NOT CHEAP, no sir. I've had possession of this amp for some time, but I only found out the price tag today. No wonder I liked it so much. £530! It sounds preposterous for a 1 x 12 combo. Until you look closer and listen hard, that is.

Aesthetically, the B100 is thoughtfully designed. Its presence is subdued by an all-black exterior and, running full width at the top of the enclosure, the narrow control panel is modern and sensible without being too high-tech. Dimensions are roughly 2ft square by 14in deep which, despite the amp's heaviness, makes it easy indeed to fit into confined spaces, cars included.

Sturdy, removable castors complete the enclosure, together with eight tough plastic corner shields, and a top-mounting carrying handle of the strap variety. While at first this was thought to be skimpy provision for shifting nearly six stones of amplifier, I can't really envisage a better method. Side-mounted handles would be far more awkward.

All controls, fuse-holders, switches and so on are recessed. Construction, in the main, is of ¾in chipboard, sprayed matt black within and finished outside with nuclear-resistant PVC.

The long row of 15 studio-quality knobs on the front control panel contribute a discreet splash of colour to the austerity of the amp: they are colour-coded into their sub-groups in shades of green, blue, white and red. The speaker grille is directly beneath, fixed to the main enclosure with Velcro strips. Judging by its classic lines and given the inherent resilience of a well-built cabinet, this amp should still look good ten or 15 years hence. As one might hope.

The speaker section of the B100 is completely sealed but for two ports on either side of the 120W loudspeaker chassis which is mounted centrally on the front baffle. Shining a torch through these ports revealed an unlagged interior, in other words no damping.

Connection to the amp section is by a wandering jack which is normally left plugged in but may be removed to allow external speakers to be used or for muting the cabinet if headphones are connected. In fact there are two speaker sockets, eight ohms each.

Another back-panel facility is a balanced line output via a Cannon (XLR) socket with its own level control and ground switch. This would obviate the need for a direct-injection box on stage or in the studio. Next to this is a loop for the insertion of an effects unit into the system (eg delay, compression etc), and lastly a pair of jack sockets which provide bi-amped output for external power amplifiers. Put simply, this means that the highs and lows of your sound may be split and directed to separate power amps and speakers for more accurate reproduction.

Again, there is a level control for each output, and the crossover frequency is adjustable between 100Hz and 5kHz. The three control knobs are located on the front panel of the amp and, not surprisingly, if no external amps are connected they have no effect.

The B100 will run on four international voltages and, of course, a fuse-holder is fitted. There isn't much else to see from the back, save the fins of a huge heat-sink situated below the amp chassis.

To the left of the row of knobs on the front panel is one input jack socket, with an impedance of 1 megohm which suits most bass pickups perfectly. I'm glad Yamaha have opted for only one input — it suggests they meant business when they designed the pre-amp. On the other side of the knobs is a headphone jack output, always welcome, and a footswitch jack, more of which later.

As I mentioned, the controls are subgrouped into four sections. The first consists of four knobs: volume, treble, middle and bass. The tone control boost-and-cut range is unspecified, but the controls give gentle and effective manipulation of sound, in conjunction with the next two sub-groups. These are a pair of identical parametric equalisers, with four controls each.

First is the level control, boosting or cutting the selected frequency by ±15dB. Next, the Q, which narrows or broadens the bandwidth of that frequency. As the Q is applied the tonal character will "sharpen" as the bandwidth narrows. The third knob selects the frequency at the centre of the band to be influenced by the previous two controls, and may be set at anywhere between 50Hz and 2.5kHz. The fourth knob (preset level) determines the actual loudness of the whole signal.

Each parametric has its own LED indicator, and using the provided footswitch either or both may be utilised as the player wishes, with the LEDs giving visual status. The footswitch has LED displays for the same reason. The layout is excellent. Placed in a logical order, these controls maintain a high degree of flexibility across the sound of the amp. It's possible to use just the tone control section, tone controls plus one parametric or the other, or both. When the footswitch is disconnected, both parametrics remain operative, as indicated by the glowing LEDs. The system is not complicated and the last sub-group on the front panel is the crossover facility described earlier.

Pressing the on/off button at the extreme right of the control panel activates the power indicator light and three or four seconds later a click is heard from inside the amp. Sound appears. Residual noise is of a very low order and in practice is inaudible, which makes the amp ideal for studio use. The flat, untreated response from the B100 is also praiseworthy. Basses used for the duration (a Fender from the flower power dynasty and a fretless Steinberger) returned pleasing results at this setting, showing no signs of dullness or lack of body.

Because the enclosure is larger than usual for a 1 x 12 system there is still depth to the sound even at low volume, but being a 1 x 12 means that loss of projection is minimal. At high volumes (the amp can develop 100W RMS) the solidity of the cabinet shows its strength by retaining a firm hold on the lower register and purposefully throwing large notes out with zest.

I can't say that the combo can cope with genuine high power reggae bass, but judicious adjustment of the parametrics will enable a fairly close rendition without causing the speaker too much distress. Of course, as it's possible to harness both parametrics at the same time, the variety of tone available is extraordinary. I ought to emphasise that neither the tone nor the parametric sections sound at all "artificial"; indeed they enliven and sculpt quite naturally, with an ability to extract real timbre and musical detail. And, like a much cherished instrument, the B100 would seem to encourage better and more adventurous playing because its capabilities reveal themselves constantly. It's a delight to hear.

No I don't work for Yamaha, but I do endorse this combo wholeheartedly. That leaves the question of the high price in your court...

YAMAHA B100/112 MkIII bass amp: £530
A 1 x 15 version of the B100 is available at £540.

Contact: Yamaha, (Contact Details).