[sdiy] universal drum machine interface

Adam Inglis 21pointy at tpg.com.au
Tue Nov 6 02:12:39 CET 2018

thanks for drawing my attention to this.
I’ve put it back up on the bench and poked around with a scope. I’m fairly sure that the pulses and polarities I’m using are pretty close to what that part of the circuit sees with the internal triggers.
Since the purpose of the interface is to trigger analog drums, I didn’t actually consider this as “circuit-bending” but I suppose there is a bit of that here!

for this machine, the best trigger pulse shape for most voices is “Open Rectangular”

The manual has this to say about the pulse shapes:

"Additionally various pulse shapes can be selected for each output: Rect- angular, Triangular, Decay, Gaussian and Open Rect. The latter is similar to the rectangular pulse, with the exception, that instead of returning to zero volts, it goes into a high impedance state. This allows it to make use of the characteristics of an existing pulse shaping network, such as an RC network built into the drum machine. The pulse shapes have different sonic characteristics, experimenting which suits best is recommended. The Gaus- sian pulse for example contains less higher harmonics and can be used to simulate drums hit by a felt headed mallet. "

In certain voice circuits you can certainly hear the difference between the Gaussian and the others. Between the others the differences are very subtle. At least, in the CR-8000.
The two trigger points I moved were Clave and Low Tom.

> On 5 Nov 2018, at 7:35 AM, rsdio at audiobanshee.com wrote:
> I’m also curious about the specific circuit changes.
> It’s potentially “dangerous” to inject an external voltage on the wrong side of those diodes. It really depends upon the output circuit on the device being added, as well as the input circuit on the vintage equipment.
> You might not have a failure right away, but over time your CR-8000 might die a premature death due to skipping past the diodes. Circuit bending can be dangerous if done without the research to back it up.
> I don’t doubt that you got better results, it’s just possible that the final result might be less than desired.
> Brian Willoughby
> Sound Consulting
> On Nov 4, 2018, at 1:27 PM, Tony Kalomiris <weplar at gmail.com> wrote:
>> Hi Adam, would you care to elaborate on the specifics?
>> I for one am curious about which voice in the CR-8000 it was and where you injected the trigger pulse.
>> Do all those trigger pulse shapes seem to make a difference in your opinion, subjective and otherwise?
>> Specifically curious about that one that goes high-impedance (guessing to avoid interacting with the machines own trigger pulse.)
>> TK
>> From: Adam Inglis <21pointy at tpg.com.au>
>>> Date: Sun, 4 Nov 2018 12:56:06 +1000
>>> I tried a few different points to find the most musical results - just moving them to the other side of a diode and changing the polarity made noticeable differences in the resulting voice.
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