This toy started out having three drum pad button things, nine pattern selection buttons, tempo up/down buttons, and a rhythm start/stop button. When certain rhythms were triggered on the toy, i was hearing a fourth drum sound, so when I opened it up, sure enough there was a point right next to where the other drum sound pads connected to, that triggered the fourth drum sound. I don't know why, but that "hidden" drum sound has become probably my favourite of the four, and probably only for that reason.
The thing I love the most about this circuit
is that it allowed me to to accomplish what I aim to do with all of
this circuit bending and electronic instrument building. Every sound and
aspect of this machine can by externally controlled and synchronized,
the patterns can be remotely changed, the drum sounds can be externally
sequenced, the tempo can be adjusted, and the drum sound pitch can be
widely controlled by external voltage sources. In short, everything
about this circuit is variable.
The control interface has
changed slightly since these pictures where taken, because I figure out
more possibilities with the circuit that I expanded upon. In the photo
to the left, the upper right hand corner houses a 16-point patchbay. I
took those points out and used it to house a pattern routing matrix.
As previously stated, there are four drum sounds on this drum machine. The circuitry consists of three chips; a sound generator, a pattern generator, and an amplifier. I left the connections from the sound generator to the amplifier intact, but severed the four traces connecting the pattern generator and the sound generator. When I did this, it was impossible to get the drum machine to play patterns. Using the individual drum triggers, it was possible to make the drum sounds, but there was no information traveling from the pattern generator to the sound generator. I installed four switches in between the points, so that when they are all toggled upwards, the four signals from the pattern generator travel to trigger the drum sounds they where originally meant to trigger. When the switches are toggled downward, the four pattern signals are routed to four black patch points. there are also patch points that go to the sound generator chip. This way, manual connections can be made from the individual patterns to the four various drum sounds, bypassing the original ordering of the pattern. The audio samples should clarify things a bit.
The first audio sample below demonstrates the pattern matrix. First, the four drum sounds will play, individually triggered. Then, a simple pattern of two drum sounds (snare and tom) will play for four cycles. Then, the switches will be toggled down to allow for manual direction of the pattern pulses. The signals are routed oppositely, i.e. the snare signal will to go the tom, and the tom signal will go to the snare. Finally, the original pattern will be played again.
The second example shows a more interesting example of what can be done with the pattern switching. Both the assignments (to the four drum voices) and the rhythmic patterns are being changed and altered simultaneously and in time with the resulting rhythms.
Drum box pattern demo 1.mp3 Drum box pattern switching example.mp3 |  |
 | The image to the left shows the left section of the top panel, which houses the pitch and tempo controls. The pitch control section consists of two tuning knobs, coarse and fine, that are used to adjust the pitch of the drum sounds. Below that are voltage and ground jacks for interfacing and powering other equipment. Contrary to the labeling, the unit runs on 6VDC, not 5. Below those jacks are the vactrol power switch. Turning on the vactrol is what enables the pitch of the drum sounds to be modulated by external voltage. Learn more about vactrols in my circuit bending 101 page. The next audio sample shows the four drum sounds modulated by the pitch adjustment knobs, followed by a simple pattern that is being similarly tweaked as it progresses. Drum box pitch knob demo.mp3 |
To the right of the pitch controls are the tempo controls. The tempo control knob has a switch that turns the funtion on and off, as well as two momentary pushbuttons. The tempo for this instrument was only manufactured to go up to a certain speed, but when pushed beyond that limit, the rhythms get played so fast they become solid tones. The following sample should clarify. the pattern starts off at a normal pace and then is brought up to blisteringly high speeds and then back to earth again by the tempo control knob. This is a similar effect to granular synthesis.
Tempo control demo.mp3
When a pattern is playing, pressing the left pushbutton momentarily sets the tempo to the fastest it can go. The right pushbutton acts like a short momentary version of the normal tempo control switch, making the control knob effective only for the length of time that the button is depressed. The audio sample should clarify. A pattern is played and interrupted by two bursts of tone from the left pushbutton. Then the pattern is changed, and interrupted by two modulated tempo changes by the right pushbutton. The tempo knob is being turned only during the depression of the right pushbutton, not the left.
Tempo pushbutton control demo.mp3
The real fun starts when both the tempo and pitch are being modulated at the same time. This takes the drum machine completely beyond its original intents and turns it into a strange tone-generating synthesizer. The following sound sample starts out with a low-pitched pattern, which is sped up until it becomes a constant tone. That tone then is effected further by the modulation of the individual drum sounds, which are now flying by so rapidly that the timbre of the tone changes drastically.
Tempo and pitch craziness.mp3
The pitch of the Drum Box can also be externally controlled by a variable voltage source. In this audio sample, the pitch is being controlled by an 8-step CV sequencer from my modular system.
Drum box pitch sequencing.mp3
This thing is nuts, every aspect of its sound can be modified and externally tweaked, and its incredibly versatile. I make extensive use of its synth-tones and pitch sequencing capabilities on my first musical release, which can be listened to on the music page.
At some point in the near future I'm going to service it and add some more components, and when that rolls around I'll take shots of the insides and identify the component values I used in the modifications, for anyone else interested. Soon.
