Dur-Bul Instruments 0009
3U/4HP Passive Analog Multiplexer

1 Operation

The Dur-Bul Instruments 0009 passive analog multiplexer allows a
single output to be switched between two inputs under the control
of a 5V-level gate signal. This is done passively, meaning without a
separate power supply connection, allowing for flexibility in system
design by reducing the total number of power connections needed.

Unused inputs are grounded, providing silence when used for audio
signals or a 0V level when used as control voltages. This allows use
of the Dur-Bul Instruments 0009 as either a two-input multiplexer
or an on-off switch.

2 Typical Uses

Hard on-off articulation

  input 0: Audio from oscillator
  input 1: Not connected
  select: Gate from input device
  output: Audio output

Turn an oscillator and an input device into a minimal instrument
with abrupt articulation for a classic chiptune sound.

Audio cut-in

  input 0: Foreground audio
  input 1: Background audio
  select: Cut-in enable
  output: Audio output

Mute background sound and replace with a foreground signal under
control of the gate signal. Can be used for a single-tracked
percussion effect or to enforce mutual exclusivity of layers.

Signal chain swapping

  input 0: Signal chain 1 output
  input 1: Signal chain 2 output
  select: Square wave LFO output
  output: Audio output

The same audio signal source can be passed through two different
signal chains and recombined at a multiplexer under the control of
a LFO, allowing real-time timbre shifts.

Rapid CV switching

  input 0: CV source 1
  input 1: CV source 2
  select: 5V LFO output
  output: Oscillator CV input

Allows combining of two melodic lines through rapid switching.

CV drone

  input 0: CV from input device
  input 1: CV from drone source
  select: Gate from input device
  output: Oscillator CV input

Similar to hard articulation, but switches in a background melodic
line instead of silence.

Clock source muxing

  input 0: Clock source 1
  input 1: Clock source 2
  select: LFO or subdivided clock
  output: Clock input of next module

To add some diversity to rhythms, differently-subdivided clocks
can be selected using a further-subdivided square wave (or another
source altogether) as input.

3 Specifications

  Min. Vgate(2)    -20V
  Min. Vgate on(1) 4.75V
  Max. Vgate(2)    20V
  Min. Igate on(1) 8mA
  Max. Tswitch     2ms
  Max. Zon         1.5kohm || 0.8nF

(1) Threshold for selecting input 1.
(2) Limits for preventing damage.

The inputs of the Passive Analog Multiplexer will not be damaged by
any voltages used in a typical modular synthesizer. Impedances are
appropriate for audio signals driving a high-impedance input. Care
must be taken when using the multiplexer for control voltage
signals to only use with very high-impedance buffered inputs to
avoid tuning issues.

4 Care

The Dur-Bul Instruments 0009 Passive Analog Multiplexer can be
expected to last for decades of use with only basic cleaning. The
use of ceramic capacitors and a solid-state relay eliminates many
of the common wear points on similar products. The connectors may be
cleaned with a plastic-safe contact cleaner if they become oxidized.