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Equipment Review

January 2002

Redgum Audio RGM175 Mono Amplifiers

by Andrew Chasin

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Review Summary
Sound "Fairly neutral from top to bottom, with a slightly soft, laid-back demeanor" and "grain-free midrange"; "proved the near-equal of the superb Simaudio Moon W-5 in terms of low-end pitch definition"; "but I’d be remiss if I didn’t point out the RGM175’s inability to render the last iota of air around and between instruments."
Features "Somewhat quirky in design and execution" -- "three chassis of identical, and relatively small, dimension": "the [MOSFET-based] monoblocks proper" and "a passive preamplifier that acts as a control unit for the amplifiers’ cooling fans and power-up relays."
Use Three chassis design as well as "the passive preamp’s dual volume controls…, the noisy variable-speed cooling fans installed in the power amplifiers…, and the lack of a power-on indicator" subtracted from the RGM175's overall ergonomics; "erred more frequently on the side of politeness, which may suit some systems (and listeners) just fine."
Value "If Redgum could find its way to deep six the passive preamplifier, then we might just start to hear everything of which this already impressive amplifier is capable."

If Redgum Audio’s intention was to distinguish the MOSFET-based, 175Wpc RGM175 monoblocks from their more conventional, me-too, black-box competition, they’ve certainly accomplished it. With solid redgum-wood faceplates and a key-operated master power switch on the integral passive preamplifier, the RGM175s make a unique visual and ergonomic statement.

The $3300 USD RGM175 consists of three chassis of identical, and relatively small, dimension -- 3"H x 16 1/2"W x 13 1/2"D. Two of the chassis contain the monoblocks proper, while the third is a passive preamplifier that acts as a control unit for the amplifiers’ cooling fans and power-up relays. Together, the three units weigh 56 pounds. A pair of supplied "control" cables (terminated with locking BNC-type connectors) tether the passive preamplifier to each monoblock. Neither the RGM175 user’s manual nor the Redgum website sheds any light on the rationale behind this unorthodox arrangement. I’d rather see the preamplifier, and the extra pair of interconnects required by it, eradicated from the RGM175 package, but the product’s current design mandated its use for the purposes of this review.

The passive preamplifier section of the RGM175 provides RCA inputs for five line-level sources: CD, Tuner, Tape 1, Tape 2, and VCR. The preamplifier’s output signal is delivered via a pair of RCA jacks, and an IEC connector is provided to facilitate power-cord swapping. Aside from the keyed power switch, the front panel of the preamplifier has an input selector and a pair of non-stepped volume controls. Although Redgum’s designer, Ian Robinson, readily admits that "no one likes the dual volume controls," they’ve been employed here because, according to Robinson, they "minimize both the number of contact points within the volume controls and the resultant distortion of the sound." Each mono power amplifier boasts two pairs of sturdy five-way binding posts for easy biwiring, a pair of RCA input jacks to accept the output of the passive preamp, and an IEC power jack.

Ergonomically and aesthetically, the Redgum RGM175 is a bit of a mixed bag. On the plus side, the small chassis dimensions and ability to stack the three chassis vertically (fully endorsed by the manufacturer, in case you were wondering) make for a relatively compact and unobtrusive package. Also, the redgum-wood faceplates added some warmth and color to an otherwise cold, sterile, black anodized audio system. And the key, while quirky at first blush, could be useful for preventing unauthorized use of one’s audio system. On the negative side was the passive preamp’s dual volume controls (which might have been more tolerable, had I not been using an Audible Illusions Modulus 3A for phono duties, itself with dual stepped volume controls), the noisy variable-speed cooling fans installed in the power amplifiers (which seem out of place in dual-mono, solid-state amplifiers of this power rating), and the lack of a power-on indicator on any of the three chassis.

Review system and space

I listened to the RGM175s in the context of my usual reference system, which consists of the VPI Aries/Graham 2.0/Transfiguration Spirit analog front-end, the Audible Illusions Modulus 3A preamplifier with John Curl-designed Gold moving-coil phono board (used here as a phono stage driving one of the line-level inputs of the RGM175’s passive preamplifier), and Anthony Gallo Acoustics Nucleus Solo loudspeakers. Isolation for the Aries was provided by an Arcici Air Head platform. The rest of the system, save for the power amplifiers, which were spiked directly to the floor, was housed in a Target audio rack. All interconnects, speaker cables and power cords were by Harmonic Technology. My usual Simaudio Moon W-5 power amplifier, another 175Wpc solid-state device, was on hand for comparison.

A few brief notes on my listening room are in order, as this is the first review I’ve conducted in the new space: The room’s dimensions are a generous 20'x20' with an 8' ceiling. The walls are 2"x6"construction and finished with plaster over lathe (my Northern California home was built in the mid-1950s). The floor of this ground-floor space is covered with oak-strip hardwood and provides a very solid underpinning for the audio system. Acoustical damping is provided by an overstuffed three-seater couch and thick drapes covering the five large double-hung windows, which bathe the room in abundant sunlight.

Power to the audio system is provided by dedicated outlets with isolated grounds. The proximity of these outlets to the electrical panel meant that less than eight feet of Romex was required for the connection. The Gallo Nucleus Solo loudspeakers sit 8' apart and 4' from the rear wall. The left loudspeaker is just over three feet from the side wall, the right speaker ten feet (one portion of the listening space is shared with the dining room, mandating that the speakers be positioned asymmetrically with respect to the side walls). The listening seat is just over eight feet from the front plane of the loudspeakers. Whatever the reason (my wife and I continue to speculate), my reference system in this room provides me with the best depth, sharpest imaging, and lowest noise floor I’ve experienced at home.


On the whole, the RGM175 had no significant sonic character of its own. If pressed, I’d characterize it as fairly neutral from top to bottom, with a slightly soft, laid-back demeanor, which made it easy to listen to for extended periods -- yet another example of the recent convergence of solid-state and tube sound. Indeed, the RGM175 seemed to elicit the best of both the tube and solid-state worlds, featuring the smooth highs and colorful (but not colored) midrange of valves, coupled to the sheer power and bass definition of the best transistor devices.

Take low-frequency percussion instruments, for example. Many amplifiers rob them of heft and weight and smudge their leading edges. Not the RGM175. On the title track of Doug MacLeod’s Come to Find [AudioQuest AQ1027 LP], the RGM175 did mastering maven Bernie Grundman proud as it managed to get all of the staccato bass-drum kicks he so impressively cut into the LP’s seemingly incapable grooves. Similarly, the fff tympani strokes heard in the dying moments of Ravel’s Rapsodie Espagnole [Decca/Speaker’s Corner SXL 2312 LP] startled with their sheer power and impact via the diminutive Redgum monoblocks. For more low-bass thrills, check out almost any track on the Classic Records double-vinyl reissue of Holly Cole’s Temptation [Classic Records/Blue Note JP5003]. The lowest of the low notes here can turn into sonic muck if the gear (and the listening room) isn’t up to snuff, but the RGM175 proved the near-equal of the superb Simaudio Moon W-5 in terms of low-end pitch definition, making it easy to follow the goings-on down below.

On top, the RGM175 continued to impress, carefully walking the fine line between detail and smoothness and rarely stumbling too far onto one side or the other. If anything, the Redgums erred more frequently on the side of politeness, which may suit some systems (and listeners) just fine. In Rapsodie Espagnole, Ravel’s brilliant orchestration makes tantalizing use of tambourines, triangles, cymbals, snare drum and castanets, little of whose shimmer and sparkle eluded the RGM175. Clamp the superb Speaker’s Corner vinyl reissue of Edgar Varesé’s Arcana [Decca/Speaker’s Corner SXL 6550 LP] to the platter and you’ll hear the violent clangor of no less than 39 different percussion instruments exploding into the soundspace, a torturous score handled gracefully by the Redgum monos, which never turned bright or offensive throughout the sonic onslaught. And although a little counter-intuitive, this is perhaps an example of one of the RGM175’s minor shortcomings -- a penchant to round the jagged edges of music like Arcana through its slight softening of high-frequency transients. No, the RMG175’s rendering of the ghoulish Arcana never forced me to recoil or wince, but it didn’t have quite the requisite "fear factor" heard through the Moon W-5 either.

Lovers of the female voice will find much to admire in the RGM175’s liquid, grain-free midrange, which lacked the bleached, threadbare character for which solid-state devices have been traditionally maligned. Although sonically superb, I’d relegated Jacintha’s debut album Here’s to Ben [Groove Note 1712 LP] to the "cure for insomnia" pile. It's another example of the great audiophile conundrum -- fantastic sound married to so-so music. But the RGM175 managed to imbue her insipid voice with a sense of life and body that I hadn’t experienced before. Holly Cole’s covers of Tom Waits’ compositions on Temptation exhibit equal helpings of edge, sardonic wit, and painful longing, all of which were communicated in convincing fashion by the Redgums (thanks to Classic’s treatment, the LP manages to kick the pants of the already great-sounding CD, and it has a couple of bonus tracks to boot). I also had some memorable evenings listening to an original deep-groove pressing of Ella Fitzgerald’s Ella Swings Lightly [Verve MG VS-6019]. Even the slight surface noise and dated recording couldn’t dampen my enjoyment of this disc, aided by the Redgum’s ability to articulate the superb phrasing and timing for which Fitzgerald was known. The orchestra, conducted by Marty Paich, is similarly brilliant.

In the areas of dynamics and pacing, the RGM175 was hard to fault, tracking huge volume swings and maintaining music’s rhythmic drive with aplomb. I don’t usually pay much attention to specifications, but the Redgum’s impressive 65V/µs slew rate and 150A of peak current may play a factor here. On Ahmad Jamal’s Rossiter Road [Atlantic 81645-1 LP], Jamal tears into his Steinway with unbridled ferocity, his pounding chords rumbling through the listening room, yet the Redgum amps barely broke a sweat, although the amps’ cooling fans could be heard grinding away in high gear between tracks. Throughout Jamal’s keyboard pyrotechnics, the RGM175 steadfastly maintained the rhythmic underpinning of James Cammack’s bass lines (played in a style highly reminiscent of the late, great Jaco Pastorius) and the inspired percussion work of Herlin Riley and Manola Badrena. Brilliant!

But I’d be remiss if I didn’t point out the RGM175’s inability to render the last iota of air around and between instruments, manifest on recordings of acoustic instruments made in a real, naturally reverberant space. On Strunz and Farah’s Misterio [Water Lily Acoustics WLA-CS-08 LP], an all-tube, purist recording made at Christ the King Chapel in Santa Barbara, California, the space in which the brilliant guitar duo is immersed, and the way in which the plucked strings of their guitars illuminate that space, were somewhat diminished by the effects of the RGM175 in the signal path. It would be interesting to hear the RGM175 sans passive preamplifier (and the extra set of cables it requires) to see if the latter isn’t hindering the retrieval of the last vestiges of low-level ambient detail on this recording and others like it.


Comparisons to the 175Wpc, single-chassis Simaudio Moon W-5, the only other solid-state amplifier I had on hand, proved somewhat surprising. I expected the iron-fisted Canadian brute to kick sand in the face of the scrawny Aussie monoblocks, particularly in terms of dynamics and low-end control and definition (the W-5’s hallmarks). While I did find that the W-5 had a hint more impact and control on the bottom and managed slightly more convincing macrodynamics, the RGM175 was only a hair off the mark. Where the W-5 did better the RGM175 was in the areas of top-end extension and transparency in the rendering of low-level ambient detail and spatial cues. Some have thought the W-5 somewhat cool and bright in the treble, but I don’t agree -- certainly not with analog sources. I’d also give the W-5 the nod in terms of build quality, ergonomics and aesthetics, although the latter is certainly a matter of personal taste. In purely sonic terms, however, the RGM175 was a close second to the Moon W-5, which, given the almost unanimous acclaim for the Canuck design, is high praise indeed -- especially considering that the W-5 checks in at around $1500 more than the pair of RGM175s and preamp.


While the Redgum RGM175 is somewhat quirky in design and execution, I came to forgive these transgressions when it was time to make music. And make music it did, unfailingly throughout the review period. The RGM175 locked horns with the superb Simaudio Moon W-5, an amplifier I’ve lived with happily for more than three years, and came away with only a few minor scratches -- very impressive performance for this young Australian brand.

I fear I’m beginning to harp on this point, but if Redgum could find its way to deep six the passive preamplifier, then we might just start to hear everything of which this already impressive amplifier is capable. I look forward to hearing that product.

...Andrew Chasin

Redgum Audio RGM175 Mono Amplifiers
$3300 USD.
Warranty: Seven years parts and labor.

Redgum Audio Pty. Ltd.
Factory 3, 25 Clarice Road
Box Hill South 3128
Melbourne, Australia
Phone: 61-3-9897-1277
Fax: 61-3-9897-1399

E-mail: sales@redgumaudio.com
Website: www.redgumaudio.com

North American distributor:
NuView Audio
446 Harrison St.,
Sumas, WA 98295
Phone: (877) 361-3630
Fax: (250) 833-4332

E-mail: info@nuviewaudio.com
Website: www.nuviewaudio.com

Redgum responds:

As always, thanks for an edifying read. I cannot suggest any amendments to the facts or technical bits, but I can offer an update as to where the product currently stands. We have been fast on our feet recently here at the factory -- and yes, we have been listening.

Namely, as of the beginning of this year, we offer the RGM175 amplifier:

  • As a single-volume model
  • As fan-free amp with a heavy external heatsink (same as the RGM300) that does not affect the front visuals; see:


  • With a power-on indicator -- i.e., the key is illuminated when turned on (via a sexy blue light)
  • With the key switch as optional -- a choice of rocker or toggle
  • With a general cosmetic upgrade (chassis, badges, and front-panel finish)

The control cables are no longer a vital part of the hook-up. They are only necessary if you wish to power up both monoblocks with the flick of one switch. It you choose not to use the control cables, there are now individual rocker switches on the rear of each monoblock.

Our thanks as always for your interest in our "quirky" products!

Ian Robinson
Redgum Audio

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