BugBrand DRM2 User manual

BugBrand DRM2
Operation Manual
The DRM2 is presented as a wide-ranging drum voice synthesizer but it is really a full
analogue synthesizer just with drum-focused envelopes. The sound path is a somewhat
traditional subtractive arrangement of scillator → Filter → Amplifier, while the control
section offers two Decay Envelopes and a Sample & Hold. This core is then garnished
with switched internal routings, an Audio Preamp and diverse 4mm banana CV
Inputs/ utputs to complete a compact but powerful sound generator.
This manual breaks down the constituent parts (see block diagram overleaf) before giving
usage examples and interfacing details.
Tom Bugs
Bristol, August 2018
[email protected] – www.bugbrand.co.uk
[A colour version PDF is available to download from the website]

The DRM2 core can be seen as a sound section ( sc,Filter,Amp) and an associated
control section (Trig, Envs, S/H). The block diagram shows the circuit blocks that make
up the DRM2, their associated controls and I/ , and the signal flow. Note the use of
colours to denote function and the use of Int for internal signal routing vs. Ext for external
control inputs.
Sound Section
Oscillator: The Voltage Controlled scillator (VC / sc) is the core sound generator, but
it can also function as a modulation source at audio or low frequencies. It is a triangle
core design with temperature compensated exponential control (1V/ ct), the frequency of
which is governed by a summation of the Tune/Fine controls and any of the modulation
inputs.
•The output is sweepable from Triangle to Square with the Shape control and its
output (+/-5V) is provided at the green sc socket.
•The Tune control sweeps the frequency over the range of approximately 1Hz to
10kHz, while the Fine control gives a 1 ctave range. The sc can go well beyond
these ranges with CV control.
•There are two Internal modulation sources – Bend from the Bend Envelope and Int
Mod which is switchable between S/H or Noise modulation (with centre off)
•There are two External modulation sources – a precision 1V/ ct input for pitch CV
(accurate over about 6 octaves) and Ext Mod with switchable polarity. Each input is
designed for typical 10V peak-to-peak signals but accepts anything up to +/-15V.
•The scillator can be synced (reset) on each Trigger Event via an internal jumper
(set N as supplied). This resets the Triangle wave to 0V.

Filter: The Voltage Controlled Filter (VCF) is a 12dB/ ct State Variable design with
temperature compensated exponential control (1V/ ct). It can self-oscillate at full
resonance to produce a pure sine-wave and has a switchable output response
(Low/Band/High-pass).
•The Source switch selects the filter input between sc or Ext (preamp) or it can be
set to centre-off for no input, useful when the filter is self-oscillating.
•The Cutoff control sweeps the frequency over the full audio spectrum and is
summed with any other modulation source.
•There are two Internal modulation sources – Bend from the Bend Envelope and Int
Mod which is switchable between S/H or scillator modulation (with centre off)
•There are two External modulation sources – a precision 1V/ ct input for frequency
CV (accurate over about 6 octaves) and Ext Mod with switchable polarity. Each
input is designed for typical 10V peak-to-peak signals but accepts anything up to
+/-15V.
Amplifier: The Voltage Controlled Amplifier (VCA/Amp) is linearly controlled and feeds
into a shaping section, which can be switched between Saturation or Wave-Folding,
before a final utput level control and impedance balanced 1/4” utput socket.
•The opening of the Amplifier is governed by a sum of the Initial (Manual) control
and any modulation sources, ranging from 0 (fully closed) to +10V (fully open).
•Internal modulation comes from the Amp Envelope via the Env Amt control, while
External modulation is from the CV source with switchable polarity (again 10V
peak-to-peak typical).
•Low settings (under c.25% depth) keep the VCA in clean range, while greater
depth brings in the effects of the shaping sections.
•Saturation is based on soft-clipping zener limiting, while Wave-Folding provides
three stages of folding to add overtones.
Control Section
Input / Preamp: The unbalanced 1/4” line input brings signals into the DRM2 both for
processing through the Filter and/or Triggering events. The Drive control offers gain from
fully off up to +20dB and zener saturation/clipping. Switch the To Trig switch to the Up
position to pass the amplified signal to the Trigger Processor.
Trigger Processor: The Trigger Processor sums three sources to produce a global
Event Trigger pulse.
•Trig Socket – this expects a gate/logic input with triggering occurring on the rising
edge. It will typically take a 0 to +10V input but lower amplitudes can be used to
provide amplitude dynamics.
•Manual Button – this triggers an event at full amplitude.
•External Signal – with the To Trig switch n (up), an external signal is rectified and
filtered to produce an event trigger. The signal can be an external gate or an audio
signal with the most regular results coming from simple, dynamic signals such as a
kick or click – the Drive control should be adjusted to give regular triggering.

Bend Envelope: The Bend Envelope is a simple manual Envelope with variable
exponential Decay, triggered with each Event Trigger. The output passes to the Bend Env
socket, LED indicator and the Bend Modulation controls. The amplitude depends on the
amplitude of the any trigger input up to typical +10V.
•Envelope time range: 10mS to 1.5S
White Noise / Sample & Hold: White Noise (+/-5V) is generated with a standard
transistor based circuit. This is used both for the S/H source and sc modulation, along
with switched output through the Mod ut socket. The S/H samples the input voltage
each time an Event Trigger occurs and holds that voltage until the next trigger (note – the
voltage can droop over time – this is normal). The output range reflects the +/-5V input
and again the section can be switched to output through the Mod ut socket.
Amp Envelope: The Amplitude Envelope adds Voltage Control to the Decay time setting
and offers longer decay times. Decay time is set by the sum of the Decay control coupled
with the Ext Mod control input with polarity switch. The output connects to the Env Amt
VCA control along with Amp Env socket and associated LED.
•Envelope time range: 10mS to 10S
First Patch:
There are a number of settings which might initially catch you off guard:
•The first half of the Tune dial covers sub-audio ranges & these will only be audible
if the waveshape has some square blended in (ie. Not fully counter-clockwise).
•Ensure the Filter Source switch is set to sc.
•n the Amp section, either turn up the Initial control for steady drone, or ensure the
Env Amt dial is turned up.
•For modulations, make sure the switches aren't in the centre-off position.
Further ideas:
•Noise Modulation – using Noise on the sc Int Mod offers a range of results.
With the sc tuned low, apply a small amount of noise for noisy kicks.
With the sc tuned high, apply a medium amount of noise for tuned noise results
or full noise modulation for something approaching white noise (good for hats)
•Self-oscillating Filter – turn Res up full and set the Filter Source switch to centre-off
for pure sines. Now set Int Mod to sc to FM the frequency – you could also patch
S&H via the Ext Mod or apply it to the sc itself.
Also try switching the Source switch back to sc.
•Variable Decay – patch S&H to Dcy Mod and adjust to taste.
•Amp Envelope shaping – patch the Amp Env into Dcy Mod to change the envelope
shape.

•External Signal Processing – plug an audio source into the input and adjust Drive.
Keep To Trig switch ff (down) and switch Filter Source to Ext. Now play with the
Amp Initial control and adjust Cutoff / Res. You can then apply Triggers to fire the
Envelopes and/or S&H for modulations.
•Switching the To Trig switch n (up) will, with Drive adjusted, create trigger events.
Take the Initial control back down to zero and apply Amp Env with the Env Amt
control. Short Amp Decay settings will gate the sound.
Something akin to Compression (fixed fast attack, variable decay) can be achieved
by patching the Amp Env output into the Amp Mod input and switching it to inverted
modulation (keep the Env Amt control down in this case)
•Self-Triggering – patch the sc output to Trig input and set the sc Shape to
something from 50% to fully Square, keeping the Tune set very low. The sc then
creates trigger events – try applying some S&H to modulate the sc for random
rate variations.
Cali ration:
The DRM2 comes calibrated, but may require small adjustments to match your system.
Always let the DRM2 warm up for 30-60 minutes and proceed with care:
•_SCL is the main scillator scaling adjustment
HFRQ adjusts high-frequency tracking, but should not generally need adjustment
_ FS offsets the scillator frequency, typically set for Tune range 1Hz-10kHz
•F_SCL adjusts the Filter scaling
•NLVL adjusts the noise amplitude (limited to +/-5V) but should not require
adjustment.
Power:
The cased / standalone DRM2 comes with worldwide (90-264V AC) power pack which
provides the required 300mA @ 12VDC via 2.1mm centre positive plug. The standalone
case holds a DCDC converter to generate the standard +/-15V bipolar supply.
The DRM2 can also be used as a module within a larger BugBrand/Frac system.
Power draw is +ve 70mA , -ve 70mA

Interfacing with Banana Sockets:
As 4mm banana cables do not carry a 0V connection, you must join the DRM2's 0V
(black banana on rear of case) to that of any external system to establish a common 0V.
Banana-to-Banana:
External banana systems should have a 0V banana socket, usually located on the case
or PSU. Connect a banana cable between this and the DRM2's black 0V socket. With this
common 0V established, signals can then be patched freely between systems.
Banana-to-Jack:
Use BugBrand Interface Cables – minijack to banana.
•The first connection is made with a two wire cable assembly.
◦The Black cable, from jack sleeve, plugs to the black 0V socket on the rear of
the DRM2, thus establishing a common 0V.
◦The White cable, from jack tip, then plugs to a CV source/destination.
•Further connections to the same piece of equipment can then be made with single
wire signal cables.
•If a further piece of equipment needs to be used, another twin assembly should be
used to again establish a common 0V connection.
Guarantee:
The DRM2 comes with a 2 year 'reasonable' warranty. If any mechanical or electronic
failure occurs within the period, I will repair the fault free of charge. This excludes failure
from maltreatment or modification and any cosmetic degradation. Contact should first be
made via email to discuss the problem. Shipping to return the device is paid by the user
and I cover return shipping. Failures that are not covered by this guarantee may be fixed
at standard rates.