oh, the memories.
Yeah... I remember my old Harman-Kardon cassette deck. Superior sound quality for a cassette deck, imho.
HK used "constant current" instead of "constant voltage" to supply the signal to the recording head.
The result was that the bass recorded did not have the ups and downs in level that most (all?) other cassette decks exhibited.
At the time, I worked for a record company, so I took home some frequency response measuring equipment one evening.
Long story short, my HK cassette deck measured +/- 0.5dB from 15Hz to 21KHz.
Yes that was an actual measurement I made on my cassette deck. I was so surprised, I measured it again. And again.
(I was using Maxell cassettes, fwiw. Though I no longer remember the exact tape used.)
But wow.
Constant current vs. constant voltage.
Who would have thought?