Where can I get a Eurorack VC EQ w/Frq knob?

[Argitoth]

I need a voltage controlled EQ with variable frequency and with a CV for that variable frequency... basically like a filter except it doesn't filter, it only boosts.

[flts]

Cwejman VCEQ3 would do that: http://cwejman.net/cwejman.net/vceq-3.htm

I didn't check the price but practically all of the Cwejman modules cost hundreds of dollars / euros, so it won't come for cheap - maybe there's a lower cost solution available.

[Argitoth]

Man... yeah it's $600. I was hoping for more like a $100 solution!

1 BAND EQ

1 input
control width
control frequency
CV frequency
1 out

Wait, isn't there a way to do it with a filter?

Osc --> BP filter --> out
Osc --> out

[futuresoundsystems]

You can get 1 Band EQ stuff easily with a BP filter yes, but to start subtracting frequencies from the original signal, you'll have to invert either signal then mix it back in.

[flts]

Yeah, thing is, all EQ circuits are just filters. I guess the distinction people commonly think of is just kind of "well, filters are the types of circuits in synths meant for more radical creative sound shaping, and EQs are similar circuits that are tuned to making more subtle adjustments to mixes"... To simplify it a bit.

By toying with applying gain and summing, you'll get a simple 1 band solution pretty easily.

[felix]

The other thing is EQs typically are flat in frequency response outside of the adjustable frequency bands.

For example, a 1 band midrange EQ leaves all frequencies outside of it's 1 band range (say 500hz - 5k) unaffected. Where as a bandpass filter is going to attenuate all frequencies outside of it's band range. It's similar in principle, but yields a different sound.

Since you mentioned getting into electronics, you could easily make a "tone stack" like ones used guitar amps. They are very simple and usually don't consist of more than a couple pots, resistors and capacitors. The only tricky part is voltage control, which you could achieve by coupling a LED and photo resistor. The LED will light up on incoming voltage which will change the resistance of the photo resistor. Only problem is there is no negative polarity.

Caveats yes, but I thought I'd throw that out there.

That being said you can do some really cool things mixing different filtered outputs of the same source. For example like futuresoundsystems mentioned, mixing in a phase reversed BP signal to the dry un-filtered signal.

Something like the plan b M12, which has BP, LP, HP, and All-Pass outputs and a Doepfer A-138c mixer (which has bi-polar knobs for phase inversion) could yield some very interesting.

Again, not exactly what you are looking for (and would be about $300 together) but just another idea.