[sdiy] TR707 to TR77 voice triggering

[Adam Inglis]

Hi All

First post - long time lurker and learner here for many years. Self- 
taught in analogue audio electronics thanks to a studio full of old  
"junk" from the 70s and 80s, an oscilloscope from the 60s, and the  
first few chapters of Horowitz and Hill!

Question: Someone here mentioned not too long ago the idea of using  
the voice trigger signals in a Roland TR707 to trigger external  
instruments. It got me thinking, as I love the interface of this drum  
machine - quick and fun.
  I would like to be able to trigger the voices in my old preset  
Roland Rhythm TR77. This uses passive LC voice circuits, which  
respond fairly dynamically to voltage triggers of between -3 to -10  
volts. Looking at the 707, I found the voice group's envelope  
generators supplied a positive envelope CV of varying decay times and  
amplitudes (about 2-5 volts) depending on instrument. These CVs also  
respond to the 2 levels of programmable ACCENT, and so would appear  
to be a good source of triggering.

Any suggestions as to a simple, low-parts-count circuit I could  
install (several iterations of) into the 77 that would convert the  
positive CVs from the 707 into brief negative pulses for the 77s voices?
I should mention there is 0 - 12 - 24 volts available in the 77 with  
just basic filtering, no voltage regulators, so I was assuming it  
would need a transistor rather than a chip based solution.

Anyone interested in my crude investigations into the workings of the  
TR77 can have a look here...
http://www.adambaby.com/studiotech_TR-77.html




regards
Adam Inglis
http://www.adambaby.com