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I've recently purchased a tape recorder (Tascam Midistudio 644) that was very cheap because the previous owner had lost the power supply. The PS-M1 power supply that originally came with this unit is a kind of rare so it's not easy to come across online. It's also a little unusual, so I can't just purchase an AC/DC adapter and have it work.

The original power supply has a plug with 4 pins, delivering the following:

  • +10 V 1 A
  • -10 V 1 A
  • +7 V 10 mA
  • GND

My first issue is that the plug is an unusual trapezium shaped plug, but I was just planning to replace the socket with a 4 pin DIN socket.

Regarding the actual power supply: For simplicity's sake, and in case I was ever to sell this Midistudio 644 on to someone else, my power supply circuit ideally would be within a plastic enclosure with one cable going in and one cable going out to the Midistudio.

Regarding the actual circuit, I've come across a few suggestions online but I'm having trouble working out what is the best option for my situation. One of these suggestions was to source a centre-tapped transformer and build my own AC/DC converter from scratch. Since I am not a qualified electrician or electrical engineer I don't like the idea of building a circuit that contains mains voltage: I'm not sure that is even legal in my country.

Another way was to hook up two 10 V DC 1 A power supplies, reversing the polarity of one. Of course, this option leaves out the required 7 V pin - I thought I would just wire up little voltage regulator circuit to the +10 V rail to get +7 V since the low current on the 7v pin should draw next to no power. However, I don't like the idea of having to plug two plugpacks into the wall everytime I wanted to use the midistudio. Perhaps my equipment could be damaged if someone accidentally powered only one of the two plugpacks?

I wondered whether it would be possible to buy a 24 V AC/DC adapter and somehow split the voltage into +/-12 V, after which could flow into three voltage regulators to produce the required voltages. Are there any drawbacks of this method? How would I design such a circuit? What current would the 24 V plugpack have to be rated for to be able to drive such a circuit?

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