YOU'D THINK that someone must have made one of these before. Well, apparently not (quite). According to fellow One Two contributor Paul Day, who knows his onions, the only other tremolo unit designed specifically for four-string bass guitar was made by Gordon Smith, the Mancunian guitar maker, around 1975. To be accurate they made four, and sold three. And you may ask yourself, "Why is this?"

Now, the American company Kahler have introduced a bass guitar version of their widely respected six-string wang bar. Importers Washburn UK will fix it to an existing or new Washburn bass for around £150 — sold separately, the unit costs nearer £215.

Once installed, the whole assembly assumes a tidy, low profile, protruding ½in or less above the surface of the guitar, and taking up only marginally more surface area than an average brass bridge. The springs and works are concealed beneath, and the finish and polish of the brass hardware used is superb. No sharp corners here, either.

The tailpiece of the unit is the part that rocks to and fro, and is connected to three tension springs. String replacement involves simply laying the string over the saddle and tailpiece, and tuning up. The ball-end is tucked away behind a lip that runs along the tailpiece itself. The "saddle" is actually a brass pulley that moves underneath the string as it stretches and contracts, thereby allowing unhindered wanging. Each pulley is mounted astride its own multi-adjustable saddle/bridge. Altogether, you do get a cracking piece of engineering for your money.

The tremolo arm screws into the aforementioned tailpiece-rocker. Provision is made for left- and right-handed players, ie there's a screw hole between the G/D strings and the A/E strings. The arm consists of a straightforward rod with a mild bend in the middle. On the bass to which the Kahler was attached, a Washburn Force 8, the tip of the arm, when in the "between" position, hovered around 3in above the single Precision-type pickup.

It was possible to depress the arm so far that it touched the pickup. The full range of pitchbend was three semitones below the root note, and about two beyond.

Kahler claim very stable return-to-tuning for this unit, and with reservations, I would agree. I did allow time for the strings to settle and so on, but tuning stability isn't quite 100%. The E and A strings were the main culprits. Drift is minimal, though visible on a strobe tuner and audible alongside piano. If and when this happens, the strings tend to return to fractionally above or below open-tuning depending on the last movement made on the tremolo arm. Of course, it's essential that the unit doesn't affect tuning and, generally speaking, moderate use gave little cause for concern. Occasionally, a subdued "crack" was heard from the guitar's neck-joint as it strained, but I expect that's OK — after all, something's got to give.

Realising that this could be next year's thing, I began to wang with a vengeance. I tried the things that H. Thomas had in mind in last month's issue: bending harmonics and chords, wobbling notes, and so on. They all work, to be sure: swooping and snaking sounds and low menacing tabla drum effects. You can play a chord and make it shimmer, or give a fast and furious vibrato to a passing high note or just leisurely pick through your favourite melodies in the Hank Marvin style.

The trouble is that bass-people have most of the fingers of their right-hand pretty much accounted for when they're playing. Several digits will be thrumming, plucking or snapping, and those left spare are usually occupied with the all-important job of damping strings. These intricate activities leave little time to reach up and out for the wang bar, let alone make coherent use of its range and mobility (about 5in between extremes), all before the next note looms up.

The rod also requires a fair amount of yank to pull upwards, and the ratio of leverage-to-pitchbend is a bit sluggish so that quite deliberate movement is necessary for the effect to be anything but vague. Naturally a slower or more spacey bass line will leave gaps for the right hand to manoeuvre the arm properly, and perhaps the idea is better suited to these areas of playing.

Fretless basses provide many of the effects that the Kahler produces (albeit a shade differently), without in any way impeding speed or flow or requiring awkward right-hand juggling that can result in missed beats.

There's nothing wrong with the Kahler as an individual tremolo unit, and it makes the sounds you'd expect. It's very good. But you'll need fingers of considerable strength, and a matching swiftness of hand if it's to be incorporated into an orthodox playing style for anything less predictable than novelty effect.

My main concern is that whereas the standard wang bar is well suited to the methods of electric six-string guitar playing, its outsize brother becomes not only proportionately more cumbersome to operate, but combines less than perfectly with present day methods of bass playing. Smug conclusion, eh? Yes it is; I wonder who'll prove otherwise...

KAHLER bass tremolo: £215

WKMAB CONTACT: Washburn UK, (Contact Details). JHS, (Contact Details).