The Truth about Modern Class D

When, oh when, will people stop commenting on components and wake up to the fact we are building systems?

Take a speaker with slightly soft top end and marry to a slightly zippy amplifier and the combination could be closer to the ever unattainable perfection.

Equipment reviews are sometimes are funnier than the comics!

Class D Output filters are load dependent. From TI:

The LC filter response also varies with speaker load impedance. The load impedance determines the damping ratio of the output LC filter and is classified as overdamped, critically damped, or underdamped. It is also important to understand the speaker load impedance variations for the application and select the L and C values that suit the expected load variations. Ideally, the LC filter value is selected for a critically damped, flat passband, and phase response. Two considerations when selecting components for the second-order low-pass filter is the cutoff frequency and Q factor or damping ratio.

Like any other amplifier, Class D will interact with non-linear speaker impedances. There are multiple output filter topologies and each will interact differently with different loads.

Stating that 1.5GHz will solve all the problems is as silly as saying a 10MHz Class AB bandwidth has to sound better than 100KHz.

As far as GaN devices, there have been countless ’type’ as the new sliced bread for the entire history of electronics, be it tube, transformer, transistor, FET, IC, etc.

ALL electronics involve a compromise and ALL electronics interact with their source and load.

Specific recommendations border on risible.

I'm going to go on record that any amp that employs deadtime to work is an amp that will become obsolete

By definition, zero deadtime means that the devices must be both on and off at the same time, a physical impossibility given any reasonable technology.

Zero dead time requires a series of perfect devices that remain invariant over temperature and time.

A Class D amp with Zero dead time is likely an amp with a short lifespan.

Left to its own devices, a switching power stage tries to do just about anything except amplify audio.

As point of reference NuPrime ST-10 uses linear PSU:

New linear power supply with a high-efficiency toroidal transformer. Reduced high frequency noise and strengthened low-frequency performance.

Ladies & Gents,

It's about matching technology to assemble a HiFi system.

I've been a HiFi'r since I was old enough to manipulate the arm on my Dad's Bogen/Lenco in the mid 50's. Over the decades I've heard many 10s of amps with the latest buzzword technology. Not all moved the ball forward in the context in which they were heard.

I have TC-50, BiWired and recapped, and tri-amped LFT-8b. Both speakers are renowned for their phase coherency, a property without which I cannot listen. AND a long list of absolute failings.

I have 4 amps: Rotel bipolar, NuPrime ST-10 Class D,  PrimaLuna Prologue 5, and a pair of VTA M-125s I reworked. Each has its ±.

Depending on program material AND time of year, each trounces the others. ALL present an excellent and engaging sound stage.

As Ralph can attest, there are 1001 details to get right, some of which are diametrically opposed. Each has it's foibles. Some genuinely beautiful boxes have no soul in some systems. AND all can be severely compromised with poorly mated cables and companion components.

The proof of the pudding is ALWAYS in the eating. AND you must eat the whole pudding!!!

It is true that knowing both behaviors is important, however Class D output impedance is well within the range of high quality Class A/B amps with feedback.

The Class-D output filter is RLC with the speaker providing the R. However, the speaker is not just R, but also has LC components. Like all things audio, the designer has to make choices. Regardless of how well designed the amplifier is, there will be loads with which it will not mate well.

Add in loudspeakers with crappy phase response and things could get ugly in hurry.

I think of it like putting an Indy engine in my motorhome. It's got boatloads of power, just in the wrong area. Put my motorhome engine in an Indy car and it will come dead last in 500 miles, but first in 5000.

IMO, one should examine the cable/speaker impedance curve when choosing ANY amplifier. Class-D can be more sensitive due to the low pass filter.

Tweeter resonances may be exacerbated with an ultra sonic rise in the filter response due to the impedance curve.

Back in the day when dealers abounded, it was often more productive to talk rather than listen at expo/shows. An audition in a well set up salon would often be diametrically opposed to the show horror.