32 Nicolas CollinsFeedback
As with the coils we used in Chapter 4, 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 the input of an amplifier,
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 amplifier 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 (ask Mark Trayle, whose piece “Capital
Magnetics” makes music out of credit data), but for our immediate 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” cards.