Last month, we looked at syncing up old sequencers, arpeggiators and drum machines with your MIDI system. Time now, to look at how you can do the same with synthesisers...

Although the process of integrating something like a CS80 or Pro One into a modern system is obviously a lot more complicated than just syncing up, there are, paradoxically, a lot fewer ways of doing it.

The simplest method, again, is to get a firm like Kenton Electronics to install a MIDI interface inside your synthesiser. In many cases this will simply turn your old synth into an old MIDI synth with all the usual functions; in others, you may not have quite the level of control in and out that a current MIDI synth will provide. For instance, monophonic synths can only be used as sound modules, not controllers; and the same (sadly) is true of a machine like the Yamaha CS80, whose pleasingly sensitive keyboard and polyphonic aftertouch don't get a look-in as far as MIDI retrofits by Kenton Electronics are concerned.

Not surprisingly, the converse is true of a Hammond. Kenton can get it to function as a (fairly basic) MIDI controller, but there's no easily affordable way of getting the 5-pin DIN to set those tone-wheels spinning. (I can't actually see any really good reason why they shouldn't, but you'd certainly run into a bit of expense if you wanted to motorise the drawbars which are half the secret of the Hammond's appeal.)

Polyphonic synths like a Prophet 5, Oberheim OBXa, or MemoryMoog should present no trouble, though. Kenton quote a price of just under £250 for a Prophet 5; MIDI-ing up a more unusual synth like a CS80 or a Rhodes Chroma may well cost more.

Monophonic synths, too, can be internally MIDI'd up with relatively few problems - and with the potential for some pretty amazing real-time MIDI manipulation of parameters. As an example, a Kenton MIDI'd MiniMoog will respond to aftertouch by changing modulation, pitchbend or high-pass filter level, and will respond to velocity by opening the filter and/or increasing volume.

But again, as with sequencers and drum machines, you're going to start piling up a pretty big bill if you get a firm like Kenton to MIDI everything up internally. MIDIing up my collection of old synths (assuming I could get them all simultaneously in full working order first) would cost something over four thousand pounds. That might be an insignificant investment for someone who makes decent money from music, but as for me...

Are there cheaper alternatives? In some cases, yes, definitely - if you're prepared to swap leads over regularly; in others, definitely not. The basic rule can be summed up like this: if your old synth is polyphonic, then only an internal mod will do; if it's monophonic and has one-volt-to-the-octave CV/gate inputs, there's unlikely to be any difficulty with using a proprietary interface box.

To take a few examples:
Roland's SH series, SCI's Pro One, Arp's Odyssey, Avatar or Solus, Yamaha CS15 - no problem.

Moog's Minimoog, Multimoog, Prodigy - quite possible as long as you can get hold of the obscure plugs Moog used for the trigger, and as long as the interface box you get has the facility to send an S-trigger signal (or you can get a circuit made which will invert the trigger).

Roland's SH2000 and other synths which work on 1 volt/octave tuning but don't have any input sockets - you need to get what ought to be a relatively simple mod performed so that they'll respond to external CV and gate as an alternative to internal.

Korg MS10 and other early Korgs and Yamahas - these might be a problem as they use a Hertz/octave tuning ratio, not one volt to the octave. In this case you'll need to get hold of Korg's rare MS02 interface, or find an interface box that lets you use the Hertz/octave system.

EDP's Wasp - complicated by the fact that it uses a six-bit digital signal for the note information. Very few interfaces cope with Wasps without extra expense, but I have it on good authority that it isn't difficult to make a little add-on converter to do the job.

What sorts of boxes are available? The Rolls Royce of MIDI-CV interfaces was for many years the MPU-101 from Roland, and I still wouldn't part with mine for less than twice its original list price. (Put another way, wave £400 under my nose and I might consider it.) The MPU101 has so many natty features it's difficult to summarise, but basically it will take a monophonic or polyphonic (up to four-note) line on any one MIDI channel and send it, in a variety of extremely useful ways, to up to four separate monophonic 1volt/octave synths or modules. It'll also route various MIDI controllers to whatever control inputs (for example filter voltage) that your synthesisers have. Best of all, to my ears, are the wonderful polyrhythmic possibilities in having four slightly different sounds playing one monophonic sequence.

You can tell I like the MPU101 - but there are alternatives. Groove Electronics' MIDI-2CV (not the first 2CV on the market, thanks to Citroen, but one of the first interface boxes) used to be made with a wide collection of tailor-made options: you want S Trig? No problem. DIN Sync? At your service. Two CVs instead of one? Simmons triggers? Wasp interface? Be right with you, sir.

Possibly this individual service, and the hand-manufacture that obviously had to follow, proved economically unviable, as I haven't seen an ad recently. (Groove have in fact ceased trading - Ed.) However, any Groove units are certainly worth checking on if you see one for sale. (They also did very reasonable MIDI retro-fits for the Juno 6/60 and Jupiter 8 range.)

Another candidate is dBm's recent EXCV unit, which seems to be good value for money at around £139 for a two-channel converter with a wide range of control possibilities. (Incidentally, dBm also do a range of retrofits for 1 volt/octave monosynths with a variety of custom options.) Similarly, Philip Rees produce a MIDI-CV converter, called the MCV, which will control two monophonic synths with different triggering requirements at the same time. They can be tuned at intervals, but they're not independent. To produce a polyphonic line, you have to buy more MCVs and link them together - a really worthwhile design feature, but quite an expensive proposition. Still, like most Philip Rees products, the MCV is well-aimed and extremely well-designed, and includes the use of S-triggers as standard for you Moog freaks.

There are, and have been, other interfaces around - for example, I'm pretty sure JL Cooper did one in the States, but they would certainly be difficult to come by. Which leaves Kenton, who used only to do retrofits, but were cajoled by numerous enquiries into doing a free-standing box for interfacing monophonic synths. For the basic price of £176, you get a two-channel convertor, with gate or S-trig on each channel (a definite advantage over the MPU-101). Two other control voltages per channel are available; sync-24 and arpeggio triggers are standard and there's an LED readout, memory, and the option of Hz/V tuning which is available as an extra for another £29 for anyone out there who just has to have their Korg 800 burbling away alongside the 01/W. Sounds thoroughly useful.

Any other options apart from retrofits or MIDI-CV boxes? Well, you could, of course, go totally retro and revert to something like Oberheim's System (which meant the only polyphonic synths you could use were Oberheim's OB range), or Roland's DCB interface, which similarly limited you to synths like the Jupiter 8 and Juno 6 or 60. In both cases, if you're going to limit yourself to one range of synthesisers, you could do a lot worse than either of these systems. And it's not beyond the bounds of possibility that musicians will come along as time goes by who do exactly that - for the same reasons as, say, a string quartet may aim, eventually, to buy instruments from the same maker.

But realistically, this is not an answer that's going to appeal to many people. Which leaves two other sidesteps you could consider (...if you're rolling in money). One is to go for the re-packaged classics like the MIDImoog or Obie Rack - neat, extremely effective, but with a price tag to match. The other is to go only for old synths that were just new enough to include MIDI.

Obvious examples are later MemoryMoogs and OB8s, Roland MKS80s, Prophet T8s, Xpanders & Matrix 12s, and, with slightly less classic pedigree, MultiTraks, Prophet 600s, later Oscars, Jupiter 6s and Juno 106s. But while synths in the latter group are still available fairly cheaply, the same isn't true for the real classics in the first group. The prime example of this is the MKS80, which, with its programmer, must be worth somewhere in the order of two thousand pounds. But all MIDI analogue synths, particularly if they're blessed with VCOs rather than DCOs, are definitely appreciating.

So back we go to the cheaper alternatives; the most cost-effective course of action may well be to pick up an interface box for your monophonic synths, and perhaps go for a Kenton retrofit for your most prized old polyphonic.