It is small, undeniably, less than 20in long to be precise, but we at One Two have never been 'shortist', especially when the CS01 usually qualifies as the cheapest mono synth on the shelves.

Doubtless while peering through the shop windows, you'll find Casios for fewer ackers, but the Yamaha is as unpunishing on the wallet as you can get and still preserve the likes of an envelope generator (ADSR), filter, pitch bend and modulation wheels and a fair degree of control over the oscillator.

The metallic grey CS01 plays a part in Yamaha's Producer range of equipment - small headphone amplifiers, monitor boxes and now a 4-track cassette system as reviewed in last month's OTT.

It shares one facet of the Casio philosophy — miniature keys. They're about half the proper size and form a two and a half octave range, from F to C. The controls are all on stubby sliders in a panel across the top of the keys, ending in a self contained amp and speaker, on the far right.

There's just one VCO with footages from 4 to 32, and waveforms including triangle, sawtooth and two square waves — one fat the other spikey. A pulse width section can be run from the modulation LFO to give the impression of twin oscillators beating together.

Weakest point is the filter which has no real guts behind it and behaves more along the lines of a powerful tone circuit than the creator of a mighty 'wang'. Still, the ADSR is snappy and the CS01 behaves well when clean, crisp, punchy lead-line sounds are demanded of it. Not too much bass available, but the square wave can sound smooth and flutey and the sawtooth is bristling and bright. Use for cut, if not for passion.

The modulation wheels are mounted on the top left hand corner of the front panel — odd you might think, but the CS01 is also designed to be played standing up, hence the strap buttons at each end. You can then wrap your fingers around the back of the case, reaching the wheels from the bottom. The pitch bend is a good one, strongly sprung so it will always jump back to zero, and the mod wheel can be linked to the oscillator or the filter.

The CS01 also boasts a Breath Controller, a plug-in mouthpiece affair which can vary the filter brightness or the volume, depending on how hard you blow. It does require practice, and I've come across few people who feel really at home with it.

Six penlight batteries (HP7s to you) squeeze into a compartment at the back, though there's a mini jack socket for a 9-12 volt mains adapter, plus the normal sockets for headphones and line out. Advantages are the lightness, portability and size, plus the reasonable price. Not an enormous range of sounds, nor an especially warm or dirty synth, but worth investigation.