Saturday, December 20, 2008

modified korg poly-800 synth / processor

The Poly-800 mkII includes a wonderful, warm (stereo) digital delay (with modulation!), a great-sounding VCF, three envelopes (one for each of the two oscillators and one for the noise source/VCF), and an LFO to modulate filter cutoff or pitch.

I've also added several well-designed modifications on this unit. First, it now has a VCF CV Input, which allows the filter cutoff to be modulated by a modular synth, CV pedal, or other signal generator. The input is designed to receive 0-5V. Clamping diodes and a current-limiting resistor ensure that voltages outside of that range will not harm the Poly-800's circuitry.

Second, I added an External Audio Input to the Poly-800's VCF and digital delay. The modulation delay provides great analog-type echoes, flanges, and choruses. Modulated filtering can also yield some very interesting effects.

This input is designed to work perfectly with guitars or other low-level signals. An added circuit provides the right impedance and just enough gain to boost such a signal, and a pot allows for attenuation before the gain stage.

The Noise / External Audio Switch disables the white noise source, so that the external signal can run through the Poly-800 alone. The DPDT switch also holds the VCA level at maximum (regardless of the settings of parameters 61-65).

The Filter FM control pot adjusts the depth of Filter Cutoff Modulation from DCO1's audio. This allows for an extreme range of sounds- from growling synth bass to ring modulator-type noises. It should typically be used with Chord Memory in 'mono' mode.

And VCF Cutoff and Resonance pots allow the cutoff frequency and the amount of resonance to be tuned in real-time.

The program parameters (31 and 32) now set the maximum levels. The filter will self-oscillate, and the resonance pot offers its full useful range when parameter 32's value is set to 12.

Here are a few examples of this Poly-800's more unique capabilities:
- FMsyn.mp3 (FM, cutoff, and resonance settings are being tweaked.)
- SHgtr.mp3 (Guitar is being processed with a random S/H input to the VCF CV Input.)
- spacegtr.mp3 (The delay sounds beautiful as a guitar effect.)
- SHsyn.mp3 (Again, the filter is being modulated by the EML101's random S/H output.)
- warblegtr.mp3 (The filter is being modulated by the Poly-800's internal modulation generator.)

E-mail me if you'd like to have your Poly-800 modified similarly!

No comments: