Roland Funny Cat SDS - decent on its own

[Mark Hammer]

The Roland Funny Cat is a quirky one-of-a-kind autowah that incorporates something that Roland labelled "SDS" (I'm assuming that means "soft distortion sound").  It comprises the upper left quadrant of this drawing from RG Keen, and uses a single op-amp.

The op-amp is configured as non-inverting, with the ground-leg resistance being provided by an FET.  The gate of the FET is driven by a very crude high-ripple rectifier (i.e., very little smoothing of the rectified DC voltage).  It is a common finding on this forum that people using, and unfamiliar with, simple half-wave rectifiers as a sidechain for a compressor, noise gate, or autowah, will ask once a year "Why does my <insert effect here> distort?".  It's not distorting in the usual sense of the word.  Rather, the ripple in that rectified/envelope signal is modulating the effect at a very fast rate, such that it sounds like distortion.

The SDS circuit in the Funny Cat uses this artifact in a deliberate way.  The rectified output of the op-amp is turning the gain up and down quickly (as the gate makes the drain-source resistance vary at the rate that the gate is being influenced by the ripple).  It's not a fuzz, nor does it sound like an overdrive or DS-1-like distortion.  But it sounds "distorted", in a pleasant and non-confrontational way.  Think angora wool distortion, rather than horsehair; it's just "furry".  Even if you don't particularly like autowahs, or this specific autowah, the SDS circuit is worth building on its own, just for something different.

The stock Funny Cat provides some gain after the level control for the SDS subsection.  And since the SDS can be loud, I'm assuming some sort of gain-recovery might be in order for the basic op-amp circuit.  But worth exploring on its own.

[11-90-an]

Will LED/LDR combination be a good sub for the JFET? I happen to have none...   

Very interesting BTW... thanks for sharing 

[Mark Hammer]

Will LED/LDR combination be a good sub for the JFET? I happen to have none...   

Very interesting BTW... thanks for sharing 

You're welcome.
In answer to your question, NO.  You need a control element that can respond quickly.  Very few LDRs will have the fast "settling time" of a FET.  The entire effect depends upon the FET gate being "wiggled" very quickly by a purposely unsmooth envelope.  It rests entirely on speed of response....in a clever way.

[garcho]

you're on a roll Mark, another cool idea from past pedals ripe for DIY noodling

[Fancy Lime]

Eerie... I have never heard of the funny cat, I think. Yet, I am currently in the process of designing a dirty JFET compressor that makes use of the same effect. It's a bit more complicated, with an active side chain and adjustability of the ripplyness but the idea is the same. Funny place, the universe.

Andy

[Mark Hammer]

Funny place, the universe.

Andy

Damn straight.
This is a perfect case of a flaw being marketed as a feature.

[Strategy]

I recently sought out a video of Funny Cat becuase I'd never heard one, and it dawned on me it might be a sort of an amplitude responsive waveshaper -- something more akin to Prunes & Custard or Wolftone / Malekko "Chaos" pedal. It also sounds similar to the Escobedo Bronx Cheer circuit. I haven't compared all these side by side with the Funny Cat, does anyone know if they work on the same principles or is it a case of parallel evolution? If so I think that this makes them more like the way waveshaping / rectification is implemented in synth circuits, like Buchla's "Timbre" modules.
Strategy

[Mark Hammer]

There are two simple half-wave rectifiers in the Funny Cat.  One is used to achieve the SDS effect, and the other is used to sweep the filter.  One of the filter-sweep modes on the Funny Cat essentially removes the envelope smoothing, such that the filter is allowed to sweep in a very glitchy fashion.  I gather that is where it begins to resemble the sounds of the pedals you refer to.

I keep gnattering on about this, but it bears repeating: the time constants and "feel" of an envelope follower (rectifier) circuit always need to be selected with respect to the particular effect sought, and the kind of feel that suits it.

One gets the sense that, much like the apocryphal tales of how the Proco Rat was developed (via a mistaken resistor choice), that third mode on the Funny Cat must have arisen not by planning, but by an error that turned into a "feature".  I.E., someone forgot to connect a cap and thought "Hey, that sounds kind of cool.  Limited use, but cool nonetheless."