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  #1  
Old 06-03-2013, 07:46 PM
tonewill tonewill is offline
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Default Triggering old drum machine

Hello,
I'll try and keep this brief:

I have an MD-24 and want to trigger the sounds of an old drum machine that requires short positive going pulses from -14V to 0V. I assume I'd use a transistor for this but am not sure. Can anyone point me in the right direction? There is a -14V power rail on the board.

Also, the service manual says:
Quote:
The voice outputs of the 460 (IC1) and 462 (IC2) are internally gated so that their outputs can be tied directly together...
"voice outputs" are the pulses to trigger the sounds. The pulses are generated from two ICs, one handles the main rhythms, the other the fill-ins. Does the above quote mean I can add my trigger pulses directly here without damaging the ICs?

Many thanks.
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Old 06-04-2013, 02:18 PM
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John John is offline
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Hi Tonewill,

[QUOTE=tonewill;6954]Hello,
I'll try and keep this brief:

I have an MD-24 and want to trigger the sounds of an old drum machine that requires short positive going pulses from -14V to 0V. I assume I'd use a transistor for this but am not sure. Can anyone point me in the right direction? There is a -14V power rail on the board.[quote]

In this thread, I suggested this workaround:



If you add a pull-up resistor on the trigger signal (pull-up to ground), then you will have a -12V (or -14V) to 0V signal.

Quote:
Also, the service manual says:

"voice outputs" are the pulses to trigger the sounds. The pulses are generated from two ICs, one handles the main rhythms, the other the fill-ins. Does the above quote mean I can add my trigger pulses directly here without damaging the ICs?

Many thanks.
This does sound like a "wired OR" arrangement. However, without having more information, I can't say for sure. It could be that the circuit I posted above could be incompatible with the other pulse-generating circuits.
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  #3  
Old 06-05-2013, 07:35 PM
tonewill tonewill is offline
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Thanks a lot John,
I did read that thread before posting but wouldn't that be 0V going to -14V when a trigger occurs rather than the other way round? Besides, I'm using some of the outputs with something else and require the normal 5V signal so it's sort of out of the question really.

Anyway, I've been playing around and have been able to get perfect triggers manually using a momentary switch connected to 0V one side with the other side connected to both a 100n cap and a 100k resistor. The 100k resistor goes to -14V, I think that is the pull-up (or would it be down?) resistor while the cap goes to my trigger point. This gives a short 0V pulse which is what I need. The drum machine circuit pulls it back down to -14V.

So, really if I'm to use the MD24 to trigger the sounds, I need it to take the place of the switch and send 0V to the cap with a note down, and on note up... I'm not sure! Leave it floating somehow as it is when the switch is released.

That's how I see it anyway, but I'm not that knowledgeable as you can probably tell.

Barry.

Last edited by tonewill; 06-05-2013 at 07:41 PM.
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