Which pot for volume box?

[MadAsAHatter]

I'm going to make a simple volume box for my bass preamps setup. I have all the preamps running through a loop switcher then output to the fx return of my bass head. I want to put the volume box between the out of the loop switcher and fx return to act as a master volume for all the preamps. I can't find a definitive answer on which value pot to use. Seen everything across the board from 25k linear to 1M audio suggested.

So is there a certain value and taper I should use or will anything work fine?

 

[Ben Waylin]

I'm going to make a simple volume box for my bass preamps setup. I have all the preamps running through a loop switcher then output to the fx return of my bass head. I want to put the volume box between the out of the loop switcher and fx return to act as a master volume for all the preamps. I can't find a definitive answer on which value pot to use. Seen everything across the board from 25k linear to 1M audio suggested.

So is there a certain value and taper I should use or will anything work fine?

I built this one a while back and it works fine. It's a 1MΩ PEC pot.

I run it between my reactive load box and audio interface.

 

[MadAsAHatter]

Thinking about it, a 1 meg pot might be the best. Something lower might suck out some high frequencies. Worse case scenario I have to swap it out for a different value.

 

[Ben Waylin]

Thinking about it, a 1 meg pot might be the best. Something lower might suck out some high frequencies. Worse case scenario I have to swap it out for a different value.

It just gives me a little more control trimming the signal going into my audio interface.

I can go without it, but it makes the trim control on the Focusrite 2i2 real touchy.

 

[CrazyNutz]

I built this one a while back and it works fine. It's a 1MΩ PEC pot.

I run it between my reactive load box and audio interface.

Rather strange way to wire the pot for volume control. You leave the ground off like that, or was it just not finished?

 

[MadAsAHatter]

Rather strange way to wire the pot for volume control. You leave the ground off like that, or was it just not finished?

I believe the metal housing acts as the common ground so connecting to the lug isn't necessary (and may cause a ground loop).

 

[CrazyNutz]

I believe the metal housing acts as the common ground so connecting to the lug isn't necessary (and may cause a ground loop).

That third lug does not automatically have a ground built in, it's just free floating right now. Without that you don't have a variable voltage divider. Which is how volume pots are wired.

Right now it's just a variable resistor, which can attenuate the signal, but it depends on the load. Basically it might work OK on some equipment, and not so well on other.

 

[mcstinger]

Thinking about it, a 1 meg pot might be the best. Something lower might suck out some high frequencies. Worse case scenario I have to swap it out for a different value.

I don't know, what preamps you use. However, output impedance of any preamp should be quite low. So lower impedance pot should be ok. But in general, anything from 10k up should work fine. I would use audio taper.

 

[Ben Waylin]

That third lug does not automatically have a ground built in, it's just free floating right now. Without that you don't have a variable voltage divider. Which is how volume pots are wired.

Right now it's just a variable resistor, which can attenuate the signal, but it depends on the load. Basically it might work OK on some equipment, and not so well on other.

You realize this is an AC signal, right ?

 

[CrazyNutz]

You realize this is an AC signal, right ?

Yup. So what's your point? You think voltage dividers don't work in AC?

 

[mcstinger]

You realize this is an AC signal, right ?

You know, voltage dividers are willing to work equally well with AC and DC voltages . Your wiring just adds serial resistance to the input resistance of the next stage, so it works to some extent, with few drawbacks.

However, unconnected terminal on the pot is generally a bad practice. If you like your weird circuit, connect that unconnected pin to the middle terminal. If you want to test behavior of the voltage divider under AC, just connect it to the ground and use left jack as an input . It should work, in the same way, as millions of gain and volume pots worldwide.

 

[dcburn]

I used a 1 meg also.