This piece, about the Redgum RGi120 integrated amplifier, isn’t one I enjoyed writing. Redgum is an Australian brand and I really wanted to be able to write great things about the design and construction of this amplifier.
In the end, I couldn’t. I wrote this piece, considered not posting it, then hit go, only to pull it down after I was literally inundated with hits! Someone mentioned my post on a local hifi forum and things went nuts. I received over 600 hits in one day, my greatest hit count ever. The manufacturer even responded, stating that using better parts would not make any difference, an extraordinary claim and one which is factually and technically incorrect. Redgum stated that they used the lowest quality parts they needed, to build the amplifier and have it function, not a great endorsement of their thinking…
On balance, my feeling is that users deserve to know and be informed about what is inside the gear they buy. Unbiased third-party information can only help people to make informed decisions. Equipment like this Redgum RGi120 amplifier is out in the public domain and my work is here to be scrutinised by all who view it.
Based on my desire to present factual information and to deal with the science behind good audio, I decided that this post, in an amended form, should be available online, for anyone interested. Readers can make up their own minds about what I found. I have no agenda, other than to debunk bullsh#t and to look at the engineering behind audio equipment. I have nothing against Redgum, or any other manufacturer for that matter.
Disclaimer: Everything I have written here is based on my objective examination of this example of a Redgum RGi120 amplifier. This article and the opinions expressed within it represent my opinions and experiences only. They do not purport to represent all Redgum products and my comments relate to my experience with this particular unit only. Other Redgum products may differ from this one and things may have changed since this one was manufactured. Please read the article carefully.
I hadn’t worked on other Redgum gear before except for one sub-woofer amp. I have however worked on a great deal of audio and laboratory gear over the years. I had heard rumours that Redgum gear was overpriced and that the parts used were of low-grade. I was recently able to find out for myself, when a customer brought in a Redgum RGi120 amplifier for service. One of the twin volume controls (more on that later) had come loose and the speaker connectors were also loose. Popping the lid, I was surprised by what I found.
The Redgum RGi120 chassis contained two small amplifier boards, attached to a fan-cooled heatsink. Fan cooling enables smaller heatsinks to be used than would otherwise be possible with convection cooling, at the expense of electrical and mechanical noise. This is usually done to save money, small heatsinks and fans are cheaper to manufacture and than large heatsinks. The Krell KSA 150 for example operates in class-A and generates an enormous amount of heat, but there is no fan to be found. Krell went down the path of massive heatsinking, which is costly, but quiet and very reliable.
Altronics for example market ‘PA’ style amps like this, with seemingly high power outputs (into an unspecified load, at an unspecified power bandwidth), for low up-front cost. These products are cheap, partly because they feature small fan-cooled heatsinks and use low quality and cheap Chinese parts. Most of this gear is also made in China.
The Redgum RGi120 also contained a modest input switching board with selector and volume pots mounted directly to it. This is good, the pots and switches chosen were however very basic. Anyway, it was the other parts inside that had me scratching my head. We are talking about cheap Chinese parts here, the same parts that are sold by Jaycar and Altronics.
Occasionally I buy parts like these for projects that need to be rigged up quickly. In my repairs however, I always use military and instrument-grade parts. Admittedly, I use better parts than fitted to most consumer audio gear, but I do that for engineering reasons and I know my parts well. I choose not to use cheap parts in my work for customers.
The capacitors in this Redgum RGi120 were low-spec, 85 degree rated Leylon/Samwa/Suntan/Hung Long brand. These are not the sort of capacitors one would expect to find in amplifier that costs over $AUD2,500. The resistors were also Altronics/Jaycar metal film types, with poor temperature coefficient, poor noise specs (guessing here based on similar priced Chinese parts because I could find no specs, not a great sign) and worth literally cents each.
The main filter caps which are so important were Leylon brand and similar quality to the other small caps. I hate Leylon capacitors and other cheap Chinese caps like them. In my opinion they do not belong in an amplifier like this, and yes they really DO make a difference, in terms of sonics and reliability. There are lots of greencaps, which are a cheap type of metalised polyester capacitor and MKT types by ERO/Wima/Siemens have better characteristics, but of course cost more too.
The transformer is again an Altronics/Jaycar Chinese toroid. It looked to be around 300VA rated, which would be marginal for the power spec of the amp. Perhaps it was 500VA item, I don’t know for sure. The output transistors were just cheap Exicon types. Exicon is a Chinese brand known to be associated with fakes of other higher spec transistors in the past – you can read about this here. They are not what you would hope to find in an amp like this.
If I had more time to spend on this amp, I would have performed a power output test, with the amp driven continuously by a 1kHz sine wave, into an 8 ohm load, which is a standard test configuration. Let’s be clear – I am not saying that there is anything fake or counterfeit in this Redgum RGi120. In my opinion, a manufacturer like Redgum would never knowingly use fake parts. What I am saying is that forI believe you deserve a much better bill-of-materials.
Yes, this amp is made in Australia, which is a great thing. My concern is that with just a small increase in the bill-of-materials cost, this amp could be made from some higher reliability, higher quality parts. Everything about this amp would be better with better parts, especially some low ESR, high ripple current, high-temperature Panasonic/Elna/Nichicon/Rubycon caps throughout.
Everything is quite nicely laid out on the boards, the boards are of reasonable commercial quality at this price, there is some glue used to hold parts to one another and this is good practice in places. Trimpots are locked with sealant to prevent movement, but the mechanical construction of the chassis and the wiring is agricultural.
Trying to maintain channel balance is hard (almost impossible!) when you have to adjust two volume controls independently. Seriously, who ever thought that two separate volume controls was a good idea? I have seen rubber bands placed around these dual volume controls in an attempt to get them to move in sync with one another! On the Redgum website, they misleadingly talk about how having two volume controls is better for sound quality, because the number of contacts in the signal path is reduced by using dual mono pots. Nonsense! The number of contacts in the signal path is exactly the same, whether using one stereo pot (two mono pots ganged together) or two mono pots – each channel has exactly the same number of contacts! It’s this pseudo-scientific nonsense that severely reduces brand credibility in my opinion.
In my opinion, this is a really bad design choice, guaranteed to create constant channel imbalance. It is not surprising that almost all other manufacturers use one volume control, with a balance control that can be used to correct channel imbalance as needed. This is a sound mechanical design choice, not one designed to save money! Or perhaps we should ask Mark Levinson, or Nelson Pass why they choose not to use dual mono volume controls… As for the amp having a ‘key’ to turn it on – cute, but let’s just leave that one alone…
For those who think parts don’t matter, I can only say that science and a whole bunch of engineers say they most certainly do. I’ve seen time and again how premium parts make a real difference to reliability and performance. Capacitors and semiconductors vary enormously between nominally similar parts. Spending a few cents more per part will potentially decrease a manufacturer’s margin, but will potentially add increased service life and improved technical performance to a product. This will then add value, long-term. I believe it is false economy to use the cheapest parts you can get away with in a product.
Peddlers of the ‘cheapest is best’ notion are either technically in the dark and unaware of the merits of using better parts, or are maybe hiding something. Yes, there is plenty of nonsense written out there in forums, but for those able to test and measure equipment parameters properly, the merits of using better parts are easy to justify. Plus I have two very refined instruments called ears – they tell me that when I use quality parts in crossovers, amps, DACs, that the sound is more relaxed, flows more easily, is more refined.
If ever in doubt, ask yourself this: why is it that HP/Agilent and Tektronix test and measurement instruments, the gold standard in engineering excellence, always contain premium parts? This gear is used by the military, NASA, NSA, CIA, FBI, Sandia Laboratories, Lockheed-Martin, Boeing etc. They buy the best they can buy and purchase equipment that can last and deliver specified performance for decades sometimes. Parts matter and if manufacturers want the best performance, they choose the best parts. If someone says otherwise, they ain’t tellin’ you the truth!
As for the loose volume knob I spoke about earlier, these volume shafts with knobs attached are held to the potentiometer shaft by a small piece of engine cooling hose, the same cooling hose you might find in a car’s cooling system. These have been hand-cut to length and then glued on to the potentiometer shafts. I was surprised, let’s just say that. Sure, it works and I am a fan of simple solutions, but there are more elegant and robust solutions to this problem. The volume knob had just been pulled out of the rubber hose because the glue had failed. The shafts didn’t even line up with the potentiometer mountings – perhaps that explains the cooling hose and the flexible attachment it allowed. Because of the slope of the shafts, the knobs are also not parallel to the front panel.
Anyway, maybe Redgum have improved things since this amplifier was made – I certainly hope so. Maybe I am expecting too much here, I work on some nice gear. Perhaps this is what we should expect at this price-point. I’m not sure, but here are some pics.