Paul White tests a new British power amplifier to see if it sounds as good as it looks.
Designed and built in the UK, and distributed by Key Audio, Mass amplifiers are available in sizes ranging from 35W per channel up to 250W per channel, and Mass also build a studio headphone amp, just to complete the range. All the amplifiers in the range are fanless, to eliminate mechanical noise, and a novel approach to heatsinking by the manufacturers also means the amplifiers can be both compact and cool running.
The model under review is the 2U‑high Mass 500, delivering up to 250W per channel into 4Ω, or 180W per channel into 8Ω. It can also be run in bridged mono mode. A chrome‑plated front panel, complete with back‑lit input level meters, gives the whole package a pleasantly retro feel.
A look at the sides of the case reveals what the new Mass approach to heatsinking is. Instead of finned heatsinks, this design uses cast aluminium fingers, which stick out from either side of the main case like heated hair curlers. This approach is said to be more effective in dissipating heat, because turbulence is caused between the fingers, helping to lift the heat away from the surface. A similar approach is being taken by the manufacturers of high‑power microprocessor chips — which adds weight to Mass's position! Certainly those castings must have cost a fortune to tool up, and I'm sure the designers wouldn't have gone to this expense if there wasn't a tangible benefit.
The amp's circuitry is based on triple‑diffused, bi‑polar output devices of a similar type to those used in leading US‑designed power amplifiers, but the front end and pre‑driver stages employ surface‑mount technology, which is unusual for power amplifiers. Though it doesn't use a fully symmetrical topology, the circuit delivers a THD (Total Harmonic Distortion) of better than 0.05%, and has an audio bandwidth of 20Hz to over 30kHz, flat within 3dB. I understand that many listening tests were also conducted during the design of this amplifier, so even though the technical specification is respectable, a lot of emphasis was also placed on a good subjective sound.
Protection against short circuit or thermal overload is built in, as is protection against DC (Direct Current) offsets and RF (Radio Frequencies) at the output, but the designers have also taken the unusual step of including soft clipping, which comes in 3dB before maximum power, to help protect connected loudspeakers from damage. Though this increases the amount of distortion when the amplifiers are run flat out, it is more benign than hard clipping, both artistically and in terms of speaker punishment.
Power comes from a single torroidal transformer feeding two separate power supplies, the idea being to minimise inter‑channel modulation of the audio via the power supply rails. Because a great many studios are run by semi‑professionals, the amplifier has been fitted with Neutrik Combi input sockets, which can accept both balanced and unbalanced jacks, as well as balanced XLRs, and a further pair of the same type of sockets are provided as sends, for applications where two or more amplifiers need to be chained from the same input source.
Power comes in via a standard IEC mains connector, and the speaker outputs are on chunky terminals that also accept banana plugs. The amplifier is fitted with separate, 41‑step detented volume controls for the two channels, and warning LEDs show the power, thermal overload, and clip status of each channel. A couple of rack handles and a centrally‑mounted mains switch complete the picture, and an electronic delay circuit mutes the speaker outputs during power‑up, to prevent thumps.
Mass Into Energy
Most power amplifiers live up to their published specifications when tested into resistive loads, but the real proof of a good design is how it shapes up to the complex impedance load of a real loudspeaker. For this test, I used a pair of ATC SCM20s, which are extremely revealing, and provided source material from a familiar DAT machine and CD player.
The amplifier delivered a subjectively vice‑free performance that was both smooth and detailed, with plenty of depth.
On powering up the amplifier, the first thing you notice is the deeply sexy red backlight used for the VU meters. You don't notice the switch‑on thump because there isn't one — the auto‑muting circuit means that power‑up is completely silent. Even with the relatively inefficient ATCs I used during the test, there was plenty of power on hand, and the amplifier delivered a subjectively vice‑free performance that was both smooth and detailed, with plenty of depth. Even with the clip LEDs flashing, the soft clip circuitry keeps the sound relatively smooth, though it's probably best not to get the clip LEDs flashing too frequently, as some sound degradation is inevitable. What impresses me more, though, is how well this amplifier behaves at very low power levels — something that can't be said of all high‑power designs. Indeed, with a CD player plugged directly into the input jacks, you could have a hell of a hi‑fi system, as well as a studio monitoring setup.
Given its sub‑£400 selling price, this amplifier performs well in a studio monitoring role — and it looks absolutely wonderful. The lack of fan cooling doesn't seem to cause any problems, and at modest listening levels, the heatsinks actually stay quite cool. You have to run the amp quite hard to get them to warm up, and even then, with typical program material running into clipping just on the peaks, it still seems to be merely ticking over.
Judged purely on performance, the Mass 500 is one good power amplifier amongst many very worthy rivals, but the keen price and stunning cosmetics make it stand out from the pack. I'm tempted to get one for my hi‑fi system, let alone the studio!
The Mass Range
Mass 4 headphone amp (1U, half rack): £199
Mass 75 (1U, half rack): £199
Mass 150 (1U, full rack width): £275
Mass 250 (2U, full rack width): £349
Mass 500 (2U, full rack width): £399
- Wonderful styling.
- Smooth, powerful performance.
- Competitively priced.
- Fanless cooling system.
- The manual is rather short on technical specifications and gives no clues as to the use of the send sockets, or how to use the amplifier in bridged mode.
A very attractive combination of good audio performance, stunning looks, and keen pricing.