The author of Alisa-1377 Eugeny Tjurlenev also took part in this project; he developed analogue frequency multipliers x2, x3, x5, ripple filters ("pseudo overdrive"); he also consulted the author of the project on the problems of electronic commutation. All the details of the synthesizers were made with the use, to the maximum possible extent, of the details Alisa-1377 (hereinafter - "the base model").
The description of the synthesizer design.
Alisa-2500 consisted of two units - the synthesizer mounted on a turning rack and the keyboard with 61 keys. The units were connected with a standard shielded cable with 5-pin plugs. The keyboard unit was made of black wooden panels (the same as in the basic model); its bottom was made of aluminum. The keyboard was divided into a bass (2 octaves) and solo (3 octaves) parts.
The design of the synthesizer unit resembled that in the basic model; its overall dimensions were 700x700x150 mm, its weight - approximately 20 kg. The front panel consisted of four parts: three upper parts were equal in size to those of the basic model, and the lowest part covered the rest of space. The rear panel consisted of three parts; the two upper parts had only fastening openings, on the lowest part were situated input and output sockets, safety devices and a power input.
The synthesizer consisted of three absolutely independent parts (synth modules) with common assigned modulation oscillators (in the number of eight); it was possible to carry out common synchronization with independent programming and synchronization frequency dividers for every part. There were a common stereo output and stereo outputs in every part (parts 1 and 2 had two stereo outputs each). In addition, there was a mono output in part 3 (a filter) with the possibility of gain adjustment. The first (upper) synthesizer was intended for "solo"; it was connected with the right part of the keyboard; it was tuned respectively. The second synthesizer was intended for "bass"; it was connected with the left part of the keyboard, with the respective tuning. The third part (a filter in a self-excitation mode) was intended for creating the sounds of percussion instruments and for creating effects; it was equipped with a noise generator (white/pink).
On the lowest (fourth) panel and in the left of the third panel, were are commutation buttons and controls of LFO and volume for each channel of the instrument. On all the panels, there were red diode commutation indicators. When the device was working, they all flashed with its own frequency each, which produced an unforgettable impression.
Both synthesizers - "solo" and "bass" - were similar to those used in Alisa-1377, with the only difference: it was possible to modulate the filter with the frequency of the main LF oscillator and to switch it from 12 to 24dB/oct. It was also possible to change the attack time and sustain of filter envelope and output signal oscillators, due to which it became possible either to get very short percussion sounds or to set both the times equal to those at the basic model. Filters of synthesizers were tuned separately, for "solo" and for "bass".
In the lower part of the synthesizer, there were mixing panels for each channel; on the rear panel was situated a headphone output. Inside the case were set three step-down transformers with three rectifiers (one for each synthesizer), and with a filter and 2-3 (8 in the aggregate) stabilizers for each rectifier; the stabilizers were modified against the basic model by using more powerful capacitors. Such a system of separated power supply was used in order to prevent the penetration of low-frequency modulating signals (especially rectangle) into the sound sections. The space inside the case was cramped full with plates, wiring, and transformers (though actually all of them were accessible); that is why the weight of the entire unit was approximately 20 kg (the case itself weighed only 3 kg).
The synthesizer Alisa-2500 was in operation since 1984 to 1991; it was lost during transportation. It has never had any comparable analogue in Russia or elsewhere!
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