It all started with the wondering about the mysterious oscillatormodes of the rare pearl "Syncussion sy-1". It has a turning switch with oscillator modes "A" to "F", all the other parameters are quite common. The Pearl Syncussion ist hard to find and the bay-prices appear much to high to me. I found 4 JPGs of the original brochure/manual from the sy-1. The parameters are:

A. one Oscillator only, manual sweep enabled

B. Osc1 adjusts Osc2-frequency - AHA

C. Mix of Osc1 and Osc2

D. Mix of Osc1 and Osc2, velocity goes to sweep

E. Osc1 adjusts Osc2-frequency plus mix of noise

F. Noise only

The second reason for building my own special syncussion was, that i always wanted something which could make this smacky "ZAPPPP". I know, the "ZAPP" is a lowpassfilter with full resonance and a very short envelope closing the filter. But why waste a whole synth for just a simple zapp. My studio is very small. And there were a few things i wanted to try out and some parts i had over...

The whole thing

A short overview here. In the following, i talk about the individual units in detail.

It is a drum synthesizer. You feed a trigger-signal into it and get a short sound out of it. There are 4 simple decay-envelopes, 2 VCA, a double-oscillator with frequency- and ringmodulation, a versatile noise source, a typical twin-t-circuit drumvoice, an attenuator and a multimode vcf.

ENVELOPES

The envelopes i used are the simple Decay-envelopes to the right. You find a more detailed schematic here with an attack parameter which i did not need. The Envelopes are user for

1. Main VCA Decay

2. Double-Oscillator Tune

3. VCA 2 Decay

4. Free envelope, e.g. to modulate the VCF

i bought an old Intellivision videogame for 4 EUR on the bay. Believe it or not: they are over 10 years old and DO NOT CRACKLE - excellent. The joystick is used to tune the color of the noise. On one axis is kind of highpass on the other lowpass. I used this schematic for the noise. The joystick-pots are 700kb and replace the 47k in the schematic. Some rude feedback experiments showed something VERY interesting: when you take to colored noiseoutput and feed it back (through a pot) to one of the 47k-pots, you get a supercool resonance-parameter. Dont know which side of the 47k-pot - just try.

Soundclip of the Noise through VCA

Soundclip of various noisecolors tweaked with joystick, 3-way-switch and feedback-pot

Ken Stone Drum-Simulator

Next Unit is one of those Ken Stone drum simulators, schematic here It is a "classic twin-T circuit" with a LED adding harmonics. Sounds quite good although the "harmonics"-parameter turnes the sound much more in a octaved squarewave which sounds kind of melodic. not what i wanted. Anyway, the rest of the circuit is really great.  

I replaced the 470k-resistor between the two 1n-caps with a pot. Ken Stone sais on his page "Do NOT bring the resonance trimmers out to the front panels as controls." - well, i couldnt resist ... hope he isnt angry on me :)

The higher you tune the pitch, the more resonant gets the whole thing. This means you will NEED the resonance-pot.

The drumsimulator is directly mixed with the Main-VCA. There is not need to send it through the vca.

Soundclip of this unit - watch out, the clip is quite loud and clipping at some areas

VCA

The 2 VCAs are the common CA3080 VCAs from the ADV-Snare. It is directly driven by one of the Envelopes and has a Mixer for 3 Signals. One Signal can be level-adjusted (on the picture, the pot should read "Mix 3 Level").

VCF

The filter has the common input- / output- / modulation-jacks and pots for frequency, resonance and modulation amount - AND - a 3-step switch for the mode: lowpass, bandpass, highpass.

The circuit is from the Böhm Soundlab, based an the CEM-Chip. This circuit is simply excellent.

Soundclip of VCF with various settings, envelope-modulation. Later the noise and Drum-Simulator ist mixed in and you will hear the famous ZAPPPPPP - watch out - also quite high level sometimes.

Free Envelope

Nothing special. Which i found useful was a single pot which allowed to adjust the envelope in positive AND negative elongation. Its simple: just take the normal envelope, feed it through an inverter; one side of the pot gets the negative envelope, the other side gets the positive. The center contact is the output.

Attenuator

Also simple but useful, sets the level of the inputsignal from full to null with a pot. One pot-contact goes to the inputsignal, the othr side to mass. The center-contact is the output. For audiosignals usw logarythmic pots.

VCO

The thumb to the right opens a bigger view in a new window.

The oscillators are based on the ADV-Snares VCO with a LM566-Oscillator. You need very few parts to make a vco with these ICs, but they are hard to find. I had 2 left over from somewhere. I tried to make a vco with the common 555 but wasnt succesful. The frequencyrange in which they operate clean was to small. The 566 directly spit out a triangle and a squarewave.

Each Osc can be tuned and ENV-modulated seperately. The Envelope is for both the same.

There is a 3-step switch to set the mode: Osc 2 only, Osc1+Osc2 mix and (of course) Osc1 drives the frequency of Osc2.

Both signals (Osc1 and Osc2) also go into a seperate ringmodulator which has its own output-jack in the upper-right corner.

Soundclip of the VCO-Unit with various tweaking, different tunes and modes. You will also hear (after a short pause where i switched the cable to the ringmod-socket) the ringmodulation-unit.