12 volt tube Voltage Controlled Filter schematic

[frequencycentral]

Found this on a Dutch synth DIY site last night: 12 volt submini pentode VCF.



How do you fancy a tube Dr Q, or a tube FSH???

I just ordered two 5672 submini pentodes off a French ebayer. Hurry! Stocks are low!

[mattthegamer463]

Hey Rick, I know I'm exhuming the body of this thread from the bowels of the forum, but it just became relevant to my interests.

Did you ever test this circuit out, or did it ever lead to one of your other designs?

I'm looking for "something different" in a new pedal build, and I don't know what to do.  A Voltage Controlled Filter sounds interesting, but how is it different from a tone stack?  You would need to feed it with a LFO for it to sound interesting, and then, is it different from an auto-wah type effect?

I've got some 5672s that need a home so I'm quite interested in this.

[frequencycentral]

When you break it down it's actually a transistor twin-t filter with a tube buffer and a resonance loop. I never did breadboard it, though it gave me a few pointers as to how to use 5672 - and how not to, as the 275R resistor is really starving the heater, which ideally wants 220R (1 watt). There was a thread on electro-music about it, though it's had no action for a while: http://electro-music.com/forum/viewtopic.php?highlight=tube+vcf&t=23067

A static filter can be useful (think stuck-wah). But voltage controlled filters really come into their own when being voltage controlled, in guitar applications an envelope follower is the most common, though LFO and sample and hold sound great too. IMO, this tube filter isn't going to sound as good as a LM13700 type filter, probably closer to a stuck-wah than a Maestro FSH, but you've actually garnered my interest to maybe find time to finally breadboard it.

One thing this filter did do for me was make me buy 5672's, which is I still use in Murder One.

[mattthegamer463]

Thanks for the quick reply.

Interesting stuff, I'm interested to hear your thoughts if you do end up prototyping it.  I'm going to give prototyping your Delirium Tremolo and Red Star Drive a shot over the next two weeks (one of which is loaded with exams) and see how I like them.  Thanks Rick!

[mattthegamer463]

Just found this on that electro-music.com forum, I assume you've already heard the MP3s on this site but just in case you havent:

http://www.electricdog.eu/

In there you'll see the "mean sucker VCF" and it sure is mean...