A switching power supply made for the Sizif-512 board: 9 V, 1 A maximum, 5.5 / 2.1 mm plug, centre positive, with overvoltage and short-circuit protection built in. It is the right supply to feed a ZX Spectrum Neo or a machine you have built yourself around a Sizif-512 motherboard, and it is sized so that the board and its sound card together leave headroom rather than running at the limit.
There is nothing romantic about a power supply, but there is a great deal to be said for the correct one. Retro computers are lost far more often to the wrong voltage or the wrong polarity than to age, and a barrel plug that physically fits is not the same thing as a barrel plug that is safe to use. This one is specified for the board it goes with.
Specification
- voltage: 9 V
- maximum current: 1 A
- plug: 5.5 mm / 2.1 mm, centre positive
- overvoltage and short-circuit protection
The current budget, if you are building
Worth knowing before you start hanging things off the edge connector. The Sizif-512 board alone draws 250 mA. With a sound card attached it draws 500 mA. The board is protected by a 750 mA polymer fuse, so external expansion cards have to be counted into the same budget — add up what your cards want before you plug them all in at once, or you will spend an evening wondering why the machine resets whenever something interesting happens.
This is one of those calculations that teaches more than it costs. Working out what a board draws, what a fuse will tolerate and where the margin has gone is exactly the sort of thing the Spectrum was a good place to learn, and it applies to everything you build afterwards.
An important warning
Do not use this supply on an original 1980s ZX Spectrum. It may damage the machine. There are two reasons. The original computers expect the opposite polarity — centre negative, not centre positive — and they draw considerably more current than a Sizif-512 does. The plug will fit. That is precisely the danger.
What it suits
The ZX Spectrum Neo and any machine built on an assembled Sizif-512 board. A supply is already included in the ZX Spectrum Neo set, so this listing is for self-builds, for spares, and for anybody who would rather leave one permanently under a second desk.
Questions people ask
Can I use this on my original ZX Spectrum from the 1980s?
No, and this matters. The original machines use the opposite polarity, centre negative, and draw more current than this supply is intended for. Using it may damage the computer, and the plug will fit perfectly well while it does so.
Is 1 A enough?
Comfortably, for the board and a sound card: 250 mA for the Sizif-512 on its own, 500 mA with the sound card attached, against a 750 mA polymer fuse on the board. If you add expansion cards on the edge connector, add their consumption to that figure before you decide.
What plug does it have?
5.5 mm outside, 2.1 mm inside, centre positive.
Will it work with a ZX Spectrum Neo?
Yes. The Neo is built on a Sizif-512 motherboard and this is the supply specified for it. One is already included in the Neo set.
Is it protected?
It has overvoltage and short-circuit protection of its own, and the board it feeds carries a 750 mA polymer fuse.
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