A Key Difference
Sydney Morning Herald
Monday August 12, 2002
Doing things differently seems to come naturally to the few Australian companies making hi-fi components. 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 speakers powered by valve amplifiers. And Redgum Audio makes the only amplifier in the world that has an ignition key as a power switch.
It isn't only the switch that sets Redgum's amps apart. The internal circuitry is also highly unusual. It came about because the company's founder and chief designer, Ian Robinson, started out repairing hi-fi equipment, which gave him a unique insight into how other manufacturers built their products. After exactly 18,244 repairs, Robinson stopped servicing amplifiers and started building them, based on what he'd learned. He now makes 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. The front panel of each is carved from a billet of
red gum, varnished to a high gloss. To switch the system on, a key must be inserted into the preamp and turned to the right. The key is a sales gimmick, but it's a great way to stop other people using your hi-fi system.
Most hi-fi amplifiers use bipolar transistors to drive the speakers. Redgum amps use a special type of transistor known as a MOSFET (metal-oxide semiconductor field effect transistor). Robinson says these are more reliable than bipolar transistors and enable lower output impedances and increased stability into capacitive and inductive loads. All internal parts are selected for reliability. The volume control uses conductive plastic instead of carbon and the input switch has silver-coated contacts. Unusually, there's no over-current protection. Instead, Redgum amps depends on thermal protection in the event of a speaker failure.
Our first listen to the Redgum had us wondering if there was a loudness contour switch hidden somewhere in the system, because very low bass frequencies were pronounced compared with The Guide's reference amplifier. It turns out the response of the Redgum is not flat at low frequencies, being +5.5dB at 20Hz and +2.5dB at 50Hz. This rise is due to a compensation circuit inside the amplifier. Robinson says the rise audibly "fattens" the bass sound, but he contends that, because most speakers start rolling off below 100Hz, boosting the bass beneath this frequency results in sound that's closer to the real thing.
Elsewhere across the audio band, the Redgum had a beautifully clean and accurate sound and there was more than sufficient power available. The absence of any protection circuitry made for a highly dynamic, realistic sound, which was helped along by the amplifier's low noise floor and the complete independence of the stereo channels.
Infofile
Redgum RGM175 Amplifier System
Price: $4995
Redgum Audio Pty Ltd
3/25 Clarice Road, Box Hill South, Victoria 3128
(03) 9897 1277
info@redgumaudio.com
www.redgumaudio.com
© 2002 Sydney Morning Herald