Saturday, June 5, 2010

CV/GATE converter for the SYNTHI

this is my new cv/gate converter for the EMS synthi. it was created with the great advise and help of the people in the EMS SYNTHI forum , especially Steve from 'digitana'

the box contains a circuit which reduces the voltage for the gate (the synthi needs about 4-5 volts to trigger while the Roland sh-101 for example outputs 8-11 volts.)
and two trimmers for accurate adjustment of the CV to 0.32 volt/octave which is quite different in the synthi , from the common 1volt/octave method. the box connects to the synthi with the 8 pins jones socket which i purchased separately.

i also applied an op-amp 'voltage follower' in the box , which makes the gate pulse more 'stiff' and acts like a buffer. that circuit alone needs a power supply but since i didn't want to modify my synthi or my sh-101, i used an internal 9v battery in the box which powers that circuit and a switch to enable it. apparently this wasn't a good idea since the voltage follower doesn't work OK. i will probably need to power it from an external power supply.

the box contains two CV and one gate inputs , one LED for the gate activity, and a switch to swich off the power for the voltage follower circuit. it works great with my x0xb0x (the sh-101 still outputs too much current i think, the sound is a bit 'dirty' with it, like its combined with another more 'silent' oscillator.
the x0xb0x can act like a hardware sequencer for the synthi , or , if connected to midi it can hook up the synthi to the entire system, using a regular midi keyboard or software sequencer.

the box was made with mahogany wood, and black acrylic surface - just some leftovers from other projects...

6 comments:

VINCENT FARNSWORTH said...

Hello, I have an EMS AKS Synthi A, I would like to communicate with you if possible. I don't have any keyboard control and I am trying to find an affordable way to get some. A guy in Poland says he can make me a cable to go from MIDI to the keyboard port in the Synthi. Do you have any insight on this or advice? Currently located in Southern California.

0ne0ff said...

hi there, sorry for the half a year delay with posting back ... i have a lot of info about what you might need , are you planning building a unit?

VINCENT FARNSWORTH said...

Hi, thanks for your reply. I just need a keyboard that will work on it. The Poland guy kind of bowed out. I was wondering if some kind of midi to CV cable, to connect a midi keyboard to an EMS AKS, exists or can be built. I can't build a keyboard myself, can't build the cable either.

0ne0ff said...

Ok , so basically it is possible to buy a cable from kenton here:
http://www.kentonuk.com/products/items/leads/ems.shtml

the problem is that it's only an interface cable and not a converter.
you see, the synthi works with about 1/3 V per octave as opposed to 1V per octave in most synths , so in order to work with midi-cv converters it should have another conversion box that will take care
of the above conversion. another thing that should be in the box is a piece of voltage regulator circuit which will take care of the GATE signal as some of the equipment out there puts out 10-12V gate and this can harm the synthi (it only needs 4-5V).

0ne0ff said...

you got a synthi A or AKS?

0ne0ff said...

and do you have a standard Midi to CV
converter?