IMPORTANT CONSIDERATIONS WHEN CHOOSING A GaN-FET BASED AMPLIFIER
We've been designing and building GaN power amplifiers for several years now and there are some extremely important things that we advise prospective owners to carefully consider before plunking down their hard-earned cash.
These features are IMPORTANT to achieve the best sound quality in a GaN-FET power amplifier:
- A stiffly REGULATED power supply. When developing our GaN amps we evaluated many different types of power supplies - and UNREGULATED power supplies sounded CONSIDERABLY worse to us. To sound their best, GaN-FETs benefit from the use of tightly regulated power supply voltage rails. This type of power supply is considerably more expensive in general, but the improvement it makes is clear and immediately audible. Simply put, please do NOT buy a GaN amplifier without a regulated power supply as it won't sound nearly as good as it should! In most cases it won't sound as good as a competently designed MOS-FET amplifier. If you are holding an opinion on how GaN amplifiers sound, in general, by having listened to one that had an unregulated power supply, you need to erase that memory immediately and hear one with a competently designed REGULATED power supply. It still surprises us to see some manufacturers offering GaN-FET based amplifiers with unregulated power supplies.
- Low or zero global negative feedback (GNF). The main advantage of using GaN-FETs over MOS-FETs is their ability to switch on and off MUCH more accurately, resulting in a much cleaner gain stage overall and reducing or eliminating the need for GNF to achieve the best sound quality in listening tests. A GaN amplifier, with better SNR and DR measurements, will sound worse if those measurements are achieved by applying large amounts of GNF. We've tried it many different ways here, and the less GNF we used the better the GaN amplifier sounded! This is one of those examples where trying to achieve better specs is actually detrimental to the sound quality of the product. We pride ourselves in listening AND measuring our designs to achieve the best results but if something ultimately does not SOUND good to us, it does NOT go out the door - period!
These features are NOT IMPORTANT to achieve the best sound quality in a GaN-FET power amplifier:
- A GaN based power supply. Some amps are advertised as "GaN" but they only use GaN in the power supply, not the output stage. An amp with a GaN based power supply and MOS-FET output stage is NOT a true GaN amplifier and will only sound as good as the MOS-FET output stage. It will have NONE of the sonic advantages of a true GaN amplifier - and calling it "GaN" is extremely misleading and deceptive, in our opinion. Check the fine print before buying any "GaN" amp and make sure it is using GaN-FETs in the output stage!
- Large amounts of GNF. In our listening tests, the more GNF that was applied, the less transparent and musical the amplifier sounded. There was a clearly audible and DIRECT correlation between the two: less feedback simply led to better sound quality. This is why our GaN 400 uses very little GNF (roughly half of what most power amplifiers do) and our GaN 1 actually doesn't use any - as in 0%, zero, zip, nada!
We have read a lot of comments about speaker impedance and how "zero feedback amplifiers can't sound good because they are susceptible to the impedance of the speaker and the frequency response of the amplifier will be wildly variable as a result". In practice, the effect of speaker impedance on a zero GNF amplifier is very minor. In most cases it is NOT even audible and is barely measurable (typically a slight reduction in top octave energy). However, if you add GNF to the signal to improve the measurement, you also IMMEDIATELY start degrading the sound quality. THIS is why we made the CONSCIOUS DECISION to NOT use GNF in the GaN 1 and to use small amounts in the GaN 400. The sonic benefits of NOT using global negative feedback FAR OUTWEIGH any of the claimed drawbacks. Both the GaN400 and the GaN 1 will drive a wide range of speakers with ease and authority and should sound better than ANY MOS-FET based designs in their respective price ranges - and well above!