Is that ground buss wire along the pot covers really any help?

[semitone]

Questions from a relative neophyte: Is the grounding wire one sometimes sees across all the potentiometer backs really needed?

The pots are torqued up pretty tight against the chassis. There's plenty of contact there. In fact, I've used pot covers as an easy place to ground tube cathodes, with quiet results.

Isn't the buss on the pot covers redundant, clutter-creating, and a possible creator of ground loops? I'd be interested in your take on this.

Thanks!

semi

[cbarrow7625]

It depends on your perspective. If you are designing the amplifier to last for 30-50 years, then it is essential. Potentiometers come loose from the chassis over time & the corrode and oxidize over time as well. If any of those things happen, then your signal ground connection will start to float above any "hard" ground connections.

How many times have you seen somebody on this forum post something like "my amp volume doesn't turn off when the volume knob is on zero"? That is usually do to a poor ground connection on the volume pot.

IMHO, the brass buss bar that Fender used doesn't really get the job done either (for all the same reasons). There is no substitute for hard wired grounds.

I think the bus wire down the back of the pots is not the greatest either. Separate ground wires from each ground node run to a star (or other) well laid out ground scheme is the best bet. That will definitely help avoid ground loops. However, if the buss wire down the back of the pots is done properly, it can work out just fine. It all depends where you connect the buss wire back into the rest of your signal ground.

If it is an amp that you think will have a short lifespan & you are happy with the noise results then, by all means, just solder to the back of the pots & be done with it. Just know that there are good reasons not to (which all require more labor on your part to implement).

[dai h.]

besides the above re: providing redundancy, to me what it looks like is when you are using that kind of grounding scheme (chassis as ground plane) connecting the pots (bodies typically made of brass I think) with a wire (copper) helps equalize the potential, lower the ground impedance, provide a strip of wire (between pots) to solder to (doesn't require as much wattage from the iron). And, if you wire several grounds (which are best brought to a point--as in a star point) to a single point on that buss, then it's basically a star ground point on a plane. (Might be easier to make sense of this if mentally you flatten the front and back panels so the chassis bottom and front and back panels make a giant plane.)

[jrfrond]

In my lengthy experience, never trust a mechanical chassis connection for a ground, in an amp, a guitar, or anything else. Pots can and do come loose, as well as develop tarnish and oxidation at the connection due to atmospheric issues and galvanic reaction. The buss wire that is ultimately soldered to ground is ALWAYS a good idea, and well worth the extra effort and time to install, as it improves reliability.

[semitone]

Thank you for these good and instructive answers.

I must admit my amps lead a wretched life of vivisection, and I'll be mindful in the future to not leave my shortcuts on "finished" projects.

Best wishes,

semi

[Enzo]

And the rear cover is not metallically connected to the mounting bushing on all pots.

And how many times have I had to loosen the nut on an input jack, move the star washer a little bit to find a fresh surface, and retighten? All because the intended ground connection had gotten resistive.