The REDGUM UltraFlex Power Supply

Rating A Power Amplifier

At a superficial glance, REDGUM amplifiers will always “lose out” when comparing brands on specified WRMS. The WRMS value is commonly mentioned in the press as the power value of an amplifier, calculated (by convention) under a continuous test load and is quoted as Continuous Watts RMS for one channel under this load into 8 ohms.
Although it is the common standard as a comparative measure of one power rating against another, it unfortunately has nothing to do with what music is made up of! Taken to the extreme, if this load = sound/signal was conducted/handed on by the amp to the speakers, the speakers would fry immediately. So, as a measure, that is not useful as a measure. (Sorry, one should retain a touch of scepticism even in the field of electronics.)

What is Needed for Music?

Music is a series of transients such that the power required to produce them is constantly drawn on, but only as short term pulses. Contrary to what is commonly perceived, the immediacy of the sound of the musical note (the transient response) depends on the responsiveness of the power supply rather than its size! You need the sound/note “NOW!!!” because the “NOW” moments, as a succession, are what make up music. This is what the REDGUM UltraFlex power supply is designed to produce better than conventional designs.

The conventional power rating comparison done via the WRMS measure is misleading when it comes to delivering real-world music. REDGUM’s UltraFlex power supply is designed quite differently from the traditional style of power supply. Contrary to expectation, all REDGUM amplifiers are fitted with a much higher voltage power supply than is necessary to give their specified power! But as a REDGUM power supply is designed to “collapse gracefully” with load…the ultimate protection feature to over-driving!!…the long term power test (giving the WRMS rating of a REDGUM amplifier) is usually done with the transformer already in ‘sag’ mode!! Such ‘sag’ measurement conditions can never be a true reflection of what is available from a REDGUM for Short Term RMS (i.e. transients, otherwise known as “Music”). Not surprisingly, when using REDGUM amplifiers as designed (i.e. for music!), they seem much more powerful than their quoted WRMS figures would suggest.

REDGUM’s Power “Bracket Creep”

For example, that means for the baby of our Amplifolia range, the Stellulata integrated amplifier, officially rated at 60WRMS per channel, has a power supply voltage that offers music transients of around 140W Short Term RMS…and would still run rings around an Asian 110W amplifier!!! An Aquilina integrated amplifier typically has a power supply voltage that is more consistent with other brand’s 300W amplifiers than its 120W/ch. Clearly, this begins to explain the startling transients available from a REDGUM amplifier! Even better, a 200WRMS/ch Articulata offers Short Term RMS of around 320W!!!

A further reason for this added power is that over the last decade or so, the power of the transformers used in REDGUM amps was gradually increased through upgrades, so that the kick/grunt/speed of the amplifiers was actually well beyond their official ratings. As other core aspects of the designs had remained unchanged, for simplicity’s sake the same model numbers were maintained. But finally, in 2015, the range was renamed as the Amplifolia models to accurately reflect the large increase in power of current production.

In Practice

Traditional designs for amplifiers and their power supplies sag as a result of the transient, leaving the woofer to continue “shuffling” after the actual musical signal has finished. REDGUM set about designing a power supply that was not affected by the sag in the power supply.

So looked at from the point of view of the speaker’s drivers…because of the method of controlled “collapse” of REDGUM’s UltraFlex power supply, in all, the bass response is tighter and more controlled. Adding to this the fact that all REDGUM amplifiers are high Damping Factor amplifiers that means really tight bass!!

The advantage of this regarding larger/any drivers is that there is no instability in their movement when delivering large transients &/or with using a large number of large drivers. At the other end of the spectrum, at low volumes, there is no resultant shrinking of the musical image just because one wishes, or needs, to listen more quietly than usual. The full clarity of detail remains.

Consequently, REDGUM customers have that secure feeling that they can choose to play ANY style of music they wish, and even at neighbourhood demolition levels! Put together, this means that all factors that are vital to the enjoyment of the music (soundstage, imaging, detail, etc.) will be there along with the very tight bass.

All this adds up repeatedly to a case of customers being more than surprised by what they hear! Could just be the reason why REDGUM dares to offer “Goose bumps for Grown-ups.”

This can, of course, be put a little more formally as “Insight for Sore Ears!”

Some History – RGi120, the First REDGUM

The first REDGUM amplifier designed was the 120W. As a measuring stick, its power/specs were decided upon to provide the buyer with “the last amp they will ever need to buy” as it provided what most customers require of such a product. (A bit like when a couple retire and they buy a car–they choose one on the basis of “This should see me out.”) Without fundamental modification over its first decade, the RGi120 delivering 120WRMS effortlessly drives most floorstanding speakers regardless of difficulty in load (ribbons, electrostatics included). (All these comments are made assuming that the amp is not being over-driven.)

The RGi120 provides high but extremely clean listening levels. Only after sales of several years, did it then begin to be necessary to install a fan internally. (It remained the only unit produced with a fan.) As customers became so comfortable with the clean high volume, they would drive it much higher than they realised they were doing. In other words, their listening levels consistently crept up on them since the sound maintained its integrity. The obvious flaw to this line of thought was checked out – this creep in volume levels happened with both younger and older customers so it was not a function of age and/or the possibility of deteriorating hearing!

That first “REDGUM” was designed to a price point as well — an affordable, major purchase that represented value-for-money. To expand an amplifier range from there whilst maintaining a sense of family meant either they were given “more of” (by using bigger transformers and more tailored components) or “less of” (fewer MOSFETS, less powerful transformer, and less-expensive versions of the top-line components and cosmetics).

But all the while, the audio design of a REDGUM amplifier was/is the same. To put it simplistically, it is still the same car but with a varying number of spark plugs or engine capacity, and the bigger the capacity fired, the more Super+ petrol that is in the mix with the basic Unleaded. One is always at a loss for words to explain what can be clearly heard as one progresses up the range — but until heard, it is not believed as being so consistently straightforward.

As straightforward as…”Once heard on a REDGUM, such expectations cannot be un-heard.”

Ian Robinson
Founder & Designer