REDGUM 

Doing it differently seems to come naturally to the few Australian companies that make hi-fi equipment. Halcro in South Australia makes one of the only amplifiers in the world with a power-factor-corrected power supply. Melbourne-based Whise makes the only subwoofers in the world with acoustic filters and Sydney's Dan A Digital builds active loudspeakers powered by Class-A valve amplifiers. Redgum, a small company based in Victoria, makes the only amplifier in the world that has an ignition key instead of a power switch.

But it isn't only the ignition switch that sets Redgum amplifiers apart: their internal circuitry is also highly unusual. It came about because the company's founder and chief designer, lan Robinson, started out servicing and repairing hi-fi equipment, which gave him a unique insight into how other manufacturers built their products. Robinson was the first service centre in Australia to become 'computerised', 'way back in the early 70's using a program Ian wrote himself, which is why he can be absolutely certain that it was only after he'd completed exactly 18,244 repairs that he closed down his servicing business and started building amplifiers based on what he'd learned fixing other manufacturers' oversights, mistakes and shortcuts. Redgum now boasts a range of 14 amplifiers, two CD players, two phono stages, two loudspeakers and a DVD player, with an FM tuner on the way.

The Redgum RGM175 system is made up of two single-channel power amplifiers and a separate pre-amplifier (all of which are available separately, and in a variety of configurations). The front panel of each is carved from a billet of solid Australian Red Gum hardwood, which is then hand-sanded and lacquered to a high gloss finish. To switch the system on, a car ignition key must be inserted into the preamp and turned to the right. That it's a great sales gimmick there can be no doubt, but it's also a great way of stopping other people from using your hi-fi system!

The same key can also act to switch the power amplifiers on and off, but this takes place via voltage sensing from the pre-amp, and requires an additional electrical connection between the pre-amplifier and the power amplifiers. It's very handy if you position the power amplifiers remotely from the pre-amplifier. If you don't want the additional wiring, the power amplifiers can be set up for manual on/ off power switching.

Whereas most hi-fi amplifiers use ordinary bipolar transistors to drive the loudspeakers, all Redgum amplifiers use MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Robinson is firmly of the opinion that MOSFETs are not only more reliable than bipolar transistors, but enable much lower output impedances and increased stability into capacitative and inductive loads. Controls are specifically selected for reliability. The volume control uses conductive plastic instead of carbon and the input switch has silver-coated contacts again for reliability as much as for performance. Unusually, there's no over-current protection in the output stage. Instead, Redgum has a unique power supply shut-down circuit to protect the amplifier in the event of a loudspeaker failure (about which more later).

No more than a few seconds into my very first listening session, 1 was reduced to scouring through the Redgum manual, because the very low bass frequencies were very obviously being boosted, yet I could not for the life of me find a loudness contour control-either as a switch or a rotary control. It being rather late at night at the time (too late to ring Redgum for advice) and I had a deadline looming, I decided to continue the session. After listening to a piano CD, I established that the boost was not exactly like a loudness contour, because there was no boost at all above G2 on the piano, which is almost two octaves below middle C, although there was a fair amount of boost below this frequency, which increased considerably with decreasing frequency.

In view of this, I switched from listening to my regular review speakers which are, rather large with a very extended bass response, to using a pair of bookshelf speakers. I was surprised to discover that not only did the bass prominence disappear, but that the Redgum amps really made the smaller speakers 'sing' across the midrange. But the bass prominence didn't just disappear, the Redgums actually gave the bass response of the small speakers quite a kick, so the bass was far tighter and more solid than I'd heard from them before, yet because there wasn't any boost above G2 (98Hz), I wasn't hearing the 'loose' boomy sound you get when you activate a loudness control. That said, if you're using the Redgums with small bookshelf speakers, I think you would be best advised to be a little careful with the volume control, because the combination of the low-end boost and the enormous power output of which the Redgum RGM175s are capable (about which more later) means that if you're not, you may end up overpowering a small bass/midrange driver.

The next day, a telephone call to Redgum revealed that there is no loudness contour circuit as such inside the RGM175, but that the rise is due to a circuit inside the amplifier associated with Robinson's other (excellent!) philosophy of having no capacitors in the signal path. Robinson says that sensitive listeners will hear that this rise 'fattens' the bass but told me that 'since most loud~ speakers start rolling off below 100Hz, boosting the bass beneath this frequency gives a sound effect that's closer to the real thing, and when you compare the sound from an RGM175 [and speakers] to live sound, what we achieve is sound that is closer to the real thing.' (The amount of boost applied is 0.4d13 at 100Hz, increasing to 2.5d13 at 50Hz, 5.5d13 at 20Hz and 9dB at 10Hz.)

I found that the bass sound that is produced by the Redgum RGM175 is certainly super-tight, so kick drum, for example, comes through with a fantastic 'thwack' but no overhang whatsoever, so the amp is obviously keeping very tight control over back EMF from the woofer.

Across the midrange, the Redgum had a beautifully limpid sound that reproduced vocals to perfection. A favourite disc of mine at the moment is Jenny Morris' new hit & myth (Yep Records YEP005), and this received many repeated plays through the Redgum system, just for the sheer pleasure of the music as much as the sound quality, the 'listening notes' from the album having been written after only a few auditions. I just loved the vocals on Downtime (despite the overproduction and overdubbing). There's also a lot of lelectronica' on this track, which the Redgum handled beautifully.

On more purely recorded vocals (Eva Cassidy), the fluid, coherent sound of the RGM175 combo worked like magic, and the atmosphere around Eva's voice was so apparent you could cut it with a knife. Like all the best amplifiers, the Redgum lets you separate multiple 'voices' and listen to them individually, or relax your hearing and hear how they mesh, or be aware of both effects at the same time.

At the extreme top end, the sound was very clean and accurate, with lots of sparkle, but never to the point of being overly bright. The definition around triangles, small bells and other high-pitched percussion instruments was beautifully delineated, and it was easy to hear them 'through' even the thickest of orchestral textures.

Switching back to my large speakers, I turned the volume up to levels 'way above what I'd normally listen and discovered I just couldn't clip the RGM175s, even though the speakers are quite inefficient and my room is larger than the average lounge room. I can, therefore, quite confidently say that the RGM175s are easily capable of delivering more power to your loudspeakers than you're ever going to be able to use. I also have to mention the way the power is delivered, which is absolutely instantaneously, which made the RGM175s sound more lively and dynamic than any amp I have heard in a long time. I suspect at least one of the reasons for this is the absence of any conventional protection circuitry in or around the signal path. Robinson has a fairly unconventional approach when it comes to amplifier protection, because his power supply circuit is essentially 'self-limiting' in that if the speakers try to draw too much current, the output voltage drops, which means the amplifier will continue to operate into a dead short (though in this situation ' a thermal cut-out on the heatsink will eventually shut the power supply down until the heatsink cools down.)

Along with the highly dynamic sound came an exceptionally low noise floor with no hiss or hum audible at either high or low volume levels. This was no doubt aided as much by the fact that the pre-amplifier is passive, as by the 'minimalist' approach to the power amplifiers' circuitry, but when you're listening to music, it does guarantee lovely silences between notes!

As you can tell, Redgum is not your ordinary hi-fi manufacturer, so it's really no surprise that its amplifiers are extraordinary. Bright, lively and dynamic, their 'real-world' performance is as exceptional as their appearance. Highly recommended. AHF greg borrowman

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