Snare Drum

> = Trig

> = Accent or Velocity (from D/A)

> = Noise


Snare Drum consists of Drum and Snappy, each further separated into two parts.

Drum voice is composed of VCO-1 (part 10) and VCO-2 (part 11) with associated Control Voltage Generator IC35 (part 8). VCO-1 and VCO-2 have similar circuitry except that charging capacitors C69 and C71 have different capacitance so that they can oscillate at different frequency. VCO-1 runs at lower frequency.

VCO's comprise a hysteresis comparator IC37a (IC38a), inverting buffers configured as voltage-dependant resistor (in IC36) and an integrator consisting of IC37b (IC38b) and C69 (C71) with Q44 (Q45) switcher. In this arrangement VCO-1,2 generate triangle waveforms . When TRIG (>) is applied to the base of Q39 VCO-1 receives a positive pulse from Q40 collector at the following places. There are similar conditions at VCO-2.

a) One input of IC37a via D62. When the pulse is applied, IC37a turns its output to low.

b) The base of Q44 which discharges C69, cancelling VCO-1 output. The combination of a) and c) resets VCO-1 to the starting point at which VCO-2 also starts oscillation, phasing the initial waveforms of both VCO's.

c) The base of Q46 which cuts off VCA Q50, muting unwanted noises in the VCO-1 path.

There is also a positive pulse starting ENV 1-5.

Output of ENV1 (part 9) influences the Control Voltage Generator. The resultant effect is a pitch bend of Snare drum sound for about 20ms. The triangle waveform (integrated square = triangle) of VCO-1(VCO-2)passes through a diode clipper (see parts 12,13) to twist the triangle into a waveform near sine. The amount of drum voice from VCO-1 (VCO-2) is determined by VCA Q50 (VCA Q51, see parts 14,15) whose gain follows ENV3 (Env2, see parts 17,16) which is in turn controlled by an ACCENT (>) coming through Q41 currently gated by the TRIG.

Snappy uses the common noise generator, which is also used for Bass Drum, Hand Clap and Tom's. Noise signal (>) is low pass filtered (IC 40a, see part 1) and then splitted into two parts. The first part is passing through a VCA Q48 (part 5) which is controlled by ENV4 (part 6). The second part has its own VCA Q47 (part3) controlled by ENV5 (part 7), but is high pass filtered (IC 39a, see part 2) before passing through. ACCENT signal is gated through Q41 by the trigger from Q39 collector and is coupled to the base of Q47 VCA as ENV 5. ENV 5 determines the amount of high frequency noise components in the SNAPPY which becomes articulate when noises passing through the high pass filter are combined with the noises from the low pass filter at IC39 (part 4).

Finally Drum and Snappy are mixed and amplified at IC40b (part 18) to provide level-control.


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