(increasing R183 to 10K reduces snare membrane frequency)

SNAPPY

(R134, replaced with 1.5K resistor)

independent

The membrane component of the Volca snare is used to shape the white noise that makes up the snappy component

filtered

(snare snappy envelope without C78)

However, unlike the TR-808 snare, the Volca snare has a variable decay. The decay is determined by the amount of feedback controlled by the decay pot, not entirely dissimilar to the decay circuit of the TR-808 kick drum. The snare decay becomes important later...Now onto the snappy component. The first major revelation about the Volca snare is that the white noise seems to be generated digitally. What looks like a train of random high frequency pulses from the microcontroller is filtered into white noise by IC9B. IC9B forms a second-order low pass filter, at least according the bible of active filter design techniques . Changing the frequency response of this filter will alter the character of white noise.Replacing R134 with a lower resistor value (eg. 1.5K) or even a 10K potentiometer will increase the gain and change the frequency response of the filter. Modifying the noise filter has been previously described . I measured an increase in the noise output from about 1.3V to 3.3V when R134 was changed to 1.5K. Other changes to the noise filter could also be done to change the character of the Volca snare's noise source. It seems the noise is also used for the hats and the toms.Now, how is the envelope generated for the snappy component? This is where the Volca snare makes an interesting departure from the TR-808 snare. The TR-808 has a fixed membrane decay and anfixed snappy decay. The Volca snare has a variable decay, which works by varying the amount of feedback of the T-bridge resonator. As far as I can tell, the output of the membrane component is fed into the snappy VCA through C91.. Thus, the snappy decay is determined by the membrane decay. This seems like a clever and efficient use of the variable membrane decay to control the snappy decay without requiring independent snappy envelope circuitry. But, to many people's ears, the Volca snare's snappy component sounds fucking awful. It's 'distorted' and 'grainy' and here's why: the output of the membrane is buffered and rectified by IC9A but it isn't. Here's what it looks like on a scope at the cathode of D14:The envelope is chopped up by the frequency of the membrane (the first ~15 ms pulse is the trigger signal coming through D13). This amplitude chopping is likely the cause of the ‘graininess’ and 'distortion' in the snare snappy that many users (myself included) complain about, which is especially prevalent with longer decay settings. The noise is being chopped up at 250 - 560 Hz, dependent on the snare pitch. C78, the legendary missing capacitor on production Volcas, has the job of partially filtering out the membrane frequency: