Whilst Yamaha's DX7 is certainly an excellent synthesiser, it is a relatively complicated and difficult machine to edit and create your own sounds on. Unlike a lot of synthesisers, the DX range of synths can synthesise many different types of sounds with a great degree of accuracy and realism. Literally hundreds of very different sounds can be produced from this one instrument alone, 32 of which can be stored in the DX7's internal memory. The DX7 also has a system for storing voices on to RAM cartridges, as only 32 memories would hardly be sufficient for such a versatile instrument.

Having over 100 different parameters per voice makes it virtually impossible to recreate a patch if it is not stored either in the internal memory or on to a RAM pack inserted into the DX7's cartridge slot. Greater is the need, therefore, for 100% reliable memory storage.

However, Yamaha's RAM cartridges have a reputation for being unreliable. Without warning, a complete set of sounds on a cartridge can suddenly be ruined by the smallest amount of data corruption. On three occasions I have had a complete RAM cartridge 'format conflict' itself, resulting in me becoming very frustrated and shouting obscenities at my dog.

I have even known a RAM pack to have been thrown across a room and to have been smashed to pieces as the result of just such an unfortunate format conflict message.

The faults occur because of the indeterminate electrical state when RAM cartridges are either inserted or removed from the cartridge slot (and also when power is switched on or off whilst the cartridge is still in the DX synthesiser). This occasionally results in the write protect switch actually generating a write operation.

Although this fault only corrupts a very small amount of data in the RAM cartridge, it is nevertheless sufficient to create a format error, making the cartridge completely unreadable.

Late February's IM&RW had a look at the Skyslip ROM and RAMs and it was found that these could lose their memory very easily as well – simply by leaving the RAM pack in the RAM port of the DX synth when you switch off the power. With such a temperamental RAM system, I almost don't see the point of having any cartridge-based memory at all.

However, a Canadian company called Red Planet Instruments have come to the rescue with an alternative static RAM cartridge called the Red Planet SR64. The SR64 doesn't just look a bit different – it also differs from Yamaha's RAM packs in several other ways:

1) A single SR64 RAM cartridge will hold a total of 64 voices, as opposed to the Yamaha's 32. Each end of the cartridge has its own set of gold plated edge connectors which access their own set of 32 voice memories. This effectively acts as two RAM packs in the one unit.

2) The SR64 is built to be failsafe. Red Planet have put a great deal of effort into making the SR64 extremely reliable and able to cope in the most unfavourable of conditions. When a cartridge is inserted or removed from the DX synthesiser, and when the power is switched on or off whilst the SR64 is still in the cartridge port, automatic delay circuitry comes into effect for a few milliseconds, disabling the memory chip and preventing any erasure of data.

3) The SR64 uses a CMOS static RAM chip as opposed to Yamaha's EPROM (Electrically Eraseable Programmable Read Only Memory). Whilst this results in the SR64 needing to use a built-in power cell soldered into the cartridge (which incidentally is estimated to last from six to 15 years) it also means that Red Planet's RAM packs can be made reasonably cheaply and the circuitry is very stable.

4) Due to their chosen form of memory storage, Red Planet's cartridge has an unlimited lifetime. Whilst Yamaha's RAM packs are limited to a lifetime of less than 10,000 write/erase cycles (although certainly quite a long life, it is still a limit which would some day prove very inconvenient), the SR64's unlimited life only requires a battery change after perhaps 10 years of use.

The Red Planet cartridge has no switch for memory protect on/off. As there is already the internal memory protection in the DX synthesisers themselves, I actually found the lack of an additional memory protect switch to be much more convenient and also an advantage because mechanical switching is always a likely source for faults, and will probably wear out at some point.

Another big improvement over the Yamaha cartridge is the SR64's loading time of a complete set of voices to and from a DX synth. The SR64 only takes a fraction over 1½ seconds, whereas Yamaha's RAM packs take over 13 seconds to store a complete set of 32 voices...

These features, added to the SR64's robust metal case and competitive price (it is £4 cheaper than its Japanese counterpart), make it an excellent buy that I would highly recommend to any DX7, DX5 or DX1 owner.

RRP: £85