2. amps-preamps
  3. 151675-68726

Time to buy a class D amp?


Will some new class D amplifiers outperforming the current ones appear soon

(the newest ones i know were released a  few years ago)?

Class D amps attract me as I consider them the most ecological ones with obvious non-auditionable benefits.

I have no doubts that they posses the maximum ratio performance/sound quality among the amplifiers of all classes.

At the same time, the sound quality the class D amplifiers that I have auditioned produce, although is quite good,

but not yet ideal (for my taste).


I use PS Audio Stellar S300 amp with PS audio Gain Cell pre/DAC with Thiel CS 3.6 speakers in one of my systems.

The sound is ok (deep bass, clear soundstage) but not perfect (a bit bright and somehow dry, lacking warmness which might be more or less ok for rock but not for jazz music).

I wonder if there are softer sounding class D amps with the same or better details and resolution. Considering two reasonable (as to the budget) choices for test, Red Dragon S500 and Digital Audio Company's

Cherry  2 (or Maraschino monoblocks), did anybody compare these two?



niodari

Showing 10 responses by audiozenology

audiozenology
362 posts
 
In a Class D amp this would only describe how loud it plays at 2 ohms without sonic impact not much else. Damping factor at the frequencies where impedance drops is far more important.

Still nothing on how it handles 2ohm loading and if it’s got good current drive down that low (increasing it’s wattage a lot from 4ohms)

audiozenology
362 posts
 
Measurements of Tommy's old amps are online. No issues into 2 Ohm except a hit of hit on frequency response.
audiozenology
362 posts
 
This can also be said about linear amps, but they sound crap when done. The goal is to have the best engineered design with the lowest distortions without negative feedback, and then if it can be done just a little local feedback around the input/driver stage to clean things up, but no global feedback compassing the output stage as well.



This is but one design methodology, and to say unequivocally it is the best is ... a leap not shared by all. It is more religion than science.

Can you define the time domain characteristics of feedback in a Class-D amp and linear amp?
audiozenology
362 posts
 
atmasphere,
Would you say there is inherent limitation in the phase shift that is a factor of the comparator speed, digital logic delays, and turn-off time of the FET? What do you think a practical limit is on that? That may put a practical limit of a few-10 degrees at 20Khz, but that would be inaudible.
audiozenology
362 posts
 
Thanks for the post Erik, I had not seen that NP article. There were some good papers in the 70s on current source amps.


I agree with Atmosphere, you can overdamp some speakers. I am not sure I totally agree with your and his explanation wrt how bass notes behave or wrt what is natural, but agree there is an effect and it may not be pleasant.


It's a complex interaction of mechanical resonance, electrical resonance, and mechanical and electrical damping which occurs when you try to stop a woofer faster than it is physically capable of.
audiozenology
362 posts
 
Tim,


In theory the "signal" stops and starts as recorded so that is accurate. The problem is the woofer does not stop right away. In a lower damping factor amp the output resistance will help dissipate the energy in the woofer which can give it a more controlled stop. With a high damping factor all the energy is dissipated in the woofer / crossover. That makes for a different sound.
audiozenology
362 posts
 
Servo controlled woofer is much different from a low output impedance amplifier connected to a woofer that will keep moving after the amplifier signal goes to 0. A servo controlled woofer can be designed to smoothly stop a woofer without any ringing if so desired.


"Damped" and damping factor are of course not the same thing. Damping factor is a simple output impedance  / 8 Ohm calc.  "Damped" refers to how or the characteristic of how a system will respond to a step response.


Speakers are designed to be driven typically by constant voltage sources. Dynamic drivers on the other hand can behave better, i.e. lower distortion with constant current sources.  To that end, all speakers are the product of trade-offs, and designing for 0 output impedance forces other trade offs a particular designer may not want to make. The amplifier is part of the circuit that governs how the speaker will behave. We can talk about a "perfect" world, but dynamic drivers are already imperfect. So better to discuss which imperfections you want to live with.
audiozenology
362 posts
 
Can you read your full last paragraph? I think the wording in your last two sentences contradicts though I know what you mean. I agree this is an issue. I also agree that the audio signal never stops, but decays within bandwidth limits. However overly low impedance can accentuate ringing.  I get the impression you would be familiar with snubber circuits?  It is similar to a resistor in series with the capacitor. The resistance is needed to damp ringing.
audiozenology
362 posts
 
This is a public forum. I will respond to the content of your posts if I please. That is how public forums work. You didn't start this thread. Lose the attitude.

An amplifier with a high damping factor may limit the total error energy in the woofer cone movement, which could be one measurement of "better", but there is no guarantee that will sound better, because the energy may be concentrated over a narrow frequency range (ringing) that is audible, compared to what happens with an amplifier with a lower damping factor. This is not a new concept, and is explored in the item linked by Nelson Pass, and has been discussed on/off since the 70's.


This is much different from a servo controlled woofer movement where the actual physical position is directly controlled, not an indirect via the coil wires (and through the cross-over).
audiozenology
362 posts
 
I was thinking more of snubbers for diodes (transformers), but realistically any circuit with reactive elements.  The output impedance of the amplifier is part of the overall electrical circuit and hence the total electro-mechanical assembly and hence impacts ringing/resonance. I guess I made my point poorly ;-)
More to discover