[sdiy] TR707 to TR77 voice triggering

[Adam Inglis]

That sounds good - and then you'd need a capacitor at the output of  
the op amp to remove the DC offset?

On 16/11/2010, at 7:54 PM, Tom Wiltshire wrote:

> 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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>>>> Synth-diy at dropmix.xs4all.nl
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>>>>
>>>>
>>>>
>>>
>>>
>>>
>>> -- 
>>> .sig
>>> -Chromatest J. Pantsmaker
>>> http://www.chromatest.net
>>>
>>>
>>>
>>>
>>
>>
>>
>>
>>
>>
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