Super Syncussion

The Super Syncussion is housed in a wooden box from IKEA.

The Bergfotron Super Syncussion is a complete synthesizer on a circuit board. It's essentially a clone of the Pearl Syncussion SY-1, but has been enhanced with some functions that add an extra dimension to the sound.
The Syncussion is an analog synthesizer that was designed to make percussion-type sounds. It came with drum pads to play the sounds from and had two identical channels with individual controls, so you could play two different sounds at once.
The Syncussion synth voice consists of two VCOs, one lowpass VCF, one VCA with envelope generator (only decay control), one envelope generator for sweep effects, a noise generator, an LFO, a sample & hold and a trig section for interfacing with the drum pads.

The original Pearl Syncussion SY-1

The Bergfotron Super Syncussion has all the features of the original Syncussion and adds to that an extra VCA with it's dedicated envelope generator and a ring modulator. Some extra knobs and switches are added to control the extra functions and to increase the sonic power of the unit. The Super Syncussion board has only one channel though, so if you want to mimic the original Pearl unit, you need two boards. Note that the Super Syncussion can do exactly the same sound as the original SY-1, if you refrain from using the extra functions. I added a knob for fine-tuning the VCO 1. On the original Syncussion, you can't adjust the relative tuning between the two oscillators, unless you open up the box and adjust a trimmer. That's probably the biggest limitation of that unit.
The idea was to add an extra dimension to the sound. This is where the extra VCA and envelope generator is used. You can add an extra component to the sound and have control over amount and decay time. So you could for instance add some detail to the attack of the sound and let the normal sound take over during the decay.
The original SY-1 offers white noise, which sounds rather soft. I wanted noise with more punch, to mimic cymbals and similar sounds. For this, I added a ring modulator. This is a very simple unit, consisting of XOR gates. By ring-modulating the two VCOs together, you can get clangy sounds, like cowbells. To get a more dense spectrum, required by cymbal sounds, I added a fixed oscillator that gets ring-modulated with the output from the first ring modulator. This oscillator is constructed around the two unused gates in one 4070 package. These two different outputs from the ring modulator are available in different combinations in some of the oscillator modes.
Since the ”oscillator modes” controls the patching of the synth, I added six more modes, to make use of the extra features. For each of the oscillator modes I also added a selection of two extra functions. This is where the extra VCA and envelope generator comes in. What component the extra functions bring in, is different for each oscillator mode. Note that the six oscillator modes from the original SY-1 have extra functions too. You will have to set the extra function amount knob to zero, to mimic the sound of the original SY-1.

Here is an overview of the oscillator modes with standard and extra functions. Note that the standard functions of mode A – F are exactly the same as on an original Pearl Syncussion SY-1.

Oscillator mode Basic function Extra function
A VCO 1 only X
B VCO 1 modulates VCO 2 frequency, the latter routed to the VCF Y
C Both VCO to the filter but VCO1 at reduced level. Y
D EG 1 modulates VCO1, EG2 modulates VCO2. Both VCO to the filter X
E VCO 1 modulates VCO 2 which has a sawtooth wave. VCO 2 to VCF X
F Noise to VCF, no oscillators Z
G VCO 2 to VCF, EG 2 modulates VCO 2, VCO 1 modulates VCF Y
H VCO 2 with sawtooth to VCF Z
I VCO 2 with triangle to VCF Z
J Ringmod 1 to VCF Y
K EG 2 modulates VCO 2, Ringmod 1 to VCF X
L LPF noise modulates VCO 2, which is routed to the VCF Z

Extra functions A B
X VCF feedback LPF noise to VCA 1
Y Noise to VCF Ringmod 2 to VCF
Z VCO 1 modulates VCF cutoff Ringmod 2 to VCA1

Note:
You can select extra function A or B with a toggle switch. 
The extra function has a dedicated VCA and EG, so you can control the amount and decay for the extra function with two knobs.

The Super Syncussion board contains all electronics and interfaces with the front panel through a large connector. This is the prototype board. The final version of the board has a lot of errors and omissions corrected.

The box contains a simple power supply that delivers -8 and +8 volts. In this picture the main circuit board is removed.

The circuit board measures 100 x 220 mm and is packed with electronics. Due to the board containing an entire synth, with on-board patching, there are a large number of wires to connect the different modules. The rotary switch labelled “oscillator mode” is really a sort of patch selector, since it controls how the modules are patched together. This makes it very quick and easy to change patches, but it requires a lot of electronics and wiring ”behind the scenes”.

Bill of materials

You should have access to the parts in the general bill of materials.
In addition, you need the following parts:

CD4050 hex buffer (1)
CD4069 hex inverter (3)
CD4070 quad EXOR gate (1)
MC4558 dual low performance op-amp (11)
Noisy NPN transistor for the noise generator. (I used a 2SC828, but note that the board layout doesn't match the pinout on that transistor)
7808 +8 V voltage regulator (1)
7908 -8 V voltage regulator (1)

Matching

The transistors that are paired on the circuit board should be matched. The original Pearl Syncussion used dual transistors – 2SA798 for the PNP pairs and 2SC1583 for the NPN pairs. If you're lucky enough to have access to these, you don't need to match transistors. For hand-matching single transistors, you can use the Bergfotron transistor matcher.

Trimming

There are only two trimmers in this unit.

Noise level
This is for setting the gain of the white noise generator. You can adjust it to your liking. I don't know how they did the adjustment at the Pearl factory.

Fixed oscillator frequency
This trimmer sets the frequency of the fixed oscillator that is used only by the ring modulator waveform Ring2. Listen to the sound and adjust the trimmer until the Ring2 sounds as much as possible like a cymbal or produces a sound that you like. You can replace this trimmer with a front panel mounted potentiometer if you like to have more control. There are two unused pins on the front panel connector that you can use for this.

Skill level required: HIGH

For this module you need to match transistor pairs or obtain matched dual transistors. Otherwise there are no particular difficulties, but there is a large number of parts on the board and you need to make a lot of wire connections between different parts of the board.

Schematics for the original Syncussion SY-1

Schematics for the original Syncussion SY-1 power supply

Schematics for the changed oscillator mode logic

Schematics for the extra functions

Schematics for the ring modulator

Schematics for the front panel

Schematics for a modern power supply

Circuit board layout

Component placement

On-board wiring diagram 1

On-board wiring diagram 2

On-board wiring diagram 3