Design Rationale

According to Ken Kessler in HIFI NEWS & RECORD REVIEW (Nov 1995, p73), “Redgum: cool name and a cool feature. The company’s amps can be locked with a key which serves as the on switch. Which is one way of keeping kids away from the hi-fi system…….Named after the wood used for the fascia, Redgum offers a solid-state, MOSFET integrated amp with high sensitivity, passive inputs and an output of 60W/ch for AUS$1500. A separate stereo power amp rated at 130W/ch is available for AUS$2000.”

Yes, we were discovered quite a while ago. And apart from the typo about the 120W integrated amplifier, this key has been a part of all amplifiers from the very first design right through to what is now called the Amplifolia (wood-fronted) range.

These days, its presence enables the use of our world-first Dual Mono remote control. That means, whether for manual or remote-controlled units, parents with teenagers have reported to us that when they go away for the weekend, they take the key with them!

From the point of view of home security, should an amplifier be stolen it will be useless without a key. Just like houses, each REDGUM amplifier has a different key as its on/off switch. A key register is held by the manufacturer to match the warranty registration by the new buyer. A key-less amp will raise suspicions when presented by an unregistered “owner”.

Before the addition of the unique Dual Mono remote control to the range in 2007, no-one really liked having two volume controls! So why did REDGUM continue using them from the very first design? Like all things in a REDGUM Amplifier, there is a very good reason for being persistently different! For any designer of hi-fi, sound quality must be the deciding factor. Therefore, REDGUM believes that a slight change in the way the controls are adjusted is a small price to pay for better sound. Having two volume controls (a “dual mono” system), makes REDGUM amplifiers visibly different. Besides this, using them is considered important as the way to minimise both the number of contact points within the volume controls and the resultant distortion of the sound. Adjusting an extra knob to get better sound quality seems worth it, surely.

If not a 100% tight fit, all connection points (in series) in a circuit can add distortion. We all have had the experience of loose plugs, speaker leads and the like, and the problems they can cause. Well, a volume/balance/tone control is the original “loose connection”. These controls (in the form of a potentiometer) consist of 1 or 2 metal fingers rubbing on a carbon deposit track and are in a little metal case open to the elements. (Imagine how badly effected the contact becomes with dust and grime over the years!) Even when brand new, these contact points react as “contacts between dissimilar materials”.

If you set up a test sending fine detail information (such as a solo instrument playing quietly in the distance) through these controls, you will find that the distortion caused is immense! The finer the detail, the greater the destruction of the signal! Obviously then, the fewer the contact points in series (eg. in the volume controls), the better the sound reproduction. Hence, with a separate volume control for each signal path, you can achieve volume and balance using only one moving contact point in each signal path. Compare this to the usual situation of one (internally dual) volume control connected to a (internally dual) balance control as well as a (dual) tone control, which is possibly connected on to other controls……….!

However, from an absolute Purist’s point of view, REDGUM believes that the best method available to minimise distortion is by not using carbon potentiometers (“pots”) at all. Therefore, in manually-adjusted units, REDGUM volume controls are made of conductive plastic! Other manufacturers tended not to use them because they are ten times the price of carbon “pots”. Remarkably, even in exotic brands of Hi-Fi, manufacturers have insisted on using carbon ones simply because the price is cheaper.

The conductive plastic controls used by REDGUM have many fingers on the “pot” and so have many contact points, but they are in parallel. It is this combination of many parallel contacts on conductive plastic which minimises the generated distortion. Distortion at -60dB using conductive plastic controls has been measured as less than one-hundredth the distortion generated by the cheaper carbon “pots”.

If any one wood conjures up the essence of Australia, it is Red Gum. The grandeur, complexity and variety of colour and texture of this wood is a reflection of the quality of the sound from this amplifier – solid and real. Each REDGUM front panel is made from one solid piece of unfilled natural timber, selected and finished to maximize the character of its grain. The more interesting the grain, the more likely that slight imperfections will be present. For the stack of chassis that make up the three piece Monoblock amplifiers, the fascias are blended to get the greatest effect from complicated grain areas.

Red Gum wood has played an important role in Australia’s history from the earliest of times. For thousands of years, Aborigines used the trees to make canoes and weapons, for food (making wonderful honey!) and medicine. Early European settlers took shelter in bigger red gums by hollowing out the boles. Later, the strength and durability of the wood was utilized for their dwellings and other structures. Nowadays, the wood is highly valued for its beauty when made into furniture.

More than 30 years in the HiFi retail industry (Chelsound Electronics, then The Contemporary Sound Centre for 26 years) has given REDGUM’s designer, Ian Robinson, the reputation of giving clear, straightforward advice. Early on, his skills as a cabinet maker (RECAB Storage Cabinets – Parkdale Vic), combined with his knowledge of electronics, led him to design and produce his own range of speakers. He marketed LINK speakers successfully for 15 years – again filling a niche that became apparent from customers’ enquiries. In those days, “bigger” meant “better” with speakers, but Ian’s back gave way under their load. (No gain, no pain?) As a result, LINK Bookshelf speakers were launched, and they were still alive and well-loved by their owners some 20 years later.

This time in the industry gave him a definite idea of what customers liked, wanted, could afford and were willing to spend on “good gear”. After all these years repairing HiFi equipment and performing authorized “under warranty” work on many major brands, he had a clear picture of what worked and what did not. He set out to create an amplifier that was worth selling – one that, above all, made you feel you were at the event, but was also reliable, indestructable and reasonably priced.

The ultimate goal at REDGUM is to design Hi-Fi products that make the listener feel that they are hearing “live” sound – facing the artist at that concert, feeling the indescribable atmosphere of “being there”, sensing the emotion of that unrepeatable moment. Owners of REDGUM amplifiers are convinced that the designer, Ian Robinson, has done this. One reviewer described it as “There are live musicians at the end of the room.” (Richard Weiner, Bound For Sound).

Listening to customers’ specific requirements of equipment and complaints that quality sound can have an outrageous price ticket attached has guided Ian in the design of REDGUM audio products. Just because customers have a true appreciation of the sonic differences between a cheap “plastic” toy stereo and top end HiFi gear does not also mean that they always have a big bank balance to fund such a purchase.

HiFi prices sometimes can change exponentially as one works through product ranges and yet the improvement in the quality in the sonics can be less than linear. For Ian, the guiding principal when designing a REDGUM amplifier is “not using insane bunches of components where one unit will do” to achieve a quality sound. As a result of this philosophy, realistic pricing is attainable.

Having moved into the area of manufacture, Ian wanted to leave the world of repairs caused by less-than-well-thought-out design. He wants to grow old making a product he is truly proud of and stands by, rather than spending his future repairing it. In the five years since their inception, REDGUM amplifiers have shown themselves to be truly indestructable. As proof, they are covered by a full seven year warranty.

Consider the following tale: A REDGUM amplifier plus speaker leads were installed for Mr L. of Ripponlea, Melbourne. A second set of leads were connected in another room and left on the floor, awaiting the delivery of his chosen speakers, Magna Planar (each the size of a door and notoriously hard to drive). Ian received a call to say that every 15 minutes the music was stopping, then starting again. Four hours later, Ian arrived to find the amplifier and speakers were still intact, in spite of the second set of leads having been permanently shorted on the floor in the next room all that time. The amp had only protected itself by cutting off on thermal!!

The debate about the virtues of CDs versus vinyl will continue, but there will always be an amplifier involved to evaluate either. Therefore, another debate must be considered, that of valves versus transistors. From Ian’s point of view, it is an argument not to be had as they both have inherent problems. (Having been involved the first time valves were popular, he is old enough to know he does not want to cope with such vagaries again!)

Valve purists are aware of the fact that the emission of a valve drops off from the moment it is first turned on. Consequently, they believe that to maintain optimal sonic quality, valves should be replaced every 18 months. A horrendous expense in itself, but even worse is the fact that the owner of the system has had to live with the constant deterioration of the sound quality from the very beginning. The heat generated by the valves ‘cooks’ the electrolytic capacitors, and the large resistors used in most ‘good’ valve amplifiers drift up OR down in value! As well, there is an inherent noise from valve circuitry, and so this intrudes on the enjoyment of today’s ultra clean recordings.

Transistors have the ultimate advantages that have made them so popular – they are cheap and quiet. However, they are inherently unstable because of their negative temperature coefficient. This means that when the temperature of the silicon in the active material rises, the resistance drops. A lower resistance allows more current to flow, which in turn raises the temperature. Because the transistor cannot be self limiting, a downward spiral begins. It must eventually fail, doing so suddenly and without warning.

To guard against this, a circuit designer decides what set of criteria make up “normal working conditions”. In a computer, for example, outside operating influences cannot effect the operating conditions of the transistors in the product. However, the situation for a power amplifier with its vulnerable output stage is different. Unfortunately, no designer of transistor circuits can factor in every possible eventuality, especially when humans, in all their variety, have control of the output stage, and the user has decided (rightly or wrongly) what the amplifier is capable of.

Consequently, birthdays and transistor amplifiers do not mix well together. Why does your amplifier “fry” itself at your annual party? Because you and your friends are in charge of what is demanded of the output stage, and this can easily exceed the designer’s criteria of “normal “ workloads. For example, at your party, the type of music chosen can be different and played suddenly at a much higher volume, or multiple pairs of speakers are played at once. These situations can lead to disaster because the thermal feedback transistor on the output stage will only keep thermal runaway under control most of the time, and so at your party it now may be running at a higher level than the amplifier has been accustomed to.

With the cost limitations placed on designers today, not all forms of overload can be prevented by the circuit design. At your birthday party, the transistors in your amplifier are likely to respond in the following way – through ‘secondary breakdown’. A momentary overload results in the overheating of a small part of the transistor junction in the output stage . This is because, with a ‘negative temperature co-efficient”, the resistance of this heated area drops. The overheated section takes a greater share of the current, thus overheating further. Consequently, the junction takes all the more current, overheating even more. Within nanoseconds, it has happened. The junction temperature will reach over 400 degrees C, so it melts, creating a short circuit and no more party music.

So why do transistor amplifiers also “die” for sober living people who never celebrate noisily? Regardless of the due care by the designer, thermal feedback transistors and their support components are unreliable in their performance. As well, they are subject to aging, or the failure of these or other components. Added to this, unforeseen events can also create sudden overloads and inadvertent short circuits (at any time). These could be a bad speaker wiring joint, or external influences causing instability (eg. power surges, 2-way radio breakthrough). Even if the owner of a transistor amplifier uses it within the limits of the criteria chosen by the designer, the amplifier can still “die” at any moment.

Paying more for your transistor amplifier in the hope that it will be more reliable does not necessarily solve the problem. A higher price for a transistor amplifier does not always indicate that the circuit design allows for a greater safety margin in the operational criteria set by the designer and/or manufacturer. The amplifier may just be running “closer to the edge” of (self-) destruction. The exotic imported amplifiers so popular in Australia are renowned for “catching fire” after a few years of use. The fact remains that in 30 years of business, Ian has never seen designers of transistor amplifiers use components that are big enough to cope with all unexpected, high-stress situations.

So what is left to use when the most frequently used components are considered not reliable enough? Is there a device that has the advantages of both, but none of these disadvantages? Mix the concepts and you have a solid-state valve that is a special form of transistor – a MOSFET (Metal-Oxide doped Silicon Field Effect Transistor). MOSFETs have a positive temperature coefficient which protects the circuit from damage – they are self-limiting because thermal runaway cannot occur.

When the original output MOSFETs were developed in 1975, one MOSFET was roughly equivalent to sixteen 2A3 valves in parallel push-pull class AB1. Substantial improvements have been made in the last 20+ years. Today’s MOSFETs have the advantage of the low internal impedance of a transistor without its thermal instability and the advantage of being voltage-driven like a valve without a high internal impedance. This combination gives a stable platform on which to build better quality sound. How to enjoy listening to Wagner without fear of your amplifier’s self immolation.

Using MOSFETs solves the technical problem of how to make a circuit so robust that it is indestructible. This can be achieved by choosing the right power devices for the final output stage so that the current available is balanced by the amount of power (that needs) to be dissipated. Two other things will affect circuit design when incorporating them. Firstly, you cannot simply replace a transistor or valve with a MOSFET- the circuit must be totally redesigned. Secondly, as MOSFETs do not experience thermal runaway (as do transistors), so the thermal feedback components are not required at all.

Having repaired amplifiers over the last 20 years as sole “Official Warranty Service” agent for several brands that used them , Ian has been able to follow the improvement in MOSFETs. For his REDGUM amplifiers, he has incorporated ‘faster’ and ‘stronger’ MOSFETs than are being used in most current designs which are “trying to” give MOSFETs a bad name. As with anything electrical, poor design can “fry” a MOSFET, when the incorrect/too low a rating is used. A transistor, by comparison, would “fry” faster.

ULTRAFLEX Power Supply   In an attempt at maintaining amplifier stability, most exotic amplifiers have a very rigid power supply voltage. As REDGUM amplifiers are inherently stable under rapidly changing power supply voltages, all our amplifiers have a power supply which is incredibly flexible giving almost unbelievable transient capabilities. Our Stellulata 60W amplifier gives RMS transients of 140W!!! (or 14,000w in terms of multimedia hype!)

High Current Delivery   Sharp transients such as ‘rim shots’ on a kettle drum require very high ‘rise times’ for the output current. In REDGUM Amplifiers, the peak output current available at the speaker terminals is maintained by the use of a power supply by-pass within 6mm of the output devices. The combined outputs feed a star network to the ultra high-current linear crystal speaker line used for internal connection to the rear speaker terminals.

Ageing of Amplifiers – How Relays Do Not Help   Powering up or down an amplifier involves a large and sudden change in the power supply voltage. Most amplifiers are highly unstable in this situation, causing what can only be described as a “frightening” noise as they are turned on and off. Fearing that customers would be horrified by this noise, manufacturers build a relay into the speaker line of the amplifier. Effectively, this turns the speaker off when the amplifier is switched on/off, so there is no resultant noise. The customer is unaware that there was ever a problem.

Unfortunately, the customer usually becomes despairingly aware that there is such a relay later on in the amplifier’s life – it is the simplest, most troublesome component/product in amplifiers. Even when new, the relay has an effect on transient currents so that the transients you hear are not as responsive. As the relay ages, it becomes intermittent and causes immense distortion to delicate signals at low volumes.

Amplifier Longevity   Because a REDGUM output board is stable during power supply changes when the amplifier is turned on and off, this provides a way of solving the problems caused by these relays. By not needing to include them in their amplifier range, REDGUM amplifiers have a double advantage over other manufacturer’s designs. Firstly, the immediate and long-term problems and costs caused by ageing relays cannot occur if the source of the problem is not included in the product. Secondly, the sound quality produced will be consistently accurate as the non-existent relay cannot become intermittent or cause distortion, nor effect the transient currents.

If this relay in the speaker line of an amplifier is not included in a circuit, what protects the speakers from this “frightening” noise when the amplifier is powered up and down? Simply because a REDGUM output board is stable in this circumstance, a “frightening” noise is not produced. This is not to say, however, that there will be no sound made at that moment in the absence of the problematic relay.

Amplifier “thunks” – good or bad?   REDGUM amplifiers make audible “thunks” when powered up and down, but usually only the latter ones are noticeable to people. A REDGUM amplifier has no need to mask this sound with a troublesome relay in the speaker line. In fact, customers can be reassured that this sound is a healthy sign that the amplifier is flexible enough to cope with such rapid changes in the power supply.

What actually causes the “thunks” is best explained for the process during the powering down of a REDGUM integrated amplifier (60W or 120W), which has both channels run from a shared power supply. When the system is turned off, the first and weaker “thunk” comes from both speakers together, as the power in the supply (which is common to both channels) “settles” below the voltage required for stable operation. The voltage available to the amplifier continues to fall till eventually the output stage of one of the channels goes into conduction, thus grabbing and dumping the remaining stored power into the speaker line of that channel. This dumping causes the remaining supply of power to collapse, causing the third and loudest ”thunk”, but only through the channel where it was dumped.

As a result, the second channel is left with virtually no power to access from the shared supply. Since the separate output stages of the channels have reached their critical cut-off voltages sequentially, the second channel is deprived of the power required to produce a sound of the same proportions as the loud “thunk” from the first channel. Because of component tolerances, the final “thunk” sound is usually heard from the same channel.

This same process occurs with the Monoblock REDGUM amplifiers, but with both channels producing their final “thunks”, each in their own time. Each channel has its own power supply, so the fall in voltage affects only that channel, causing it to collapse as described above.

Oversized Power Supplies and Capacitance   It makes an impressive party trick to be able to turn off a REDGUM amplifier and still hear it play. The combination of oversized power supplies with no need for relays in the speaker line make this possible. But is it necessary to have an excess of power available? Oversized power supplies are the norm in Hi-Fi, but when is “too much” more than enough? A “plastic fantastic” import would offer a measure of capacitance in the order of 2-3,000uF. REDGUM amplifiers offer you 10,000uF which is enough to play 2-3 transients after the system has been turned off. REDGUM’s designer believes this is more than sufficient as the amplifiers instantaneous energy store (like sugar/glucose is to the body). More is not needed to do the job it already does so well. In this area, one is to be cautioned when thinking that “more is better”.

No Multiple Point Contacts   Not only cheap amplifiers use multiple contact points as a way of connecting several circuit boards in an amplifier. It is a cheap manufacturing method to make a product quickly, but the need for it is more the result of clumsy design and assembly. These contact points, in the form of metal pins or plates, are not accessible to be cleaned. The presence of atmospheric moisture plus the very fine electrical signals between the contact points causes electrolysis, resulting in deposits on the junction. The more these junctions deteriorate, the more the distortion that is added to the circuit. The effect of this distortion is cumulative as a signal can pass several dozen times through these contact points before it arrives at the output stage. To overcome this problem completely, REDGUM amplifiers are designed using independent circuit boards.

No phono preamp improves sound quality   Why doesn’t REDGUM include a phono input in the REDGUM amplifiers? There are 2 reasons. Firstly, a system will sound substantially better if the phono preamp is installed in the turntable. This is because the phono preamp really should be located as close as possible to the cartridge in order to reduce background noise. If the phono preamp is installed in the amplifier, there will be at least one metre of lead (internally and externally combined) responsible for transferring the minute signal. Such a low level signal is very prone to being swamped by the noise inherent in the circuitry already in the amplifier. After this preamp modification is installed, the sound of a vinyl collection improves dramatically! And the second reason is for when customers don’t want to pay for a circuit that they will never use.

According to H. Richard Weiner in “Bound For Sound”, 9/98,p8: (Reporting about REDGUM and its co-exhibitor, Ambience at the 1999 Las Vegas Winter Consumer Electronics Show) “…. They did not claim to have repealed, set aside, or received exemption from the laws of physics as some visitors from Western Europe asserted……they played – no, not stale jazz classics- Waltzing Matilda on a banjo. Again, an amusing change of pace. Then I realized that the banjo sounded as though it were in the room. Realistic reproduction of a string’s attack and overtones can defeat a lot of equipment. In the REDGUM/Ambience display I forgot that I was listening to equipment, and concentrated on the music. This year, their gear did justice to The Goldberg Variations. “ …. I don’t know about you, but I’ve had enough metal in my listening room, be it black matte, champagne finish, or machine turned. Redgum products are finished in a wood indigenous to Australia: a colour something like maple. I’m sure there’s an electrical justification for wrapping components in wood, but there’s also a strong aesthetic argument to be made: this is handsome stuff. Redgum has a new CD Player/DAC, which sounded relaxed, articulate and musical….. “…. I asked how the fellows could manage to ship stuff across the Pacific, allow the dealers to make money, and still stay in business. They explained that this was the result of the Asian economic crisis, which was pretty plausible until I remembered that their prices were attractive in January 1998, six months before several currencies collapsed. My own feeling is somewhat less geopolitical: these guys, like Greg Osborn, are very serious about engineering in the service of music, but not obsessed with making a fortune. Does such a philosophy translate into good equipment? Put another way: Do other high end manufacturers’ obsessions with exotic materials and proprietary technology distort their perception or skew their priorities? I can tell you that there were whole wings of the hotel full of people far more serious than Tony and Ian, but there were only a few where I had as much fun with the music.”

K.K.Chew writing about the 60 W REDGUM amplifier in “Perfect Sound Vision” (Malaysia), Aug-Sept 1998 (translated from the original Chinese): “The external appearance of the equipment is elegant. The simplicity contains poise……..The design of REDGUM is one of soft and transparent dynamics and ‘feet on the ground’ musical flavour. ……..Listening to “Paganini For Two” (PGD/DGG), played on the violin by Gil Shaham, the sound was natural and elegant……..the guitar played by Goran Sollscher showed that the degree of separation of the two instruments was presented accurately……..And all those instruments accompanying them, such as the aeolian bells, harp and piano were able to individually express their beauty. ……..When you listen to a sensational symphony recorded in a concert hall that was full of people and the sound source was a little bit distant, the presentation of depth of sound was better than its width……..REDGUM can handle the situation with ease…”as easily as eating beancurd”. Then I played a saxophone CD “Antiphone Blues” (FIM). Arne Domnerus’s saxophone was on the left, giving people the feeling of “the wind is mild and the sun is bright”. Gustav Slokivist’s pipe organ even gave a “shaking” performance…….. (After the reviewer changed his speaker leads) Arne’s saxophone sounded as if “the red sun is rising over the eastern horizon”. The feeling of air and smoothness had been increased. ……..Finally, if you want to challenge (a 60W) REDGUM,….it can also work well. ……..The mid-bass of ‘Uakti Mapa’ (PGD/Verve) is sweet and mellow……..When a banquet of sound is played on it, its rhythmical performance may surprise you and make you drop your spectacles. Low frequencies sound deep and strong and the feeling of quality is homogeneous. Though (a 60W) REDGUM produces a smooth sound, it is undeniable that if you want ultimate grunt you won’t be satisfied unless you buy a Mark Levinson 33.” (Ed.- costing over $AUS100,000!) A full translation is available on request.

According to Martin DeWulf in “Bound for Sound”, 11/97: “A speaker that was sounding very good was the Ambience ribbon hybrid ($US4,575). Fired up by Redgum electronics, this combination from Australia was resolute enough to keep Rich Weiner and me in the room for about twice as long as the customary stay. What struck me about this combo was the natural ebb and flow of the music, all without an unnatural electronic edge. The sound just kind of flowed, and I could see Rich making mental comparisons to his stacked Quads. I didn’t need to know which he preferred, The Quads or the Ambience, the mere fact that the comparison was being made was enough. The US importer is Universal Sinema Systems at 312.669.1949.