How's this for an idea? Build a demagnetizer
into a cassette shell. When you put it into your tape deck and hit play. It improves
the sound quality of your music system. This was given to me last year. It's a TDK HD-01,
and I've been learning all about how it works. This was 22 dollars when TDK released these
in 1978. That's about 100 bucks today. From what I've read, these operate by
generating a sine wave. Then slowly reducing the strength of that sine wave down to
zero. To remove magnetic buildup from tape heads. Cassette decks such as this Walkman, have
a play and recording magnetic tape head. Tape heads are basically small coils of
wire. As the tape moves past the head, variations of magnetism on the tape cause
a fluctuating magnetic field on the head. That changing magnetic field generates an
electrical signal across the coil in the head. Amp up that electrical signal and you
get some banging tunes to listen to. The problem is, over time all
this exposure to magnetic fields, can leave a residual magnetic field on the
head itself. This introduces distortion in music. That can be heard as decreased high
frequency crispy sound, and more hiss and noise. When a demagnetizer is used with a tape head. The
signal from the demagnetizer can smooth out any magnetic fields that have built up over time.
On the back this one says turn down the volume to zero. Because this signal can damage audio
equipment. Such as speakers, headphones or ears. The other thing I learned is that there's
been a debate going on for decades. About how effective these things actually are.
This debate has continued online with some great arguments on both sides. In places like the Tape
Heads forum and the cassette culture subreddit. The topic of demagnetization is complicated.
There are other types of demagnetizers. Such as this wand based unit. That can demagnetize
not just the head, but the entire tape path. There is a solid use case
for professional settings. Where equipment maintenance is arguably
more critical. The question remains. What are the benefits of spending the
equivalent of a hundred dollars on one of these? When a tape head pushes into the bottom of the
cassette. There's a switch inside that activates the unit, and a red light comes on. It's amazing
the battery still works in this after all these decades. There's not many things from the late
70s that are still working with their original batteries. In fact the only other thing that
I can think of, is the Voyager space probes. To test this, I'm going to use this
CD tape adaptor. This has a head in it. These are normally used to feed audio
from a CD Walkman, into a car tape deck. For this test I'm going to use this adaptor
to feed the demagnetizer into a computer and record the signal. I need to take the adaptor
apart. To get the head out for this to work. To record the signal I'm
plugging the adaptor into the mic input in this laptop. Then I'm running
Audacity to grab the actual signal. It's just a matter of pushing the head into
the demagnetizer to activate the process. The signal is very short.
Zooming into the waveform shows it's only about 120 milliseconds long.
From a human time scale it's more like a pulse. The signal fades out over time. So the end point
depends on where you decide the zero point is. When zooming in further, we can see the sine wave. Measuring the wave reveals that there are
10 cycles every 17 milliseconds. With a bit of calculation, this comes out to about 588
cycles per second. Or a 588 hertz sine wave. Having a closer look inside at the circuit
board. Reveals eight transistors. With the smattering of capacitors and resistors. A couple
of diodes and even a coil. It's a neat design. But probably the best part is the clear
cassette shell. It just looks so cool. Looking at various different models from different
manufacturers. It looks like one of the most common features of cassette based demagnetizers
is the clear or windowed shell designs that were used. I think that's the key. These were bought
because they looked cool. Sure they do operate on a sound principle. That gives you a feeling
that they're doing something. And it's clear that maybe in some cases, with some decks, at some
points in time, they actually did make music sound better. But I think their main function was
to look good sitting with your Hi-Fi system.
