Two sounds enter. One sound leaves. That’s the basic concept of this module. Built around a DG419 analog switch, the Thunderdome uses an internal 7555-based, square-wave oscillator to switch between two input signals at audio rate, producing sounds ranging from atonal and metallic, to rhythmic and musical.

Use the range toggle to select between two oscillator frequency ranges: the low range dips down almost out of audible frequencies, while the high range gets up to kHz frequencies.

Optional External Mod input bypasses the internal square-wave oscillator allowing for the use of external voltage sources to trigger the switch. Different waveforms will produce different results, determined by the length of time the waveform stays above the reference voltage threshold. Patch in an LFO or a clock signal to slowly switch back and forth between sounds.

Schematic

Schematics are provided as-is. Never trust that any schematic on the internet is foolproof. Test your build in isolation before introducing it to the rest of your modules.

Download Thunderdome v1 PDFDownload

BOM

  • Capacitors
    • 30pf ceramic capacitor (1) C11
    • 0.01uf ceramic capacitor (1) C5
    • 0.1uf ceramic capacitor (1) C2
    • 1uf ceramic capacitor (1) C1
    • 10uf ceramic capacitor (5) C6, C7, C8, C9
    • 10uf electrolytic capacitor (2) C3, C4
  • Resistors
    • 1k resistor (3) R1, R2, R3
    • 300R resistor (1) R4
  • Potentiometers
    • A100k (2) RV2, RV3
    • B100k (1) RV1
  • Transistors
    • 2n3904 transistor (1) Q1
  • ICs
    • 7555 timer (1) U1
    • TL074 op amp (1) U2
    • DG419 analog switch (1) U3
    • L78L05 5v regulator (1) U4
  • LED (1) D1
  • Eurorack power header (1) J1
  • Audio jacks (3) J2, J3, J5
  • Switching audio jack–e.g. Thonkiconn (1) J4
  • SPDT toggle (1) SW1

Demo

Long demo of Thunderdome, using internal and external modulation sources
Lovely Pulses demo
Cancellations demo

Patching Ideas

Lovely Pulses

  • Tune three oscillators, with pulse waveform output, harmonically
  • Patch all three oscillators to the same 1v/oct source (sequencer, sample & hold, etc.)
  • Patch the pulse outputs of two oscillators into inputs 1 and 2 of Thunderdome
  • Patch a clock-synced or looping envelope into the PWM of the third oscillator
  • Patch the pulse output of the third oscillator into the External Mod input of Thunderdome
  • Tweak the pulse width and PWM depth of oscillator three until the pulse width is modulated sufficiently narrow (or broad) to be inaudible when the envelope is open or closed, creating a rhythmic pulsing in the Thunderdome modulation

Cancellations

  • Patch a saw and pulse wave out of the same oscillator into inputs 1 and 2 of Thunderdome
  • Patch a clock-synced or looping envelope into the PWM of the oscillator
  • Tweak the pulse width and PWM depth of oscillator three until the pulse width is modulated sufficiently narrow (or broad) to be inaudible when the envelope is open or closed, creating a rhythmic pulsing in the Thunderdome modulation
  • Adjust the modulation Frequency knob on Thunderdome until desired timbre is achieved