Insulating pots from chassis

[MikeDL]

In trying to chase down some hum in a preamp I built, I've started learning about ground loops. It seems that the guidance in the library here is to treat the preamp section as a group with only a single ground (often one of the input jacks) and tie all the other input jacks, pots, etc. to that single ground point through a buss wire.


What I'm not understanding is a good way to isolate the pots (alpha, purchased here) from the chassis. I've got shoulder insulators for the jack(s), fibre washers for switches, but I don't seem to find any good way to isolate the pot (especially the shaft going through) from the chassis. I expect I'm missing something, but could someone point me in the right direction?


Thanks!

[sluckey]

There is no need to isolate the pot bodies from chassis.

[jjasilli]

Ditto. 


But if you really want to, I believe a matched pair of these will do the trick for ea pot.  The shoulder washer insulates the pot body from the chassis.  The flat washer insulates the nut.  Not sure if Doug has these. 

Mouser.Insulated flat washer 502-S-1028Shoulder Washer 502-S-1029

[MikeDL]

OK. Not doubting any advice, just trying to understand the ideas...what then is the purpose of the recommended buss wire soldered to the outside of the pot bodies?


From reading old threads, rounding strategies seem to be a bit of a religious issue.

[shooter]

...what then is the purpose

convenience, but most have quit soldering to the pots an just make a dedicated preamp-buss
the pot "case" has no connection to the pot, just a chassis for the pot to fit in

[sluckey]

...what then is the purpose of the recommended buss wire soldered to the outside of the pot bodies?

Who is recommending doing that? Fender, Marshall, Sunn didn't do it. I don't do it. And I've never seen anyone insulate the pot bodies from chassis.

[jjasilli]

OK. Not doubting any advice, just trying to understand the ideas...what then is the purpose of the recommended buss wire soldered to the outside of the pot bodies?

From reading old threads, rounding strategies seem to be a bit of a religious issue.

I had the same question when I first joined the Forum.  I agree that there's technically ground loops:  the ground bus wire connects to multiple chassis points at ea. pot body, etc.  But it works.  It's empirically tested & proven.

[Sonny ReVerb]

I think the key is to NOT use the pot body as a ground. Don't solder anything to the back of the pots. If the pots have lugs that are tied to ground, connect them to a buss wire that is subsequently connected to [chassis] ground at a single point (as shooter said).

[ginger]

A buss soldered to the back of the pots can be a bit of a mess , if you replace a pot.... but Doug Hoffman DID recommend doing that some time ago

[ginger]

I know, without a doubt , that a grounding buss , running from pot to pot is not needed

[ginger]

And he showed you how to do it

[labb]

Just got to ask, is it 60 cycle or 120?