[sdiy] TR707 to TR77 voice triggering

[Adam Inglis]

Cheers - I was hoping to avoid building a negative rail, the 77  
manages without one (The negative-edge detector circuits that make up  
the matrix generate a brief negative pulse on the falling edge of the  
square waves from the multivibrator counters).

Hanging a common-emitter amp off the 24 volt rail to invert the  
signal, and running this into a similar edge-detector seems to work,  
but thats a lot of parts if I have to make one for every voice.

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

On 15/11/2010, at 2:37 PM, Chromatest J. Pantsmaker wrote:

> I'm thinking a voltage regulator to get you your -7 volts.. and then a
> transistor for each voice. use the 707 CV to trip the transistor
> letting the -7 through?  Probably a current limiting resistor on each
> one?
>
> Of course, this is how I design my own stuff... and sometimes it
> works.  I really have no idea of the "correct" way to do things.
>
> On Sun, Nov 14, 2010 at 9:30 PM, Adam Inglis <21pointy at tpg.com.au>  
> wrote:
>
>> 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
>>
>>
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>>
>
>
>
> -- 
> .sig
> -Chromatest J. Pantsmaker
> http://www.chromatest.net
>
>
>