Elby Designs + Paula Maddox MonoWave

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Paula of course is the woman behind Modal Electronics, and previously, vacoloco.

"Old Nik says: "The MonoWave(X) is a early GEM from Paula Maddox... The unknown (to many) ancestor of the Modal Electronics 001/002! It's super! Think PPG Wave and Moog Model D had a baby, and that is the MonoWave(X)..."

Manufacturer Description:
The Monowave was the brainchild of UK electronics designer, Paula Maddox. Paula has been designing and building synths for many years as well as releasing her own unique music realized on her impressive modular creations.

Paula wanted to build a synth the roots of which lay in the PPG. Originally intended as a monophonic bass synth, the Monowave has uses beyond that.

The Monowave is a wavetable synthesiser with 256 waves available for each of the two oscillators. Each oscillator also has a sub-oscillator. The filter is a copy of the Moog filter, there are separate envelope generators for the filter and amplifier, and a simple LFO. The panel is very 'retro' and 'traditional' with knobs for every function and a simple display. Internally, the circuitry is all analogue (except for the digital circuitry used in the oscillators)... no wimpy DSP thank you very much - this is a 'real' synth!!

Paula has now released the MonoWave as GPL and has given me permission to release the PCB and a Component Kit for those that unfortunately missed the first, limited run.

The new MonoWave (X) is a rebuild of Paula's popular MonoWave I and is being re-released with her permission. The new design reduces the original multi-pcb design down to 2 pcbs.

In addition, the front panel design incorporates a 2x16 LCD Module (the original MonoWave only had a 1x16 Module) allowing software developers to extend the user-interface.

Technical Information:
Envelope Generator's (VCF-EG & VCA-EG)
These are the same as the design in Modulus 8, these are compact (needing only two chips) simple to use and fast.

MIDI to CV
Again Paula went for simplicity, with a little modification to the scaling , you could use it to generate a CV/GATE output for another 1V/Octave synthesizer. Two DACs are used, U403 holds the NOTE CV, U402 the Velocity CV and U406 has the GATE signal. When the main CPU writes the NOTE value, the MSB is also the gate value (note data on midi is only 7-bits wide).

VCA1 & VCA2
These again are based on a Modulus edition. The VCA uses a CA3046, this is configured as a Gilbert Multiplier and gives a superb SNR!

VCF
No secrets here, its a Moog Ladder clone. Giving 24dB/Octave cut off slope. This was based on TomG's adaptation of it and includes some modifications by Paula.

Wave Generator
Ok, now we start showing some secrets. Essentially the wavegen is just an EPROM feeding a DAC, nothing more. The secret here is the set of NAND gates on the address lines. What these do is allow you to DROP the resoloution from 256-bytes per cycle to 64-bytes per cycle and hence give you a whole stack more harmonics and aliasing.

Oscillator1 and Oscillator2
Some more secrets now, the oscillators. Again, nothing too radical, The main oscillator is the ATtiny2313 micro, This feeds a 4024 to allow octave selection. This, in turn, feeds a 4040, Q0-Q7 give the 8-bit address needed for the Waveform (Q0 is the clock into the 4040), Q8 gives us the sub oscillator. Also the waveform selection latches are shown in these drawings. These 16-bits are then fed to the wave-generator circuit.

CPU
Nothing too major here, you can see the main CPU, LCD interface, Interface to Buttons and also MIDI. The MIDI interface is fully MMA compliant. The LCD has been upgraded to a 2-line display. U203 is the latch used for reading the buttons (to see if they are pressed or not) as this PORT on the CPU is used for other things it needed to have an output enable, the NAND gate ensures that when you want to read it, it latches the data (positive going edge clock) and then enables the outputs (active low enable), simplifying the interface to the CPU.

ADC's
Here the ADC schematic is straight from the datasheet. The ADCs are self clocking and the CPU just reads values every so often from the ADCs internal latches.

Power Supply
The MonoWave(X) requires an external well regulated +18VDC supply."