BACKPACK COULD DO BETTER JOB
A NEW IDEA from Kelwood Computer Cases is the range of Backpacks for the Spectrum and ZX-81. They have a range of facilities from a simple LOAD/SAVE-ON/OFF switching device to one which also includes a sound amplifier and a mains distribution board. Also from Kelwood is the Microstation, a large tray on which can be placed a computer, tape deck and choice of Backpack.
Overall, Backpack One does the job it was designed to do but the job could have been done far better. The LOAD/SAVE switch merely switches the EAR signal line and could induce an earth loop, a common problem on the ZX-81; it is also a mains switch and is therefore not really suitable.
The sound board contains a 1W audio amplifier chip, the LM380N. It also contains, among other things, three Mullard 'liquorice-all-sorts' capacitors which although they do the job are about 20 times too big.
The volume control is a IM logarithmic potentiometer which, apart from being too highly-rated, is wired incorrectly and so the volume needs to be turned up to about two-thirds before anything is heard; it then needs fine adjustment.
Finally the overall soldering can have a number of dry joints, which leads to oxidisation and bad connections.
The Microstation is a metal tray approx 445mm. x 435mm. to which five rubber feet have been riveted.
Backpack One seems overpriced at £27.50, as does the Microstation at £7.50. The full range can be obtained from Kelwood Computer Cases, Downs Row, Moorgate, Rotherham S60 2HD. Tel: 0709 63242.