I recently for fun tried running a long lead of wire from my amp’s ground screw all the way to the safety ground electrode. No results there really, but…
The right channel has been buzzing for a long time, but now it’s gone, with the other end of the wire still in place tied to the amp’s screw, the other end is disconnected! The right channel hums no longer.
Just what might be happening here? I unscrewed the wire lead from the screw and yes, it started humming again.
Might it be that the copper strands now tightly tied to the ground screw give the amp somehow better grounding? The wire itself I guess is pretty much just an antenna right now, so don’t see why it’d make that difference…
Probably a ground loop yes, it’s just mysterious that screwing a wire end to the chassis screw and having the other end not connected could fix it.
Oh well I cut the wire and left the end onto the screw. I guess it’s just making better contact to the chassii with the copper strands…
Now I’m wondering, could there be additional benefit if I were to screw some copper strands under every single screw on the chassis…
Well yes it was a ground loop in the chassis, I had previously measured with a multimeter quite some millivolts along points on the chassis, now there’s pretty much none.
For added measure I screwed some copper strands under every screw and I think (might be bias) the hum is just a tad more quiet now (when listening ear an inch from the woofer… heh)
No, bizarre hum, as stated before.
And it certainly was, only the right channel was affected. My amplifier is dual mono though, but still, fixing a chassis ground loop by enhancing the gnd screw’s contact resistance is strange.
I can tune the hum level up and down by gently adjusting the gnd screw now
By making that long connection, I would have bet you would actually create a ground loop… by definition, that is what you did. But if it had no affect, then OK.
Could there have been a source of hum near a piece of equipment that was moved or turned off. A transformer in almost anything could do it. Hum is not always from ground loops nor can be fixed by better grounding. It may be another piece of equipment. I always like to put amps on the bottom and preamps on the top of shelving… or at a minimum, distance all equipment from each other. Sometimes 12 inches will do. Do you have an older, two-prong piece of equipment plugged in? That stuff does not have the chassis grounded and be a hum generator. I just soldered in an aftermarket power supply into an old Adcom amp and converted it to a three-prong cord. Only then was the chassis grounded.
Did you unplug-plug in any of your equipment from one socket to another. A big source of ground noise is when you plug interconnected equipment into different wall outlets. Those outlets can be on different circuits (breakers) and induce hum.
It’s a “modern” Electrocompaniet amp with grounded chassis. It just seemed like the chassis was somehow partially not grounded well, since the right channel was humming and buzzing. Simply adding some silver-plated copper strands tightly screwed under the ground screw removed this entirely.
The length of the wire didn’t matter, I cut it so that it’s just the strands under the screw.
Maybe importantly, the gnd screw is on the right side…
Does this somehow suggest the amplifier is internally grounded separately for the two mono channels?
Be careful, disconnect the power, open the chasis and look for a broken solder joint around that screw. Put on some magnifiers, and gently push and pull against any board or connection between a board and external connection. Look for cracks in the solder joints.
If you find one, just a touch of a solder iron will fix it.
If you dont feel comfortable doing this, then with your unit on, and hum humming, gently twist the chassis, then go around and press, pull on, torque all swtches knobs, sockets, and screws. A broken joint can usually be exposed this way.
I would start by wiggling the power cord in it’s socket. A lot of times, a bad connection can start there. If you hear pops or crackles in the speakers, you need to clean the contacts until you don’t anymore. A good first step.