Re: [motm] Panning VCAs - a different approach
2004-09-12 by J. Larry Hendry
OK, I'm gonna step up to the plate on this because it has been something I have been thinking about for a while. I'll say what I think a good panner fader should do. Then, I will offer a very inexpensive solution in my mind that can also be a useful utility module when not in use as a panner fader: What should a panner fader do: - Use a single input signal - Allow each control to be annenuated for desired effect and vaioed input out requirements. - Allow each control to be biased to contol the amount of signal overlap, or lack there of in the pan / fade - Support different response curves. - not add a lot of real estate for specialized VCAs. So, while Paul's does plan a MOTM-130, which I will own, I have another suggestion. Instead of creating a VCA fader panner, create a fader panner control voltage module. This single 1U wide module would work with your external control signal and not act as a VCA, but instead process the control signals into the format desireable to control your already existing quaility VCAs. Unless I am overlooking something completely obvious, the processing of the CV signal is no more than how much gain and how much offset. And, if you use a single input, you want an internal inverter for the second CV processing. So, the module looks like this: 4 knobs and 4 jacks. It is a CV processing module. The 4 controls are offset A, gain A, offset B, gain B. I'd probably make all 4 controls reversing. The gain of each is 2.0 so you have the flexibility to take 5 volt signals to a full 10 volt swing or attenuate a 10 volt signal to 5 V. The offset is probably +/-5 volts. 2 of the 4 jacks are the 2 CV ouputs that go to our VCAs. One input jack is required. for A and B. A forth jack could very easily be the B channel input normalled from A so that for panning and fading, only one input source is required. Or, a forth jack could be an output that was equal to A+B. In this case a 3rd voltage is generated that represents a voltage that could be used "fill in the gap" between two faded signals or just the opposite. The advantage of the B input jack is that this module is now a neat little 2 channel CV processor that can be used anytime you want to bias or attenuate or apply some gain to a CV in a 2-in, 2-out format. The advantage of the A+B output is a unique 3rd CV so that a 3rd VCA can be entered into the equation in some creative fashion. Real estate does not support 5 jacks. So, that is my 2 cents on the subject. This would be a simple module to construct. Essentially if is a handfull of op amps wired up in the correct configuration. You put one of these next to a MOTM-190 and you have panning fading with maximum control in only 2U. And, you get to take advanage of VCAs you already own, Larry H (seeing a Stooge panel run for a simple CV DIY processor module).