Secondhand synths and how to buy them. Paul Colbert passes on some tips for the shopping bag.

One of the most common calls that finds its way through the valve and tin can One Two switchboard goes like this: "I'm thinking of buying a secondhand polyphonic synth — what should I get and what should I pay?" This month, to relieve the strain on the taut length of string between us and the reception desk, we provide some form of an answer... by asking our own questions.

1 Who are you?

Not as ludicrous as it sounds. Very broadly speaking us punters can be split into two parties — (a) keyboard players who want another, an extra or a better synth and (b) non keyboard players making their first venture into the land of white and black notes.

Each category has different requirements. We spoke to a drummer who wanted to enlarge his home recording set up, and a synth player looking for a more powerful polyphonic. Both had phoned us asking for advice, so we turned the tables.

2 What do you do?

The drummer was after a cheap poly mainly for string sounds to flesh out the guitar and drum machine recordings on his 244 Portastudio. He wasn't interested in acquiring a brilliant keyboard technique and, since he was playing drums and percussion in a full time band, wouldn't be dragging his new purchase onto the road.

We suggested a Roland Juno 6, a Korg Poly 800 or a Casio 202 as first investigations. Because he was based at home he'd have plenty of time to jiggle with controls to perfect sounds so memories were not vital, hence the Juno. The single trigger filter of the Poly 800 which can annoy some proficient synth players wouldn't trouble him and the 202 was a simple supply of 49 separate sounds with the minimum of confusion and clutter.

He'd placed an upper price limit of £500 and though there are plenty of other excellent synths to be found secondhand at that level, we'd recommended the Roland, Korg and Casio as barometers of price and performance.

The experienced ivory jabber had additional demands. She, too, had some home recording to do, but already owned a Casio 101, an electronic piano and a Roland SH101. Demo making was the most important concern and a synth that offered a wide variety of polyphonic sounds was needed, but there could be some gigs in the future so a few memories would be useful. As she wasn't a three-sets-a-night performer then 32 memories would be plenty — 64 or above would be wasted cash.

This time we proposed the Roland Juno 60, Korg Poly Six and Korg Poly 61, plus the Roland JX3P even though it was more than she was planning to pay.

3 What do you want?

The drummer began scouting round, also investigating rivals to the Casio such as those produced by JVC and Technics. But he found that in most cases he didn't need the extras he was paying for — auto-chords, simplistic built-in drum machines, arpeggiators etc. He already had a fully programmable drum box and preferred to find his own chords for the arrangements.

In the end he settled on the 202 which he picked up for £150: "Although I was thinking of spending £500 I realised that for that price there's always something a bit better for another £100 or £150 — you'd always be thinking you could have got just a little more. So I decided to spend the money I'd saved on some good effects units which could make the Casio AND the rest of my guitars sound better. Okay, so there are no new sounds on the 202, everybody's already used them, but with a flanger or another effect you could come up with something different.

"Also there were quite a few 202s around in good condition which made them cheap. They either seem to be a first stage for a keyboard player who's gone onto something better, or a sort of rich man's toy like the bloke I bought mine from. He'd got his to do some recording at home, but had never had the time."

In the time being our other guinea pig had developed an interest in computers and put off the purchase of a synth in order to pick up a Spectrum and that changed matters entirely.

"The big thing is MIDI — I would never buy another keyboard without it. If you buy a keyboard with lots of arpeggiators or sequencers on it, well, those are the sort of gadgets that go out of date very quickly. With the right MIDI interface a home computer could do all those things for you far better, and do a lot more besides.

"But you've got to have a good, basic sound to begin with — that doesn't go out of date, and a computer can't help you there."

Even without a computer, the potential for expansion is essential. At present each time someone buys a better synth, he's only buying better electronics. The keyboard, contacts and case are likely to be no better than those of his previous synth, yet he has to junk the original and fork out for another set of black and whites. With MIDI it should eventually be possible to buy just a new set of oscillators and filter or additional memory banks, without starting from scratch again.

And it's a system common to more expensive synths like the Yamaha DXs, currently out of our £500 secondhand price range but, when the bank manager's in a better mood, who knows?

So she decided to wait for a Roland JX3P though was still tempted by the cheaper Poly 61 from Korg who have said there is a MIDI retro-fit kit available. Her closing warning was this: "No one should put themselves into hoc for a keyboard that could be obsolete in six months time. You don't have to."

4 What do you look for?

You'll either find your potential purchase among the classified ads (Melody Maker is still the best source here), or in stores as the result of part exchange deals.

Either way the rules stay the same. Unlike guitars or basses, there are few physical defects to look out for. Any faults are likely to be electronic.

1. Turn every knob and switch (a) to make sure that they all do something (b) to ensure they do not crackle. Noisy pots can be a sign of poor quality components or bad treatment such as being stored in a damp or dusty environment. One or two noisy controls are allowable, half a dozen is a danger sign. Not all controls will alter the sound, for example, vibrato speed will only function if the sound has vibrato included in it. But if the control does nothing to a sound you've selected, ask the seller/salesman to demonstrate one where it does.

2. Touch every key, both lightly and hard — some key contact faults such as a missed or intermittent trigger will only show up at one of the extremes.

3. Check all the memories if the synth has them, and ask the seller/salesman to write in a new sound, change the front panel controls, and then prove he can recall it.

4. Take a turning fork or other pitch tester, check the tuning of the synth immediately after it's switched on, five minutes later (by which time it should have settled down), then 15 minutes later. Engage seller/salesman in banter during this time and DON'T let him fiddle with the tuning controls while this is going on.

Beware of a synth that is turned on when you arrive. Likewise, put your hand (cautiously) near the mains socket on the back panel as soon as you see the synth for the first time. If it's hot, it means your host has had the keyboard on and warming up then turned it off as soon as he heard you arriving.

Obviously, be cautious of purchasing any keyboard that drifts alarmingly in pitch in a short space of time (these days a semitone in 15 minutes is bad news), or gets very hot, very quickly. Most modern synths are rock solid in tuning and conspicuous pitch drift is a fault, not a characteristic, whatever the host may claim.

5. While on the subject of opinions and promises from the seller/salesman, don't fall for the old 'well, there are plenty of other people interested' routine. Okay, there may be, he doesn't owe them any favours, and you're standing there with the money in your hand.

6. Take a set of headphones with you (a) so you can check that the headphone socket works (b) so you can experiment with the sounds and controls without embarrassment or being treated to the seller/salesman's rendition of "Bridge Over Troubled Water".

7. Look at the back panel. Are there lots of small scratches on the paint work around the output socket? If there are it's not a bad sign unless the owner is claiming 'it's hardly been used and it's never been gigged.' Those scratches are from inconsiderates repeatedly stabbing for the socket with the end of a jack plug.

Likewise for the back as the front. Do all the sockets work (including those for footswitches), does the mains lead join neatly to the panel or has it been mauled by bad treatment, does the fuse holder look untouched (good) or thoroughly battered? If the latter, then perhaps there's something dodgy about the power side of the synth that means constant blown fuses, or maybe it's been gigged in dubious venues with even more suspect power supplies not known for their benefits to a keyboard's health.

This is also the time to ask for a test of cassette dumping facilities, if the synth features them, since you'll be starting at the sockets required.

8. Does it have all the leads, footswitches, dust covers and manuals it came with? These are the items you think you will never need. They are also the items that turn out to be ridiculously expensive when you discover a week later that you do.

9. How does it sound? Putting aside all the technical guff, do you like it? Can it produce the tones you require, will it be varied enough for your needs? Okay, so the strings are very sharp and clear, but can these also be toned right down to be soft as a barmaid's moustache? It does a great electronic piano, but is that all it does? Ask the owner to produce the tightest, punchiest and most aggressive sound he can (don't let him just turn the volume up), followed by the gentlest and slowest attack. Does it sound as interesting to you when you hold down three notes (the most you can manage) as when Howard Jones, here, heaves down eight with a single elbow?

If this is the only keyboard in your home recording set up, can it make a solid, monophonic bass line sound, and a handful of bright monophonic lead voices as well as the normal chord stuff? Remember, it will have to do every job.

Finally, be wary of instruments that very rapidly pass onto the secondhand market, especially in considerable numbers. It may be 'as new', but if it's only £50 cheaper than in the shops, is it worth the risk of having already been through one owner? And anyway, if he's flogging it that quickly, doesn't it imply that he became very bored with it very fast. Might you feel the same way?