Wednesday, April 21, 2010

MegaOhm Audio

MegaOhm Audio

MS20-style VCF
* FREQ - manual cutoff frequency
* RES - Resonance control (sometimes called Emphasis)
* Filter will oscillate once turned past 12 o'clock. FM 1 - level control for FM 1 signal

Controls for the second VCF are a mirror of the first.
Inputs and Outputs
Functions of the second filter's jacks are the same except where noted.

* LP - audio input for Low Pass response of filter
* HP - audio input for High Pass response of filter
* FM 1 - CV input for control of cutoff frequency
* The FM 1 jack for the LEFT VCF is normalled to the FM 1 jack for the RIGHT VCF. Plugging into the RIGHT FM 1 jack will break that connection. FM 2 - CV input for control of cutoff frequency
* RES - CV input for control of Resonance level
* OUT - Final output

Important Notes

First off, does this filter sound like the Korg MS20 VCFs? I don't know! I've never had the opportunity to play one. I have heard sound samples of other clones and have built a few other MS20 clone designs, too. They sound tame compared to these two! Though the others may sound "truer" to the original MS20 VCF sound, I find this circuit much more exciting.

Each module consists of two identical voltage controlled filters. Each VCF is completely independent of the other (except for the RIGHT FM 1 jack, which is make-and-break connected to the LEFT VCF FM 1 jack). The filters can be operated in parallel by mixing their outputs with an external mixer. They can be run in series by patching the output of one to the input of the other. Series connection will give a steeper slope.

The high pass input is interesting in that it can be used simultaneously with the LP input. Even more interesting is that this jack gives you direct access to one of the filter caps. If you "dummy" plug it, the cutoff frequency will change and the output signal will be boosted. If you then start turning the Res pot clockwise, the oscillations will become very distorted (and loud). Res pot full up and it's a huge, crunchy sound. Tell the guitar player to go home. :)

One more cool thing, you can influence the cutoff frequency by dummy plugging with a patch cord and then holding the other end in your hand. If you roll your finger (squeeze your hand shut, whatever) across the tip and sleeve you become the "ground" and the cutoff frequency dips down. It doesn't span the whole Freq range, but it can be used effectively to add a little (literal) "human" touch."

"Presenting a dual LFO module to fill your MU format needs.
Based on the LFO found in the MS20.

* Shape control varies the waveshape at the mult'ed Shape Out jack, from saw to triangle to ramp. Shape control simultaneously adjusts the width of the Pulse wave output.
* Range switch control. Runs from just under audio rate to a low of approximately 4 minutes per cycle.
* Reset input restarts cycle when signal rising is above 1V and is great for getting the LFO in time with drummers, beat machines, etc. The point where the wave will reset to is selectable via pcb jumper: Hi, Low or 0V.

Based on the LFO found in the ARP Odyssey

* Runs down to 30 seconds per cycle. Low Range jumper enables low times of approximately 2.5 minutes per cycle
* Sine wave and square wave outputs.

Many pcb jumper selected options (nine of them!) so users can easily customize their module to suit their needs.

MU format (will fit in and STG cabinets and rack frames)

Built with love and care in Chicago using high quality parts including:

* Switchcraft 112 jacks
* NKK toggle switches"

Delta VCF
"The Delta VCF is more than just a clone of the filter section from a vintage synth of the same name. All of the supporting circuitry has been changed and additional features were added.

Includes a high quality, independent VCA, so it's like two modules in one. Linear AC coupled FM input is rare on a VCF. At low settings it works well in adding depth to bass and horn like sounds. Some settings and input combinations produce wildly chaotic results. There is a wide variety of in-between sounds to be had.

MU format (will fit in and STG cabinets and rack frames)

Built with love and care in Chicago using high quality parts including:

* Switchcraft 112 jacks
* NKK toggle switches"
PDF on site.

more details including samples on site. You can find videos featuring MegaOhm here.

via this post on large format modules on Sequence 15.

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