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Product Review - Redgum RGH-900 Six-Channel Home Theater Power Amplifier - July, 2001

David Wurtz


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Specifications:

Power Output: 150 Watts RMS/Channel into 8 ohms

Frequency Response: -3dB @ 0.2 Hz and 300 kHz

THD: 0.009%

S/N: 100 dB

Input Impedance: 10k Ohms

Size: 3" H x 16 " W x 13 " D

Weight: 18 Kg (40 Pounds)

MSRP: $4,500AUS (About $2,500 US)


Redgum Audio, Factory 3/25 Clarice Road, Box Hill South, 3128 Melbourne, Australia; Phone 61-3-9897-1277; E-Mail redgumaudio@hotmail.com; Web http://www.redgumaudio.com

Introduction

Early last year, I had my first serious experience with a Redgum amplifier. To say I was impressed is an understatement, so much so, I ended up purchasing the unit I had for review. Ian Robinson (Redgum’s designer) has been working on a six-channel version since then, and sent us (Secrets) the first unit for review. With the popularity of multi-channel audio and home theatre, the market for such items is very large. When using five or six matching speakers for DVD-V, DVD-A, DD, and DTS, it makes an enormous amount of sense to have the same type/model of amplifier driving all these speakers. Let’s see how it went through my testing regime.

The Unit

The RGH-900 resembles all other Redgum products in having the unique key type on/off switch, a black textured metal chassis, and a solid piece of Redgum timber as the front panel.

The main external visible difference appears at the rear of the amp, with six gold plated RCA inputs and six pairs of gold plated banana plug terminal speaker outputs (photos below, left and right). These terminals are well mounted and very sturdy. The six inputs and outputs are labeled from left to right as; Centre – Right rear – Right front – Left front – Left rear – Subwoofer. Realistically, the subwoofer module would not be used for this purpose, as most subs these days have their own internal amplification. This is not a wasted module, of course, as it could be used for the "Centre Rear" in Dolby or DTS EX applications.

Weighing 18 kilos it is heavy for its physical size, and the build quality is excellent. Internally, the RGH900 has a 300 VA toroidal transformer with DC rail of 63.1 Volts and 8 x 4700uF (total 37,600 F) electrolytic capacitors (photo below). This gives the power supply a total energy resource of 75 Joules. After the transformer, the power supply is actually split into two separate paths with each of the two supplies powering three of the amp modules.

The individual amplifier modules have two "flat pack" output transistors, two per module (1 NPN 10P20 - 9602 and 1 PNP 10P20 - 9621) mounted on individual heat sinks. These use the same PN junction as the T03 packages used in the two-channel and monoblocks that Redgum produces, except that Ian had them manufactured into a T0220 package, as space and cost were the premium in the box he had chosen. It was far less expensive to use and mount flat packs than T03s, and he wanted to keep the cost down to make the unit available to more users. The minute PCB on which the outputs (and other associated components) are mounted is extremely well designed, and ultimately makes a very short signal path. Each module also has thermal protective circuits installed. These are set to cut out when the temperature on the heat sinks hits 800 Celsius.

The review unit's individual test report (which comes standard with all Redgum amplifiers) states:

Short term RMS Watts, 2 Channels Driven into 8 Ohms: Left - 288.9 Watts Right - 288.9 Watts

Continuous RMS Watts, 1 Channel driven into 8 Ohms: 168.9 Watts

Continuous RMS Watts, 2 Channels driven into 8 Ohms: Left - 168.9 Watts Right - 168.9 Watts

(These figures are calculated from Voltage readings taken just below clipping.)

I replicated these tests using an 8 Ohm dummy load and received almost identical results.

Each of the 6 modules is theoretically capable of producing 150 Watts RMS of output power (into 8 Ohms), but the measurements (both Ian’s and mine) show it is closer to 170 Watts RMS. This is realistically not going to happen for all six channels at one time, since the power supply is obviously not large enough to drive all channels @ 170 watts (totalling a specified output of around 950 watts). He maintains an expected 10 - 15% duty cycle (the actual time all channels are used at any given time during a particular sequence in a movie or musical sequence) will maintain all channels with enough available power out of the supply.

The Sound

I first spent several weeks using the amp as a straight two-channel stereo amp. In this configuration, I believe it to be slightly better sounding than its sister unit, the RGi120 that I own and love. The main reason for this is the larger power supply. Needless to say, I have contacted Ian in regards to beefing up the power supply in the RGi120. Speaking in absolutes, the high frequency response was slightly more controlled than the 120, and bass transients were a little tighter but more dynamic, while still being very weighty. Low mid and mid range speed and control were fantastic. Overall, I was very impressed with the unit as a stereo amp, albeit at twice the price of the RGi120.

In a home theater situation, using the Yamaha DSP-A1’s preouts, I connected six individual loudspeakers (for the record it was four 6 Ohm Osborn F4s [for Front and Rear, Left and Right] and two 8 Ohm JBL 4410A Studio Monitors (which I had set up as the centers), and the listening results where just as impressive. Playing the DVD "Gladiator", I found the sense of realism and involvement to be emotionally frightening, even to the point of having to wipe a little tear from my eye from a movie that I have seen several times before. In my opinion, you just can’t put a price on realistic audio production, and the RGH900 delivers in spades. I auditioned several DVDs and was never let down.

"The Matrix" had me on edge again with superlative bass reproduction and transient response being pumped into me by the Redgum. Basically, it lacks nothing and gives you everything. At listening levels in my sound room of around 90 dB (this was the approximate average, with transients measured up to 100 dB), the Redgum held together nicely during different scenes (chosen because of complex information and/or large amounts of bass) that I auditioned from "The Fifth Element", "Lost in Space", "Independence Day", "Gladiator", "U571" and "The Matrix". I knew the amp should run out of go at some stage, but it just didn’t!

I also ran the amp with the DTS Surround (20 Bit - 5.1 Channels) when playing the discs, "Classic Beethoven" and Sting’s "Ten Summoners Tales" with more than admirable results. I was presented with a wonderful soundstage, impressive dynamics, depth, and an all around beautiful reproduction of the source.

At no time did the thermal cutouts on any channel activate, even though the overall temperature of the casing was noticeably hot and the internal cooling fan was pumping out enough heat to make me want to turn up my home air conditioning!

Conclusion

This amp delivers nothing short of a superlative home theater listening experience. If you are looking for one of the illusive "one box amplifier solutions" give the RGH-900 a demo. You won’t be disappointed!

 

- David Wurtz - 

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Copyright 2001 Secrets of Home Theater & High Fidelity
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