Why does GanFET topology sound like tube?

Why is GanFET a game changing and likely the most dominant amplifier technology of the future?

Short GanFET primer by Michal Jurewicz, Mytek Chief Designer

Mytek has been designing digital audio converters for recording industry since 1992. In 2017 we undertook a strategic decision to build the complete digital audio path “from the wifi to the speaker”. Our extensive experience in all types of DAC circuits, including 1 bit and multibit delta sigma designs became valuable when designing our first Class D amplifier - the Brooklyn AMP, because the architecture of the Class D amp is somewhat similar to a DAC - it’s a digital loop with PWM instead of DSD. When we began work on the Empire Monoblocks in 2020 with engineer Grzegorz Jankowicz, we quickly noticed, that the existing MOSFET based Class D designs can approach, but never surpass the best solid state A/B designs and that the core issue is the nature of Class D distortion, ie the effect of these masking the finest resolution of incoming audio, resulting in flat and reduced soundstage, sounding like audio truncated to 14 or even 12 bits, with particular harshness on the top that’s always there, impossible to overcome. While there are new MOSFET amp modules on the market achieving very good measured specs through application of massive negative feedback, we were not impressed by their subjective sonic performance. For variety of reasons related to circuit dynamic performance, large amount of negative feedback just never sounded good to my ears. We have hit the wall with Class D MOSFET and took upon examining the new breed of GanFET Class D designs, championed, in the form of eval boards, by distinguished Skip Taylor. We also listened to early new GanFET designs from a handful of companies, the AGD of California, Atmasphere, Orchard Audio and Technics and deemed them extremely promising soundwise. We decided to built our own, most advanced, high speed version of the GanFET circuit which fixes the MOSFET Class D problems, starting with its sound quality. The mechanism of why GanFET sounds better is simple: it produces a waveform that’s much closer to an ideal square one, as explained in the graphs above. Fixing the waveform shape, fixes the sound, but there are more advantages: faster transistors allow for faster clock and thus higher bandwidth of the amp. Efficiency jumps from about 85% to 95% eliminating the need for heatsinks, EMI is also reduced. This approach, combined with very low negative feedback creates a topology almost identical to a Class A or tube circuit resulting in unmistakable subjective similarity of perception of the type of sound; the highs are unmistakably tube like. Unlike in tubeamp though, the bass is precisely controlled by ultra low output impedance. Unlike tubeamp, GanFET does not have output transformers, resulting in more immediate and more realistic detail and transients. It’s not an accident, Atmasphere having traditionally built tube amps chose the GanFET, nor that AGD designed a Gantube TM . Mytek opted to highlight this sonic aspect with a decorative tube imitation. GanFET delivers the best sound of both worlds, it is a modern design with Class A sound but 95% efficiency. It never gets hot. No feedback GanFET sound is extremely promising too. For the Empire GanFET amps, we have opted for a large linear power supply, because of its ability to deliver better transients than a switcher. Empire Amps are powered by a unique Mytek GanFET Power Module TM hybrid circuit which contains the main amp circuits and controls. Design of GanFET circuitry is not trivial. Because of 50 Amps being switched in few nsec, it requires a high speed layout and components, dedicated special protection circuitry and microcontrollers. My prediction is that in the next 10 years, GanFET Class D will become a dominant amplification technology in both HiFi and Pro Audio. When properly implemented, GanFET is a technology with numerous breakthrough advantages and pretty much no downsides. And finally, all GanFET designs we heard do not sound the same. (c) Mytek, New York, June 2024

for more try this podcast: https://parttimeaudiophile.com/2024/04/03/ what-is-the-future-of-digital-audio-class-d-gan-more-an-interview-with-michal-jurewicz-of-mytek-audio/

"The Class D GanFet Empire Amp exhibits a hybrid of tube-like, analog soundstage and a modern character of fast transients and bass extension that is oh so real," said DC HiFi Group Founder/President John Gatski. "It delivers all this without a hint of harshness or thinness — at any resolution.”

Proprietary Mytek GanFET AMP POWER Module, the 2x400W, 768kHz, Model GAN01V01 contains the advanced high speed stereo GanFET power and protection circuitry and is the heart of the Stereo Monoblock. Massive 800W special shielded audio grade toroid power supply delivers plenty of transient power while the chassis is sculpted from a single block of aluminum and is using the highest grade components and connectors such as WBT and Furutech. 

Empire GanFET Monoblock top cover features a faux tube immitation to reflect the sonic qualities of the amp. No matter how you look at this tube, it does make you and the environment fill warmer and calmer. In our casual  client polls about 70% appreciate this design while other 30% would prefer tubeless cover. We have just created such cover (below). 

We have just designed an additional cover without the tube. Eventually when they ship in about 2 months, each amp will come with tube cover mounted and regular cover separate in the box. Owners of all amps already sold and these being sold now will receive complementary cover when we have them. This cover can be replaced by the user by removing and then reinstalling 6 hex screws holding the cover from the bottom of the chassis.