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The ASM303 was created from a 'design idea' by Harry Bissel in EDN December 26,2002.


Envelope followers extract amplitude information from complex audio waveforms. The resulting dc voltage often drives nonlinear stages, such as voltage-controlled amplifiers or filters.You must make a careful trade-off between the speed of response to a rapidly changing input signal and the amount of ripple in the dc output that you can tolerate. If the system is too slow, the output has low ripple but badly distorts the envelope shape. If it’s too fast, ripple can modulate the nonlinear stages, causing audible distortion products.


Audio sources, such as a guitar, pose special problems. The instrument has an attack of a few milliseconds and a long decay time. The musician may “mute” the strings at any time, causing the normal exponential decay to terminate abruptly. The waveform is sometimes unsymmetrical and may have multiple zero crossings. The fundamental frequency range is typically from approximately 80Hz to 1.5kHz.


Previous circuits have used a full-wave bridge and a large averaging filter. A filter time constant sufficient to reduce ripple makes the circuit unable to follow rapid changes in amplitude. Peak-detecting circuits can follow the rapid attack and provide low ripple during the exponential decay but cannot follow the rapid decay of a muted string.


The design here features fast attack and low ripple with minimal filtering, and it can follow a rapid decrease in signal (mute).


The ASM303 takes this design and adds a GATE/TRIGGER detector circuit to increase the connectivity of the module to a modular system.




This Module is available to buy as - 


  • A fully assembled module with 3.5mm sockets. (Eurorack 1/8" Standard)
  • A fully assembled module with 4mm sockets. (Banana Jack)
  • A full DIY kit, all parts and components to build your own 3.5mm sockets.
  • A full DIY kit, all parts and components to build your own 4mm sockets




Width: 7hp

Depth: 60mm

Contents: Panel, PCB/s, Components, Ribbon Cable, Screws

Build and Technical Information: Click Here

Elby Designs ASM303 Envelope Generator DIY KIT Eurorack Synthesizer

3.5mm or 4mm Jack
  • Shipping Transit.

    With Tracking 7-14 Business Days (Estimated)

  • Sales & Taxes.

    The sale price listed is AUD (Australian Dollar), and is the final price to pay.

  • Payment.

    Credit Card (Visa, Mastercard, Amex), PayPal.

  • Warranty/Returns.

    1-Year warranty against defects, and manufacturing faults. (Click for more)

  • Additional Notes.

    This module is available to buy with 3.5mm (1/8" Jack) sockets or 4mm (Banana Jack) sockets.