG.

[vibratoking]

Did you ever find a solution to this?

[surfsup]

Yea i removed the VVR ... Long answer, i pulled it, discovered a weird oscillatioon/feedback. If you saw my other thread about 5-10 threads down about "voltages at idle and u nder load" you'll get the full story. Short answer, i'm gutting the amp and starting from scratch...amp building, I hate it, but I love it...

Oh well. It's an "opportunity" to start from scratch....

[gingertube]

Bit late now but that sounds suspiciously like a parasitic oscillation in the VVR MOSFET. My thinking here is that those pot positions you noted are the positions where the impedance from the gate back to 0V are highest. A gate stopper resistor of say 1K right on the MOSFET gate would perhaps have fixed it. MOSFETs are like Pentode Output Tubes, they are RF devices, if you are not feeding them RF then they like to make their own (parasitic oscillation). A gate stop resistor IS required.

Cheers,
Ian

[surfsup]

gingertube, thank you for your suggestion. I do plan to reuse the VVR when i rebuild the amp, so better late than never. I will see if your suggestion fixes it once I get to that point.

[vibratoking]

The reason I asked is that I installed VVR in a 5E3 Tweed Deluxe clone and had the exact same problem. After looking at it, I noticed that the noise was related to the wire from the standby switch to the B+ input on the VVR board. The solution was to re-route that wire by running it close to the back wall of the chassis. Less than a half inch location difference in the wire causes the noise to return. Just wanted to mention that for anyone with a similar issue.