MATRIXSYNTH: EMS Synthi A Mk. I, extensive mods, 1971

Thursday, November 14, 2019

EMS Synthi A Mk. I, extensive mods, 1971

via this auction

"EMS Synthi A Mk.I, 42xx S/N, with extensive mods designed to integrate with the modern studio, with no compromise at all in terms of sound quality and character. Every signal path has a beautiful warm distortion when overdriven, or a full, rich and very clean sound when not. Last serviced Jan. 2018 and further modified by excellent and very well known tech in Belgium. Unit is housed in a special wooden box with protective foam for easy transportation.

Description of modifications:

1) CV inputs #1 and #2, and gate to trigger the trapezoid generator. These are available on three 1/8” cables, hardwired to the EMS keyboard cable, which plugs directly into the keyboard slot (see picture). The signals on the “CV” and “Filt” cables take over the inputs #1 and #2, respectively, and are useful for either audio or CV.

2) Tempco resistors on VCO #1 and #2, to stabilize pitch

3) Oscillator sync (1->2, 1->3, 2->1, 2->3), by three-way switches. Sync is variable from hard to soft via added controls.

4) Buffer boards VCO #1 and #2 and VCF frequency columns, and on both input channels and joysticks rows, to ensure no change in pitch from patching additional inputs and outputs. This is extremely important in using the Synthi for melodic work. [Total rows and columns buffered: 5,6,8,9,15,16,I,J,N]

5) Filter unslew mod, switchable on/off by pulling up the filter cutoff knob. This is essential for audio rate filter FM with oscillators or the filter itself, or in getting better attacks with the trapezoid generator when it is routed to the filter.

6) Trapezoid generator inversion, by pulling up the “trapezoid” knob, for other distinct envelope shapes

7) Ten-turn knobs on inputs #1 and #2, to get as precise as possible tracking from external inputs. This makes the Synthi very easy to tune and use for melodic work. [Tracking is good for about 3-4 octaves, becoming nonlinear at very low frequencies.]"

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