I visited the High end trade fair two times. This gallery contains some photos of my second visit in 2018. I spent only a single day at the event and was focused on very specific products only. I was interested in technical details of solid state amplifiers, especially how the chassis is designed and made. I find the chassis is the most difficult part of an amplifier and was curious how professional companies do it. Furthermore, I was interested in having a look at the electronics under the hood. Judging electronics just by the looks is difficult, but nonetheless I share my personal opinion about what I have seen. I did not listen to any of the products depicted and discussed here. High end audio is an interesting niche I never was really interested in. Being a Munich resident, I should have visited this trade fair more often because the products shown here are extraordinary and interesting from an engineering pint of view.
The image gallery shows a large photo on click. The large picture is more or less straight from my phone and really large in file size so please allow some time for loading from my tiny server over a slow internet connection.
This is a really large cube. Straight and simple chassis design. They do not attempt to hide any screws holding the chassis together, instead they seem to be part of the design. Apart from the heat sinks, the whole chassis is made from nicely brushed and anodized aluminum plates. Clear anodizing is pretty tolerant towards different alloys resulting in more or less the same tone in the end.
The backside panel is black anodized and illustrated in white. I like the clean and straightforward layout. Apart from the extra ground binding post near the speaker binding posts, there is nothing unusual to see. I wonder why some controls the listener might want to access, like the mute button, are on the back side.
Apart from some nice details like the mirror plate at the front and the milling in the cover plate, the design is pretty basic and simple. Nonetheless, the high quality finish together with the sheer size of the cube transports some value and helps to place this amplifier in the high end segment. Unfortunately I could not peek under the hood so I don't know what is inside, whether it is full of electronic components or just a lot of hot air.
The amplifier from Air Tech comes with a very massive front panel and three unusual heat sinks at each side. The heat sink design is not exactly my personal taste and I wonder whether the split design is good for heat distribution. I tend to see a pattern here: The more expensive amplifiers tend to have more minimalistic front panel designs. The whole amplifier is available either anodized clear or black.
The backside looks a bit disappointing due to the speaker binding post. While lots of plastic is good to lower the risk of electric shocks and short circuits, I would expect huge and gold plated binding posts in the high end segment. The amplifier works using "zero feedback", which probably means it has no global negative feedback, which is pretty uncommon in the average consumer segment, but seen often in the high end segment.
Under the hood, there is a lot to see. First, the separate heat sinks are backed by massive aluminum plates that help to spread the heat to each sink. Two really large toroid transformers indicate this amplifier could be running dual mono. Ten large capacitors per channel further back this assumption and make clear that the designer is serious about the power supply. Apart from the power supply and the amplifier modules, there is surprisingly little electronics inside. I wonder where all the control circuitry for housekeeping is? I also wonder whether the two small heat sinks per power supply might be for the PSU rectifiers. In case they are, I wonder whether the amplifier runs in class A.
The previous two amplifiers were pretty much in line with how any engineer would approach an audio power amplifier chassis design. The amplifier from Ayre features a chassis milled from a single massive block of aluminum. This is super expensive to manufacture and usually only seen in military or aviation equipment. While this results in huge thermal mass of the chassis, the chassis is not a very efficient heat sink due to lack of air convection. In case I would ever design a chassis this way, I would take advantage of the possibilities the manufacturing process offers and design the whole equipment to be submergible in water. Nonetheless, the design from Ayre stands out of the crows with this unique design, be it technically reasonable or not. After all, this is the high end segment where things do not have to make any sense.
As usual, the rear side features the interface connectors and shows how difficult it is to deal with the massive wall thickness of the milled chassis milled from a single block. The mains AC input is filtered by a small common mode choke placed in an extra compartment. I guess a real filter would provide much better attenuation than just a common mode choke alone. It appears as if the area between the AC input and all the way back to the power transformer is just unused massive aluminum and could be spent for something more useful instead. The actual amplifier circuit seems to be both simple and unusual. There are six groups of eight transistors each bolted together. I would assume that the purpose of doing so is thermal coupling and this leads to the assumption the circuit could be a current feedback amplifier, although it likely does not use global negative feedback. Some components are mounted on the other side of the PCB, likely mostly passive components.
All electronics is placed on a single PCB with the power semiconductors placed underneath. The PSU rectifiers do not seem to feature any RC snubbers for dealing with RF emission from the rectification process, but there are some very unusual chokes in this section. The chokes feature a resistor as the core and the resistor has its terminals shorted together. The technical background of this arrangement is unclear to me. Tightly integrating the PSU with the amplifier power output stage is a very good idea since this reduces overall circuit loop area. There are a lot of film capacitors on the PCB (re-) labeled as Ayre and they all have some polarity mark hand drawn or maybe this is just excess sealant. Pretty esoteric.
The "Mono Block" amplifier by Block Audio is the most impressive in the solid state category I have seen so far. As the name implies, the Block is a block. Huge, seamless and apparently massive like it was made of a single piece with fins attached. It runs in class A with the option to lower bias into class AB (eco mode) in order to save energy.
A close up of the chassis corner reveals that the block is not made of a single huge piece of aluminum, but is made of six massive aluminum plates instead. They are machined very precisely, bolted together and probably painted over to achieve the stunning seamless effect that still puzzles me. The surface finish looks like anodized, but I guess it is painted.
Block audio allows to have a look inside and they have nothing to hide here. Everything looks surprisingly clean and tidy. An extra oversized toroid transformer together with some large capacitors form the power supply. The green components in the center are huge resistors that are used to limit inrush current during powering up the transformer. The amplifier modules are mounted underneath and cannot be seen. Note that the amplifier has only three feet to stand on. This avoids wobbling when being placed on uneven surfaces.
An interesting detail is the heat transfer pipes for the PSU rectifiers. Since the Mono Block is running in class A, the dissipation in the rectifiers is substantial. I haven't seen heat pipes used in any amplifier before. Usually one would aim to locate the rectifiers in a way that they can be cooled on the main heat sinks directly.
The backside not only offers the nicely laid out interface, but also massive grips to handle this monster. All connectors are mounted in extra panels that cover large cut outs in the massive rear panel of the chassis. This is not only a convenient way to deal with unpractical chassis wall thickness, but also allows to quickly change the interface independent of overall chassis design. Some status LEDs indicate mode of operation and errors.
The amplifier by Cambridge grabbed my attention due to its unusual, and in my opinion very attractive, exterior. I designed a chassis that looks similar earlier and was surprised that there is so much similarity between my design and theirs. The main difference is that Cambridge not only designed their chassis more aesthetically pleasing, but also economically attractive to manufacture. I like the four radius at the vertical edges of the chassis. The lid that seems to hover is also a great design idea. The large dial at the front looks great, too. From design point of view, this is what I would prefer most to place into my living room.
Removal of the cover reveals a large toroid transformer in the center surrounded by several PCBs. So far, nothing unusual apart from the fancy transformer cover. Overall, the inside looks like consumer electronics designed for mass production instead of boutique hand made high end amplifiers. This is by no means a negative point as it implies a certain level of professional development and manufacturing. It also indicates that the design likely is reduced to the necessary, instead of over-engineering for the extraordinary.
The analog input section is designed pretty compact by using SMT components. Most of the resistors are MELF type, which is a very unusual choice nowadays since pick and place assembly machines prefer flat surface components. I guess that an engineer had the last word here. I also see some LM4562 operational amplifiers, which is a good sign because there are countless cheaper and inferior ones available on the market. Together with NP0 / C0G capacitors, the component choice is excellent. I guess that the electrolytic capacitors are solely for the power supply, which is also a good choice. Seems like Cambridge has high aspirations here and mindful engineers won against inconsiderate procurement guys.
The power amplifier module features an Ab biased output stage with crossover displacement. I believe that Douglas Self works with Cambridge and likely has developed this power amplifier. I vaguely remember he mentioned something about crossover displacement in one of his books. I believe nothing actually beats class A operation, but there may be good methods to deal with crossover distortion. Four times 10mF of capacitance per channel is not bad in terms of decoupling. Also, five pairs of output power transistors can handle a lot of power. An interesting detail is the stacked metal sheets for power distribution. I've seen that before in a 50 years old Aiwa amplifier. This is an economic and technically good method to distribute power without having to use expensive multi-layer PCBs. I wonder why part of the circuit was placed on a daughter PCB.
Nubert may be known for their affordable loudspeakers and likely has no extensive history in audio amplifiers. I mainly mention the amplifier since the article has its focus on chassis design. The approach here is rather conservative, but implemented pretty well. I like the rounded corners. This makes the appearance less aggressive and reduces the risk of injury during handling of such a huge and heavy amplifier. Handles would be a useful addition. The marketing material does not convince me that this amplifier is something extraordinary. Just a very high powered class AB amplifier.
The amplifier chassis from Phison caught my attention because it has some DIY character in my opinion. It is made of straight sheet metal and the design is pretty basic. Apparently one can still show up and be successful on the High End trade fair with a basic chassis design. Probably the inside is much more interesting than the outside, but the outside matters a lot for the first impression. My observation is that people tend to rate anything by the appearance first.
The amplifiers from Sugden come with colorful front panels. I love colors so I like the playful colors contrasted by clear or black anodized control elements. The rear part of the chassis appears to be steel sheet metal painted black. Overall, the chassis is economic to manufacture and pleasing to look at.
The ugly chassis award goes to Symphonic Line. I find the oversize monster amplifier chassis is out of proportion and not pleasing my eye. And I wonder why the chassis is so huge. Is is stuffed full of electronics inside?