Parapedal pot range question

[pacealot]

Hello all and sundry,

I've breadboarded up a Parapedal, and while it sounds terrific "in theory," I'm very concerned about how to get it to function at the full range of pot rotation. Since there are limited options for dual-ganged A10K pots, there's nothing available that has "plateaus" at the ends of the sweep like the common wah pots do. Unfortunately, for me, the most interesting and distinctive parts of the circuit are at the extremes, so putting it in a standard wah enclosure with a standard gear is going to truncate one end or the other (or most likely both) and leave me with a frustratingly stunted wah, knowing what it could otherwise be capable of. I've looked into the world of smaller gear sizes and other mechanical solutions, but I can't find 12- or 13-tooth wah gears to buy on their own, only on some of Joe Gagan's pots, and even those don't look cross-compatible with the dual pots I can get ahold of. (I have an Alpha and a TE Connectivity currently — not great, but they're what I could get.)

Has anyone overcome this obstacle?  I know the Wilson Freaker has a very good set of ranges and seems to have most of it on one throw depending on the cap selection, but I'm just not matching that with my circuit/pot combos. I've tweaked the caps to the most extreme values that still sound good (I've gone as low as 0.15µF on the bottom and 0.01µF on top — I've noticed that "widening" the values like this tends to push and pull the sweep range around, rather than making it very much wider overall), but I can't get it so wide that it can overcome the hobbling of the physical sweep limitations. (I'm also fighting the noisiness of the "thump" at the bottom, but that's a somewhat different problem, and some of it is just plain noise, which might be breadboard-related, or pot-related. Or both. Or neither. Ugh.)

Any thoughts or suggestions? I wanted to build the Parapedal circuit because I'm looking for the most extreme sweep available for a wah, but currently I despair of closing the deal...

[nocentelli]

Weird co-incidence, I breadboarded the parapedal last weekend (from the pedalpcb "parasite wah" schematic), had exactly the same issue. Came to diysb this morning, typed "parapedal" in the search box expecting to wade through zombie threads, and this is on the front page!

I only have 100kB dual pots in my stash (from previous klon attempts), so have a 12k resistor in parallel with each gang. I should state that I am making a small box (possibly even guitar-mounted [probably not]) with a single pot, designed to be hand-tweaked. As such, I also want to extend the filter sweep across the pot range.



I first upped the 220r a bit, and it hasn't made much difference to the sweep.With my set up, the taper from the 100kB||12k dual pot and a 1k in place of 220r on the end of the pots, the LPF cuts everything until 3/4 o'clock, whereupon there is a slight DC-ish thump and  more virtual silence until the fat monstrous bass emerges around 1pm.

Looking at the schem, it seems to be a mutron III type LPF, but the second swept stage diddles with the resonance or gain or something, as well as sweeping the frequency in tandem with the first gang. I am now considering hugely increasing the 220r stopper resistors to try to bring the frequency sweep in earlier in the pot's travel, but I am unsure about how the might affect the previously synchronised resonance swell.... 🤔

[pacealot]

I played around a little with bypassing/reducing those 220Ω resistors myself (going the other direction though), and I found it didn't help the range on the pot in a very usable way, and it made that DC thump noise even more unpleasant, which sounds about like what you experienced as well.

One thing I did which was instructive at least was to reverse the direction of which sweep cap goes up in value and which goes down. Wilson's Mini-Freaker comes with the caveat that one cap has to always be equal to or higher than the other, but I found that it just "breaks" the circuit differently. Using RG's component numbers, if you increase C2 and decrease C4, it increases the Q to an eventually unusably high extreme of resonance; the other way around, it decreases the Q and eventually distorts (in a bad way). Chasing it by putting R12 on a pot or trimpot helps somewhat, but eventually either direction will collapse and sound bad.

I needed a new pot for a more traditional inductor wah I put together anyway, so I ordered a Gagan pot from Small Bear, and will try to play around with the gear and see what I can come up with in the land of mechanical solutions.

I hope I can get this thing to work consistently with a treadle, because it's a very powerful and useful filter sweep for the guitar — makes me think of Mike Oldfield's description of a parametric EQ pedal he commissioned: "it's like a wah-wah, except it's a much nicer wah-wah"...