Tape Head

You will need:

• a tape head;
• some magnetic media: cassettes, plastic cards with strip, hard discs, etc.;
• battery powered amplifier with much gain;
• additional sound source, e.g. CD or tape player;
• optional: a credit card reader.

A tape recorder works by translating audio signals into a fluctuating electromagnetic field - essentially flipping the north-south orientation of a magnet in response to the audio signal's wobbling between its plus and minus boltage extremes. This flipping magnet is the 'tape head', the small metal blob you can see inside a cassette player or answering machine. The tape head's undulating magnetism in turn aligns tiny magnetic domains in the iron-like powder covering one surface of the recording tape, as if they were tiny compass needles. As the tape is played back the process is reversed. Similar to a record groove and needle, or a set of digital on/off switches.

Obtain a tape head from a broken/unwanted answering machine or cassette player. You can buy them separately, but they won't have the wires attached to them already. Leave as much cable as you can, and solder a connector to the free end - make sure you solder the shield to the sleeve of the jack and the inner conductor to the tip or you'll get a lot of hum. If there are no wires connected you'll have to experiment.

Playbackq

Plug the head into a high gain amplifier. You'll need a lot of gain. Rub it over some recorded media: bank cards, cassette tapes, computer discs. With cassette tape stretch it across a table top and stick it down. Use the side with the emulsion coating. If the signal is weak you can preamplify it by connecting it to the microphone input of a mixer or guitar amplifier.

Recording

You can try recording with the head as well. Stretch cassette or reel-to-reel tape over a desktop. Plug a CD or cassette player into the input of a mini-amp; plug the tape head into its external speaker output. While playing the CD/cassette, move the tape head over the tape surface keeping the head in close contact with the tape. After a while stop recording and try playing back the tape. John Cage once made a piece by covering a table-top with tape, inviting the public to scribble across it with tape-heads attached to pencils, then wound the tape onto a reel and played it back.

Feedback

As with the telephone coils used in Circuit Sniffing, sometimes you can get nice feedback between a tape head and a speaker, or between two tape heads, or the left and right channels of a stereo head. Plug the tape head into the input of an amp, move it near the speaker and listen for the squeal. Split the output of one head with a y-cord and send it into two amplifier inputs; plug another tape head into the output of one of the amplifiers. Raise the amp gains and listen as the head coils feed back and interact.

Card Readers

Surplus outlets often sell 'card readers' from ATM machines, public telephones, etc. The reader consists of a tape head inside a housing that guides the card smoothly past it, along with circuitry needed to decode the digital data. Stealing credit card data is advanced hacking (see Mark Trayle, 'Capital Magnetics') but for our purposes you can discard the circuitry, wire the head up as above, plug into an amp and end up with a very nice instrument for 'scratching' all kinds of data cards.