Wiring a push pull potentiometer for channel defeat

[mlannoo]

I'm attempting a few mods on my '68 Traynor YBA-1 Bassmaster - one in particular is a "Channel Defeat" mod that is designed to improve the "transient fidelity" by removing unnecessary elements from the signal path. It calls for replacing the 1M volume pots with 4M-A push-pull pots so that you can pull the switch to eliminate one of the channels.

There is a nice schematic on this mod here on page 4:
http://www.kilback.net/Traynor_Tweaks_rev12_sk2007.pdf

The trouble is, I don't understand how push-pull pots work. I don't know how to wire this thing up so I was hoping someone here could help me out. I do understand that it is a pot with a DPDT switch incorporated with it but I haven't been able to find any detailed explanation as to how they are wired up.

thanks in advance
M

[Bruce / Mission Amps]

I'm attempting a few mods on my '68 Traynor YBA-1 Bassmaster - one in particular is a "Channel Defeat" mod that is designed to improve the "transient fidelity" by removing unnecessary elements from the signal path. It calls for replacing the 1M volume pots with 4M-A push-pull pots so that you can pull the switch to eliminate one of the channels.

There is a nice schematic on this mod here on page 4:
http://www.kilback.net/Traynor_Tweaks_rev12_sk2007.pdf

The trouble is, I don't understand how push-pull pots work. I don't know how to wire this thing up so I was hoping someone here could help me out. I do understand that it is a pot with a DPDT switch incorporated with it but I haven't been able to find any detailed explanation as to how they are wired up.

thanks in advance
M

Well, first of all you don't install 4m audio pots in the amp... many of them came with 4m audio pots so you replace those with 1m audio pots.
The push pull thing is so you don't have to drill any holes to have some switching capability.

You can buy 1m audio pots with a DPDT or SPST switch attached to the back... personally I find most of these to be cheap Chinese pieces of crap.
There are different kinds but the ones with the DPDT allow the knob to be pushed in with the switch being able to be used in either direction. on or off.
Regardless, I have been forced to use them in some applications anyhow.

WeberVST sells something like this too:
https://taweber.powweb.com/store/potsord.htm
aprt number... wp105A-PPSW

What Sean is doing is using two of the contacts on the DPDT switch to break open the signal path from one of the pots... see the two RED dots in his #2 schem?
That would be the two contacts closed.
So the signal from volume pot R1a's wiper goes to the 100K isolation resistor (use bigger values there anyhow) and back to the two lugs on the switch so that when you pull the knob, the contacts go open and thus... disengages that output from that volume control.
The only difference is that you would actually install the 100K resistor on the switch lugs, not the eyelet board.
By the way, I think it sounds much better if you replace those two 100K resistors and use two 220K to 270k resistors instead when using 1m audio pots.
Make sense?

[black_labb]

dpdt means there are 6 connections. 3x2. the middle of the 3 is a common connection, the top and bottom are the connections. push it one way, and the top one is connected, push it the other, and the bottom will be connected. double throw (or is it double pole) means that there are 2 of these, which is why there are 2 sets of 3. you should be able to figure it out fairly easily with a cheap multimeter if that doesnt make too much sense.

[mlannoo]

Wiring a push pull potentiometer for channel defeat

[QUOTE=Bruce / Mission Amps;53482]Well, first of all you don't install 4m audio pots in the amp... many of them came with 4m audio pots so you replace those with 1m audio pots.
The push pull thing is so you don't have to drill any holes to have some switching capability.

thanks for the reply. i did make a mistake in my post - i got the pot values backwards ...oops.

i've attached a drawing - this is my attempt at understanding what i've read - for channel 2. i eliminated the 100k resistor on the board and changed the value of R11 in this picture like you suggested mounting it directly to the switch on the Vol 2's pot. am i on the right track? even close?

thanks for the help!
m

[loudthud]

It won't work the way you have drawn it. You have the 220K connected to the wrong switch terminal. Hook it to the terminal closest to the front of the amp on the same side as the center lug on the pot is connected.

Note: You don't really need a push-pull pot for this application, the pot like on a single knob Champ will work except you have to turn the pot all the way down to disconnect it. It gives you more options in finding a pot.