[sdiy] TR707 to TR77 voice triggering

[Tom Wiltshire]

If you've got 0V/12V/24V, you could regard it as -12V/0V/+12V and use it to drive an op-amp wired as an inverting highpass filter (edge detector). Inverting so you get a negative-going pulse from the positive input. Since you'd get 4 such filters on a quad-amp chip, it wouldn't take up much space.

But I'm only saying that 'cause the sight of all those transistors gives me the willies. Discrete! Even flip-flops! Yikes!

T.

On 16 Nov 2010, at 01:20, Adam Inglis wrote:

> 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
>>> 
>>> 
>>> 
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>>> 
>>> 
>> 
>> 
>> 
>> -- 
>> .sig
>> -Chromatest J. Pantsmaker
>> http://www.chromatest.net
>> 
>> 
>> 
> 
> 
> 
> 
> 
> 
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