Wiardgroup

The Wiard Classic VCO and Waveform City modules contain 
circuits with knobs labeled Attack and Release. In the case 
where the Gate input is fed a clean 0 to 10 volt gate signal, the 
output of the circuit will look like an Attack and Release envelope.

This is not and actual envelope generator, but a bi-directional 
slew rate limiter. Labeling it like an envelope has caused some 
confusion.

An actual envelope generator would have an input comparator 
that forces the envelope ouput to 10 volts, no matter what the 
input Gate voltage. The installed circuit does NOT have this 
comparator.

This has casued problems when interfacing to MIDI to CV 
converters that output a 0 to 5 volt gate signal. The output 
envelope amplitude is then only 5 volts and the VCA has only a 
30 dB range rather than a 60 dB range.

Also, the exponential decay of the envelope produces a long tail 
which keeps the VCA open and appears as VCA bleedthru. The 
VCA is working properly, the envelope voltage is not going to zero  
rapidly enough to completely close the VCA.

There are a couple of work-arounds for 5 volt gate MIDI to CV 
units:

1. Use a different envelope generator with 5 volt gate units. (The 
Envelator has an input comparator set to 1.5 volts for use with 5 
volt TTL level gates/triggers such as Roland Drum Machines and 
Kenton MIDI to CV converters. The Roland MPU-101 MIDI to CV 
converter generates a correct 10 volt gate and was used for 
circuit testing, along with an ARP 2600 keyboard. The use of a 5 
volt gate directly into the AR module was not anticipated)

2. Process the 5 volt gate signal with a gain offset module (such 
as the excellent Blacet Mixer Processor) so that the gate signal 
is compatible with the slew rate limiter input. Summing a 5 volt 
signal twice, doubles it's amplitude to 10 volts allowing 60 dB 
range. And the gate signal can be offset negative to "clip" the 
exponential tails and make the envelope more percussive, and 
assure complete shut off of the VCA between notes.