OPS Hodonín Syntezátor 3-83 Unisono super rare synth + schematics (partially working)

Selling this monophonic OPS Hodonín 3-83 synthesizer, made in February 1983. It's a very rare synth, not more than 50 units were built by Mr. Jožka Řihák from Czech Republic. Most of its functions are working, but not all. The envelope generator isn't working fine, some potentiometers are working the other way around, and some switches / potentiometers need cleaning. That's why I sell it as-is, as a project. A copy of the schematics is included in the sale, and I can also send it as a PDF to its new owner.

The original power cord and a new made 5-pin DIN to 1/4" female jack cable are included in the sale.

It's working on 220v and the serial number is: 029

This can be something for a museum or collector. The sound is pretty cool for a single oscillator synthesizer!

Please check all the photos for an impression of the optical condition.

Some information about this synthesizer, found on internet:

On the top panel, on the left, we find a master volume potentiometer, a potentiometer and push-button switch for the Sinus 1′ register, and three filter switches (HP = high-pass, PP = band-pass, DP = low-pass). In the middle there are two rows of controls for two independent “channels,” which gives the impression that the instrument has two tone generators, but this is not the case. The two channels serve either to allow presetting two different signal shapes or to mix them together. Each channel has an on/off button, another switch determining whether the signal goes through the filter or not, a volume control, and five switches for octave pitches (16′ to 1′). The signal generator has an indefinable shape - it is neither square, sawtooth, nor pulse. By combining the octave pitches, in addition to transposition one can obtain a number of different signal shapes.

Next come the VCA controls: sustain (aka release), attack, percussion length (decay), and a switch for a percussive envelope shape. The envelope behaves a bit wildly: sustain works only when the glissando delay function is switched on, the percussive envelope shape does not mute the sound after it decays to zero, and the attack is fast only when the sustain potentiometer is approximately in the middle of its range; otherwise the attack is always slower. Unfortunately, the envelope does not control the filter.

All the way on the right are potentiometers labeled In. Osc. Frequency (infra-oscillator frequency, i.e., LFO), Vibrato, and VCF-Aut (LFO modulation of the filter). In the upper right corner there is an eight-position rotary switch for the glissando delay function, which, after releasing a key, lets the oscillator tuning slide down until it stops. The switch sets the duration of this effect. Both extreme positions are “off.” On a small panel to the left of the keyboard there are two slider potentiometers: the left one, called VCF, controls the filter cutoff, and the right one, labeled glis, controls retuning the instrument by more than one octave. There is also an LED power indicator and a small trimmer for fine tuning. On the back we find either a “remoska-style” socket for the power cable (apparently on older units), a rocker switch for power on/off, and a five-pin connector for the audio output.

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