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In Reply to: Do I have bad pot? posted by trippyloaf on October 31, 2001 at 13:14:35:
It may be ground soldering problem or ground loop problem. If the noise level would be affected by the pot rotation angle, it might show that buzz would be canceled or not canceled by the dividing ratio of the pot, The pot works as if a hum balancer.Confirm signal ground wiring between the RCA jack to the pot. It should be connected to the chasis near the RCA jack at a point. (The minus side of RCA jack should not be touched to the chasis directly.)
Follow Ups:
Hi all,
I replaced the pot with a similar one and the exact same thing happens. So i figure it probably isn't the pot. I moved the ground to a spot near the rca inpit jack, that didn't help. Note: Joseph doesn't use a star ground nor bus ground scheme. He uses a local one - power supply, input/driver, and output.
I put in some snubber caps in the filament. see: http://www.audioasylum.com/forums/set/messages/9975.html
and that didn't help.
I don't have my 6.3V CT grounded nor do I have my 5.0V CT grounded neither. Could that be a problem? I also have my 5V heater wire run near the volume pot (about 1/2 inch).
It is definitely a buzzing sound and not a hum.Worse case scenario, could I measure where the audio pot has the least amount of buzz, take that value and place a grid input resistor of the same value into the circuit and use a preamp?
thanks for any suggestions.
I found out it was the 6.3V filament CT that I had floating. I looked on JE's site and he had his floating as well. I guess in mine it should be grounded. It looks like he also floats his negative speaker terminal tap...I always thought those should be grounded as well.
As I don't have the circuit diagram, I suppose that 6.3V-AC supply is used for the driver stage that has indirect heating cathode. In most case hum ballancer or CT is not necessary for the indirect heating tube because heater circuit is isolated.If there is no CT in your transformer, you can check it by adding hum ballancer in 6.3V. Maybe you won't be able to get the good result. For my experience I got the best (Least hum) point at the both side of hum ballancer. That ment hum ballancer wasn't necessary.
But 6.3V circuit should not be floated, as you wrote. Because floating means being coupled with stray capacitors to the signal line, and it may be affected by noise easily.
I solved similar problem by changing ground wiring and ground point before. You should better try one point grounding carefully.
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