Grounding ?

[etneccas]

Is it better to ground the potentiometer body or just the terminal?
What about the input jacks use isolation washers?
I recently did a trinity OSD kit and used a bus above the pots and a plastic input jack and the amp is dead quite when dimed and way less chance for a ground loop......

[shaun]

the amp is dead quite

Yes, my amps are often quite dead, too. But you probably meant dead quiet.
In any case, there is all sorts of good info available on proper grounding in this forum and elsewhere - search "star grounding." The quick answer is that you do not want to ground the pot casings to the chassis (even though we see this done in older construction). Where necessary, run ground lugs to a common point for the preamp section - which is where all preamp grounds should go before connecting to a single, main ground terminal near the PT.

In a perfect world, input jacks should be isolated, but they are often not and are sometimes used as a grounding point for the preamp section. However, if you really want to control ground noise, control the ground paths from each section (Power, pre, output) by keeping them disconnected from the chassis except when routed to one ground point - usually near the PT. If the input jacks are grounded to the chassis, there will be two paths available for ground, meaning a chance of ground noise. If there are three places where ground is connected to the chassis - even more opportunities for ground to cycle the wrong ways back to earth. Using non-isolated jacks is not always the biggest grounding boo-boo, depending on the build, and many don't bother.

I'm certainly not an expert, but I've recently learned this myself and now apply it in my builds.

[sluckey]

the amp is dead quite

Don't fix it if it ain't broke!   

[PRR]

Pot "body" is normally grounded by being mounted to a metal faceplate.

IMHO no further bonding is needed. And can get in the way of eventual pot replacement. However there is a long tradition of soldering a wire or bus to the backs of the pots (mostly not plated to be solderable...).

[etneccas]

the amp is dead quite

Don't fix it if it ain't broke!   

I’m not gonna mess with that amp...(trinity OSD)
I building a tweed bassman and just trying figure out an improved grounding layout

[jjasilli]

Is it better to ground the potentiometer body or just the terminal?

Ditto to all the above replies.  N.B.:  Both the pot body and the terminal should be grounded; but there's a difference.  The pot body belongs to chassis ground; the terminal belongs to signal ground. 

Chassis ground is the return path for the various currents in the amp:  heaters; B+; bias; signal, etc.  Ideally, each of those circuits (circular path of electrons through a load) would pull there own specific electrons through the body of the chassis.  But in practice, noisy electrons from other circuits can get pulled into the signal circuit.  Proper grounding schemes avoid or minimize this.  One tactic is to keep signal grounds far from the grounding points of other circuits.  Thus the inherent resistance of the chassis keeps unrelated electrons away from each other; but there are no iron-clad guarantees.

Usually, the input jack combines both its chassis & signal grounds at the point where it is mounted to the chassis.  This usually works, because that point is physically distant from the grounding point(s) of other circuits.  As you move from the input, closer & closer to the power supply, combining signal with chassis ground -- such as soldering the ground terminal to the pot body -- may or may not work well.  Proven designs and layouts are a good guide.

[Willabe]

Grounding info from Merlin's web site;   

http://www.valvewizard.co.uk/Grounding.html

Grounding info from Aiken amps web site;

https://www.aikenamps.com/index.php/grounding

(I use Merlin's.)