[sdiy] TR707 to TR77 voice triggering

Adam Inglis 21pointy at tpg.com.au
Tue Nov 16 12:42:46 CET 2010


er.. I'm not yet actually up to the chapters on logic in  
Horowitz&Hill, ha ha!!

You're right - there are negative triggers to be found in the 707 (+5  
to ground) going to the bases of each transistor in each envelope  
generator. The Accent line is a positive CV line going to all the  
collectors of these transistors, can't remember the levels, prob  
around 5 volts (there are two levels of accent).
Not sure - does that sound like something I could AND??

On 16/11/2010, at 6:11 PM, cheater cheater wrote:

> Hi Adam,
> can't you use the trigger that goes into the 707's envelopes? I
> believe there's a separate accent line (as far as I remember the
> schematics). You can AND that with a separate copy of the trigger
> lines, and add it to the original trigger lines. That's probably one
> AND array, together with just some logic buffers or whatevers (I'm not
> that great with digital logic hardware, just software!)
>
> Maybe you can use those directly in the 77 without any conversion.
>
> Cheers,
> D.
>
> On Tue, Nov 16, 2010 at 02:20, Adam Inglis <21pointy at tpg.com.au>  
> 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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