grounding the "other" terminal on a volume pot

[speciallittleguy]

Hey everyone,

I'm new on here and tried searching but couldn't find any discussion. Probably because so often people are discussing using the case of a volume or tone pot for ground wire soldering.

Anyway, I've noticed that quite often a wiring diagram will have the "input" for the volume knob on one side (from underneath, the left?) The "output" on the wiper, and the "other terminal connected to ground.

Now, I understand that shorting your output to the TRS jack to ground guarantees no noise. But doesn't grounding the volume pot third contact also add an unnecessary load to the pickups?

Wouldn't a no-load pot do as well completely silencing the guitar without flushing some of the high frequencies?

[speciallittleguy]

Nevermind; I searched for "no-load volume pot" and found plenty of discussion on the concept, and the application of no-load to tone lots. The pros and cons are all mostly what I expected to find.

[newey]

speciallittleguy-

Now, I understand that shorting your output to the TRS jack to ground guarantees no noise.

Wiring the third lug of a pot used as a volume control is not done to reduce noise, it is done so that the volume control will operate as we expect it to. Will removing that ground connection result in more noise? It certainly could, but that's not why the 3rd lug is wired to ground.

Whether a pot is used as a tone pot or as a volume pot, the pot is loading the circuit. If the load of the pot (or multiple pots) is not desired, switching to bypass the pot (or pots) is often employed.

A tone pot is wired with only 2 of the 3 lugs used, that is called a "rheostat". A "no load" tone pot is often used to eliminate the load of the pot when the pot is at maximum. But the 2-wire tone pot is nonetheless still loading the circuit even though the 3rd lug is unused.

A volume pot is wired as a potentiometer; meaning all 3 lugs are used. Wiring only 2 of the lugs doesn't eliminate the pot from loading the circuit, but it does result in a crappy volume control. So does using a no-load pot for a volume pot.

So, live with the slight loss of treble, or use a switch to bypass the pot (or pots). These are variously called "blower" switches, "direct out" switches, or other names but the idea is the same- get the full signal of the pickups when desired, have the pots for adjustment otherwise.

guarantees no noise

There are no guarantees in Life . . .

And-

Hello and Welcome to G-Nutz2!

[speciallittleguy]

I see now, the output of the volume pot is the wiper so that the signal from the guitar is a voltage divider between the pickups and ground.

I had gotten myself confused because I've been working on understanding how blender pots work and the circuit behavior that I've internalized is that if a pickup has 250k ohms between it and the output that pickup is effectively off. So my perhaps naive assumption was that a volume knob acting as a rheostat would adequately block signal from reaching the amplifier.

[ashcatlt]

Two weeks late, but what the heck.

A pot wired as a series rheostat relies on some other part of the circuit to be the "bottom resistor" in the voltage divider.

In a blend pot, that will be other other pickup, which is significantly smaller than the full value of the pot, so we get significant attenuation. In a V pot, that "bottom" value is mostly dominated by the tone pot except at pretty low frequencies where it's probably going to be the Input-Z of the first active stage in the chain (amp, pedal, whatever). This basically means the ratio can never go all the way to 0, and in fact probably won't even get close. The blend pot never really gets to 0 either, but it usually will get closer and for the full spectrum. But it kind of only needs to go down to like 1/10 so that this pickup's contribution to the mix is less than the 1db we consider to be significantly perceptible. In the (master) V pot, there is no other signal to mask it, so not going to silence matters. You'll find that with dual V guitars, you don't really have to turn the one V down very far before that pickup stops making much difference in the mix also.