I got a request to show how band level controls can be added to the project. Here are some illustrations and some explanation.

I am illustrating the idea of how to do this by explaining the procedure for adding a level control for the 3330 Hz. highpass. You can add a band level control to any or all of the bands by doing the same thing on any channel. To do this you need to carefully desolder and remove (unless you have a replacement) the capacitor that couples the output of the band's VCA to the band's mixing resistor. For example in the case of the 3330 Hz. highpass filter the coupling capacitor is C30 (10nF ceramic cap). The direct output of the 3330 Hz. highpass channel's VCA (U6B pin 9 which was formerly connected to C30) must now be connected to one side of the 100K level adjust potentiometer (the other side of which should be connected to ground). Bend the lead of the cap you intend to use for C30 out to the side so you can stick it into the PC pad opposite of the pad connected to U6-B pin 9 and have the other lead sticking up. Solder the wire from the pot wiper to the capacitor's lead which is sticking up. Voila - you just added a level control to the 3330 Hz. highpass channel. The shorter the wire runs to the pots the better.

Here's a list of which capacitor is the main buss coupling cap for each band.

Band Frequency	Coupling Cap Designator	Value
3330	C30	10nF
2546	C48	10nF
2001	C55	22nF
1495	C72	22nF
1013	C79	33nF
720	C96	33nF
542	C103	47nF
395	C120	47nF
285	C127	47nF
208	C144	47nF
154	C151	.1uF
101	C168	.1uF

Schematic Details

PC Board Details

This image of the PC board shows the position of the caps that are affected when adding level controls for the 3330 Hz. highpass channel and the 2546 Hz. bandpass channel. The pad formerly used by one side of C30 now goes to one side of the potentiometer. The other side of the potentiometer is grounded. The wiper of the potentiometer must be wired to the side of C30 that was formerly connected to pin 9 of U6-B. Bend the lead of C30 out at a right angle and insert the cap's bent lead into the PC pad opposite of the side that connects to the VCA's output. Solder a wire from the pot's wiper to the cap's other lead. The shorter you can make the wires the better. Running coax from the pot's wiper to the PC board will probably reduce noise pickup. I would ground the side of the coax at the panel and only connect the center conductor on the board side.

More PC Board Details

This is what I mean by - bend the lead of the channel's coupling cap (C48 in this case) out at a right angle and insert the cap's bent lead into the PC pad opposite of the side that connects to the VCA's output. The wire from the wiper gets connected to the cap's remaining lead. The cap's former pad now goes to one side of the channel's level pot.

You must ground the correct side of the pot for it to work normally. An easy way to determine which terminal to ground is to hold the pot in front of you - shaft toward you and terminals up. Turn the pot's shaft all the way down (counter clockwise). The terminal that the wiper is now closest to is the one you should connect to ground.

I got a request to show how part of the vocoder's circuitry could be used to control light controllers that translate 0 to 5V signals into light intensity. This application takes an audio input for the Control input buffer and then runs that signal through the vocoder's filters. The output of each filter's envelope follower is a control signal that goes from 0V to +5V depending on the audio energy in each band. The 0V to +5V signal is then used with a light controller for each band.

Most of the circuitry of the vocoder is not used in this application. Only the control audio input path, control filters and envelope followers are used in each band. Neither the VCAs, audio signal path filters, noise source or internal oscillator are used in this application. The PC layouts show the components necessary for this functionality. The grayed out areas indicate components that are not needed in this application.

Schematic Detail Page 1 Changes

As shown here the great majority of the components are not necessary for this application. Only the control signal buffer amplifier and bypass caps are needed from this page of the schematic.

Schematic Detail Page 2 through 8 Changes

Here we see how each band is modified so that the control signal goes through it's filter and envelope follower but the audio signal path components and VCA components are not used. The two diodes in each envelope follower must be reversed from the original configuration as shown. Whereas the original vocoder circuitry had the diodes arranged to give a negative going envelope voltage, the light controllers need 0 to +5V which is why the diodes are reversed from the original circuit.

To ensure that the control voltage does not exceed 5V a 1K resistor into a 5V zener diode is used at the output of the envelope followers. The control voltage signal is then taken from the junction of the 1K resistor and zener diode's cathode.

PC Board Details

This image shows the components that are not necessary when building the light controller application as grayed out. Additionally the 1K resistors and 5V zener diodes are shown installed using donut pads from formerly used components. Each of the bands must be modified in the same manner.