MONOLITH
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МОНОЛИТ / MONOLIT is a radio message format used by the Russian Armed Forces. Each message contains a series of codewords accompanied by two 4-digit numbers. The codewords are matched to sealed envelopes,
which contain instructions to decipher the 4-digit codes.
Monolit transmissions are sent at the highest level of urgency and supersede all other communications.
THE VCO
Monolit is built around the Alfa AS3340 chip, a reproduction of the Curtis CEM3340 used in classic analogue synthesisers
including the SH-101 and Prophet-5. The Alfa and Curtis chips are almost identical so the circuit will work with either, but if you
use the Curtis chip you should swap the 51K pulldown resistor on the pulse output for a 10K.
The design is largely a combination of my favourite parts from Look Mum No Computer’s
Performance VCO
and the Skull & Circuits
Oscillator One,
with a redesigned octave switcher and voltage reference to accommodate 6 octaves.
FEATURES:
- Octave selector and 1 octave fine tune
- Linear and exponential FM
- Soft and hard sync
- Pulse width and pulse width modulation
- Triangle, saw and pulse outputs
BUILD NOTES:
- Don’t miss the trace cut hiding underneath the 620R resistor.
- The voltage reference is an LM4040AIZ-4.1. The A denotes a higher accuracy grade and 4.1 is the target voltage. This component is the hardest part to find so it is tempting
to substitute it for a regulator like the LM7805, but you shouldn’t do this as the voltage output from a regulator is not stable enough to maintain a reliable tune.
- Use a multimeter to match the resistors on the rotary switch as closely as possible. They are used to split the 5 volts from the voltage reference into single volt steps
which must be equal for the octaves to stay in tune.
- Daisy chain the grounds of the jacks and potentiometers together and connect the end of the daisy chain to the board at the wire marked GND.
CALIBRATING MONOLIT:
- Power up the oscillator and leave it for about 5 minutes to warm up.
- Plug your sequencer or keyboard into the V/Oct input. Start by playing a low note and the same note an octave higher, then move the scale adjust trimmer (VR1) until the interval
between the notes played by the VCO is the same. Repeat with 2 and 3 octave intervals until satisfied.
- With your sequencer or keyboard holding a single note, use the octave switch on the front panel of the VCO and the octave adjust trimmer (VR2) in a similar manner to set the
correct interval between octaves for the switch.
- Set the VCO to play a high note somewhere around 2kHz. Alternating between this note and the same note an octave higher adjust the HF Tracking trimmer (VR3) until the interval
between these notes is correct.
Monolit is now calibrated and ready to play. Program the notes below and baptise your new VCO with Deutsch Amerikanische Freundschaft’s Der Mussolini.
E1 | B0 | D2 | B0 | B1 | B0 | B0 | B1 | B0 | B1 | B0 | B1 | A1 | B0 | B1 | B0