Having the new Prophet and Oberheim OBX-a to review at the same time might seem something like an overdose, but it's been useful to compare the two instruments and play them through my own keyboard amplification set-up at home. So far there's been a lot of window rattling, but touch wood, no complaints.

Many professional keyboard players will be familiar with this instrument and will be asking why another review of the Prophet? Well it has been updated in several ways and it's worth comparing this latest revision with the changes that have been worked on the Oberheim also reviewed elsewhere in One Two. I'll not dwell too much on the standard synth controls, but look at the differences between the two and make comparisons.

The controls affect all five voices. The two oscillators per voice both have frequency controls with a fine tune on oscillator two. There are sawtooth, triangular and square waveform choices with pulse width controls and a sync option to lock the two oscillators together. Osc 2 may also be used as an LFO and can track the keyboard or not as you wish.

The two oscillators are then mixed with rotary knobs into the filter section. It's important to be able to finely mix the signals at this point to create subtle changes in sounds. The OBX-a has only on/off switches and that seems a grave mistake to me. For instance with a bass sound you probably would not want the two oscillators at exactly the same pitch, but put one up an octave to add some bite. Just the right amount can be mixed in on the Prophet, but not on the Oberheim.

The filter section has all the usual controls you'd expect — frequency, resonance, envelope amount and an ADSR envelope generator. There's an additional ADSR for the loudness envelope. The modulation section has an LFO with waveforms and a frequency control, and either this or white noise is routed via the modulation wheel to a variety of destinations — the filter as well as the frequencies and pulse widths of the oscillators.

In a section called Poly-mod, the frequency and pulse width of osc 1 and the filter can be affected by either the filter envelope or osc 2 when it's being used as an LFO.

Here in my view is an area for criticism. It would have been nice to have had an extra LFO for the modulation wheel in order to use it as a performance control, leaving the present LFO and its modulation routing (which is excellent) just as part of your programmable sound making sources. Then a sound which has LFO modulation already on it can be given vibrato expression as part of a performance override. The OBX-a has this facility.

Next to the modulation wheel is a pitch wheel, and both are at the left of the five octave C-to-C keyboard. Back to the OBX-a again for a moment. That machine has modulation levers with exact interval choices at the extremes of their travel and the facility to transpose the keyboard up or down an octave, something that's missing from the Prophet.

The Prophet can be played in unison with all 10 oscillators locked to one note and has a monophonic glide ability but not polyphonic portamento, which is a shame. It has none of the split keyboard or sound layering effects of the Oberheim (but then it is cheaper).

The rear panel has footpedal inputs and a socket for connection to Sequential Circuits' own polyphonic sequencer.

This new model now boasts 120 memories (all of which can be dumped onto cassette) instead of the original 40. There are three "files" — each with five memory banks containing eight positions, and they are far easier to sort out than the Oberheim's puzzling system.

To call up these files you hold down bank select button, then press the position switches for 1, 2 or 3. Dots light up in the LED display to show which file you're in and then you flick through the banks to find the right location as with older Prophets.

Stepping through these files and banks makes sound changes on stage slower than the OBX-a which, though more complicated, can still carry out instantaneous changes from anywhere to anywhere else.

Prophets have been frequently revised in the past and this current model is far from the cranky original which often wandered in tune. One of the alterations this time round has been to use a new make of microchip manufactured by the Curtis company (the older ones were SSM).

These are generally held to be better quality components, less prone to drift or unpredictability. It does appear to have "tightened up" the sound of this Prophet and there were none of the tuning problems which the OBX-a suffered from.

This latest revision has a brittle punchy quality and seems to react faster, but it has lost some of the looseness which made the older Prophets very warm. This one wasn't as warm as I remember Prophets being, and the Rev 2, which many keyboard players still worship as the "classic" Prophet looks like staying there.

Remember the Prophet is a five voice instrument, whereas the OBX-a comes in three voice models (four, six and eight) and the six and eight are certainly more expensive than the Prophet. I still find five notes a little restrictive, four note chords with one hand and octaves in the other are out, for instance.

When editing a program on the Prophet, the knobs, once moved a fraction, immediately jump back to their panel settings. The Oberheim, on the other hand, adds or subtracts to the setting in the memory and I found this ability to lightly tweak the controls both smoother and more useful than the Prophet's sudden leap, especially on the filter cut-off.

I would have liked an extra LFO on the modulation section, like the Oberheim, but then the OBX-a doesn't have the Prophet's Poly-mod which does make some gentle and vibrant sounds.

£3334