Introduction: DIY Cassette Tape Echo
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.
- Basic soldering, splicing wire
- Understanding audio signal flow and using a mixer
- Patience to work with something as thin and finicky as cassette tape
- Four-track cassette recorder* with at least two inputs (I used the Tascam Porta02)
- Regular cassette player (preferably name-brand and '90s-era for higher fidelity, i.e. Sony Walkman or something similar)
- Blank cassette
- Scotch tape or special splicing tape
- Small piece of foam taken off a foam brush
- Thin hookup wire
- Heat shrink tubing
- 500 Ohm, 2W linear-taper potentiometer (value may vary based on your recorder)
- Various resistors (to fine-tune the value of your potentiometer, if necessary)
*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.
- Soldering iron
- Regular and jeweler's screwdrivers
- Needlenose pliers, wrenches
- Hacksaw or Dremel
Step 1: Remove and Prep the Extra Play Head
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.
Step 2: Reconnect and Mount the Extra Play Head
Remove the screws in the bottom of the four-track and pop off the lid. Drill a small hole in the side of the four track and another in the side of the Walkman, then guide the wires from the extra play head through these holes. Solder the three wires back to where they were originally connected to the PCB.
At this point, it may be a good idea to test that everything still works. Pop some batteries into the Walkman, press Play (you don't need to insert a tape), and plug a pair of headphones in. If you tap the tape head with your screwdriver, you should hear a small thunk in the headphones. Or grab an old credit card or something with a magnetic stripe, and move the tape head back and forth over the stripe. You should hear scratching sounds that resemble a DJ scratching vinyl records. (Make sure it's a credit card you don't need to use anymore because it will end up covered in scratches after this).
Moving on, dab a small drop of superglue on the left edge of the extra tape head. Don't use too much. I had good luck with Krazy Glue but not with Gorilla Glue. Carefully position the extra tape head to the right of the four-track's tape head and hold it in place for about five minutes while the glue dries. Be sure not to get any glue or scratches on the part of the tape heads that touches the tape.
Take the ground wire from the extra tape head and screw it down to the four-track tape head's mounting post or any other screw you can find inside the four-track. Reassmble the four track.
Step 3: Create a Custom Cassette Shell and Tape Loop
Take apart your blank cassette by removing the 5 small screws that hold it together. Remove the tape, tape reels, and pressure pad. Next, remove any parts of the shell that will get in the way of the extra tape head you've mounted. I did this using my pliers to snap bits off, but someone who owns a Dremel could probably do a more elegant job. Don't remove more than you need to. For the top cover of the shell, use a hacksaw or other tool to remove the entire area covering the tape head opening, since you'll need easy access to this area for making adjustments later on.
Place the shell inside the four-track and check that you can press Play all the way and that the transport mechanism can move forward and back freely.
Remove the foam from your foam brush and cut into two small rectangles, about 1/4 inch thick. These will go opposite the tape heads in order to put pressure on the tape as it moves along. You may also need to put a thinner bit of foam opposite the erase head as well. The amount of pressure needed isn't an exact science, and you'll need to experiment with different thicknesses of foam to get it right. For this reason, don't glue the foam in place yet.
The Tape Loop
Contrary to some people's first impression, the tape loop itself is not responsible for the echo effect at all. The tape loop is necessary because the regular supply and take up reel setup won't have enough tension to be compatible with your new Frankenstein cassette shell, and the four-track will most likely "eat" the tape when you hit Play. A tape loop will have more tension and prevent this from happening.
Make your tape loop. Here are two good tutorials: Youtube, Instructables. You can use either Scotch tape or fancy specially made splicing tape available on Amazon. It's important to make sure your tape loop has just the right amount of tension. If it's too tight, it'll get stuck and won't play properly. If it's too loose, it may start getting tangled or the four-track will eat your tape. The linked tutorials recommend measuring the exact length, but it may require a bit of trial and error to get it right. You will probably become a tape loop making expert and develop your own technique for them by the time you're done with this step.
Reassemble the tape shell with the tape loop inside, insert it in the four-track, and press Play. Double check that the tape is moving smoothly and not getting stuck or tangled.
Step 4: Connect, Test, and Troubleshoot the Tape Echo
If you plug in your guitar and amp at this stage, there's a good chance the tape echo won't work perfectly right away. That's most likely going to be caused by the foam pressure pads applying either too much or too little pressure, but there are a lot of other factors that can go wrong. For this reason, it's best to connect and test each part of the signal flow individually
Connect the guitar to channel 1 of the four track, turn on the four-track, and connect the headphone out to your guitar amp with an instrument cable (mono). Set the volume fader on channel one to about 7, and turn up the gain until the guitar starts to distort, then dial it back a notch. If you're not hearing anything, check the volume on the guitar is turned up, your cables are working, and your amp is turned on and working.
Hit Record on the four-track. If the Record button is stuck, check that the tabs at the top of the cassette shell are intact, and cover them with electrical tape if they're not. Check that the tape loop is still moving smoothly. Strum the guitar for a few seconds, then hit Stop. Turn up the monitor volume on the four-track, press Play, and check that you can hear a few seconds of your strumming looping over and over on the tape. If you recorded to track one, make sure the volume for track one is up.
If you can't hear anything, press Stop and press Record again. This time, take a small flathead jeweler's screwdriver and gently push down on the foam rectangle across from the record head while strumming. Press Stop, press Play again, and while gently pushing on the foam, check if you can hear a few seconds of your strumming. If yes, it means you need a thicker foam rectangle. Experiment with different sizes and positions until you're able to record and playback onto the tape loop using just the four-track.
If, on the other hand, the sound is warbly, it means the foam pads are too thick, and the tape isn't moving along at a constant speed.
Press Play on the Walkman. Again, you don't need to have a tape inserted; the Walkman just needs to have Play pushed down to work. You can press Pause on the Walkman to avoid hearing the transport squeaking along. Connect a pair of headphones to the Walkman and turn the volume about halfway up. Press Play on the four-track. You should hear the same few seconds of strumming you recorded earlier through the Walkman now. If not, experiment with the foam pad across from the extra play head you glued on. If the strumming you recorded earlier is on track one, try recording some on the other tracks and test again, since the two tape heads might not be aligned perfectly.
Connect a cable from the headphone output of the Walkman into channel 2 of the four-track. Make sure the Walkman is still on, and press Record on the four-track. While strumming, slowly turn up the volume on channel 2. You should start hearing the echo effect at this point. If not, try messing with the foam pads again while the tape is running. Try gently moving them a few millimeters over, or try gently moving the entire cassette a little, if there's any give. Experiment. You should be able to crank up the volume on channel 2 and get crazy, self-generating echoes, or dial it back for a more reasonable effect. Channel 2's volume is equivalent to the "Feedback" knob on a regular delay effect.
Once you have the pressure pads' thickness and position dialed in, carefully glue them down with a drop each of superglue.
If you're getting a build-up of sound with each pass of the tape loop, it means the erase head isn't working properly. The erase head is the one all the way to the left. Try putting in a smaller, thinner rectangle of foam in the cassette shell across from the erase head.
Step 5: Wire Up a Motor Speed Control (Optional)
In order to get different delay times, you can wire up a potentiometer to the four-track motor to slow it down. Unfortunately, I don't know any way to get faster speeds, so you can only go slower (although some four tracks have faster speed settings than the one I used).
First, press Play on the four-track and use a multimeter to measure the voltage across the terminals of the motor. Next, clip one of the leads (doesn't matter which), and use your multimeter to measure the peak current draw across the splits. Use the voltage (V) and current (I) to determine the power rating (P) you will need for your potentiometer, using the formula P = IV. In my case, I ended up using a 2 watt pot. To calculate the resistive load (R) of the motor, use the formula R = V/I aka Ohm's Law. Start with a potentiometer with the same resistance. In my case, it was a 500 ohm potentiometer, linear taper
Connect one end of the split you cut to lug 1 of the pot, and the other end across lugs 2 and 3. Press Play and try slowing down the motor. If the resistance is too high, the motor will stop completely, which you don't want. You can use resistors to fine tune the range of the potentiometer, using this guide, or use trial and error with several different pot values. Use alligator clips or breadboard to experiment with different values, until you land on a range that works.
I ended up using a 500 ohm potentiometer with a 330 ohm resistor across lugs 1 and 3 to take the range down from 500 ohms to about 150 ohms, and a 47 ohm resistor in series with lug 1 to get a range of 47 - 197 ohms, give or take.
Drill a hole somewhere on the four track enclosure to mount your pot. On my Porta02, the only space I found was to the right of the power jack, right behind the motor. I used some sticky foam to keep the pot from damaging the motor when I reassembled the four-track.