[sdiy] TR808 accent question

[stewart pye]

Hi. I haven't been on the list for a few years but I want to get back in 
to building a modular so I've come back...

Yes. The accent level is set up globally, then for each voice an NPN 
transistor is triggered, which turns on a PNP transistor that passes 
through the accent level voltage for that voice. (If the accent is not 
on for that step or is set to zero the it will be 4V if Seb remebers 
correctly).

I played around with the 606 and 808 circuits a few years ago, 
triggering from a home built Midi to trigger unit. I used an 8 channel 
DAC that had 0-5V outputs followed by non inverting amplifiers to 
increase the output trigger voltage. I don't have the circuit handy but 
I think I fed the triggers via a diode straght into where the collector 
of the PNP trigger transistor would have been. (Q46 in the case of the 
snare drum). You can omit the two transistors and associated resistors.

You may want to check what sort of buffering your midi device has, and 
what voltage it is capable of.

Regards,
Stewart.


Seb Francis wrote:
> Yes.
>
> But no reason from an analog point of view not to have individual 
> accents.  If I remember the circuit correctly you have a couple of 
> transistor on the trigger input of each sound and they kind of AND 
> together the individual trigger signal and the accent/timing signal.  
> So the actual timing, pulse width and accent amount is set by the 
> accent/timing signal (common for all voices) and the individual 
> trigger signal comes on for an imprecise period around when the drum 
> needs to trigger.
>
> If you are triggering each drum voice from MIDI you need to send a 
> pulse of the right length (1ms) with voltage between 4V and 14V.  Feed 
> this signal instead of the accent/timing signal and leave the 
> individual trigger signal always on.  You can probably even dispense 
> with 1 or 2 of the transistors on the trigger input of each voice.
>
> Seb
>
>
>
> Dino Leone wrote:
>> Hi all,
>>
>> I'm building a TR808 clone (without the seq) and  I have a question 
>> regarding the accent signal:
>>
>> In the original, is there just one single accent signal, controlled 
>> by a pot on the front panel ?  I'm using a midibox core to control 
>> the the voice cards and I was thinking if I should try to implement 
>> individual accent voltages for at least some of the voices (using a 
>> AOUT module)?   Obviously, I've never touched a real TR808 (I'm too 
>> poor a student ).
>>
>> Best Regards,
>> Dino
>>
>>
>>
>>
>>  
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