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In Reply to: RE: Odd hum issue - suggestions ?? posted by Triode_Kingdom on May 30, 2017 at 15:59:58
It is a Counterpoint sa-12 hybrid amp with greenstreet upgrades.
The neutral to ground lug on the chassis was also enamelled, so cleaned that off. No improvement in the hum. I then ran a jumper wire between the the neutral bus of a large capacitor pair directly to the ground lug - hum gone.
I am thinking that with an enamelled coated chassis like this the conductivity is pretty bad. With the neutral to ground connection on the back of the chassis, and the ground lug at the front of the chassis, there is just not a good electrical connection. I'm going to get a ring terminal and wire, and run the neutral to ground lead directly to the ground lug. Right now it runs from the middle of the chassis to the back, and instead this will run from the middle of the chassis directly to ground. Hopefully that will put paid to the problem
regards - Roger
I'm glad you fixed it but what is a "neutral to ground lug"?
The neutral wire (white wire) connects to one end of the primary of the power transformer and does not connect to earth ground (the green wire) or anything else within the chassis.
Do you mean you ran a wire between "signal ground" and "chassis ground"?
The schematic show such a wire to already exist.
Have Fun and Enjoy the Music
"Still Working the Problem"
"The neutral to ground lug on the chassis was also enamelled, so cleaned that off. No improvement in the hum. I then ran a jumper wire between the the neutral bus of a large capacitor pair directly to the ground lug - hum gone."
I strongly suggest that you use a multimeter or other tester (or call an electrician) to be sure the Neutral and Ground wire at your AC outlet are correctly wired.
Buy Chinese. Bury freedom.
I don't know what those upgrades are. Is this a new problem in this preamp, or did you buy it like this?
"Sure enough, the ground lead was secured at one of the inside foot screws."
Do you mean the green wire from the line cord? If that's connected to the chassis, touching the chassis should have no effect. This might be a problem with your house wiring.
Buy Chinese. Bury freedom.
Obviously it is a grounding issue related to the "upgrade". The chassis either has a bad ground to signal ground or too many grounds. Try taking a wire and touching it to the chassis and the other end to another component. What you may find is that the RCA grounds have been messed with.
The dude who designed the component was pretty bright, probably a lot brighter that Mr. Greenstreet, or whatever.
Could be the unit is picking up AC hum from house wiring. Outlet grounded properly? Polarity of house wiring (Hot, Neutral) consistent?
Are the input wiring of the amp shielded? Grounded at input side, only?
Check all grounding points within the unit. Tight and clean. With least amount of potential between grounding points. Near zero resistance between points of grounding.
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