Tuesday, December 22, 2015

Monotribe - Removing clicking sounds

I really like the sound of my Monotribe and so far have not experienced the clicking sounds so many people complain about as really noticeable. This changed when I needed to run it through a reverb...

The clicks and pops are caused by the phase of the oscillator when a note is triggered (in the envelopes reverse saw and square setting). The following schematic visualises that:

When a note is triggered while, by chance, the VCO is at TO or T2 of its wave cycle (I know that the Monotribe has only square, saw and triangle wave shapes, but it really is the same as for the sine shown here), the resulting sound will smoothly "start". In contrast, at any other point in time, the generated sound will jump-start at the current point in the wave cycle, resulting in a noticeable click or pop sound. This can be avoided by either re-triggering the VCO with every note played (the Monotribe does not do that), or starting each note at a low volume and only turning it up after the pop has occurred (a.k.a. the attack phase of an envelope). Since the Monotribe's envelope, at least in its square and reverse saw setting, is really fast, it gives a very snappy tone - but with clicks and pops. A good electronic description on how and why this happens in the Monotribe is well described by Mark Madel in this YouTube video.

Based on Mark's and Snyder80's suggestions in the  30+ page Monotribe modification thread on Muff Wiggler, adding a 1 µF WIMA foil capacitor (any above 16V will be fine) to the base of Q24 and GND softens the envelope and gets completely rid of the clicking problem of the Monotribe.

As seen in the photos, I attached wires to the corresponding points on the pcb instead of directly soldering the capacitor. This not only enabled me to easily play around with different capacitor values (but Snyder80 was absolutely right by using a 1µF capacitor), but also allowed for putting a switch between the capacitor and the Q24 transfer, to turn the mod off when a most snappy envelope is desired.

As a side note: The above mentioned Monotribe modification thread on Muff Wiggler is a must read for anyone aiming to improve their Monotribe. While also being fun to read, the highly informative thread contains many good ideas and solutions to common Monotribe problems and often renders it unnecessary to reinvent the wheel.

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