Cassette Tape Project

March 13th 2025

Background and Motivation

Last year (or maybe two years ago, its been a while) I aquired a Yorx steoro in a thrift shop for maybe $30.. I used for its intended purpose for a while until it became too much space and I cannibalized it for parts.. It took a lot less space without the case of particle board and plastic.. This leaves me with the dual cassete player that was in there.

I spent some time figuring out how to power it (12VDC) and built an amplifer for the left cassette, so I could listen to some cassettes.. However In the interest of starting anew, I'll spare you the history and only talk about it when it becomes important again..

My current problem: recording

(Current recording test setup)


My first cassete recording setup used my radio ( set to a high enough volume ) plugged from its headphone jack straight into the the read / write head.
The read head basicly consists of two inductors ( one for each channel, left and right ) positioned right next to the cassete tape. When playing back, signal from the tape is picked up by these inductors, then it's amplifed so it can become audible.
When recording signal is amplified and sent into the head to do the reverse, effecting the tape. ( This is my understanding anyway :D)
I say read and write head because, although some cassette decks have separate heads for recording and playback, this is a cheap player and uses the same head for both thingies.
Listen to me doing some tests of this horrid simplified idea:

Biasing

It sounds like crap because I need something called biasing, which is basicly a signal injected to the tape, which (although not directlly audible) mix with audio you want to record and minimize distortion like what you just heard.
There are two types of biasing, AC and DC..
As you would figure DC, is just a constant voltage mixed with the audio signal. Makes the signal a bit bettet better, but at the cost of introducing some noise.. This has only been used seriously in early (1950s and earlier) tape machines and now replaced by AC bias.
AC is a sine wave around 50-100khz that does the same thing, except for better in every single way, less noise, better frequency response..
Ill try to make a DC bias for simplicity, as well as it seems fun to go through history a lil as I learn this..
My first design:


Used a potentiometer to vary voltage and mixed it with the audio signal.. That 680ohm resistor in series with the tape head is from something I read saying that it made the frequency respone a little more linear.. Maybe i should get rid of it however, as all it does is drop some voltage.
This did nothing, until I realized that I put a capacitor (capacitors being used in this case to block dc and allow only ac current) in front of the potentiometer xD.
Next design:



Here is a recording of what happens now.. It sounds like the audio signal rapidly drops as I turn the voltage up:
Doing some research and letting it rattle around in my brain some, I think the solution would be to feed the dc to the erase head (which comes before the write head and wipes before you record)..
I'm not sure if i have to bias the erase head and the play head? Maybe its a DC quirk that the audio distorts. Maybe i need much more voltage on both the audio and the DC bias? I was also hoping to be able to overdub signal by disabling the erase head.. If i record on top of a already biased cassete (no erase head or any type of bias), will the audio sound not as distorted?
Pictures of my next setup to test:


Anddd Heress what it sounds like! Much the same god damn it xD This is when I wonder devoting energy to learning old tech like this :D On one hand I could buy something functionally equivalent (and better) for a little under $100, but then there is also a value to up cycling old use tech. This skillset or technology couls be used in an age where computers and intergrated circuits are less prevalent, and reused technology make more sense. I guess im not sure how to create any difference in the world with technology.. However thats just me trying to validate my real reason for doing this - its fun! (Plus, Cassettes are cool) At the moment it is anyway, I have too many projects lol. Should probally take it easy so I dont get sick of it..! Also would love to make music and edit the old school way of splicing tape together.

But to talk about my vision for this project, I would like to design and build a recording/mixing/djing/equalizer to record music/interviews/podcasts and to send out to a radio transmitter / computer. Then build or 3d print a panel, add a battery and a heavy duty pelican case to make it portable.. Hey even if it isnt perfect frequency response, it would still be cool.

Pictures of the concept for the panel: