Hello Mark,
> A quick couple of questions, for which there is no rush for an answer....I saw in the hints
a tips Grant mentioned that a 5V gate on the Classic VCO and WC won't fully open the
VCA on those units.
>
> 1. I have a Kenton convertor that gives 5V or 15V (no 10V). Is 15V safe for the
oscillators gate?
The "Attack-Release" generator on the Classic VCO and Waveform City is a hybrid of an
envelope follower and an envelope generator. If a gate is just a step function, 0 to 10 volts
and back to 0 again. Then by slew rate processing that signal, it will naturally make an
attack release envelope.
To make an envelope follower, you need something to remove the negative portions of the
analog audio, otherwise that average of the + and - is zero.
The Gate input has a current limiting resistor and a 10 volt zener diode at the input. When
processing a normal 10 volte gate, the device is not even activated.
When processing audio, it removes the negative portions of the audio signal, in what is
called "have wave" rectification. Not an ideal envelope follower, but a usable one essentially
for free.
In you case of a 15 volt gate signal, it will "chop off" (limit) the signal to 10 volts, and the
output envelope will be 10 volts, just what you want. There should be no problem using
the 15 volt gate signal, it will be converted safely to a 10 volt envelope.
>
> 2. Presumably the Envelators (with the envelope generated into ZMOD of the Mixolator)
 are fine with just 5V?
The ARP 2600 was such a well thought out synth that I actually divide synth history to
before and after the 2600. It is not completely perfect, but it was the first one to get
almost everything right. Two well know problems are
1. DC offsets on the audio which causes "thumping" with the filter and VCA
2. The envelope trigger voltages (once you modded the unit to get at them) had six volt
thresholds. So you could not take your shiny new 808 or 909 or 606 and run the
envelopes from the rhythm box external triggers. There were work arounds but it was
clumsy and a repeated pain. And you really did want to link your rhythm box and
sequenced synthesizer together, oh yes you did. Just trust me on that.
So in the design of the Wiard modules, trigger threshold were set to work with TTL (5 volt)
technology like the rhythm boxes from the 80's, and other modern stuff that uses 5 volts.
The thresholds are nominally set to TTL "High" which is around 2.5 volts.
So a 5 volt gate or trigger will work fine with the Envelators. All the Sequantizer inputs
also have this 2.5 volt threshold, Step, Reset, Glide, Octave + and Octave - should work
just fine with patched out 606's and other rhythm boxes.
They will also accept clock, gate and trigger sources from Serge modules in general and
the TKB in specific.
But that is only the beginning of the story. Here is the deep stuff.
Morton Subotnick worked out an advanced synthesizer technique on the Buchla he call the
"player piano" technique. Normally a tape recorder can not store the very low frequencies
that are the control signals humans generate as control signals when we "play" a
synthesizer.
Subotnick brilliantly came up with a work around using AM (amplitude modulation). All
that requires is simply controlling the amplitude (volume) of a simple "carrier" wave and
the very slow signals are stored as variations in the volume of the carrier, and can be
recorded on magnetic tape.
Upon playback a simple "decoder" recovers the control signals from the amplitude
variation of the tone recorded on the tape.
To "encode" the signals you need a sine wave carrier from a VCO followed by a Voltage
Controlled Amplifier (VCA) then going to the tape recorder. The control signal to be
recorded is used to control amplitude (volume) of the carrier (VCO sine wave) as it is
recorded to tape.
In the Classic VCO, to record a control signal with a 0 to 10 volt range, patch the SINE
output to the VCA1 input, set the "VOL" knob to zero, patch the VCA OUT to the tape
recorder input, patch the control signal to be stored to the VCA ENV jack.
To record control signals that have negative voltage portion, just advance the VOL knob
until the most negative excursion, just shuts the VCA off.
Most any VCO frequency (pitch) will work, but since we only have "half wave" envelope
following, a higher frequency like 1 kHz will give the best results in terms of the "ripple" or
error signal generated by the "decoder" during playback.
As you have probably guessed, the "decoder" for an AM encoding technique is an envelope
follower. The "Attack" and "Release" controls are used to modify the control signal after
recording. Normally, another unit called a "Gate Extractor" is needed to interface the
incoming envelope follower signal to trigger onboard envelope generators.
The low threshold voltage on the Envelators and "forgiving" design of the Envelator GATE
input, allow direct connection of the AR ENV output to the GATE inputs with only some
tweaking of the Release control needed to get a repeatable envelope trigger. A "Gate
Extractor" is optional for use of the AM encoding technique on the Wiard instrument.
I hope this explanation will help to clarify why the "AR" generator on the VCO modules
does not precisely follow the trigger thresholds and behavior of the Envelator and
Sequantizer modules. Some compromise was needed to allow the Classic VCO to be used
as a self contained "channel" for the play piano control voltage storage technique.
The ability to record and store long complex controls signals, which can then be brought
back into the instrument and used like "live" playing signals is extremely powerful. It
allows you to use all the modules to generate the complex control shapes, and then the
same modules can be repatched for use at audio frequencies, this doubles the
effectiveness of the the instrument. It also allows the player to have both hand free for
"knob twizzling" and other techniques which add dynamics and expressiveness during
playback. Essentially the ability to "conduct" the stored performance.
Thanks for reading and have a Happy Holidays
Grant Richter