THIS IS ONE of several expansion boards currently available for the DX7, one which adds a number of features to your favourite (if recently discontinued, see elsewhere this issue) FM synth. Although not as wide-ranging in scope as, say, Grey Matter Response's E! board, DX-MAX is still quite a neat achievement.

A relatively simple installation procedure calls for you to open up your DX, remove three chips and insert the DX-MAX in their place. Unfortunately, the board has to partly slide under a long piece of aluminium which separates the keyboard from the DX's motherboard, and it's a bit of a hassle unless you remove the metal separator. To do this, you have to remove the keyboard to get to the screws that hold the aluminium in place.

Once you've navigated these points, and after carefully prying out three easily identifiable IC chips, you position the DX-MAX card so that the main EPROM fits in one of the original slots.

When you now power-up your DX, the LCD shows that DX-MAX is installed and you're ready to go. All the added features are accessed by first depressing the Function button and then pressing either button 12 or 13 (these are normally unused by the DX7's operating system). These buttons now cycle you forwards or backwards through the new features.

First off, you now have eight banks of 32 sounds available onboard. That's 256 patches instantly at your command, with no loading from disk or cartridge. Additionally, you have the option of storing function parameters for each voice, plus additional features included with DX-MAX. So not only do you have the sounds available, but also any function parameter settings for each individual patch. This doesn't limit your number of voices, so there is still a total of 256 voices and functions available for storage.

If you are using your DX as a master controller, you'll now be able to send on any of the 16 MIDI channels directly. Bear in mind that any DX-MAX function can be stored in its function memory, so you can now set up patches that include a MIDI channel number - a very handy feature, especially in live situations with multiple-synth setups.

Upper and lower key limits are now programmable, and although you can't combine two patches on either side of your limit point, you can at least simulate a split mode on your DX if you're MIDI'd to another synth. Just throw a bass patch up and limit it to a high note of G2 or C3. Your right hand can play anything above the high limit, and it will be muted on the DX but not on any external synths.

Another feature included (although I don't really see much use in this one) is programmable volume levels for each voice. I don't know anyone who owns a DX who doesn't own a footpedal as well. But for those who want to set an output level for the whole patch, you can specify it between 0 and 7.

The last feature is a new Poly mode, where you can stack voices and detune them individually to achieve harmonies and chorusing. Three modes are used: 16x1 (the standard DX 16-key polyphony, one note per key); 8x2 (eight-key polyphony, two notes per key); and 4x4 (four-key polyphony, four notes per key).

Each note can be tuned within a four-octave range (+24.99 to -24.99), so chordal lines can be achieved by tuning each stacked voice to the appropriate interval. Or detune each one slightly to achieve a chorusing effect. Again, any of the special features can be saved within the fuction memory of DX-MAX, so new versions of traditional FM sounds can be stored on a single DX.

Regular DX cartridges can still be used with the expansion board, and you can save sounds to cartridge just as you always do. You can also use cartridges saved using DX-MAX with standard DXs, but be sure certain functions are set to 0 for the 32nd memory, otherwise you'll get a format conflict. A small price to pay for stored voice and function parameters on a cartridge.

I had little problem installing my DX-MAX (I'm no tech wizard, either), and it worked as promised, right from the start. I got a little worried when I put in a cartridge, pressed a key and got no sound, but a rapid search through the skimpy documentation (four pages) revealed that all the function values are set to zero (Volume = 0, high limit key = C2) when you first attempt to load a ROM/RAM cartridge. It's easy enough to fix (just set the board to read Voice Only), but my heart definitely skipped a beat.

Overall, the best feature of DX-MAX is the immediate expansion to eight banks of 32 voices. But almost every one of the other additions comes in handy at one time or another. DX-MAX is a nice addition to your DX7, and although not as powerful as some other expansion boards, it certainly expands the power of your DX a few notches.

Price £249 including VAT

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