Any issues not using ground lead on potentiometer?

[Gordy]

Re: Any issues not using ground lead on potentiometer?

If I wanted to 'ground' the amp to the board, how would I even do it? I don't see metal showing on any of the mounting holes on the amp board. The only place I can think of to ground it would be on the negative terminal of the power coming in.
I'm assuming that the main volume pot mounted on the amp board although it is metal, would not actually be conducting anything to anything else. TomZ

I have read the thread and could not find or maybe I missed it but the pot needs to be grounded to the amp. Using the aluminum mounting plate is only adding to your issues. I have been though this exercise several times. Touch a wire to the metal case of the pot and the ground of amp input. See if that works. With issues like this that I have had this has pretty much solved it.

Find a flat metal spot on the pot. Use sand paper to rough the surface up. Solder a wire to it. run that wire to the negative input on the amp. start their.

Also dump the aluminum plate. You are mounting the pot's metal shaft to a metal plate with a metal power input and a possible metal collared 3.5mm input that is not isolated then you will get noise. Anytime I mount a power input with either a pot or 3.5mm line in I always use a plastic plate. I found these from Erse work well and are plastic.

http://www.erseaudio.com/Products/TerminalCups/TC9

http://www.erseaudio.com/Products/TerminalCups/TC-5

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

I have read the thread and could not find or maybe I missed it but the pot needs to be grounded to the amp. Using the aluminum mounting plate is only adding to your issues. I have been though this exercise several times. Touch a wire to the metal case of the pot and the ground of amp input. See if that works. With issues like this that I have had this has pretty much solved it.

Find a flat metal spot on the pot. Use sand paper to rough the surface up. Solder a wire to it. run that wire to the negative input on the amp. start their.

Also dump the aluminum plate. You are mounting the pot's metal shaft to a metal plate with a metal power input and a possible metal collared 3.5mm input that is not isolated then you will get noise. Anytime I mount a power input with either a pot or 3.5mm line in I always use a plastic plate. I found these from Erse work well and are plastic.

http://www.erseaudio.com/Products/TerminalCups/TC9

http://www.erseaudio.com/Products/TerminalCups/TC-5

Gordy, I appreciate your input.

I had some concerns going with an alum. plate because of the issues you mentioned. I will try the resistor and grounding fixes on the alum. plate version and see if it works. If the power in is grounded, that's probably not a big deal since the negative on the 12v is getting grounded anyway... the input as you mentioned is another thing. I'll see if what I've mentioned works okay or not. Hopefully it will.

TomZ

[Æ]

Re: Any issues not using ground lead on potentiometer?

I just tried the other amp mounted on a sheet of 1/8" thick ABS and the amp made the same noise on the sub channel, loud when the sub pot was turned down, and it got slightly quieter when turned up, then quiet when all the way up. Could it just be a fault in this amp design? Two out of two amps present with the same symptoms.

On that amp I went direct in with the power and inputs (used on-jack plug-in connectors)

TomZ

On one of the original S5 tube amps, there were several hum and noise issues. One of the fixes was to run a ground wire from the actual potentiometer body to the circuit ground.

You have three wires from circuit board to pot, I'd twist them all together.

If you are unable to figure out where the hum/noise originates, then it's time to bust out your oscilloscope and start looking for the source of the problem.

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

You have three wires from circuit board to pot, I'd twist them all together.

AE, would that help with the noise issues? I'm new to this stuff, would you mind explaining a little on why that might help so I could understand things a bit better. I've seen this done before, but didn't know why.

Thanks,
TomZ

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

Quick update...

This morning I soldered the resistors to the subwoofer pot on the alum. board mounted project. I turned it on expecting to need to ground the sub pot to the 12v (-) terminal, but the noise was again, basically gone. I did run a wire by hand to try and ground the sub pot to the 12v (-) terminal on the amp board, but when I did, the tiny and acceptable amount of remaining noise was not reduced.

Here's what I think is happening...

The subwoofer potentiometer is making contact with the alum. plate it is mounted in which is also making contact with the 12v (-) side of the power input jack which is also mounted to the alum. plate, thus essentially grounding the sub pot to the 12v (-) side of the amp board.

I made no attempts to get a good ground on the alum. plate as I mounted any of the components. I just drilled the holes, cleaned the little shards of aluminum that were sticking out of the plate, and went from there.

Here's what I think I should do from this point to be sure this will be a noise free project:

When I get the new 10k pots hopefully tonight after work, solder the wires from the existing alum plate project to that pot free standing, not mounted to the alum. plate.
Then if I still get the whine, I will ground that pot to the alum plate and/or the 12v (-) on the amp board to see if that fixes it.

I just checked for continuity between the 12v input power jack casing and the outer negative (-) terminal and there is continuity, so mounting that jack does connect the 12v (-) to the alum. body if there is good contact.

It sounds like I may just need to make sure there is a good metal to metal contact between the sub pot and the alum. plate, as well as the 12v input jack and the alum. plate. if my assessment is correct.

If I get the parts in tonight, I'll test this out and report back...

Again, thanks everyone for your continued input. I appreciate the much needed help!

TomZ

[tomzarbo]

Re: Any issues not using ground lead on potentiometer?

I used the 10k audio taper pot from PE and wired it in. The noise is still quiet enough to be a non-issue.

Funny thing is, grounding the pot or not really had no difference. I wired it in off of the alum. plate, ran it, then grounded the pot body to the 12v (-) and there was no difference in sound.

Also, I've been playing some bass-heavy tunes for over a half hour at close to full volume with the sub at 90% and the heatsink doesn't get more than 6-7 degrees warmer than the rest of the objects on the workbench. The PS I've mostly been using is a 16v 4.5 amp Switching unit by the way. This PS sounds cleaner than the 12v 5 amp one, has more oomph.

So, at any rate, it looks like I have a working solution to the whine issue.

Thank you guys very, very much for the help.

TomZ

[HiTechHillBilly]

[HiTechHillBilly]

"If you are unable to figure out where the hum/noise originates, then it's time to bust out your oscilloscope and start looking for the source of the problem"

The problem is the local oscillator in the chip(s) getting back into the sub input. The added pot/wiring is acting as an antenna with no filtering on the board to stop it.

The RC filter I added is a low pass filter and will only allow ~800 Hz and below to get into the amp. The oscillator on the chip(s) can be anywhere between 376 to 1278 KHz. The mod really cleans the amp up and is totally silent. I've modded several with great results..