REDGUM Black-series Design Philosophy

Extracted with permission from Mono & Stereo’s review of the REDGUM Black RGi120ENR integrated amplifier. In the review, Matej Isak did an email interview with Ian Robinson, REDGUM’s founder and designer.

RGi120ENR is very different sounding and performing integrated. Can you elaborate on why it sounds so different?

Always a tricky one to answer as I have never been enthusiastic about the sense of presenting just one or two specific features of a design as being what makes the REDGUM sound different, because that isn’t the way electronics work. Clearly there are the headliners – what sets our design apart from the mainstream e.g. Audiophile MOSFETs, Dual Mono, our UltraFlex power supply to create great Transient power. But in truth, the final sonic character achieved is a result of a multitude of electronic factors, some being more prominent in the outcome than others, while all remain vital to the mix. 

In other words, it is not only the use of particular components but how each is then Goldilocks-ed within the total mix. (Am not trying to invoke that over-used word, synergy, but if you compare the result against the sound from a standard, non-Goldilocks-ed design, then it has definitely become “more” than its parts! )

I would prefer to turn the question around to what has always been the driver of any of my design decisions. Just one thing – to accurately reproduce the sound of live instruments. From that stand point, the decisions seem to make themselves. But if there is one thing that holds it all together, it has to be the ability to supply sufficient and timely Transients as they are what music is entirely made of. From the very first design in 1993, the flexibility of the power supply was paramount, otherwise the sound was not believably as real as being at the actual performance. (My partner likes to sum up this “live” effect as “Goosebumps for Grown-Ups!”)

The unanticipated beauty of being at a live performance is that it is also calibrating our brains to “know” the sound of each voice or instrument. So that when we get back home and experience that “rightness” again from a well-captured recording, it means the brain critic has been able to tick the box of “I know that sound! All present and correct!”, and take a back seat. Only then can the listener relax fully into the moment (or momentousness) of the music … (and you sure can’t fool REDGUM owners who are also musicians!) … rather than the brain needing to continue to check it all out on a technical level. 

Speaking of technicalities, one I should also mention, is the focus on supporting an extended frequency range – 0.8Hz to 100+kHz. As this was present from the very first design, that made REDGUM amplifiers SACD-ready 6 years before that hit the market. 😉 But such detail at the top cannot be added in isolation. Untrained ears can substantiate that balancing an extended top with good bass extension, along with all of the middle in between, gives the most believable reproduction so your brain decides it isn’t a reproduction!

On the topic of bass, another factor that is definitely palpable is the high Damping Factor from REDGUM amplifiers.( And that’s as measured at the speaker terminals.) And that bass needs to be offered with its sub-sonics as we need to hear and feel it to make sense of it.

Bring it all together with Dual Mono’s ability to adjust for an image that snaps the performer into position as “flesh and blood” … maybe that’s enough as I think you get the sense that it isn’t just one factor! And if they really work together, one can then boldly say that a REDGUM’s neutrality is distinctive … even if it is a new kind of oxymoron! 😉

Your signature heatsinks clearly stand out. They seems too have a story of it own?

Yes, it is a case of “cool” steam ahead with that heat sink! I once went off to China for 2 weeks leaving our biggest Monoblocks, the new Magnificata (>350/>550/>900W / ch into 8/4/2Ω) in my partner’s care to try and destroy them in my absence as she put a musical programme together for The Melbourne Audio Club presentation. The ultimate test was on a series of stinking hot days and the air con was left off. i.e. 40+°C outside/ 39°C inside the room and with the amp running at orchestral “ffff” for the whole day. The heats sinks just tipped blood heat. ;)
 
Firstly, the name…

We call it the SignWave heat sink because it was designed for our bigger Signature Series (ENR) amplifiers, and because the front edge line formed by the fins looks like a sine wave. (As to the “ENR” it sounds just like I sign my name – IanR – hence it is used to denote our Signature amplifiers!)

This heat sink was introduced in 2005 on our first Signature Series amplifier, the RGi120ENR (now the Articulata in the Amplifolia range), then the Monoblock power amplifiers followed suit. And since our 21st Birthday, with the re-designing of the biggest Monoblock (RGM300ENR) into the Magnificata Monoblock System (in the Amplifolia range), all of its 3 units (pre and powers) include this distinctive heat sink.

As to the “Why?” …
”Technically”, I just love the look! 😉

As to the “Where?!!” … well, I could say it is just a reflection of how Aussies are seen by the Rest Of The World. We hang by our feet as we “live in a land Down Under”, so why not have a heat sink Down Under?! ; )

More formally stated, our design always leads to this questioning as to why not have the fins on the sides or the back. Agreed, fins dissipate heat most efficiently when they are vertically orientated. But when you factor in the sheer size (as in surface area) of this heat sink, it then doesn’t need such a lot of air flow to keep it cool. And the openness of the “sine” curve allows a generous clearance for air to convect through and up from the heat sink. In fact, with one of those “through” directions always being forward, this creates a real positive for dissipation when units are positioned in cabinets.

So, as the flat “back”/top surface of the heat sink then becomes the base of the amplifier, even driving low impedance loads long and hard means the metal never gets warmer than blood temperature. A case of because the area of the heat sink is “overkill” to the nth degree, the amp doesn’t raise a sweat with the more difficult loads. This was the only technical test it needed to deliver on, so we knew after one long, hard session it had passed with flying colours! Along with being rock solid as a heat sink!

As implied, the initial impetus for this design was to meet the changing market urging the use of drivers with ever lower impedances. So that there was plenty of heat sinking to “future proof your system”, it seemed only logical to re-design our bigger ENR versions (prior to the Black Series) to use a heat sink as the whole base plate of the amplifier.

A little detour: I find it interesting to reflect on how “how much?” heat sinking has changed over these two decades, going way back before Car Audio had an effect. (For this I have to refer to our original wood-fronted REDGUM amplifiers.) When the first Integrated (RGi120) model was released in the 1993, there was never a sense of any need for fan cooling!! (And that heat sinking design, as an internal column, remained the same, and effective, for the smaller Integrateds till 2014!) However, later in the ’90’s, some RGi120 owners, after a couple of years of use, began reporting their amps had started “cutting out on thermal!”. Once they checked, it was an embarrassed “yes”, they had let the volume levels creep up over time. But not a surprise, thanks to the amp’s lack of distortion!

So the fan was then made a standard feature on the RGi120. Come the early Noughties, the lowest impedances used in Car Audio were beginning to have their effect on some RGi120ENR amps, even with fan installed. That is when the idea of “seriously big” heat sinking aligned with our wish to create a Signature look for the existing Signature amp, the RGi120ENR. Enter the SignWave heat sink. Exit any talk of thermal events! 😉

REDGUMs are designed so that all circuits are efficient and that must include heat issues!! In fact, the very first REDGUM design had all MOSFETs mounted directly onto a thick metal plate bolted to the internal heat sink. (Within a few years, all MOSFETs were mounted directly onto that internal heat sink.) Then with the advent of the SignWave heat sink, an even more effective connection could be made as the MOSFETs of all Signature Series models were close coupled to the top/”back” of this immense surface. Also for the first time (in the industry?) we could use this heat sink to cool the mains transformer. And as to the rigid mounting of the transformer, it, too, is bolted directly to the casting.

Unsurprisingly, the heat dissipation is very effective on this “BBQ grill” (as it has been called!). As you would be only too aware, some Audio brands have heat sinks visually well placed, but actually with no heat-generating components mounted onto them directly!!!!!! I find that technically weird as naturally it is most ineffective. 😦 Indeed, we have tried placing heat sinks where they are “meant to be”! Prior to this, we had interim models using heat sinks at the rear, or completely forming the sides of the amplifier (e.g. earlier models of our 6 channel Home Theatre power amp), but in comparison, that side coverage was only about two-thirds of the surface area the Sign Wave heat sink offers as a base.

I’m sure the thought has crossed your mind that for the power of the “baby” (RGi35ENR) of the Black Series amp you are testing, the amount of heat sinking is excessive. 😉 Indeed, yes, but, on the other hand, it really does come in handy for the rest of the Black Series ramping up to 244W/ch and 500W/ch into 2Ω. So it was decided when presenting a new series it made more sense to have one physical style. (It is always the customer who cops the cost of new model, so that is why the Black Series heat sink is the same design as for the Amplifolia range.)

 For the last 10 years, the SignWave heat sink has been the visual hallmark of our larger ENR models in what is now called the Amplifolia range. As the Black Signature Series are clones of the Amplifolia designs, then having the same heat sink seemed to fit the visual logic. As the Black Series were focussing on providing the grunt for those more difficult loads, it made even more sense for the technical logic.

Why you implemented Mosfets?

The short answer is “Why live with the “sudden death syndrome” of transistors when you can afford robust MOSFETs!!!?” MOSFET amplifiers can still function even when there are dead MOSFETs in the output stage, so the music doesn’t have to stop when “Party time!” might otherwise have cooked a transistor amp. A MOSFET’s positive temperature coefficient protects the circuit from heat damage – they are self-limiting because thermal runaway cannot occur. Unlike transistors.

With a MOSFET being a solid-state valve that is a special form of transistor, it has the advantages of both, but none of their disadvantages with the exception of price! Of course, the design process has to be a little different and I took my time to be sure of their worth.

Having repaired amplifiers over more than 20 years as sole “Official Warranty Service” agent for several brands that used MOSFETs, I was able to follow their improvement. By the time it came to the core design period of the amp (1991-93), there were Audiophile- quality ones available that were ‘faster’ and ‘stronger’ than those being used in then- current designs and which were helping to give MOSFETs a bad name.

From then on, over the years, as more powerful Audiophile ‘FETs have come onto the market, they have been incorporated as a matter of course into our amplifiers. But as it was done without any change to their model names, this is how the “bracket creep” in power and capability has occurred over the years. It recently got to the point with our 21st birthday that we finally had to draw a line with the Amplifolia models and give them all higher power ratings!

In sum, using ‘FETs as the pivotal point in your design puts you up into another sonic “ball game” altogether. So if a REDGUM adds anything to the pleasure of listening, it is because we aim to add nothing!! An effective amplifier design should not leave its mark on the sound.

Dual volume? Not at all the usual path?

I have been in Audio for so many years and seen all the fads come and go! And the “latest” fad that was around at the time of the amp’s initial design period (1991-93) was Dual Mono amps. They didn’t stand the test of time with the market because the need to adjust a second volume control was considered a fiddle. But selling them meant I, too, fiddled at length and found how Dual Mono transformed the ability to present the image! And so it became a key feature of every REDGUM amplifier.

Actually, Dual Mono offers a greater degree of flexibility to the listener than is perhaps immediately obvious, and that is even without very careful adjustment. But one can still go all out to reveal that absolute “last iota” of detail.

Being able to independently adjust the volume level for each channel means you cannot suffer the drawback of the more traditional Volume-Balance control designs where the “other” channel drops out quickly and totally!

The most demonstrable benefit of Dual Mono is the ability to bring the position of the performer back to centre stage (should the recording present them as off-centre). By varying the positioning of the control knobs up to 10 degrees, thus adjusting the “balance” between the channels, it is possible to move the image of the performer about 30cm/1 ft back to a more central position. (Our worried brains seem to like this feature!)

A further subtle but vital advantage of Dual Mono is that the infinite variation within room acoustics can be directly compensated for. This micro-adjustment is possible by just moving one or both of the volume controls. (Gone is the need for the speaker forward-backward shuffle, repeatedly moved by hand to find the best position for a good image. Now you can nail the image with one speaker sitting out in your open-plan room while the other speaker sits in a corner!!)

Instead of what appears to simply be a change in the volume level via the Dual Mono controls, actually the listener is subconsciously adjusting for the effect of the room acoustic as heard in terms of how the image snaps into position. In this way, our ears tend to be the best judge of what sounds balanced (as in the best image), rather than accepting what visually lines up as “balanced” via the knob positions.

It might have seemed that I was a stick-in-the-mud over too many years by maintaining this design choice. And it did cost us some customers! But it was done to support the optimal sonic result gained via that imaging potential. Any mainstream reservations were removed once we released REDGUM’s Dual Mono remote control in 2007. As it also works in Couch Potato mode – Volume Up/Down – it does what every family user expects. And now with our Android App offering these same remote functions, you don’t have to keep an eye on the dog any more! (Yes, we really have had to replace remotes because “the dog ate it!”.; )

RGi120ENR is bursting with power output even with speakers with heavy demanding load. How did you achieve this?

One can only go straight to the tech talk on this!

Very high power supply voltages, combined with extremely low internal resistances right from power supply capacitors to the output stages and on to the speaker terminals. All these areas are wired with high current cable, not lightweight PCB tracks. The end result is a very high current capability even into very difficult loads.

Though purpose-designed to power ultra-low speaker impedances, the Black Signature Series amplifiers remain clones of the original wood-fronted Amplifolia designs. Hence, they share those designs’ ability to drive into impedances as low as 0.7 ohms (our suggested minimum impedance).

Below 1 ohm, a slight sound degradation can be expected; at less than 0.5 ohm there is obvious distortion.

Tell us more about the “gain” volume attenuation…

Again, straight to the tech talk! As passive preamps have no gain (or added noise or distortion), in order to achieve the necessary listening levels the power amplifier section needs to be a little more sensitive than standard. By having ‘just enough’ overall gain, the extra hiss, hum and distortion generated in the ‘whole’ amplifier itself is reduced to minimum.