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Alesis S4 QuadraSynth Rack

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    The Alesis S4 QuadraSynth is a 64 voice, rackmount MIDI sound module featuring built-in parallel-matrix digital signal processing. The 64 has a large, easy-to-read, back-lit LCD display for "Composite Synthesis," which is an innovative combination of subtractive and additive synthesis.

    Each program can be made up of as many as four individual "sounds" each with their own set of 3 envelope generators, 3 LFO's, tracking generator, dynamic low pass filter, and very comprehensive modulation matrix.

    In the "Program Mode," the S4 has 128 present and 640 user programs in which the user can program up to 7 simultaneous effects which can be independently assigned to any of four effect busses. This allows different programs or composite sounds to be routed to different effects with dynamically controllable amounts.

    In the "Mix Mode," the S4 has an additional 100 preset and 500 user programmable "Mixes" which can be used for multi-timbral sequencing applications. In this mode, different programs may be assigned to each of the 16 MIDI channels simultaneously, and have allows you to have separate discrete effects on different sounds with complete mix control. That's why we call it "Mix Mode" rather than a simple multipatch.

    Programs may be routed to any of the four audio output jacks on the back and the S4 supports optional PCMCIA Sound cards.
    Type: Digital
    Synthesis: ROM, Subtractive
    Oscillators: 4
    Waveforms: ROM
    ROM Size: 16
    ROM Resolution: 16 bit, 48 kHz
    Osc Modulation: Continuous Controller, Envelope, Keyboard, Knob, Mod Wheel, Oscillator, Pitch Wheel, Glide / Portamento
    Envelopes: 3
    Evelope Paramerters: Delay, Attack, Decay, Sustain, Release
    Filters: 1
    Types: 12dB Slope (2-pole), Low Pass
    LFO: 3
    LFO Parameters: Noise, Sample & Hold, Saw Up, Saw Down, Sine, Square, Triangle, Clocked, Delay, Key Sync
    Polyphony & Tuning
    Polyphony: 64
    Timbrality: 16
    Tuning: Standard
    Patches RAM: 640
    Patches ROM: 128
    Multipatches RAM: 500
    Multipatches ROM: 100
    Storage: Internal, RAM Cartridge
    Editing: MIDI
    Up to 7 effects per patch based on QuadraVerb 2 chip set.
    Case: Rack
    Case Details: 1U rack 19 inch
    Controls: Knobs, Pedal - Patch Change
    Audio Output Connections: 1/4" Phone Jack, ADAT, Stereo Main, Stereo 2
    Audio Output Notes: 4 Audio, 2 Adat Optical, Stereo Headphones
    Inputs: 48K Clock
    MIDI Ports: IN, OUT, THRU
    DAC Bits: 16
    DAC Frequency Rate: 48
    Power: 120V AC
    Year Released: 1993
    Year Discontinued: 1995
    Manuals & Documents
    MSRP List Price: $995 - convert
    Retail Street Price: $899 - convert
    Used Price: $75 - $175 - convert
    YouTube Videos
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Questions on the S4 rack (1993),  what is required to upgrade to the S4 Plus rack (1995)?

1) EPROM OS update, new CPU, 4 MB piano ROM expansion board?  Other chips?

2) Does upgrade require a new mainboard (S4 Plus uses S8 mainboard)?



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They used to sell kits for this, but they are long gone. Here is information on the changes:


IDK if these are the right EPROMS, but sellers on Ebay are offering upgrades:



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Thanks, I think the eBay EPROMS are version 1.07.  Which I already have installed in my S4 rack.  This EPROM 1.07 does not upgrade the S4 to S4 Plus.

I also own an S4 Plus (with version 2.00 EPROM) and just swapping EPROM did not work - there must be other chips needed.

It would be good to know what was included in the kit.

I note my S4 main board is marked S4 and the S4 Plus is marked S8, so maybe the S4 upgrade required a complete swap out of the main board and not just the EPROM and other chips.   Maybe circuit board modifications were needed?  (trace cuts, jumper wires?).

Edited by mjkirk12
Added more info and clarification.

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