Serge Wilson Analog Delay
The CGS208 WAD module is a recreation of the Serge Wilson Analog Delay module.
The schematic of the Wilson Analog Delay. Click for larger view
The component overlay for the VER1.0 PCB.
Connections to jacks can be established from the schematic diagram
There are two variants of the vintage WAD. Both use the same PCB. The only difference is the value of some resistors.
The following readings were taken from a working late model GENUINE WAD.
Very Important: before power is applied, turn Trimmer B fully clock-wise. Failure to do so before power-on may damage the 3080s.
The following tests are to be done without the Analog delay chips installed.
Despite the above, as I was taking readings from someone else's working WAD, my tests were performed WITH the SAD1024 still in their sockets. The test document also assumed the board was not connected to any panel controls, where here it very clearly is. The only real differences this makes is instead of injecting external voltages into some pads, you adjust the pots to set the voltages. Initially the pots are set to output 0 volts. For the Filter frequency, this means turning it fully CW. For the Delay pot, it means setting it to the center of its rotation.
VC clock tests
1) check for a square wave at 15000 Hz +/- 40% with a 0 to +12 Volt amplitude at pins 4 and 12 of the 4050. (The period of the wave may be anywhere from 50 through to 70 through to 100 microseconds). If you do not get a square wave +/- 10% duty cycle, then check the CA3046.
2) check for pulses about 1.5 microseconds long (at 15000 Hz) at pins 10 and 4 of the 4093.
If these tests fail, check components in the VC clock section of the PCB.
Input VCF tests
1) feed the square wave from pin 12 of the 4050 into pad L (the input). The output at pin 1 of U3 should be almost a sine wave of about 5 Volts peak to peak. Adjust trimmer A if there are flattened spots on the wave. (If test 1. fails and the sine is more or less than 2.5 Vp.p check resistors and caps in the input VCF section.)
2) Input a variable voltage of 0 to -5 Volts at pad P and check that varying the voltage results in a smooth and undistorted attenuation of the sine wave.
3) Connect a voltmeter to the output as above (pin 1 of U3).
Disconnect the VCF input and CV.
Measure the voltage. Input +12 into pad D.
+6 volt regulator check
Negative volt regulator check
Test of the dual S&H sections and the output low pass filters.
1) Take a 2000Hz sawtooth (0 to +5) straight from a VCO (e.g. the blue jack of a PCO) and feed it into pin 3 of U16 (CA3080). Use a 1k series resistor between the VCO and the chip to protect it. Check for a stepped replica of the saw at pin 1 of U4. (The bottom of the sawtooth wave will be flattened out.)
There are two waves superimposed on each other here. Both are set with the center line being 0 volts. Sync is being taken from the triangle wave (input). The stepped wave at P1 of U4 appears to be affected by some sort of jitter here, possibly via some feedback from the SAD1024 via another part of the circuit. Without the SAD1024s installed, the wave would probably be clearer. Note that P1 is sitting well above 0V, centered roughly around 4V
2) Now connect the scope to pad A and check for a rounded version of the saw. You may have to adjust Trimmer C to center the trace (around 0V). Repeat step 2 of the "Input VCF Test" above, but check for a progressive attenuation and filtering of the sawtooth wave at A.
Feed a sine wave of about 200Hz (via a mixer) to input pad L. Monitor pin 12 of U13 and adjust Trimmer A until the (clipped?) sine wave is well centered (around 0V). Using the mixer, drop the amplitude of the sine wave until it is just barely clipping, and readjust Trimmer A for most symmetry.
Now monitor pin 7 of U4. Adjust Trimmer B for the most symmetrical sine wave. As above, you may need to adjust the amplitude of the incoming signal to be able to successfully adjust this trimmer.
This is the signal at pin 7 of U4.
If there is no signal at pin 7 of U4, monitor the outputs of the SAD1024 chips, one stage at a time, starting with pins 12 and 5 of U13, and pins 12 and 5 of U14. Also check the resistors in the analog delay section.
Final musical tests should be done with a short transient sound at a 2 per second repeat rate, with a 100Hz saw into a VCA. Feed CVs into the proper inputs, check ranges and proper filtering action, check the flanging output (pad E). If this doesn't work refer to the S&H, LP filter and output flanging sections.
This module is designed for +/-12 volt operation.
This is a guide only. Parts needed may vary with individual constructor's needs.