ALL-NEW TWA Octoverdrive: <br>selinium-diode based Overdrive with Octavia!</br>

ALL-NEW TWA Octoverdrive: <br>selinium-diode based Overdrive with Octavia!</br>


The following info was provided by our engineer Robert Derby—The Mad Scientist who designed the Octoverdrive as well as the majority of TWA’s audio oddities:

"So after repairing and updating an Ampex tape recorder’s electronics, I had some selenium rectifiers on my bench. I’ve seen these things most of my life, and they are usually replaced with silicon diodes if and when they go bad.

Staring at them, I got to thinking – germanium diodes sound different, LEDs sound different, Schottky diodes sound different, and silicon diodes all sound different in audio circuits.  Why have I never seen SELENIUM DIODES in audio circuits?  Since they will not be used in a stressful way – as in power rectification – there should be no concern of failure or any other issues.

I decided to set up a little test jig to drive that old rectifier pair from the Ampex and hear what they sounded like with audio going through them.

Surprise! Almost from the start, cool things happened. Very warm clipping, able to tune in a great octave up, and that certain something that sounds juicy-magical-saturated......

I found that selenium diodes are somewhat similar to germaniums when used in audio, but there is an N factor. I checked inductance, capacitance, and voltage drop versus frequency. All had very surprising results. There is a high inductance in these things, as well as capacitance. The voltage drop is similar to Schottky or germanium diodes, making them clip softly at a lower voltage than silicon or LEDs.

I then began testing other takeouts and also some eBay purchases, and found out that they are all cool sounding, but vary a lot!

So I perf-boarded a circuit, and tweaked it a lot, and was amazed at the musicality of a drive box using these obsolete selenium components.

I added a 3-band EQ - much like what is on mixers/consoles - so the sound could be sculpted. Wow.

I found an alternate mode that has thick, heavy distortion, a nice complement to the singing, sustaining octave voice.

More tweaks based on user wishes, and there it was - the Octoverdrive.

Simple – Yet, if you were to examine the circuit, not really that simple. Kind of crazy, actually.

The result is a sweet musical drive and sustain, from subtle to over the top."

Robert surprised me with the Octoverdrive prototype in July of 2021 during one of our regular R&D meetings.

We were going over some other pedal designs (probably the Krytical Mass!), and when we were done he pulled out this metal project box the size of a small amplifier. The excitement on his face was palpable – a rare emotion for him to exhibit.

Robert titled this original proto the “Steam Punk” since it had this crazy Road Warrior future/retro look to it (Robert has a tendency to assemble prototypes with whatever spare parts AND hardware he has within arm’s reach).

We played through the pedal and it was uber-cool. Thick, super-saturated drive that had a decidedly tube-like personality to it.

The octave-up voice had even more goodies in store – the selenium diodes do some weird stuff with audio, and there were hints of filtering, phasing, and even flanging going on that the upper octave harmonic helped to accentuate. I t was really cool to just hit a sustained note and listen to it morph and decay into weirdness.

Robert passed the Steam Punk off to me so that we could get some more ears on it and put it through the paces.

The next big lift to get this pedal off the ground would be to find a reliable supplier of selenium rectifiers. Robert even suggested just scavenging them off of eBay or electronics clearance sites, but we both eventually agreed that component consistency was required in order to mass-produce this pedal.

After some searching we located a company that specialized in current-production of selenium rectifiers (which are still used in some high-power industrial devices).  They were willing to build the part to our specs, so we got some prototypes made and started shrinking the circuit down to a manageable size.

Despite Robert’s suggestion above that he tweaked the Octoverdrive to our beta team’s specs; the production unit is remarkably close to his original prototype, and the entire control complement and functionality of the pedal wound up crossing over from his original design.

The next, and perhaps most difficult task, was to come up with a product name worthy of the TWA brand that simultaneously described the function of the pedal.

I felt that Robert’s original Steam Punk moniker was a little too confining, as we would have to dress the pedal in that style in order for it to make sense.

This is where TWA co-owner George Schwab comes in.  George is mostly a silent partner, but when he gets an idea he loves to share it with me and I’ll store them away for (hopefully) future use.

Since we’re both of German descent, George had pitched the idea of an Oktoberfest pedal.

I kept spinning that around in my head and eventually that morphed into Octoverdrive, which made perfect sense since the pedal was both an overdrive and an octavia.

Last but not least came the LED array, and what says October better than a Jack o ‘Lantern?!?

Will Sapanaro came up with the creepy-yet-cute graphics that now adorn the Octoverdrive, and a new Halloween legend was born.

We actually wound up sitting on the Octoverdrive project for over a year, as we just couldn’t pull things together in time for an October, 2022 release date.

This year we decided that, come hell or high water, the Octoverdrive was going to get released for Halloween 2023, so here it is!

I hope you enjoy this pedal as much as we enjoyed creating it, and I hope you create music with it that’s as unique and intriguing as this pedal’s origin story.



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