6 V Power Supply – Sharp CE-152

The Sharp CE-152 does not have an internal mains transformer; however the manufacturers have thoughtfully provided a socket to power the unit from a suitable mains adapter that provides 6 V DC. I had many orphaned adapters; therefore, I decided to make a small regulator circuit, which provided 6 V when fed with 9 V.

The tape recorder circuit is good, but the down side of the design is that it has no power supply of its own and is at the mercy of the adapter regulation and smoothing. The alternative is to use batteries. Unfortunately, adapters generally tend to be cheap and poor quality designs. Many adapters do not even have a bridge rectifier to provide full wave rectification. Therefore, I decided to build my own power supply, which provided regulation and smoothing.

6 V Power Supply Circuit

I had plenty of orphaned adapters providing voltages in the range 12 V to 7 V. The only thing I needed was a 6 V regulator in a T0220 package. This is readily available from Maplin, order code AW69A.

I also decided to use a 1000 µF capacitor to produce extra smooth dc current. The 0.01 µF capacitor is a ceramic disc type, and it must be close to the printed circuit board and their power planes. With this type of power supply circuit, it is possible to obtain a very clean audio free of any kind of mains hum. At full volume, it should produce pure hiss, and I tested it out with my ZX81 by "Saving" and "Loading" programs onto cassette, and it was successful every time.

DC Power Socket

On this tape recorder, the centre pin of the DC socket is negative.

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