"The Crank" dual gang pot question

[markm]

How critical is it for the Drive pot on Mark Hammer's "the Crank" to be 10K dual gang?
Would a 50K Dual Ganger work out okay?
Just wondering 'cause, this thing looks interesting!
  MarkM

[petemoore]

  You could try adding resistors from wiper to pins 1, wiper to pins 3...you can fairly closely [I think] replicate the function of a smaller value pot.
  Each pot of the DG would have a resistor from lug 2 to lug 3, and an equal resistor from lug 2 to lug 1.  [using four equal resistors...something like 7k?, you can use the DMM to find the 'new' value of the pot.
  50k DG linear might even work ok there...?
 

[markm]

Hey Thanks Pete!
I have such a mental-block on changing pot values with resistors it's not even funny.
Maybe I'll have to give that a try!
  MarkM

[petemoore]

  I haven't built The Crank, perhaps the value/taper is perfect for you as 10kl, perhaps some diddling gets you response curves from a DG pot...when used in this circuit, which provide you with a response from turning that pot you prefer...the prospect of a fair bit of messing about would make me tend to opt for wiring some pot concoction in there to 'be the values shown in the schematic...but...
  You can always 'diddle' with teh tapers if you feel the inclination, even using pots to trim and taper other pots [a small value between wiper and outside lug] to find tapers not available in standard DG pot values...like I say, alot of diddling...

[Mark Hammer]

In theory, you COULD use a 50k dual ganged pot, but you'd need to do a heap of math and adjust a bunch of other component values so that the right amount of gain is introduced in each stage.  Dual 10k pots are pretty common, actually, though what's common for me may well be rare for others.

The suggestion to stick a fixed resistor in parallel makes eminent sense, since the two pot halves are being used as variable resistors anyways.  A 12k resistor in parallel gets you a max resistance from each pot section of around 9.7k, which is pretty much what you'd get from a standard 10k pot anyways.

Actually, you might be better off using a 12k for the pot half on stage 1 and a 25k trimpot to adjust for the second stage.  I wanted it to be pretty clean with just a hint of dirt at higher gains, but I can see where some folks may want a little more or where diode values may vary a bit.  So, for instance, if your 1N914's measure 527mv forward voltage you might want to set that trimpot to around 12k, but if the diode had a 580mv forward voltage (all realistic values), the two in series adds another 106mv of "clean" headroom in the second stage so maybe you could tolerate jacking the trimpot up to 15k or so.

[markm]

I guess I was trying to save a few pennies!
I have a 50K, I don't have a 10K and I think the only one RS offers in 10K has a switch as well.