søndag 11. august 2019

VCO and Digital sample player

It's that time of the year again - I'm on vacation in Nordfjord and finally have both the time and the energy to think about the XM8 project.

Some days ago I did a CEM3340 circuit design based on the data sheet and the implementations found in the Prophet 5 and Memorymoog, as well as others, found on https://electricdruid.net/cem3340-vco-voltage-controlled-oscillator-designs/. I have yet to test the circuit, but it has the following features:

- All three waveforms
- Soft sync
- FM modulation
- +/-5V waves
- Pulse wave hysteresis
- HF tracking and osc scale trimmers

I will try the circuit using the AS3340 come fall. I also need to see if the circuit has any issues with PWM affecting pitch, it is mentioned both in the data sheet and elsewhere, for example here.

Untested circuit



Next up is the digital oscillator/sample player. It should be able to do both sample playback (for sampled attacks, D50 style, and sampled waveforms like the PPG and Waldorf synths. Some keywords/ideas: Pitch changing using FFT, needs 24 bit for good quality. Use stereo dac, allow separate outputs to each of the output busses.

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