"The Crank" Weirdness

[jimmy54]

Hi fellas,

I built Mark Hammer's "The Crank" a few months ago and it's now one of my favourite builds by far.  I built a second one but for some reason never sounded as good as the first (this could be due to putting a 1k resistor in series with the diodes in the second stage in my first build, per Mark's suggestion in one of his posts).  I used Spudulike's vero layout shown here:

http://www.diystompboxes.com/smfforum/index.php?topic=44095.0

Anyway, I opened up my orginal one and found that I had never wired the connection to the dual-gang pot labelled 'VR2-B Lugs 2 & 3'.  I connected the lugs to the vero but I could not notice any discernable difference in tone (granted, this was at low volume as it was 11 at night and the baby was asleep).  Should there be a huge difference between having these lugs wired up and not?  Without the connection the gain pot still works, adding grit to the tone, and seemed to work in the same way when wired.

[jimmy54]

Bump, Mark are you out there?

[Mark Hammer]

Sheesh.  Can't a guy eat lunch?

As long as the pot is in the path in some form, fixed or variable, there will be gain associated with it.  Keep in mind that this circuit uses multiplicative or composite gain (stage 1 x stage 2).  If only the outside lugs of the pot are used in the second stage, then the pot adds a fixed 10k of feedback resistance, yielding a combined feedback resistance of 32k and a single-stage gain of x5.7.  Varying the gain of stage 1 will still produce noticeable changes in gain and dirt under those circumstances.

If it is the case that the pot is not connected at all (i.e., the 22k is just hanging there all on its lonesome), then what you have is sort of a 2+2 version of the op-amp Muff Fuzz, that used diodes only as the feedback path.  Now normally, the feedback resistance and ground leg resistance (6k8 in the second stage here) form a sort of voltage divider that shunts negative feedback to ground so as to allow the op-amp to come closer and closer to the maximum gain-bandwidth product (which is why a simply wire link in the feedback path and NO resistance to ground is what produces a unity-gain stage).  I gather the diodes and 6k8 resistor do something like that, but I'll be darned if I know how to calculate it.

[jimmy54]

And I bet it was iron fillings with a solder sauce wasn't it Mark?

Thanks for the explanation.  I'll have another try with the bottom part (lugs 2&3) of the dual-gang pot connected and disconnected and compare the tone.  It may be that I actually prefer the lower gain without the bottom lugs connected.

Cheers

Jimmy

[Mark Hammer]

It may be that I actually prefer the lower gain without the bottom lugs connected.

Possible. Someone else posted a note saying that they didn't really like the Crank but were using an EMG-equipped Les Paul with a very hot output.  I suspect there are probably a whole bunch of just-at-the-edge-of-breakup pedals, both DIY and commercial, that need a certain type of input signal to sound pleasing.  I absolutely hated the TS-808 clone I made some years back....until I switched from the guitar with the on-board preamp to a 100% passive guitar.  That stuff happens.

[jimmy54]

I was actually using my Strat with single coils rather than high output pickups.  I agree with your assessment re just-at-the-edge-of-breakup pedals.  I think there's a fine line between having just a nice amount of grit on top of the clean tone and sounding like a very weak distortion/OD.

I also like the way the Crank cleans up with the volume on about 8-9.