Super Saturator

Or, what to do with all these 12AU7s?

This starved plate valve clipper was inspired when a friend asked me to create a pedal to give his electric banjo more grit and sustain, especially for finger tapping and solos. He has a very avant-garde approach to bluegrass, running guitar effects pedals with his banjo to create new and interesting sounds. I had also bought an old tube-based electric organ at an auction as a kid, and had been lugging around a bin full of tubes pulled from this unweildy monstrosity for about 20 years. Ah-ha! Finally, something to use them for.

After some trial and error, I ended up with an interesting (if somewhat unrefined) low voltage overdrive circuit, using two valve stages in a single 12AU7 bottle. It does have a linear region, but also features some delightfully non-linear effects as the signal level increases. It's somewhat reminiscent of a high-gain amplifier, and has features of both the gain staging found in the preamplifier of Marshall-style amplifiers, plus the incorporation of negative feedback which simulates the power amplifier's influence on tightness or "feel".

Essentially the circuit functions as a compressor/limiter at low signal or gain levels, and an overdrive pedal at high gain. Negative feedback also affects the onset of distortion, making it more sensitive to dynamics with a sharper transition between clean and overdrive.

The challenge with banjo is knocking down the sharp transient and bringing out the body of the tone, without introducing pumping or undesirable artifacts. This means the attack must be fast, giving the pedal limiter-like behavior for a fairly unique sound.

While the dynamic range of a plucked banjo note is much greater than guitar, it resonates differently as well. Due to the floating bridge, the lowest note on banjo is a subharmonic, lower than any guitar fundamental. To me this sounds "bigger" when used with guitar, while still keeping the overall sound tight.

Super Saturator Demos

Recorded directly into an Mbox 3 Mini, with basic band limiting (60 Hz ~ 10kHz) applied in post-processing. The only other pedals in the chain are a Ditto x4 for looping, along with a Tech 21 Boost RVB for its nice medium plate reverb. Aside from this, it's just the guitar into the Super Saturator, routed directly to the audio interface.

Next, an overdriven 5F6-A Bassman style preamp is run into a single-ended 6V6 output stage, with tube-driven spring reverb.

This pedal was fun to protoype. Someday I hope to return to this design and tweak it to its fullest potential.

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