I messed around with primitive PWM amplifiers a little in the 80s, and always wanted to - but never got around to - replace the conventional HF bias + audio drive scheme in my home-made cassette deck with a straight square wave drive width-modulated with the audio.
In those days you had to roll your own, but these days there are some - already long in the tooth - PWM power amplifier configurations that can run at around 50kHz. Stick the audio signal into that and drive the resulting current into the head - should produce a myuch broader dip in the distortion curve and be less critical of bias level versus metal formulation. Simpler circuitry too - no separate bias power amp and record driver.
When (not if, Max!) this gets published in EET, I'd like to get hold of a table of the frequency response data, pre-equalization. I'm the first person to get excited about doing special filters, but this is a case where a digitally-implemented equalizer could probably do a super job. Implemented on the replay side, you could use a reel of calibration wire to give standardized excitation, and then everyone's wire recorder can be calibrated to have a super-flat frequency response! If that's what floats your boat, anyway.
@DrZuhoch: I still have one in my shop somewhere...I'll see if I can find it and send pictures.
Please do send the pictures to me at firstname.lastname@example.org and maybe we can do a follow-up column on this. I'd also love to see some pictures of a wire recorder being used as a form of computer memory as mentioned elsewhere in ths icomment thread.
I never throw anything away,and I still have one in my shop somewhere...I'll see if I can find it and send pictures.I don't remember the last thing recorded on it, it was used as an office stenographer.
As we unveil EE Times’ 2015 Silicon 60 list, journalist & Silicon 60 researcher Peter Clarke hosts a conversation on startups in the electronics industry. Panelists Dan Armbrust (investment firm Silicon Catalyst), Andrew Kau (venture capital firm Walden International), and Stan Boland (successful serial entrepreneur, former CEO of Neul, Icera) join in the live debate.