Harnessing the Unstable Distortion of FM Radio // Fairfield Roger That

Hello out there, has anyone seen this crazy FM distortion pedal?

And has anybody seen a schematic for it anywhere?


+1 here ! Looks super interesting !

You can find photos of the boards on their website. It helps finding out which ICs they are using, etc…

I couldn’t find a schematic (unsurprising, as it appears to be a new product) but I have some ideas about how it works. I’d have to experiment a little to be sure, but I’m thinking that the audio signal from a radio receiver in the pedal is being mixed with your audio input, providing the distortion. The Tune control changes the frequency of the receiver–essentially changing the radio station. Shift, I think, is an LFO or something similar that modulates the Tune setting. The more ‘Shift’ you add, the more the Tune setting wobbles around, not staying on any particular frequency. Wet and Dry are just the usual modulation of signal you would expect from a wet/dry setting. Though it says if you turn them to the same level they can cancel each other out, so maybe they’re wave shapers inverted from each other? The Voice Tuning bit, IDK.

Might be fun to play around with. The interesting thing, if it’s receiving actual radio noise, is that it’s entirely location dependent. If you’re in a city with lots of stations you’ll get entirely different results from someone in a less populated area with mostly static on the radio. Pretty cool!

ETA: I see a couple of CD4046BE PLL chips in there, so maybe that’s what they’re using to get the complex noise that comes from the Tune setting? It’d be more interesting if it was using an actual radio receiver.

Also, I can’t figure out what this thing is and it’s starting to drive me a little crazy.

RF-Gut-Official-MID_1024x1024 (1)

Vactrol? I can’t quite make out the number on it.

Added: I took a closer look at the image from the website. I thought it said NSL 7050 but perhaps it was NSL 7053, which is indeed the number of a (discontinued) vactrol from Luna / Advanced Photonix, mentioned e.g. here:

Whether that’s the part number or not I’m pretty certain it is indeed a vactrol.

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Your logical reasoning is acceptable. A vactrol it is. Huzzah.

It’s hard to believe that there’s an actual radio receiver in there. Not that it can’t be done (e.g. Koma field kit), but it doesn’t sound like there’s one in there. Sounds more like a combination of noise, PLL/waveshaper, modulated by an LFO with some filtering on top. I guess we’ll find out when someone gets one and traces the circuit!

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Cool! Yes, I guess i’ts only a matter of time!

Interesting, looks complex, but like anything when broken down is manageable.

Here it says:

Inspired by Roger Grant’s idea to mimic loss of fm radio signal through the use of a simplified fm modulator/demodulator scheme.

Controls interfere with demodulation accuracy resulting in familiar yet unexpected signal degradation and noise

and one of the video comments says

The only other device I’ve come across that operates in a similar manner is the interstellar radio module from Schlappi Engineering.

leading to here:

The Interstellar Radio is a destructive transmission line. It modulates and demodulates a signal with different clock references which results in extreme distortions and frequency modulation of complex and noisy timbres.

with this block diagram


and some more information.

So apparently no, there is no radio involved, but (radio frequency??) modulation and demodulation with some kind of distortion in between.


FM radio frequency modulation so, I am supposing, destructively noodling with a signal that’s between 88-108MHz? That’s the carrier wave signal though, not the audio signal, so IDK.