Build an experimental echo pedal

Build an experimental echo pedal

I have made some changes to the schematic I posted this morning. The schematic posted below reflects these changes.
-C1 has been assigned a value of 47uF
-R19 has been removed.
-An unmarked resistor at pin 5 of the op amp has been removed.


This crazy echo circuit is the design I’ve been using in my EchoBender pedal. Check out some videos of the circuit in action.

The heart of this circuit is the PT2399 echo IC. View the data sheet here. They can be found pretty cheaply from various distributors.

The fun starts when you push the IC beyond it’s intended parameters. Drastically lowering the pitch uncovers digital noise and strange blipping effects. I’ve also included a fun audio feedback feature which can be used to create intense distortion as well as interesting octave and pitch tracking effects.


Thanks to Dan Wagoner for sending in a parts list!



Collin’s Lab: Guitar pedal modding with Arduino

20 thoughts on “Build an experimental echo pedal

  1. Pete says:

    I don’t know how these type of sounds have become so popular. Nothing in the videos sounded like music or even for that matter, remotely pleasing to the ear.

    1. Walter Jr. says:

      If you really care to understand that (in oppose of just being annoying) then maybe it is time you do a bit of homework and start revisiting your concepts. It all sort of dates back to the 1910’s, when people realized that machine sounds and “unwanted” sounds (noise) would become an integral part of our daily lives and change our perception forever.

      Here you go:

  2. shivlu jain says:

    whats the use of it?

    1. aaron says:

      pretty cool – especially for such a (relatively) small circuit.

      the use of it is primarily to delay the sound, but the circuit has enough flexibility to push the chip beyond its “safe” limits for conventional clean delay. the result is the bizarre synthesis and distortion you hear.

      i agree, the samples in the videos are rubbish, and do not do justice to the type of sounds possible with the pedal. I dont know if he was just strumming an arbitrary “dummy” type pattern, or not, but my guess is that he was. rest assured, such a pedal could very easily create gorgeous and lush tones.

      can we get some shots of the guts?

  3. Dan Wagoner says:

    thanks for sharing this circuit! when i saw the videos of this a few weeks back, i scoured your site for the design. i will definitely be making one of these. adding casper to the make team was one of the best ideas ever!

  4. Elliot says:

    If you want a design with a cleaner delay/regen, try the Rebote (2.5) delay. There’s PCB layouts and even pre-fabbed boards at:

    Indeed, I’d start out with the Rebote design (or the reference design in the PT2399 datasheet) first, and work on your own mods. That’s half the fun of bending, IMO.

    The basic circuit is quite tweakable, and very very fun. All the timing/feedback/filter resistors and caps are rewarding if you “play” the raw circuit with your fingertips.

    But man, you gotta admire that case that Casper puts it all in. (Mine’s just a hairball of wires with some alligator clips sticking out.) Kudos for a beautiful job!

  5. lizentrail says:

    hey… emh nice… ive got really interested in this, but im pretty new to these kind of things, anyhow in the list theres written that you need DPDT switch … but in the picture theres just that sompbox switch… so which one is it??? and how does it work with the schematic, well I would want the one that you can just push, couse well its easier if your playing guitar….


    yeah yeah I know I should start with building an overdrive etc. but well iv never used an overdrive for playing guitar, And this looke fairly difficult but simple for me … so I decided I want to make this…

    1. lizentrail says:

      nevermind… got it … :D

      1. lizentrail says:

        nope… emh still i am not getting it… so could someone reply please???

  6. Thomas Mahoney says:

    Hey this pedal sounds great in the videos, i was breadboarding it up and noticed the C3 0.082 isnt on the parts list. Is it meant to be 0.082F or 0.082uF?

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