Armed with bass guitar and dummy load, Simon Bateson accepts the challenge of reviewing an imposing new addition to the Gallien-Krueger amplifier range, in the shape of the 2000RB 1kW bass head!

After nearly three decades in the business, Gallien-Krueger have recently added two new bass amplifiers to their range: the 2000RB and the 1000RB. The 1000RB is a mono head, delivering 500 Watts into 4 Ohms, while the heftier 2000RB offers three operating modes and can deliver 1000 Watts into 4 Ohms. It was the imposing 2000RB, which arrived on my doorstep for review.

My first thought on taking the G-K 2000RB out of its box was 'well, this is a bit of a lightweight', but be assured that this is only the reaction of someone used to breaking his back every time he picks up his bass amplifier. My usual amp is an Ampeg SVT, the most ridiculously heavy and overpowered valve amp in the world and my competition for the GK — this upstart of a solid-state amp. It's less than half the weight of the Ampeg, only 30 pounds, and half the price, but it's rated at about three times the power — 1000 Watts. 1000W in a 3U rack case, continuous RMS into 4 Ohms — look out windows! In the end, I didn't ever verify this rating into a speaker, because my 8 by 10 is only rated at 400W. However, my 400W dummy load was on the receiving end, and I got about 1D050W out of the amplifier for a while before the load started smoking and I gave in. This amplifier is not short of power.

In a similar vein to the Ampeg, G-K have steered clear of actual effects, such as compression or limiting, but have decided that a little grunge is needed as part of the amplifier circuit. Consequently, they have included 'GIVE' technology — an acronym for 'gate induced valve effect' and which probably means FET based soft-overload amplifier stages. Apart from that, the amplifier path is clear and clean and all the better for it. Let's have a little trip through the controls.

TWIDDLY BITS

On the front panel, from left to right, we start with a plastic jack input socket. Although some exotic basses have XLR connectors, I see no need for anything better than a jack in this position, so long as your cable has a good plug. Next is a clip indicator, followed by a 10dB pad switch, intended to prevent overload from active basses. I must say that 10dB is neither here nor there in the great scheme of preamplifier design. If the circuitry really did suffer overload, it probably wouldn't be saved by a 10dB pad; 20dB would better justify the inclusion of a switch. There is a tacit admission of this in the advice of the manual "... if clipping still occurs, turn down the volume on your bass...". I used a Music Man five-string active and couldn't overload it at all but then I know this bass doesn't have a very high output. For interest, fed from a signal generator, the 2000RB clipped at 4.8V peak to peak, pad switch in.

Following the input stage is a button to mute the main output, while still feeding a buffered signal to the tuner output socket on the back. This function is also controlled from a (supplied) footswitch, but the button has to be in for the footswitch to work. You can, therefore, choose to prevent over-enthusiastic footwork from accidentally muting yourself!

BASSO PROFUNDO

The next control is labelled volume but is actually preamp gain; it sets the level into the voicing filters. An additional overload LED helps you adjust this. The filters, actually well chosen active equalisers, are very nice indeed. First is 'bottom', and as we all know, a nice firm bottom is very important. This filter, which is centred at 20Hz (!), decides whether or not the windows stay in their frames. 'Contour' is the bass voicing filter, boosting at 80Hz and 4kHz, while dropping out the honk at 600Hz. 'Presence' adds a real zing by boosting at 6.5kHz. Not content with this, the preamplifier offers a further set of four wide-band active tone controls centred at 60Hz, 250Hz, 1 kHz, and 4kHz to define your sound.

The filter/EQ section is followed by a send/return facility using ordinary jacks; plugging into the 'return' will disconnect the preamp signal. This is the place to insert a limiter if you use one. The signal then goes one of two slightly different ways, depending on the setting of the second button on the footswitch, the RF2. The 'Boost 1' channel is a pretty straightforward clean gain stage, adjustable with the Boost 1 volume control on the front.

For extra level, eg. for solos (bassists don't do those, do we?), extra gain, to the extent of mild overdrive, is available through 'Boost 2'. Like Boost 1, it has a gain control, but it also has a 'Level' control. It's like the rhythm/lead switching on a guitar amp, except that the overdrive available is a lot less (sorry, Lemmy). Tonally, the Boost 2 overdrive is as good as any preamp overdrive for the bass. The 'Level' adjustment, which alters overall level relative to Boost 1, has a rather limited range. After some playing about, I concluded that 'Boost 1' was actually completely unnecessary and might as well be removed, and the gain range of 'Level' extended.

The final controls are Aux Level, with which you can mix in a line-level source from a socket on the back (is this turning into a mixing desk?) and two master controls; left/low/bridge and right/high. The names refer to the possible configurations and corresponding master functions.

So versatile is the signal routing that G-K have printed a system diagram on the back panel, and it explains things pretty well. In words, the signal routing facilities need a page to themselves!

"This amplifier is not short of power."

ACTIVE CROSSOVER AND FACILITIES

There are three main operating modes for the amplifier. The first is mono bridge mode. Selected by a rear panel switch, this takes all the preamp and auxiliary signals and feeds them in mono to the left power amplifier at a level controlled by the left/low/bridge master volume control. The same signal is inverted and fed to the right channel amplifier, and the outputs are routed to Speakon connectors. A suitably wired lead (provided) takes the bridge mode signal to your speakers, which should have a minimum impedance of 4 Ohms. The individual power amp outputs are available on jacks, and you could cobble together a lead to bridge them if you lost the correct lead, but you shouldn't; jack sockets were never meant to carry these power levels.

The second mode is bi-amping, used in conjunction with the internal crossover and selected by another rear panel slide switch. The crossover point is variable between 100Hz and 1kHz. Here, the right master controls the high-pass level, which you would typically feed to a 4 by 10-inch cabinet, perhaps with horns for brilliance. The left channel master controls the level of bass to a 15 or 18-inch bin, for instance. The choice of crossover frequency range does not reflect PA practice, where you might span 60-250Hz, but has to do with the fact that you can send post-crossover signals to effects units. Effects like delay, chorus, and reverb are best applied only to high frequencies. To facilitate this, the crossover outputs are provided on back panel jack sockets as well as feeding the master controls; they are available at all times, not just in bi-amp mode. I did have some fun using the low-pass channel alone — it made a really smooth sound!

The third mode is stereo. Of course, to have stereo, you need a stereo source so this mode is very much connected with the auxiliary input. There are two possibilities; either you can play a stereo line source, such as tape or CD, into the aux socket and mix it in with your playing; or you can use it as a stereo effects return for chorus or stereo reverb.

The versatility of the bi-amp and stereo options is further enhanced by the fact that you can take your effects feed from the full-range 'send' socket, or from the crossover 'lo-out' to feed an octave divider or from 'hi-out' for chorus/delay — in fact, you can do all three at once if you like. You could octave the bass end and feed that through one channel to a bass cab, chorus the high end and feed that to a high cabinet, or return both to two full-range cabinets. In fact, with a second power amplifier you could have mono bass, with bass enhancement, and stereo chorused and reverbed top, all controlled from the Gallien-Krueger! And then you could get led away gently by the nice men in white coats...

As one might expect from this grade of equipment, there is an electronically balanced output provided through a male XLR from the back panel. A small 'ground lift' pushbutton next to the socket deals with the vagaries of earth loops, and level is adjustable with a rear panel knob. A pleasant refinement is a second pushbutton marked 'pre/post'. In 'pre', the line out is fed direct from the input stage, just after the tuning mute switch and would be appropriate for a large live PA feed, while in 'post', the signal is taken from the top of the master volumes. It therefore reflects everything except the loudspeaker volume and would be appropriate for recording.

CONSTRUCTION

The case has been folded out of one piece of sheet steel forming base, sides, and back. It is powder coated with a silk black finish. There are a couple of boo-boos on the back, such as the socket identification printed so close to the sockets that the plastic nuts cover the words, and the lid having to be notched to accommodate the balanced line out DI socket. The front panel is also steel, so it is relatively thin but very rigid. Overall, the casing uses a relatively low-cost construction method whose main disadvantage is that access for service is much more difficult than a frame and panels construction, but on the other hand, it doesn't rattle!

I would, however, draw the assembler's attention to the in-service vibration a bass amplifier must suffer. In the course of dismantling it, an essential part of the review, I noticed that the external and internal screws were very easy to undo, which in turn means they can shake loose. With the currents and voltages available in this amp, you don't want loose bits of metal shaking around, believe me! I would suggest a little extra torque for all the screws and maybe a periodic (unplugged) shake and listen, which is a sensible maintenance check for any piece of stage equipment.

"The amplifier controls are very versatile and I found it easy to get a good sound."

The circuit boards are made to a good standard and the preamp/signal conditioning boards are supported by their sockets and potentiometers, a perfectly acceptable arrangement. The power amplifiers devote about half their area to the power devices, which are sandwiched between the board and heatsink. G-K make much of their 60 amp output capability, obtained by paralleling pairs of absolutely massive TO246 cased plastic power MOSFETS. These are almost indestructible and can carry more current than the power supply can give, so they don't need any nasty distortion-inducing protection. Electronically, they are a little difficult to drive because of their large gate capacitance, hence the power transistors in the driver stage — paralleled transistors, in fact. There seems to have been a post-production modification with extra driver transistors clipped onto the heatsink and current-sharing with the pair on the board.

POWER RATING

The literature says that the amplifier can deliver 10,000 Watts instantaneously, with its limit-free 60 amp output capability. To deliver 10kW into 4 Ohms, you need a voltage of 200V, ie. one amplifier outputting -100V and the other +100V. Since the power rails are only 78V and you must drop several volts across the FETS, I don't think it will quite do that. It will, most likely, deliver a couple of kW, and in audibility terms, there isn't much difference between 2000 and 10,000! In practice, the sheer acreage of power MOSFET and the voltage benefits of bridge drive ensure that you are not likely to run short of power at any feasible stage volume.

There is a variable-speed fan which, in a very Pentium fashion, is arranged to blow straight into the heatsink, which is the most effective arrangement possible — plenty of turbulence. The amplifier stages operate with very little quiescent heat dissipation. At the end of a fairly solid two hour rehearsal, the fan was running at a very low speed and the heatsink was only just warm.

Although I didn't have a circuit diagram, there was a reference to '2-step high efficiency drive', and this almost certainly means there are two power supply voltages; the amplifier only using the lower voltage until large peaks are encountered when the higher supply comes in. It is a very efficient arrangement, which in one form or another has been used in many well-respected power amplifiers (eg. Carver) for several years.

One nice feature is the speaker protection function. As usual, there is a short delay after switch-on before the speaker is connected, just to settle the amplifier down. Unlike some amplifiers, which make you hang around for 30 seconds for unnecessary dramatic effect, this one clicks in almost immediately; even better, the relays cut out the instant power is removed. So many amplifiers have switch-on delay then subject you to a long drawn out and agonising switch-off thump (plus hiss, oscillation, radio reception, etc.), which indicates very careless design. Not this one, I am pleased to say.

CONCLUSION

The amplifier controls are very versatile and I found it easy to get a good sound. In fact with three active tone controls on my bass and seven on the amplifier, I was somewhat spoilt for choice! The extent of cut and boost on the amplifier controls have been sensibly chosen, with the voicing filters trimming the sound exactly where any bass guitar will benefit. At rehearsal and performance, the overall impression of the sound was that it was round and solid, with perhaps a little less transient impact than my SVT (which does have the benefit of an enormous output transformer to resonate with the speaker), but far more involving and less clinical than, say, a Trace Elliot, in my opinion. At a gig, I did find myself looking for a 'frequency' control on the lower mid. At a lot of the 'slightly less than acoustically ideal' venues which real people play, you can site the bass cabinet as carefully as you like, and there will still be one strong resonance, usually around the lower mid/upper bass. In the past, I have found a sweep low mid to be a very useful control, and I wonder if G-K might consider adding this facility?

There is very little circuit noise; I found some hiss when boosting the 'Presence' but that turned out to be coming from the electronics in the bass guitar! The 2000RB is also a very practical unit. Unlike valve amps, it runs cool, and the fan only works when necessary. This, together with its light weight and the well-behaved and quiet circuitry, means it is just as suited to a little quiet practice in the living room as it is to full-on performance. You also have free access to a decent stereo power amplifier, which always comes in handy and you can mix an external stereo source to practice with a tape for instance. And can it go loud, or what?!!

GALLIEN-KRUEGER 2000RB £1100 inc VAT.

Beyerdynamic (GB) Limited, (Contact Details).