An actual resonant lowpass filter

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metasonix
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An actual resonant lowpass filter

Post by metasonix » Wed Apr 25, 2018 10:36 pm

For a couple of years I've been struggling with the design of a usable LPF that is capable of resonance and is all-tube. As you have been lectured before, there is no "prior art" in this area. Pls do not listen to nerds babbling about the Novachord or whatever. This kind of thing just didn't exist until monolithic opamps became available.

So by taking a different tack and working from the lowpass gate circuit, I've finally put together something that resonates. It's boiled down to the minimum possible: one dual triode, two vactrols (or a dual), and an audio transformer to invert phase. Part of what Metasonix is all about is to make "1950s voltage controlled circuits" that did not exist before, and this qualifies. No semiconductors at all except LEDs in the vactrols.

This circuit is totally new. Theoretically I could patent it but patents are horribly expensive and sales of such a device will never pay for the legal fees. Perhaps I should put the schematic on a t-shirt with a "Copy this, fuckers, just remember I invented it" slogan or something.

It's a two pole filter and only resonates at higher frequencies, but it could be used in a monophonic synth. The Polivoks filter wasn't very "nice" and neither was the Wasp filter. People have cloned those before. So there.
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Post by Don T » Wed Apr 25, 2018 10:42 pm

Cool! I'd like to hear it, but I do have to say that I LOVE that proto-board! I'm assuming that's your own design?

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Post by chvad » Wed Apr 25, 2018 11:06 pm

looking forward to hearing it!

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Post by ritchiedrums » Wed Apr 25, 2018 11:30 pm

doesn't a NICE polivoks put this in moog tone territory?

I would love a tube polivoks filter!!! :woah:

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Post by xthrasherx » Thu Apr 26, 2018 12:14 am

I know prototype and all that fun stuff, but any ideas on rough panel size (assuming eurorack)? Also looking forward to hearing it :mrgreen:
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Post by Yes Powder » Thu Apr 26, 2018 2:06 am

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OMGSAMPLESPLZKTHXADOPTME
metasonix wrote:Perhaps I should put the schematic on a t-shirt with a "Copy this, fuckers, just remember I invented it" slogan or something.
I'd buy one!

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Post by appliancide » Thu Apr 26, 2018 7:20 am

Yes Powder wrote:
metasonix wrote:Perhaps I should put the schematic on a t-shirt with a "Copy this, fuckers, just remember I invented it" slogan or something.
I'd buy one!
XL for me please.

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Post by EPTC » Thu Apr 26, 2018 9:08 am

Love your work, Eric - This is terrific news.
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Post by luchog » Thu Apr 26, 2018 12:05 pm

Very cool. I would definitely love to have one of these sitting next to my Polivoks clone.

Will it have voltage control over resonance? IIRC the IME Polivoks clone that I have does not have vc resonance control, only manual. What tube does it use? A out-of-production NOS, or one of the in-production tubes like the 12AX/AT/AU7s?
appliancide wrote:
Yes Powder wrote:
metasonix wrote:Perhaps I should put the schematic on a t-shirt with a "Copy this, fuckers, just remember I invented it" slogan or something.
I'd buy one!
XL for me please.
Same, and on a black tshirt if you please. Have to keep up my Goth image.

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Post by Yes Powder » Thu Apr 26, 2018 12:51 pm

Guize, I don't think it's a tube Polivoks. I think he was just using it as an example of a non-nice sounding filter that people have cloned.
metasonix wrote:This circuit is totally new

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Post by metasonix » Thu Apr 26, 2018 8:45 pm

Yes Powder wrote:Guize, I don't think it's a tube Polivoks. I think he was just using it as an example of a non-nice sounding filter that people have cloned.
metasonix wrote:This circuit is totally new
Not a "tube polivoks", totally new and original. Might act a bit like a Polivoks filter. That's purely accidental.

The Polivoks sounded weird supposedly because it uses programmable opamps in a way you rarely see in vintage OR modern gear. Personally I think it's just a "cheap hack" sort of design. Actually quite clever, no capacitors except for the parasitics in the chips. Ask Marc Bareille.

It still amazes me that non-Soviet people liked that synth, long after production stopped. Americans never even heard of it until examples started to sell on eBay and in specialty shops in the late 90s. Its filter has been cloned at least a half-dozen times.

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Post by ritchiedrums » Thu Apr 26, 2018 10:00 pm

Well I’m really looking forward to WHATEVER THIS IS!!!!

:guinness:

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Post by lisa » Thu Apr 26, 2018 11:56 pm

It would be really interesting to hear it. :party:
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Post by metasonix » Fri Apr 27, 2018 1:44 am

Here is a short demo using a drum track and then a square wave:

https://soundcloud.com/metasonix/lpfdemo1wav

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Post by Yes Powder » Fri Apr 27, 2018 3:08 am

Very nice :beer:
I'll definitely be buying one as soon as it's available— whether or not I've gotten another case by then...

I've already picked out which of my current modules I'll sacrifice to make room for this!

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Post by ritchiedrums » Fri Apr 27, 2018 9:13 am

:yay: very cool!

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Post by luchog » Fri Apr 27, 2018 10:08 am

Sounds good, definitely going on my list when it comes out.

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Post by EPTC » Fri Apr 27, 2018 11:13 am

metasonix wrote:Here is a short demo using a drum track and then a square wave
That's really interesting! Almost sounds like a wooden resonating box, especially on the square wave - makes other resonant filters sound much more digital or artificial. Would love to work with this!
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Post by lisa » Fri Apr 27, 2018 12:14 pm

metasonix wrote:Here is a short demo using a drum track and then a square wave
Nice! I could do cool things with that. :omg: ETA?

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Post by metasonix » Sat Apr 28, 2018 3:25 am

lisa wrote:ETA?
2-3 months probably. It's that whole fighting-with-suppliers thing.

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Post by EPTC » Tue May 01, 2018 8:04 pm

metasonix wrote:2-3 months probably. It's that whole fighting-with-suppliers thing.
Man I don't think you get enough credit for how freaking quick to market you bring your stuff out. That's awesome.

RK format? Any CV control of the resonance? (looks like maybe not? a dial and one input/output from your example) - I can't wait.
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Post by Robscorch » Tue May 01, 2018 8:22 pm

MY god this thing is wonderfully brutal. :omg: This needs my horsecock and needs it stat
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Post by Mephitif » Tue May 01, 2018 8:41 pm

:hail:

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Post by FatRocky » Wed May 02, 2018 9:57 am

:fap:

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Post by otoskope » Fri May 11, 2018 8:14 am

Great news, Eric! Looking forward to see/hear it as a module. RK format? I put it on my list!
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