Diamond Audio HX600.4

A quarter century of involvement within the car audio industry has resulted in me becoming quite intuitive when it comes to juxtaposing companies’ ambitions versus actual ability. I’ve seen numerous high-end brands appear with promising achievements galore only, to vanish when the going becomes a little challenging. Other manufacturers, however, operate to the contrary; they arrive on the scene with very little fanfare and ado, unobtrusively spruiking their wares and letting the results speak for themselves.

Diamond Audio or simply Diamond as it is colloquially known is a perfect case study for the aforementioned ideology. Arriving on the scene ironically around the same time as this writer, back then Diamond offered only component speakers and was anything but renowned. However, gaining traction as it went around decimating the competition scene Diamond struck while the iron was hot, wasting no time expanding its stable to include subwoofers and ultimately power amplifiers with the performance and build standard remaining exemplary throughout.

Hard facts
Sporting a legacy nothing short of enviable, Diamond showcases this achievement impeccably with its flagship components, the acclaimed Hex series, letting these do the talking, literally. A name synonymous with engineering acumen, the Hex stable incorporates everything from component speakers and subwoofers through to amplifiers, and from the latter sitting here for testing is the mighty HX600.4 amplifier.

An astute performer, it successfully blends impressive power, efficiency and ancillary figures with a small footprint and a modest asking price. Class-wise it operates with a digital switching Class-D topology, offering 160 watts continuously from its four satellite channels when measured at 4 ohms. These figures rise significantly to 250 watts when the channels are loaded down to 2 ohms, and running the channels bridged will return you a mammoth 500 watts continuously for each pair at 4 ohms. As if that’s not intimidating enough; it does so with a total harmonic distortion of just 0.06 percent and signal-to-noise ratio of -80dBA thus ensuring it plays quietly so far as induced hiss and artefacts are concerned. Cone deceleration is aptly controlled thanks to a damping factor over 250, while reciprocal speed and dynamic integrity is overseen via an impressive slew rate.

Succinctly speaking, the HX600.4 represents an extraordinary marriage of grunt and fidelity, an art form often lost on many manufacturers today. While many companies can produce amplifiers capable of shattering eardrums, they often overlook the ancillary specifications to their own peril; as the ensuing sound is comparable to that of a un-tuned sistrum. Thankfully, Diamond’s obsessive nature has put paid to this conundrum, ensuring this new design can deliver performance aplenty.

The instantly recognisable element of the design is that it exudes smoothness via its stark appearance. Not that Diamond has ever made a bad looking amplifier but this new look and feel has placed the Hex range well and truly ahead of the amplifier peloton so far as aesthetics are concerned. The unit is enshrouded in a solid cast aluminium case that’s anodised in copper. Serving as the primary heat sink, this magnetically inert case also offers serious protection for the components residing within. Boasting a footprint of just 195mm by 302mm with a height of just 51.5mm, it’s anything but a titanic affair. Clearly labelled and plated terminals line the front edge and they are recessed for protection. These include 4AWG power and earth terminals in addition to speaker terminals able to accept up to 10AWG cable.

Diamond Audio HX600.4

On the signal input side of the equation the amp features balanced differential inputs and although space won’t permit me to fully expand upon this concept, put simply, the amplifier measures and compares the positive pin impedance to that of the negative shield before using this and other criteria in order to recreate an input signal which in theory does not suffer from noise and ground loops. Not to be confused with fully balanced connections the likes of professional audio equipment, balanced differential inputs are conducive to a far cleaner input signal regardless of whether you’re feeding it with high level or low level voltage. There’s also a full range line output if you desire to feed signal to an adjoining amplifier.

Removing the front portion of the top plate gives access to the primary controls, which range from the mandatory gain for each channel pairing in addition to a fourth order high- or low-pass crossover settable between 40Hz and 400Hz. There’s also a small clip warning light in addition to a 0dB to 18dB bass boost ability centred at 45Hz. The amplifier is also switchable between 2- and 4-channel modes, meaning if you only have one pair of RCA interconnects you can still feed all four channels the same signal.

Diamond Brilliance
Removing the steel bottom plate to eyeball the internals is an equally rewarding experience as Diamond has attained quite the reputation for masterful amplifier design. The HX600.4 is no different; the design starting with a four layer glass epoxy circuit board bolted firmly in place. Upon this resides an array of high quality componentry starting with a cluster of 25v/2200uf Samwha stiffening capacitors placed right behind the power input to smoothen the voltage. From here the power is shunted through two large air core transformers for voltage step up before moving to the 50v/2200uf Zhuohao power storage capacitors. Here the charge lays dormant until required, upon which point it’s fed through to a multitude of transistors that are firmly clamped along the rear wall of the heat sink – this is the most efficient location thermally speaking. Logically the power capacitors, transistors and just about anything else intrinsic to power has been kept well away from any signal handling components. Not only are these located up the other end, they also live on their own completely separate circuit board. The omission of a cooling fan may raise an eyebrow or two, however, being Class-D in design dictates that it shouldn’t experience the kind of heat its Class-A/B comrades are forced to endure.

Diamond Audio HX600.4

Installing the unit is straightforward enough thanks to the apropos combination of small size, smart terminal layout and clear labelling. Included in the box are basic tools and mounting hardware in addition to an instruction manual. The amplifier comes packed in a neat cloth bag to keep greasy finger prints away from that superb case.

Before reaching its test car destination the HX600.4 first had a date with the test bench. Not that I dare doubt Diamond Audio, you understand, but no matter how you paint it that’s quite an audacious power claim given the amplifiers diminutive proportions. After a good half an hour of happily ‘fiddling around’, for want of a technical term, I can report she’s certainly got the horsepower where it counts! Metaphors aside, it’s one menacing little powerhouse, with current to boot. It’s a quiet little operator too, remaining all but hiss-less until near on full tilt is reached with the gain potentiometers.

So far so good, the first two tests equating to two ticks on my clipboard. Just reiterating why I was somewhat apprehensive; you need to understand that here we have an amplifier claiming to possess power in droves, with enviable control statistics and all for a price south of four figures. Put simply this combination is plain unheard of. So I was understandably circumspect as I moved from the test bench to the car for some real world testing. The test bench is one thing, but how would it handle a solid day’s worth of cruising around working? Would it really be the performer proclaimed or would she stumble at the last hurdle? It’s was time to find out.

Oscilloscopes and real time analysers beeped, gains were wound back down and the processor feeding it was tuned. I spent a good hour idly running through the usual suspects of test music genres before moving onto general cruising music. One thing straight up; it’s a tenacious little number. Not only does all that ability equate to a performance that’s bedrock solid, it’s also measured and controlled in every sense of the words. Rather than threatening to kick you in the groin at any moment, the HX600.4 instead retains complete authority over the music no matter what you ask of it, and no matter the volume. Even at full tilt it continues to provide linear and articulate sound across the entire 10Hz to 35kHz response range, albeit we’re unable to appreciate the upper third of this.

Allow me to touch once again on that impressive trinity of quality, power and price. When dealing with high-end amplification the norm dictates that you’re restricted to any two of these three criteria. I’m happy to stand corrected but fairly certain this is the first amplifier I’ve tested, in literally years, that’s nailed all three of these criteria with aplomb.

Diamond Audio HX600.4 4-channel amplifier
Price: $949

+ Superb engineering & design
+ Excellent performance + total control

- We struggled to find negatives!

Type: Class-D 4-channel amplifier
Power rating: 4 x 160 watts at 4 ohms, 4 x 250 watts at 2 ohms continuous
Features: Adjustable crossovers, bass boost, input shunting