VTL hum

[speakerfritz]

Please read my whole post before reacting. I have 3 VTL designed amps. had the same problem. I installed this mod on the amps and the preamp and problem solved. The mod goes from the chaiss to the ground wire of the electric cord inline. A low or no ground fault, the diodes forward voltage drop results in a virtual open circut to ground (basically a virtual cheater plug), at ground faults with a voltage greater than the voltage drop of the diodes (about .75 volts), the diodes bias and the virtual open turns into a virtual short and operates as a normal ground. The gotcha is that you must use diodes at the continuous current rating of any expected circut breaker, or it will not be safe. I used 30A diodes that had a surge rating of 45A. Make sure your diode voltages are better than 240 volts.

 

[directdriver]

Thanks for all the suggestions, everybody. I ended up using a 5-ohm resistor parallel with two diodes in either direction and soldered between circuit board ground and chassis ground per Fran's suggestion. It works but not ideal. It's quiet enough.

What still baffles me is that it's absolutely quiet when only ONE channel is connected and very slight hum when TWO channels are connected. Deadline is tomorrow and my speaker is 100dB horn so when hooking to bookshelf speakers the hum will be negligible.

If I had more time, I would try Fritz's suggestion but I hope I never have to see this amp ever again!

Thanks again guys.

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[directdriver]

Another strange thing is when both inputs are connected the amp is extremely sensitive to cable position. I need to move the cable around to find the lowest hum level. But when only ONE channel is connected, there's no hum at all the cable is immune to positioning.

I just don't get it.

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[Zen Mod]

you're wasting your time ;

you got few solutions - try them and choose most efficient one