The TD404 machine is an instrument for textural exploration in audio. Its sound is derived from something of a sonic playground.

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The TD404 features three sections of guitar strings, one vertical spring, three horizontal springs, a kalimba, a drawstring, a tunable guitar string, and a clasp. All of which are fed through a preamp and delay system within the unit.

The TD404 offers a broader range of exploration for music, engineering, and production enthusiasts, alike. Its simplicity invites users of all skill level to engage in a sonic adventure beyond the realm of any instrument conceived before.

The core of this project involves three key components: a contact/piezo microphone, a Velleman K1803 Preamp, and a Synthrotek PT2399 Delay. They are chained in said order to mono output. The intent stems from music producer/engineer legends such as King Tubby and Scientist. First, the various parts (e.g. strings, springs, and in between) offer textural tones which are picked up by the contact mic and amplified by the preamp. While stimulating, this is taken further by the delay system which features feedback, mix, and repeat rate control. Stemming from influences of dub and techno, one may expand the reach of the system by repeating sounds and maxing the feedback to obtain extraordinary results from otherwise ordinary components. 

In all, this was a 60 dollar build. Considering it's huge return (aka bang for its buck), I plan to add a low pass filter and CV control on future iterations. 

Disclaimer – Velleman, Inc..pdf

It appears velleman is quite strict about reproduction. Therefore, a substitute preamp would be required if it were to go further

Adobe Portable Document Format - 290.56 kB - 09/18/2018 at 19:50


  • 7 × 100k ohm resistor
  • 1 × 2k2 ohm resistor
  • 1 × LM78L05 U2 Voltage Regulator
  • 1 × 220k trim pot
  • 1 × 1k ohm resistor

View all 39 components

  • video!

    Nick09/18/2018 at 19:47 0 comments

    Full video here of what it can do here: 

  • Complete

    Nick09/17/2018 at 17:12 0 comments

    TD404 is Complete.

  • Finishing up

    Nick09/16/2018 at 13:40 0 comments

    After a bit of calibration, I have the preamp at its most efficient level for the delay module. I'm going to run a few test runs, but I will have a proof of concept video in the next log. This should be followed by the required video submission for the Hackaday2018 Musical instrument contest


    Nick09/15/2018 at 13:53 0 comments

    So this log is unique to my project. Using a diamond bit, I drilled holes in some of my old wisdom teeth. Using hot glue, I am fixing them to the buttons for the warp and feedblast mods. (TD404-Tooth Decay404)

  • Preamp

    Nick09/15/2018 at 13:51 0 comments

    In order to get the most out of this contact microphone, I'm using a Velleman Preamp. It's very small and should help boost the sound. I'm not thrilled about the high end distortion that will probably result, but I think a simple RC Lowpass filter can solve it if it proves to be unbearable. 

  • Wiring

    Nick09/15/2018 at 13:50 0 comments

    All pots are wired. Next is the modifications on the PCB and then wiring up the power supplies. 

  • Fitting the Delay Module

    Nick09/14/2018 at 12:56 0 comments

  • Box construction

    Nick09/11/2018 at 15:07 0 comments

    I've begun adding the top layer components to the box I picked up from a thrift store. 

  • Test Run 2: The Spring Machine

    Nick09/11/2018 at 14:57 0 comments

    Again, I am testing the ability of the concept. 

  • Test Run: The String Machine

    Nick09/11/2018 at 14:55 0 comments

    Here, I test the project concept but outfitting a metal box with a number of guitar strings to review the ability of the microphone and overall concept. 

View all 12 project logs

  • 1
    Synthrotek PT 2399 Delay

    At the following site, one may obtain all parts and instructions for the delay module.

  • 2
    Velleman K1803 Preamp

    At the following site, one may obtain all parts and instructions for the preamp module.

  • 3
    The Box

    It is advised to use metal or wood. Begin with a general design session of how you want the layout to be conceived (i.e. random, symmetric, modular-esque, etc). After a plan is sketched, locate a place for your contact mic and note this area cannot be drilled into. Begin install of springs, strings, etc. 

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