Melbourne Audio Club does REDGUM
________________GM 15th September 1999 Willis Room
Redgum Amplifiers
By Ian Mackenzie and Hugh Dean
On Wednesday 15th September at the Willis Room we were treated to Ian Robinson's presentation of Redgum Audio products. Ian is an inspired and accomplished speaker, and he provided a fascinating story of the evolution of his HiFi business and the development of Redgum amplifiers. He also demonstrated each of his products, proving to any doubting MAC members that Solid State - and in particular Mosfet - designs can be sonically excellent and full of energy.
He began by explaining that he had started out 25 years ago as a retailer, at various times had produced loudspeakers and only quite recently had moved solely into amp manufacture. Ian's retail business started in Brighton (Actually Beaumaris - Ed.), moving after a couple of years to Hawthorn, and the business spent a great deal of time on repair, seeing the whole range of amplifier problems from the seventies, eighties and nineties.
Ian warmed to the topic of amplifier design by explaining that he had seen many silly, avoidable mistakes in consumer hi-fi amplifiers over the years, and had mused long and hard over 'a better mousetrap'. Realising that the mass production techniques of Japanese brands was almost impossible to best, he resolved that if he ever one day branched into amplifier manufacture he would be forced to compete not on price, but on quality and reliability.
In the early nineties, when the Redgum designs were prototyped, Ian spent considerable effort on the stability issues of conventional mosfet amplifiers and eventually hit on swapping the gate/source capacitors over from the N type devices to the P type. This was a serendipitous discovery, and flies in the face of convention, but works very well with all Redgum amps displaying high slew rates and unconditional stability - even into heavily capacitive loads.
Ian had been appalled with how easy it was to destroy the output stages of modern hi-fi amplifiers, and marveled at the complexity of the protection circuits which were often ineffective anyway. He resolved to devise a better way, and after careful discussion with his transformer manufacturer was able to specify a transformer which delivered a limited, sustained current in the event of a short circuit which would not destroy the output devices. All Redgum amplifiers can withstand short circuited outputs at full power - a valuable feature too often ignored on much more expensive amplifiers.
The components
The Redgum RGCD2 is a high quality CD player featuring a uniquely serviceable and upgradeable replacement drive. This enables the transport, including the laser, to be replaced by a readily obtainable transport from a Personal Computer CD-ROM - at very low cost. The quality of the design automatically compensates any deficiencies in the transport with clever electronics, and according to Ian there are absolutely no penalties.
This is a novel approach to the manufacture of a HiFi CD player, but by way of confirmation the sonics of the complete system gave nothing away to ultra-expensive players.
Ian informed us that the Digital to Analogue Convertor (DAC) uses the high quality Burr-Brown PCM1710U Dual 20 bit Digital to Analogue chip with audiophile grade support components. This is configured for 8 times over-sampling, a digital filter, multilevel Delta-Sigma DAC, and an analogue low pass filter. The player achieves 92db THD+Noise and 98db Dynamic range with 110db signal to noise ratio. The digital circuitry was designed by Jon De Sensi of MusicLabs, another Melbourne company. Cabinet finish is solid redgum wood front panel, textured black steel chassis & cover. The audio output uses gold RCA connectors at the rear.
All Redgum amplifiers are visually distinctive with a redgum front panel, a lockable key switch (a useful feature for those who jealously guard their hi-fis!). An unusual feature is the dual mono volume controls using high quality, conductive plastic potentiometers.
The REDGUM RGi60 is a 60W x 2 integrated power amplifier/passive preamp capable of 60 + 60 Watt RMS into 8ohms continuous sine wave at the onset of clipping with less than 0.009% THD at all levels below clipping.
The Redgum 175w monoblocks include a passive preamp and produce a power Output of 175 + 175 Watt RMS into 8ohms continuous sine wave at the onset of clipping with less than 0.009% THD at all levels below clipping. This amplifier also uses a super quiet fan on its purpose-designed heatsink.
The Redgum RGS38I floor standing Loudspeaker features an attractive red gum wood veneer and a bass reflex, twin rear ported design. The 2-way, three driver system, employs a 25mm soft dome tweeter, and two 165mm polypropylene woofer/midranges with a combined frequency range of 28hz-20khz and a sensitivity of 94db/W/m, and a nominal impedance of 6 ohms. The crossover point is 2.8kHz woofer to tweeter and suggested amplifier power in the range 50 to 200Wrms. These speakers include BI-wiring as standard and five way gold binding post. The crossover uses polypropylene capacitors, air-cored inductors, wire wound resistors and a lead shot Chamber.
The Redgum equipment performed very well throughout the evening easily filling the Willis room with sound at high levels. At lower levels, which would be extremely loud for the average listening room, the equipment showed no hint of strain - a difficult feat in a revealing venue. At very high, almost deafening levels there were occasional hints of overload, but the amplifier was clearly working to maximum output and the overall performance must be judged excellent.
Initially Ian demonstrated a Chinese percussion sound track especially chosen for its 'difficulty'. We were amazed with the authority and bass impact of the amplifiers and speakers, and wondered how such impact could be produced by such drivers of such modest dimension. At times light fittings could be heard resonating as the Willis Room approached low frequency saturation point. I was struck by the life which emanated from the speakers; this system had strong vigour. There was no sense of 'flatness', so common a problem with most Solid State systems I have heard.
A broad variety of program material was played throughout the evening, covering most of the musical genres. If asked to sum up the sound I would say that the amplifiers are very truthful, with perhaps a hint of dryness in the top end. The midrange is well balanced, and the bass astonishing. On very heavy passages, far above normal listening levels, there is almost imperceptible intermodulation, but this system is overall very detailed and clean. The immediacy or attack on steep wave forms was impressive while the amps maintained a sense of utter clarity on whatever we played indicating immense control and transparency. There was some depth in the sound stage - a credible achievement for a mosfet amplifier in my experience - but the real strength lay in the portrayal of instrumentation detail as though everything was close miked.
The overall impression was of outstanding value for money, and system versatility suitable for both hi-fi and home theatre, with the happy combination of detail and attack required for both.
Our thanks to Ian Robinson of Redgum Amplifiers for a fine demonstration, a fascinating talk, and an excellent opportunity to assess these fine Australian Audio products. We wish him well exporting these fine products.
Hugh Dean & Ian Mackenzie.
Personal email follows:
"I do hope this meets with your expectation. Matt Jelicich and I - President and VP are our positions - take the view that anyone who is prepared to show us their wares in the Willis Room should be commended for their efforts, and if there are downsides to the product, we will hint at them but never can them. There were very few downsides to your products; I believe they are outstanding, and in this competitive market, you have in our view succeeded on quality as well as cost. We congratulate you.
BTW, a copy of the newsletter should be sent on to you, so you have a hardcopy as well. "
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