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The Harmonic Valve

2012 November 29

Copy of 494

Harmoninc Valve(?)

Ok, more capricious wordplay*.

The ‘Harmonic Valve’ is a vacuum-tube-based VCF. The core circuit was inspired by a very nice design from Rene Schmitz, in combination with a few very helpful ideas from Ken Stone. I added a feature that also does some voltage-controlled tube-clipping.

The gizmo is huge , about the size of a toaster oven,  and it’s sound is distinctive and rich with the even harmonics that , to paraphrase little Richard, makes the big toe of tube-sound aficionados shoot right-up in their boot!  It also has plenty of circuit points carrying lethal levels of current…

I started this project with a bit of macho swagger in my step. My earliest instruction in electronics came from hams from my parent’s generation. These guys*** all came from the WWII U.S. signal corps and cut their teeth (often, LITERALLY)  on 400VDC plate voltages. Every one ’em strips wire with his teeth too. (this imparts the bonus of getting to spit at the floor a lot! Hot Dog!)

After building this behemoth I must sheepishly report that the subsequent generation has gone a bit soft.

I have, anyway.

The process of experimentation, development and prototyping was a protracted white-knuckle ride for me.  I was very nervous about the exposure to lethal juice. My work area and more pointedly, my working-habits evolved very ‘organically’ , and they did so in an environment wherein a dropped tool  might short out  low current at 30-volts (max) and damage some gear but never with the risk that such a boo-boo might turn lethal. Admittedly this is attributable to the slack that I indulge in my methods. Working-up a tube circuit left me  too nervous to have any desire for further explorations. I’m content with this cowardice because I do this as a means to play my music not to prove that I have testicles of steel. (which are perilously conductive, incidentally)

The sound is terrific but the DIY path to get there is just a bit too well-paved with anxiety for me.

If you are enthralled by the idea if analog synthesis using vacuum tubes I wholeheartedly recommend the work of Eric Barbour at Metasonix. I’m very enthusiastic about the idea that I can enjoy the unique sonics of tubes while paying Eric to assume the risk  to his testicles of steel.  Next time I get the tube-itch, Metasonix is where I’m going!




*a’ la Harry Partch.  I LOVE Harry. I love his music, his iconoclastic engineering**, and the commensurately iconoclastic use of language in the imaginative naming of his astonishing creations.

** keep in mind-  The Watts Towers are still standing…as of the 21st century, in one of the most active earthquake zones on the continent! Viva Amateurs!

***sorry ladies, but every one of them I ever met is unmistakably male!

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