Compared to modern MP3 players, where storage is fully digital, old tape decks are ridiculously complicated. When the Compact Cassette (standard “cassette tape”) first hit the market in the 1960s, digital audio was still a dream. Proper analog-to-digital conversion was available, but affordable storage was not. So people turned to cassette tapes with complex electromechanical recorders and players. He seems to be something of a masochist, but… Igor Brychkov is trying to make his own tape recorder/player..
Since Brychkov still has some concern for his sanity, he seems to focus only on the electrics and electronics. He doesn't try to recreate the various winding mechanisms, which is probably for the best, since winding mechanisms are notoriously unstable, even in mass-produced tape decks. Instead, Brychkov uses old tape mechanisms in his electronics.
These circuits fall into two broad categories: playback and recording. In mass-produced tape decks, these circuits are often mixed together to cut costs, but in this case, Brychkov has mostly separated the circuits to make them easier to understand.
The two most important components here are the recording head and the playback head. Brychkov reused the playback head from an existing tape deck and created his own recording head, which is basically just an electromagnet. When a voltage from an audio source signal is passed through it, the recording head produces a similarly changing magnetic field. When a magnetic storage medium, such as tape, is run nearby it receives a magnetic imprint of the audio. The playback head then does the same thing in reverse to play back the audio.
While the concept was easy to understand, the actual execution required diving deep into analog signal processing. Brichkov used an op-amp as a preamp to bring the amplitude up to a usable level, but he also needed to incorporate the ability to mix an AC bias into the input signal. He also needed record and erase functions, as well as an eight-LED VU meter for basic level visualization.
Brichkov feeds the output of the preamp directly into a wired amplifier, but has also connected a Bluetooth receiver module to the input, which allows you to send and record audio signals from a smartphone or tablet. The components are still on the strip board, but it will be interesting to see where Brichkov takes this project next.