This is a guide for those wanting to build a cheap, fun and different 'lo fi' tape delay from microcassette tape dictaphones. Originally I've posted a guide for the build on my site/blog (dogenigt.blogspot.com) but the project has gained a lot of popularity over the past years so I decided to make this my first 'structable in here :-)

What is it and how it works:
It's basically to tape machines with a tape loop going through both through the sides of the cassettes. One machine is set to record, the other is set to play. What happens is that the 'recorder' records the incoming signal onto the tape strip and when the recorded signal enters the 'player' the signal is sent to the output so we can hear it with a delay determined by the amount of time and the distance it took for the signal to go from one head to the other.
The output signal is fed back into the 'recorder' and mixed with the input so a bit of the played signal is re-recorded onto the tape again, therby creating 'repeats' in musical terms. The motors controlling the speed of the tape wheels can be controlled to determine the time it takes for the delayed signal to be played, thereby it's our 'delay time'.

If this is a bit confusing to you, the video should explain most of it. :-)

Step 1: Preparing the Players

First you need to strip the players from the plastic casing. The design may vary depending on the type of dictaphones you've got but the crucial thing is to clear the area around the cassette's (in my case) right side where the motor isn't in your way. That way we can make a small crack in the cassette case in order to allow the tape to travel in a loop between both machines.

Next step is to connect both players to the same power supply and find the points on each pcb where the motor is slowing down or speeding up (depending on what delay time range you are looking for). The faster speed of the motor, the shorter delay time you get and the other way around.
Maybe it's even possible for you to vary the voltage directly to the motor (very good for voltage control!)
Connect a potentiometer where you attach your wires from both players so the speed is the same as in both motors. It's a good idea to get two identical dictaphones if possible as the motors may differ and thereby the speed could too.

After you've done that, attach the players to a wooden board and make an oval hole for the bolts too be able to adjust the distance between the players which is convenient for adjusting the tightness of the tape loop when it's done.

Step 2: Make the Tape Loop

Now for the trickiest part.
Cut two slices in each cassette so they face each other when one players in turned on it's head (see picture in step 1) and measure the length of the tape slice going around both "turn wheels" and the roller in the bottom left side so that it aligns with the pincher, roller and tape head and is kept in place. It's important that the loop is tight but not too tight. Find an instructable for making tape loops if you are not experienced. My approach is too calculate a few milimeters of tape to overlap, tape on the non-magnetic side and cut the excess milimeters of tape afterwards.

When you've made the tape strip for your loop, carefully descent it onto the bottom halfs of the cassettes lying in your players so that the loop goes through the slices in the sides (refer to the pictures in this step)
Tape the top halfs of the cassette on top so it's easy to disassemble when you find out your loop is too tight or loose (be patient for this, as it can be very tricky to get it right. Use pinchers and have a buddy help you hold the loop when you tape it.)

Step 3: Make the Circuit

The (rather messy) layout above is meant to show the signal path the sound undergoes to create the delay effect.
Start with the audio jacks (input and output) the input goes to the mic or line in of the 'recorder' and the 'output' goes to the existing jack output on the 'player'.

4 x audio potentiometers for attenuating the signals are needed all in all. They are:
- INPUT VOL
- FEEDBACK VOL
- DRY OUTPUT VOL
- WET OUTPUT VOL

The dry and wet signals are necessary to be able to hear both the non-delayed signal and the delayed. The feedback potentiometer determines the amount of the playedback signal being re-recorded thereby determining the amount of time it takes for the signal to get inaudible (or totally incomprehensible noise)

The circuit is quite simple, it's a passive mixers using capacitors to mix the signals. Ideally one should be using op-amps to buffer the signals... I might do a v2.0 of this some day.

Step 4: Encasing

Attach the sides onto the bottom woodboard into a box and add a piece of clear acryllic board on top. (we want to be able to see the beauty spin around while listening to it! :-) )
Drill holes in the acryllic for the the potentiometers (the 4 audio pots and the motor speed pot), the audio jacks and a power toggle switch and you are done!

I've attached a recording directly from the device for your listening pleasure.