Will GanFET be cheaper to achieve the same sonic goals?
Expanding the Class D Conversation: How Would You Characterize Their Differences?
Expanding the Class D Conversation: How Would You Characterize Their Differences?
I'm currently trialing the NAD M23 (1st gen. Eigentakt-based), and I find it intriguing enough to want to understand it better — which means understanding the broader sonic landscape of class D. So I'm crowd-sourcing.
In a recent exchange, the estimable Ralph Karsten (Atma-Sphere Music Systems) made two comments that stopped me cold. For those who missed it, here's what he said:
"IME, class D amps vary in sound more than tube amps, which is to say, quite a lot."
"IMO there is a bigger difference between various class D amps than you hear between various tube amps. IOW just because you heard one class D amp says nothing about how the next one might sound."
Link: https://forum.audiogon.com/posts/2885828
As I think through this more carefully, these are genuinely important claims. My own experience with tube amps confirms that they produce audibly distinct characters across topologies and designs. If Ralph is right and class D exceeds that range, then generalizing from one class D experience to another is even more hazardous than I assumed.
One specific question for Audiogon members:
If you have a Class D amp or have compared class D amplifiers, how would you describe their character(s)?
Here are some criteria I use:
- Frequency balance — Is the tonal response even across bass, mids, and treble, or does it favor certain regions?
- High-frequency texture — Are the highs extended and smooth, or edgy, grainy, and fatiguing?
- Bass definition — Is the low end tight and articulate, or loose and bloated?
- Midrange character — Does the midrange feel present and natural, or recessed and thin?
- Transient speed — Does the amp respond quickly to dynamic attacks, or does it sound sluggish and rounded?
- Dynamic range — Does it scale convincingly from quiet passages to loud ones, or compress the difference?
- Soundstage width and depth — Does it create a convincing three-dimensional image, or sound flat and narrow?
- Image specificity — Are instruments and voices placed precisely, or do they blur and wander?
- Background noise floor — Is the silence between notes actually silent, or is there grain, haze, or hash?
- Long-term listenability — After an extended session, do you want to keep listening, or has something been quietly fatiguing you?
If you can include relevant system context — room, speakers, preamp — please do. Those variables will help me interpret what the amp itself is contributing.
I'm less interested in rankings than in understanding what Ralph mentioned, namely the [vast] range of sonic signatures class D is capable of. Eigentakt, Hypex, Pascal, Purifi, GaN-based, etc. — all fair game.
Price is no constraint here — I'm interested in the full range of what's out there.
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@earthbound no. It's way more expensive than silicon D. |
The way it was explained to me by Alberto at AGD is the speed of GanFETs. Here is an explanation as to why speed matters. Gallium Nitride (GaN) transistors switch much faster and with fewer parasitic effects than traditional silicon MOSFETs. In a Class D amplifier, the output devices rapidly switch on and off hundreds of thousands of times per second. With silicon devices, designers must insert a small delay called dead time between switching the high-side and low-side transistors to prevent them from conducting at the same time. If that dead time is not perfectly controlled, it can introduce small nonlinearities around the zero crossing of the waveform, which may contribute to subtle distortion or “grain.” Because GaN devices switch more cleanly and have virtually no reverse-recovery charge, designers can reduce dead time and achieve more accurate switching transitions. Additionally, Class D amplifiers use an output LC filter to remove the high-frequency switching carrier and leave only the audio signal. Faster, cleaner switching allows for higher switching frequencies and smaller filter components, which can reduce phase shift and interaction with complex speaker loads. GaN’s lower capacitance and cleaner commutation behavior also reduce ringing and high-frequency noise, which can make the amplifier’s behavior closer to the theoretical ideal. That said, while GaN can enable cleaner switching and potentially lower certain distortion artifacts, the overall sound quality of an amplifier depends far more on the complete design—its modulation scheme, feedback topology, power supply implementation, and output filter engineering—than on the semiconductor material alone. GaN is a powerful tool, but not a guarantee of superior sound by itself. Basically, there are advantages to GaN but a bad design is a bad design and GanFETs are not going to magically make it sound good. Alternativey, Bruno Putzey mastered the control of switching timing and feedback behavior so well that silicon device limitations became largely irrelevant within the audio band. If that timing is not under control, you get the cold, unpleasant sound of older Class D modules. What is impressive to me is that people have found multiple solutions to the same problem and all are excellent and sound amazing. |
So, Nord is a value-proposition, IF they sound good. Here’s some of what they say on the Nord website:
Do Nord amps sound good? Well, from what I gather, your random amp of this type will have (borrowing Nord’s language):
But:
And those last two are deal-makers or breakers. That plus tonality, which also needs to be checked. The Nord Web site and many posters return again and again to the easy-to-quantify factor -- the "module" involved (Purifi, Hypex, Ice, GaN). The Nord company has all three -- but how are they implemented? Which to choose? I cannot tell. But the key point was alluded to by @atmasphere (when he said how different all Class D amps sound from one another) and articulated well by @verdantaudio:
The very nicely built DIY Hypex (recent module) I tried sounded harsh with my speakers, in my room. The M23 first gen Purifi Eigentakt sounds better. An earlier version of a GaNfet amp I heard sounded bright, forward and harsh. But the AGD Audion GaN sounds quite amazing so far. Regarding my AGD vs. NAD comparison, I have one more listening session to do to feel confident about the differences I am pretty sure I am hearing. Report to come.
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- 355 posts total