hexinverter Mutant Bassdrum User Manual

Mutant Bassdrum
analogue bassdrum user manual v1.05
Thank you for your interest in the Mutant Bassdrum (MBD)! The MBD is a 13HP eurorack format synthesizer
module available both as a ready-assembled module and a printed circuit/panel set you can build yourself if
you have the skills.

THE BASSDRUM

The MBD is really two modules in one: a feature-rich analogue bassdrum synthesis module and an
aggressive voltage controlled distortion effect. The distortion features UV purple LEDs as hard clipping
diodes and optocoupler-based voltage control of the distortion amount. The distortion can be used to
process external signals at the same time as synthesizing percussive sounds.

FEATURES

 entirely analogue bassdrum circuitry capable of vintage TR-808 sounds
 built in distortion effect (batteryACID topology) with modular level output levels
 distortion accepts external inputs when not being used with bassdrum (great for acid synth leads)
 voltage control of distortion amount
 voltage control of decay from short hits to long "oooomphs"
 voltage control of pitch (not v/oct) from subsonic bass frequencies to high tom drum sounds
 non-invasive analogue vactrols used for voltage control, so, vintage sounds can still be had
 completely redesigned, hi-fi signal chain spares no expense by replacing cheap transistor amplifiers with low
noise opamp equivalents
 dial in super hot, eurorack modular level output levels (up to 20Vp-p!)
There are already some really excellent clones of vintage gear out there in the modular world. The Mutant
Drums were not made to try and fill that role. Although each Mutant began as a favourable classic drum
topology, we wanted to create something modern and different, while still maintaining an analogue
nature. Features like CV inputs and signal routing not found on classic analogue drum machines were
incorporated to make the circuit a powerful creative tool in your modular synthesizer, rather than just

TECHNICAL SPECIFICATIONS

A little bit of technical stuff...
The MBD gets its organic sound from a twin-t damped sinewave oscillator just like the legendary TR-808
made famous. This seemingly simple circuit does a lot with very few components, and as such, the
frequency of the oscillator by way of voltage control is costly to linearize. So don't expect perfect tuned
musicality from the oscillator when using it like a synth voice! It is not volts/octave response, though it is
approximately exponential. We used optocouplers (aka: vactrols) throughout this design so you may notice a
slight amount of slew on the CV inputs' response. This is a natural effect of vactrol control and is nothing to
be concerned about!
6.16.2014

The Mutant Philosophy

transplanting a vintage drum circuit into your machine.
Width: 13HP | Depth: 30mm
Current draw: +55mA, -45mA @ 12V
Mutant Bassdrum user manual v1.05
hexinverter.net electronics, 2014
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