volume pot connections

[peterg]

Schematics always show the circuit connnected to lug 3 and the output jack connected to lug 2. Is there any reason why they can't bbe reversed?

[deadastronaut]

You can, .it'll just be backward volume....CCW full  on...instead of CW.

[peterg]

Rob. If you switch lugs 1 aand 3,  ground to 3, you get more volume the more CCW you turn. I'm referring to keeping ground on 1 and the circuit to 2 and lug 3 to output.

[Seljer]

If this is what you're describing

Code Select Expand


        +-----  OUT
        |
      _____
      |   |
      |   |
IN -->|   |
      |   |
      |   |
      _____
        |
      -----
       ---
        -




In that case the potentiometer stops being a voltage divider so it basically doesn't work.

What exactly will happen depends on the impedances of the preceding/next stage.
If you have a very low output impedance driving the pot + a very high input impedance after the pot nothing at all may happen (other than when the wiper is grounded).
If you have a high output impedance  before the portion from the wiper to ground will load down the preceding stage and it'll work as a kind of volume control.
If you have a very low input impedance after the portion from the wiper to the top of the pot will load down the next stage and it'll also work as a kind of volume control.

[peterg]

Thanks Simon

[nocentelli]

I have seen lots of Death by Audio pedal circuit schematics where they use this way of wiring a volume pot. This may help confirm your opinion of DBA as being either a) fearless sonic innovators who hold no respect for boring convention, or b) clueless hacks who just throw circuits together without understanding what they're doing.

[FiveseveN]

boring convention

In Soviet Brooklyn, current flows from anode to cathode.

[Seljer]

boring convention

In Soviet Brooklyn, current flows from anode to cathode.

Because they didn't know electrons were negative when they defined current, the electrons themselves do actually flow in that direction.

Curse you convention!

[peterg]

I have seen lots of Death by Audio pedal circuit schematics where they use this way of wiring a volume pot. This may help confirm your opinion of DBA as being either a) fearless sonic innovators who hold no respect for boring convention, or b) clueless hacks who just throw circuits together without understanding what they're doing.

I'm going with option b. I'm a clueless hack and was pulling my hair out over the weekend trying to to figure out why my latest build's volume pot wasn't working. I had wired it up DBA style.

[duck_arse]

If you have a very low output impedance driving the pot + a very high input impedance after the pot nothing at all may happen (other than when the wiper is grounded).

smoke will often happen, conventionally. can't speak for soviet smoke.

[PRR]

> Schematics always show the circuit connnected to lug 3 and the output jack connected to lug 2. Is there any reason why they can't bbe reversed?

As R.G. likes to say, in his own words, "look at the whole circuit".

A 3-leg pot has two circuits, conventionally In and Out.



"Most" circuit design goes *from* a lower impedance *to* a higher impedance.

In the "Ideal" case, the potentiometer is connected "normal", is fed from a zero impedance, is loaded in an infinite impedance, and the percent output voltage can be calibrated from exact physical measurements.

In audio systems we do not need precision ratios (we turn by ear), we don't pay extra for ideal zero or infinity, and the "normal" connection gives good service.

HOWEVER. Sometimes we come from a higher impedance to a lower impedance. By basic duality of nature, the situation is reversed, and we should connect the pot "backward".

One well-known music-audio application is the Fender 5E3 DeLuxe. The preamp tube plates are fairly high impedance. For mix-action, Leo connected the pot-tops together, and fed Input to the wipers.



This is a fairly subtle problem in Ohms Law, considered over the whole range of the pot. If you are not experienced in such design, you really should go with the way the designer decided what was best.

One serious extreme: with "normal" connection, full-down is least-loading on the source. With "backward" connection, full-down shorts-out the source. In small audio, shorts may be "safe" (no smoke), but may not give the best sound at very-low settings.

[duck_arse]

also, this:

http://www.diystompboxes.com/smfforum/index.php?topic=97109.msg891129#msg891129