This Instructable will show you how to make an analog tape echo effect for use with electric guitar or any other audio source. The cassette tape echo employs the same basic principle as legendary vintage units like the Roland Space Echo or more primitive reel-to-reel tape echo setups, but using much cheaper and more readily-available used cassette technology. Unlike the classic commercially-made units, this project has more limited features, more unpredictable behavior, and a noisier, more lo-fi sound-- whether those qualities are desirable or not are up to you.
How It Works
Before starting, it's important to wrap your head around the basic principles behind all analog tape echoes and to an extent magnetic tape recording in general. To put it briefly, cassette and reel-to-reel recorders are able to record, play back, and erase audio using tape heads that generate magnetic fields to align tiny metal particles on the tape. Old reel-to-reel recorders have three separate dedicated tape heads for erase, record, and play functions, arranged in that order with respect to the direction of the tape's travel. Since the record and play heads are separate, there is a few milliseconds' delay between the time the audio is recorded to tape with the record head and the time it's played back with the play head, depending on the distance between the two heads and the tape speed.
At some point, audio engineers figured out how to create an echo effect by taking the output of the play head and mixing it with the audio source being sent to the record head, creating a feedback loop. This is crudely illustrated in the diagrams above, with the audio source being an electric guitar. The commercial tape echo units like the Space Echo use the same basic signal flow plus some additional features.
Making a tape echo out of a cassette recorder is tricky because, unlike reel-to-reels, most cassette recorders have a combined record/play head instead of separate record and play heads (Those who own a high-end 3-head cassette deck might be interested in building the Echo-Matic instead). To make it work, you are going to have to attach an extra play head to a working tape recorder, amplify the signal of that tape head somehow, and hack up a cassette shell so that it will accept the extra play head.
*Since a four-track recorder is just a tape recorder with a built in mixer, you can probably just use a separate mixer and two regular cassette players to make this (although I've never tried), which might make the project even cheaper to build. I chose to use the Porta02 because it's more convenient to move around and because I already had one. The fact that it can record four separate tracks isn't necessary for the project.
The first part of the project involves removing the tape head from your Walkman (I use the term generically), mounting it into the four-track, and reconnecting it back to the Walkman to use its preamp circuitry. If you'd like, you can use some other commercially available or DIY preamp instead of the Walkman to amplify the signal from the play head.
Take apart your Walkman to expose the circuit board. Locate the play head and trace its wires back to where they're attached to the PCB. There should be three wires-- one for left, right, and ground. Make a note of where each wire connects on the PCB by taking a picture. Desolder the three wires, being very careful not to damage any components on the PCB.
Use your jeweler's screwdriver to remove the play head from the player. You may have to remove the flip cover (there should be a way to pop it out without breaking it). Press play in order to move the transport mechanism up and make it easier to reach the screwdriver inside. There should be two small screws holding it down. Carefully take the tape head and its attached wires all the way out without damaging the wires.
If necessary, lengthen each of the three wires attached to the tape head by splicing on a few inches of wire and using heat shrink tube to insulate the splice. Take some thicker heat shrink and pull it over the new wires you spliced on to make the whole thing neater and more durable. Remember, it needs to be long enough to reach from inside the four-track to inside the Walkman.
Last, use your needlenose pliers to remove the mounting brackets and tape guide from the tape head. You will probably have to bend it back and forth repeatedly until it gives and pops off. Be careful not to scratch the front of the tape head, where it touches the tape, or to tear off the two wires attached at the back. There should be one wire attached to the brackets. This is the ground wire, and you can leave it loose for now.