[sdiy] LM3914/Voltage Controlled Electro-Optical Mixer Question

[Grant Richter]

This is the simplest possible circuit to do the job. There is no buffering
or other "luxury" elements. The design assumes a low impedance (~1K) drive
into all the Vactrols.

The actual current through the LEDs is set by R2 per the LM3914 datasheet.
There is enough voltage head room to series an indicator LED.

Use 10K as a starting value for R6.

The "VCAs" are just the simplest implementation of the Buchla 292 Lowpass
Gate, a Vactrol over an 18K to form a voltage divider. It will always have
attenuation. For unity gain, the op-amp could be a summing node with a
variable feedback resistor.

The "dither" amplitude controls crossfading between channels.

If you run it backwards with a single low impedance source routed to 8
outputs, it is an octal panner, but you have to add 8 x 18K and 8 voltage
buffers.

> From: "Fahl, Romeo" <RFahl at extensis.com>
> Date: Mon, 14 Jul 2003 11:24:53 -0700
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] LM3914/Voltage Controlled Electro-Optical Mixer Question
> 
> I'm planning on building a pair of Grant Richter's Voltage Controlled
> Electro Optical mixers soon.  Before I lay out the front panel, I'd like to
> know the following:
> 
> I'd like to add an LED to each input to indicate which input is active.  Can
> the the 3914s outputs drive an extra LED in series with the Vactrol LED to
> accomplish this? 
> 
> The original schematic is located here:
> 
> http://www.musicsynthesizer.com/Corpse/VCEOM.html
> 
> Thanks, y'all!
> 
> Romeo
>