Warp control n' more...

[brad]

I'm thinking of experimenting with a warp control that sweeps between two contrasting sets of clipping diodes (like this), but I've got two problems:

a) What pot value would be best, and should it be linear?  The AMZ article suggests a value of 2k for one warp control, but that seems way too small for this application.

b) How can the volumes between both diode pairs be matched more evenly?  LEDs are loud as heck, so could their volume be lowered by adding a resistor to ground in series after them?

[vdm]

the problem with adding a resistor in series with the LEDs is it will not decrease volume, it will rather increase it!
adding a resistor makes that path to ground harder to reach and as such less clipping occurs. You will find with no clipping diodes attached it is louder again.
Sorry, im not sure how to combat this in the configuration you want (ie a single pot).

Im not sure about the value of the pot, but you might be interested in using a larger size so that in the middle of the rotation (it should be a linear pot) you will have very little effect from the clipping diodes (because of resistance to both sets), and it will be a cleaner sound as if you had no diodes attached.

*enjoi~

[brad]

Ahhh, you're right!  A resistor in series with the diodes would make ground harder to reach!  Doh.  I was hoping there'd be a way to get close to a 50-50 mix of both diode pairs at the center of the pot's rotation.  Oh well! 

[jrc4558]

Here's what you may do:
1) place the clipping diodes directly before the volume control.
2) use a dual linear potentiometer anywhere from 10 to 100Kohm. Ideally it should be at least twice the value of your volume pot.
3) on one section of the pot, soder a 2.2k resistor in parallel with the outer lugs and use that section as a warp control.
4) the other section will go right before the volume control as a vaiable resistor. wire it so that resistance increases as you shift towards the LED clippers.
5) tweak the values for smoother transition.
Its not the ideal solution, a DIY one rather. However, it will save you from adding any active components to your pedal. Simple, yet effective.

[brad]

Thanks Constantin Necrasov.  I suppose I'm stuck with the volume jump on soft clippers with the diodes in the feedback loop.

btw, the pot size really doesn't matter for this type of warp control does it? 

[Paul Perry (Frostwave)]

I'd duplicate the distortion stage, and then have a mix control after that. You can use say a 100K B pot then.
Use a resistor divider pair to bring the Si output down to the Ge. I don't know why you want to call it 'warp', though!

[JimRayden]

Thanks Constantin Necrasov.  I suppose I'm stuck with the volume jump on soft clippers with the diodes in the feedback loop.

btw, the pot size really doesn't matter for this type of warp control does it? 

Yes it does. If you use a very large pot, you'll have strictly the clipping of one diodes on the extreme settings and a clean sound in the middle setting. If you use too low of a value, the extreme settings will always have the clipping diodes mixed, more or less. So you really want a carefully chosen pot value. Use SPICE simulation, you'll get quick results. Or PM me the signal and diode specs, I'll test it for you.

------------
Jimbo

[brad]

Thanks for the offer Jim, but I haven't settled on any configurations yet.  I'll have to check out all this spice guff!  So it IS possible to find a value that will give more or less a non-interupted sweep from one set of diodes to another by finding the right pot value?

Is this even possible in a tube screamer style soft clipper?  The example on AMZ is only for hard clippers.

[WGTP]

I used one in a Rat with a 10K pot "panning" between an LED & GE diode.  I would recommend a linear pot.  At around 3/4 of the pot, there is resistance between both diodes and ground and this is the loudest setting, the LED with no resistance is slightly lower.  The other diode is a fixed SI. 

You could use a dual 10K pot and pan between 2 different sets of diode combos. 

I haven't tried to address the volume difference. 

[brad]

That sounds like what I'm after!  I thought it'd be possible to run two sets of diode pairs off a single gang pot though...

[WGTP]

OK, then 4 diodes.  1 to each side of a pot.  You can use either singles like I did, or sets.