Rangemaster Pot miswired?

[ZtaRDuZT]

I've got two versions setting up the 10k log pot in my Rangemaster:


Tonepad shows lug 3 going to collector and lug 1 going to 470k resistor.
GGG shows lug 3 going to 470 k resistor and lug 1 going to collector.


Does anyone know which one is correct?

[petemoore]

  The one where the wiper gets closer to the collector [lower resistance wise] as the pot is turned CW will increase volume at CW settings/

[ZtaRDuZT]

I acctually don't know how the wiper moves when you turn the knob but I geuss it tells me that if
the volume decreases when turned CW, switch lugs 1 and 3.




Thx

[petemoore]

  Set the DMM to an R range larger value than the pot for this test.
  Use a testclip or testclip wire for the black DMM lead, clip that to center lug of pot.
  Turn the pot to the middle, test both sides [connect DMM's red lead to one outside potlug, read, then the other outside lug, read].
  Turn the pot with the DMM hooked up, notice you have a varaible resistance on either side of the middle lug [which is connected to the wiper].
  Turn the pot all the way CW, you should measure 0 resistance between the wiper and one of the outside lugs, that's the lug you connect to the collector on the RM so CCW turning of the pot increases volume, reverse the outside lug connections for reverse pot action [Ccw is max].
  This helped show me how pots work.
  See GEO 'secret life of pots'
 

[Rick]

And once you get it all worked out, try a 20-25k pot for some fun. It really makes quite a difference in this pedal, brings it alive.

...Rick

[Plectrum]

And once you get it all worked out, try a 20-25k pot for some fun. It really makes quite a difference in this pedal, brings it alive.

I know the output pot on the rangemaster affects the transistor biasing, but how do two different value pots that are fully "open" differ in this circuit?

Grant.

[Rick]

Good question Plectrum, but it must be that the circuit is seeing 20k instead of 10k when maxed ...seems to drive the transistor harder. I'll have to re-read RG's tutorial on this to better understand why. Try the mod youself and see. I think you'll like the result, it gives more output / distortion ...raunchy !
...Rick

[Plectrum]

Good question Plectrum, but it must be that the circuit is seeing 20k instead of 10k when maxed ...seems to drive the transistor harder. I'll have to re-read RG's tutorial on this to better understand why. Try the mod youself and see. I think you'll like the result, it gives more output / distortion ...raunchy !
...Rick

I'll give it a go...Thanks for the pointer.
I think the DC voltage attached to one lug must have a bearing here...(?)

Grant.

[ZtaRDuZT]

Thx for the DMM tip, I've tested trimpots that way so I don't know why I didnt think of that.


Testing another pot could be interesting. I'm not sure yet if I like the sound of my Rangemaster.
I haven't had the time to test it fully yet. I got some sweet tones out of it but I also got some strange
sounds where allmost all low frequencies were filtered out. Gotta work on it some more before I decide
which way to go. Thx for the tip though.

[petemoore]

  Here's what I did.
  10k pot on box, like regular RM..connected to collector, and attenuating gain output...
  But on top of that I put a 10k trim resistor. This allows the volume control to work the same [at a different total output level], and allows adjustment of the R value on the collector bias....2 x 10k pots in series, one on board, one on box. Adjust the second pot to 0 ohms and it's a standard RM.
  Between lugs 1 and 3...that's a fixed resistor of about whatever value the pot is labeled, measuring it'll probably be a touch lower that what it's labeled..but it doesn't change. How far the wiper is across the electrically resistive potwafer from lug 1 and, lug 3 [depending on shaft position]....you can read what resistances are available between 0 ohms and max with the DMM, between the wiper and either/one or the other outside lugs [ 1&3 ].

[Khas Evets]

pete - Doesn't that 10K trimmer move the bias off ~7V (I believe downward)? Have you measured the collector voltage with the collector resistor at 20K? I would have thought you'd need to re-bias the circuit. It's possible that you're moving toward 4.5V making it louder and more symmetrical.