The concept of the keyboard amplifier is relatively new, and is the natural result of the electronic keyboard/synth revolution. Within the register of the instrument, a guitar amp might be required to produce ultra-metallic brightness, fat middley raunch, or round, sweet Jazz tones, and its performance characteristics will be contoured accordingly. A bass amp will also be expected to offer a certain range of sounds, obviously including a huge bottom end capacity with enough Eq and mid/hi response to usher forth that serious slap or creamy fretless tonality.

Owing to the ability of modern keyboards to replicate any instrument, however, a keyboard amp has to cope with most of the audio frequency spectrum with a high degree of fidelity. Raunch doesn't really come into it, and in fact most timbral changes can be left to the instrument's own controls to create. In terms of performance, then, the keyboard amplifier is probably more about fidelity than anything else.

McGregor manufacture a large range of power amps and instrument amps most of which are MOSFET based. The model under review is a 100w keyboard combo which is rather unique in that it is a relatively inexpensive stereo instrument amp combo. Although its power amp is mono, its front end (preamp) is stereo, and in conjunction with a second slave power amp combo, it can be the basis for a stereo system.

The mixer amp offers one mono mike/keyboard input, and two stereo keyboard instrument inputs. The first is on a standard ¼" mono jack socket, whilst the other two use single stereo ¼" jacks with tip for the left, ring for the right and a common return on the sleeve. This means that, using 'Y' leads with a stereo jack to two mono jacks or phonos, you could connect either two stereo synths (the obvious configuration) or, conceivably, four mono synths, plus a microphone or fifth synth in the mono input. Each of the three input sections features a gain control plus very simple bass and treble Eq. A little extra control comes via a master volume and master presence control, but it's really down to each instrument to create the right sound at source, which the McGregor will then faithfully reproduce.

Also to be found in each section is a reverb on/off button and an effects on/off button. The reverb is a built-in Accutronics spring with a single overall level control effecting all three channels, whilst the effects button relates to a master set of effects loop in/out jack sockets, providing send and stereo return. These can be used for the connection of an auxiliary effects unit, which can then be brought to bear on each instrument via the relevant channel's effects in/out button. There is no effects return level control, however, not even a master one, and so it is necessary to use an effects unit with an output level control. The loop is designed to work with a nominal line level of -10dB, which should suit most of the lower cost effects systems.

A five-pin DIN socket is included in the master section allowing the connection of a tape machine for both recording the amp's output and playing-back pre-recorded tapes.

Mono or Stereo

On its own the Keyboard Raider 100 can be used as a normal, mono keyboard combo with standard mono ¼" jack connection leads. The cabinet contains a single McKenzie 15" driver in a ported reflex enclosure with a Piezo HF driver. The result is capable of producing a very clean, clear sound at high volume. The tone controls are less than spectacular, but if you're in need of better Eq, there is a 200w version of this amp with a built-in seven-band graphic.

For stereo operation, a standard jack-to-jack lead is used to come out of a link socket on the mixer amp into the input of the Raider Slave 100w combo. This latter item is identical to the main amp, minus the preamp and controls. It simply has an input, a link socket for adding a second slave, and a single volume control.

The cosmetic design of the Raider is less than spectacular, but it is very sturdily constructed and reasonably priced. Inch thick timber is covered in heavy duty black vinyl with the standard plastic corner protection pieces designed to allow stacking of a number of amps slaved together to create larger systems by slaving. It's mainly black with red and silver inscriptions. The overall appearance of the thing is not unlike that of a Carlsbro, though less sophisticated. The drivers are well protected by a heavy-duty metal mesh over the front of the cabinet which would probably take a fairly liberal clobbering without submission.

At 98lbs for the mixer amp and 45lbs for the slave, castors would be a bit of an overkill, but the inclusion of a sturdy, flush mounted, bar grip handle on either side of both cabinets is a very welcome one, and makes it quite conceivable for the average brawnless muso to lump the amps about solo.

The term MOSFET refers to the type of semiconductor devices used and, as compared to normal bi-polar transistors, they offer a number of positive attributes. These attributes are basically due to the fact that they operate in a similar way to that old favourite, the valve, in that control voltage derived from the input signal is used to 'squeeze off' the amount of current passing through them, in a similar way in which the grid voltage in a valve controls the current flow. The distortion from a MOSFET is rich in odd harmonics, as with the valve, and so the resultant sound is nearer to the much loved soft-edged tube characteristic. In the case of the Raider Keyboard, this overdrive characteristic is irrelevant, but there are other good points in the MOSFET's favour. For instance, they are very stable at high power output levels, because they are 'self-limiting'. Systems using bi-polar transistors need to incorporate special circuits to prevent what is termed 'thermal runaway'. This is caused by such a device's tendency to conduct more current as it gets hotter, which in turn increases its temperature, which makes it conduct more power, which increases its temperature, and so on until eventually it burns itself out. The MOSFET, on the other hand, being a vastly more sensible semi-conductor, starts to limit itself as it gets too hot, thus precluding such a disaster. This fact can also cause them to momentarily limit when subjected to unusually hefty amounts of low frequency input (low frequencies being where all the energy is required), this precludes distortion, thereby giving a clean sound, but it can also have an adverse effect on the bottom end dynamics. The positive points tend to outweigh the negative, however.

Conclusion

Most musicians can only afford an academic interest in the very best; it usually comes down to doing the best you can with the available funds.The McGregor Raider 100w is not a flash amp, nor is it phenomenally brilliant in its performance. However, it does offer this rare stereo facility, a very acceptable sonic quality, and at the price its performance undoubtedly proves it to be excellent value for money.

McGREGOR RAIDER — RRP: £345 (COMBO) and £208 (SLAVE)