The Indifferent Engine "Janky" Tape Echo

A project to design and build a janky retro tape echo effect from readily available parts. Eventually STLs and PCBs will become available for you to build one of your very own!

Tape echo effects sound cool, but are expensive and/or hard to find and maintain. Whilst there have been many DIY examples over the years these usually rely on finding a 3 head tape machine as a prerequisite requirement of the build. As a result, 3 head machines are becoming scarce. So, I decided to try and build a unit from a 1 head cassette player and then add in the extra heads by 3D printing a new section for the transport that allows the erase and record heads to be mounted. It would also use custom electronics as much as possible.

I want this build to be "easily" repeatable by other people, so all parts need to be easy to source or easy to create at home.

Below is a video demonstration of the completed Mk I design.

The Prototype


1. Top view with enclosure lid removed

Here you can see a little more clearly the tape path as it runs from the read head, through the pinch roller (only the pinch roller at the top is engaged - this transport has auto-reverse and the second roller isn't used in this configuration), through the first reel (top), over a steel rod that acts as a tape guide, back down over the second reel (bottom), then past another steel rod before passing through the erase head (black), then the record head, and finally over another steel rod guide.

2. Back plate removed, PCB (rev 1.01).

This version has 2 custom PCBs - the main board which is clearly visible here, and a second board at the top that's partially obscured by the 3D printed enclosure. The purpose of the second board is simply to mount the front panel controls and LED lighting. It interfaces with the main board via ribbon cable (those 2 IDC box headers you can see). The mainboard is held into the enclosure by the board mounted audio jacks. This probably needs some extra support adding to take the pressure off of the solder joints on those jacks. 

The 3rd jack (the silver one, bottom left) is the remote jack for effect switching - this works like an amp switch in that it just passes out a +5V signal that can be grounded by an externally connected momentary switch to tell the microcontroller to switch the effect in/out. The microcontroller then controls the miniature relay to handle true-bypass switching.

Note-worthy stuff you can make out on the mainboard PCB;

  • The green Arduino Nano with USB port facing up. I opted to just include pads for a off-the-shelf Arduino board you can grab from anywhere rather than integrating the microcontroller directly on the PCB. It didn't add much extra space and makes the build much simpler, I reckon.
  • Board mounted audio and DC jacks. There's a lot of off-board wiring so I'm trying to keep that to a minimum. Note that the only reason the switching remote jack isn't board mounted is that I hit the maximum board size on the free version of Eagle :<
  • Components that comprise the bias oscillator are clearly marked (top right). This is likely to be the first part you'll build yourself as it needs to be tuned and tested independently of all other parts of the system.
  • PWM driven motor controller (top left). This is driven by a high frequency PWM output on the Arduino.
  • Switching relay (orange, below the Arduino). For switching the effect between dry and effect signals. Just to the right you can make out a 2n2222 transistor, which interfaces the 3V3 logic from the Arduino with the 5V relay.
  • The two op-amp sections which deal with input buffering, output buffering, record pre-amplification and output dry/wet mixing.
  • Those 3 huge capacitors (they're 2200uF caps). These act as current reservoirs to stop the motor/oscillator from sucking too much current for the other to operate correctly. Both the motor and the oscillator are very current hungry!
  • The IDC box...
Read more »