|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
PAiA Drum Tone
This board, still available in kit form, was once part of PAiA's discontinued Thumb Drum product. It consists of six ringing oscillators with names such as Tom-Tom, Conga, Wood Block, etc. All typically retro. It also has a Snare Drum, and seemed an acceptable replacement for my damaged and nearly useless Synsonic. Here's a nice, cleaned up scan of the complete Schematic.
The d.i.p. patterns J1 and J2 at the top left corner are for mapping the (discontinued) finger drumpad outputs to the voices of the user's choice. Of particular interest to me was the SynthDrum voice, and its Theory of Operation. It seemed to me it should be capable of more than disco-age pitch "Glide."
Looking at the schematic, I saw that if resistor R4 were made variable, that would give control over the Pitch. I also saw that there was no control over the depth of the frequency sweep brought about by the diodes and other parts that connect to R4, so that would be something to correct. Lastly, there was no control over the Decay length of the "ringing."
That last shortcoming seemed easily fixed by replacing the "Q" trimpot with a potentiometer, but it wasn't that simple: the trimpot's range included no oscillation at one extreme and constant oscillation at the other. By cutting pcb traces and adding a jumper and fixed resistor, I rearranged that part of circuit so that the trimpot limited the range of Q (resonance,) controlled by a front panel Decay pot.
Varying R3 (R29, below) to control the depth of pitch sweep didn't work. I removed one diode and put a pot in its place, and that worked very well. But modulating with an LFO had problems, hence the big red X.
Click for details, including wiring and audio files
Other features added were cross-over distortion, (labeled "Warp,") which sounds more percussion-like to me than clipping, and an optional Impact click. Click the schematic for full details.
"Conga" Modifications
Given the similarity of all the the DrumTone oscillators, I saw no reason why they couldn't all have the same features. Seeing that the SynthDrum pitch-controlling resistor connected to ground, instead of +5V, I reasoned that the other oscillators could be that way, too, so that's where I put the Conga's Pitch pot.
Studying other ringing oscillator schematics, I saw other ways to control the Q/Resonance/Decay. The simplest to retrofit to the pcb was to put a pot to ground in series with the capacitor in the R-C-R "T" network. (C10 in the schematic below.) Trimpot R21 then limited the maximum decay length that the Decay pot can be set for -- which was quite long. long_conga.mp3
Click for details, including wiring and audio files
To bring about voltage control of Pitch, I replaced the diode(s) of the SynthDrum with a transistor paralleling the Pitch pot. This addressed two problems with the diode method: First, if the CV is from an LFO, and at too great an amplitude, the peaks will constantly re-trigger the oscillator. Second, if the modulation is also at an audio rate, as when trying to bring about a pseudo ring-mod/metallic sound, it will bleed through to the output -- even when the oscillator isn't ringing. The transistor method greatly minimizes, but still does not completely eliminate, both problems.
Click the schematic for full details, again including wiring and audio samples.
DrumTone Overview
(Although I still consider this a pretty good plan, what I want is a self-contained system, one in which the electronics isn't a module external to the drum pads. Given my skills in mechanical construction, to make everything fit, such a setup would end up being too large for apartment living. I've purchased a commercial product that I can enhance or augment with minimal d.i.y. circuits. I will post details when that project gets further along.)
See also the DR-110 pages.
|
|
|
|
|
|
|
|
|
|
| Back to Projects or Publications |  softhome.net
|