USING THE EMS SYNTHI A, AKS AND VCS3 WITH A MIDI TO CV CONVERTER

Although the EMS synthesizers were designed well before the advent of MIDI and lack actual CV and
gate input and output sockets, it is quite simple to adapt them for use with MIDI to CV systems.


CONNECTING THE CV INPUT

Synthis have two HI-LEVEL INPUT CHANNELS, which can function as line
level signal inputs AND control Voltage (CV) Inputs. This means that two
channels of CV information can be connected simultaneously and patched to
control any function on the matrix - not just pitch.

The only complication in connecting CVs to these inputs is that due to
the high gain of the input amplifiers it is necessary to include a lOOK
resistor in line (in series) with the incoming CV. This is best done by
making up two special quarter-inch jack leads with resistors incorporated
labelling them to avoid mixing them with normal jack-leads.

CONNECTING THE GATE INPUT

Gate input on an unmodified Synthi is only accessible on Pin 5 of the
8-way KEYBOARD socket, A simple modification is recommended which should
internally link across from this pin to the adjacent CONTROL OUTPUT CH2
socket (via a diode), so that the Gate Input is available on a quarter- inch jack.

Connections to this Gate Input should be made with a normal jack lead,
not the special lOOK resistor lead described above.



A moderately competent technician should proceed as follows to make this modification:

Remove Synthi from case or remove back and bottom panels if a VCS3.

Remove two retaining screws from the reverb spring box - if a suitcase
synthi, and rest spring unit on bench. The thin blue and red wires are
very delicate, so try not to wrench them off.

Locate Pin 5 at the back of the keyboard socket. This is normally a
yellow wire on later machines, but the pins are numbered on the black
plastic housing - use a bright lamp if need be.

Pull black sleeve back up the wire to expose soldered terminal.
Use a soldering iron to detach this yellow wire temporarily.

We want to have two wires coming from this pin 5 to join another short
length of wire - say 20 cm's of yellow 7/0.2, reconnect to pin 5 and
replace sleeve.

6) Snip off the thin wire going to the Control Output Ch2 Jack 'hot'
terminal, and insulate with tape or a sleeve. This is now abandoned.

7) Connect a small signal diode - a lN4l48 for example - to this 'hot'
terminal. The dark polarising band must be at the opposite end from the jack terminal.

S) Connect the end of the diode with the polarising band to the free yellow wire end and sleeve over the diode.

9) Re-label the control Output Ch2 socket as 'EXT GATE INPUT'.

Alternatively a plug-in harness can be constructed with a male 8-way
keyboard plug and jack socket, but this involves more parts and labour as
well as being more untidy in use.

If you have any problems or need any further advice please contact Robin wood on 0726-883265 (UK).




This info care of Robin Wood by way of fEEd. Synth Fool thanks both!