Gate Invert?

[Rene Schmitz]

At 09:53 10.01.1997 PDT, you wrote:
>Hey people,
>
>I've got a Kenton Pro-Solo that I wish to use to Midi up my PowerTran
>Transcendent 2000 (the kit synth from ETI in the early 70's).
Unfortunately, the
>T2000 takes negative gate (< -3v), while the Pro-Solo only puts out positive
>gates.
>
>Now, I'm sure this is easy to you groovy electronic hackers out there, but I'm
>just a poor software guy! I figure the solution would involve the negative
input
>of an op-amp, but 've never grokked op-amps, no matter how many Brabanti
books I
>read.
>
>Will the circuit to invert the signal need a dual-rail power supply? I'd rather
>build something that runs off batteries, 'cos I'm wary (= scared) of building
>power supplies at this point in my electronic hacking career.
>
>Thanks for any help,
>Anthony.
>--
>Anthony Bowyer-Lowe. Audio Programmer @ Mindscape (UK).
>                     The Essence Of Anthony @ Amudarya Studios.
>


I would suggest a simple opto isolator hooked up like this

                                       3V Bat
                220 Ohm                + - 
  5v gate  -----////-----+        +----o o---- -3V Gate 
                         |        |
                      A  V  ->  |/ C
                LED   K  -  ->  |\ E  Phototransistor
                         |        |
     GND   --------------+        +---////---- GND 
                                     protection   
                         
The only thing that remains to be checked is wether your Gate out 
is able to drive about 15-20 mA.
The value of the protection resistor depends on the input of your T2000
As opto isolator i would suggest a CNY 17-2
As you see you don't need a dual-rail supply and not even an opamp.

Comments/Questions welcome!

Bye 
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