There has been a lot of buzz around new GaN FET amplifiers and, subsequently, a lot of hyperbole of how they “sound”. With this brief write-up, I hope to tackle what Gan FET is, what it isn’t, and on a broader scale what people mean when they say an amplifier has a “sound” associated with it.
First, what is GaN FET? To keep it simple, it is a transistor material composed of Gallium Nitride. Using our Hypex and Purifi offerings as examples, most Class D amplifiers use MOSFET transistors, which are composed of a Silicon based material. GaN FET is merely replacing those MOSFET (silicon-based) transistors with gallium nitride transistors. The advantage of GaN FET transistors is faster switching frequency, better power efficiency, and smaller size. This can translate to a smaller overall footprint for the consumer that delivers the same (or more) power output as a larger amplifier while running cooler. Power efficiency advantage over MOSFET, however, is mainly confined to idle usage. For those who may leave their amplifiers on (but no signal playing) this may save on some idle power loss that can be beneficial over a long period of time. But for those who have their amplifiers trigger on/off with sources or signals, the efficiency advantage of GaN FET will likely be subtle.
Now, let’s talk about what GaN FET isn’t. Current GaN FET amplifiers are not a new class of amplifier technology, nor are they a groundbreaking circuit design that has significantly advanced current Class D offerings. As discussed earlier, GaN FET is, essentially, replacing existing transistors of an existing amplifier design with new material (gallium nitride) to possibly provide the advantages discussed previously. A good example of this is the article ICEpower wrote (linked at the bottom of this discussion) in which they took an existing amplifier module with MOSFET transistors and replaced them with GAN FET transistors. Their goal was to directly compare MOSFET and GaN FET to show real-world differences. You can read their full article but to sum it up: at best, there were only slight measurable differences. And due to the high cost of GaN FET transistors as of current writing, the consumer will be paying more upfront vs. a completely comparable/identical MOSFET amplifier for these very slight differences.
This brings us to amplifier “sound”. In this hobby, there has long been the discussion of “Amplifier A has a more musical sound while Amplifier B is more clinical” or other variations of subjective impressions. A properly designed amplifier should have no impact on sound signature. It should merely be a device that amplifies the audio signal and sends it off to the speakers so that only the source material and the speakers themselves are “responsible” for how your music or movie sounds. Both Hypex and Purifi have designed their Class D topologies to act like an amplifying wire: what comes in, goes out. You can verify this by their completely flat frequency response and low distortion throughout the entire frequency range. If any amplifier has a “sound” to it that is independent of the source or speakers, it usually means there is some influence happening on the frequency response (maybe it rolls off early, so highs drop off giving a “warm sound” impression) or there is distortion happening in certain frequency ranges.
What does amplifier “sound” have to do with GaN FET? Well, the few companies currently selling GaN FET amplifiers love to imply that GaN FET (compared to MOSFET) is better for music (“they have that Class A sound”), that GaN FET sounds “cleaner” or less “harsh”, among lots of other adjectives and subjective musings. But when you objectively measure and validate GaN FET vs. MOSFET Class D amplifiers, these musings fall flat. You can reference the ICEpower article, for example, and see that both the GaN FET and MOSFET measurements are virtually identical. If a GaN FET amplifier has the same exact frequency response/distortion as a MOSFET amplifier, then where exactly is this night and day sound difference coming from? That is the question I would keep in mind when reading subjective descriptions being touted, not just for new GaN FET amplifiers but for all amplifiers in general.
I want to be clear this is not meant as a subjective write-up of Buckeye Amps trying to deter business away from competitors, but rather an objective approach to educate consumers. I know this hobby can be full of a lot of opinions and subjective impressions. Our approach is that the amplifier should not be another component the consumer needs to “worry” about when reading through many different reviews and descriptions. It should be a piece of equipment that one buys to amplify their source, not a subjective variable one has to wonder about. I fully support the performance of properly implemented GaN FET amplifiers and, once prices on the technology come down, it is another line of product we plan on offering. But I do not support the subjective writings companies put out there trying to convince consumers GaN FET is a ground breaking technology that makes their amplifier sound a certain (better) way when compared to MOSFET amplifiers. I can guarantee that a Hypex NCx500 or Purifi 1ET400A will sound identical to any of the current GaN FET amplifiers on the market. Which is why it does not make sense for us to offer GaN FET at this time: why would we want to charge our customers more money for identical performance?