Power Amp Disappointment

[QMuse]

In fact, you have been avoiding the 20Khz phase shift problem of Class D amplifiers

Plz, not again..

 

[March Audio]

In fact, you have been avoiding the 20Khz phase shift problem of Class D amplifiers

There is no phase shift problem with Hypex or Purifi.

Once you join the dots and understand the relationship between phase, frequency and time you realise its a non issue if the change is liner wrt frequency.



Q: Class D has achieved very low levels of distortion, but is it possible for class D amplifiers to continue their evolution into something close to a straight wire with gain, i.e. minimal phase shift in the audio band? (A similar question from maty).

Bruno: The 1ET400 module has the frequency and phase response of a 2nd order Butterworth filter cornering at 60kHz. If you look at the phase shift of that, it’s very nearly “linear phase” in the audio band. To take some rough numbers, it if you have a circuit that has a 0.2 degree phase shift at 200Hz, 2 degrees at 2kHz and 20 degrees at 20kHz, that’s the same as saying it has “0.001 degree per Hertz” phase shift. That’s another way of saying that the whole signal is simply delayed by 2.8 microseconds. If you plot phase shift on a linear frequency scale that’s immediately obvious because you get a straight line. Of course a simple delay doesn’t change the sound. It’s literally the same as starting your music a few microseconds later.

Lars: My dad used to say that if you left a CD in its case without playing it back, it’d just sit there accumulating massive amounts of phase shift as time went by.

Bruno: What that matters to sound is how much phase shift differs from a pure delay. Anyone who’s ever done phase measurements on speakers will remember that you have to remove the time-of-flight delay from the data, for instance by marking the leading edge of the impulse response. Otherwise the linear phase shift corresponding to the distance between the speaker and the mic completely clouds the picture. In the case of the 1ET400 module it’s just under 1 degree at 20kHz. There never was a phase shift problem in class D, it’s simply a trick of the light that happens when you plot the phase response on a log scale without removing the fixed delay.

 

[Matias]

Sounds to me as if you also know the technical reason for that. Is it a problem with current delivery in the low frequencies?

ICEpower higher distortion on high frequencies means high frequencies are reproduced with added higher tones = more treble energy = lower perceived bass.
NCore and Purifi has this fixed.

The popular 125ASX2 below.

 

[March Audio]

 

[BDWoody]

In fact, you have been avoiding the 20Khz phase shift problem of Class D amplifiers

 

[j_j]

In fact, you have been avoiding the 20Khz phase shift problem of Class D amplifiers

Please do not spread that myth any farther. A time delay is the same as a phase shift of 2*pi*f*t. So-called "linear phase", also known as "constant delay" has *NO* relevant phase shift, but a pure delay.

And if you plot that phase on a linear-frequency scale, it's a straight line. (Which it why people call int "linear phase".) What you must consider is the deviation from the straight line. THAT is the only phase shift.

And telling me I haven't measured this is, frankly, obscenely insulting, it's part of the very first thing I measured, and yep, it has a CONSTANT DELAY.

Are you claiming, now, that you can hear a DELAY IN ALL CHANNELS of 3 microseconds? Yes or no? Do tell.

Do you think there's no delay in your old-fashioned amplifier? Why don't you measure THAT? (Yes, I have, you're wrong, sport.)

 

[Running4shape]

I am a technical guy, but not in the Class D space. I am loving reading this tread, time for popcorn.

 

[Mutsu]

Just to update here, I replaced the amp with one of March Audio's HypeX amps and never looked back.

 

[Tacrolim]

one of March Audio's HypeX amps

Intrigued. Mind sharing which one (vs your original choice of Teac AP 505 )and why? In a similar spot myself!

 

[Mutsu]

Intrigued. Mind sharing which one (vs your original choice of Teac AP 505 )and why? In a similar spot myself!

I never had the chance to hear the Teac, really poor customer service in Japan in that respect...

Audio quality wise, March Audio has become my 'end game' for almost everything now.

 

[Observer]

My experience with XTZ Edge A2-300 is different, quite good actually. Speaker that I use with XTZ are Magnepans LRS, for sure different to mentioned Tanoys. XTZ got very high damping factor, It controls magneplanars well, and it is clean sounding . Amp sound best in direct setup Streamer>DAC>XTZ, without preamp. I didn't notice problems with energy in bass region, compared to my AB class amp (190W/4 ohm) it got more grip and sounds more linear in bass region. It performs well with speaker like LRS around and below 4ohm. I measured LRS in room using REW with XTZ and with AB class amp, here is low end region:

Bought it to be my summer amp (Ice power ) but it is much more .

I like it more than NC 252MP which I got for a few days to try. Btw .... XTZ is rated 2 x 300 W (1% THD, 4 Ω), 2 x 460 W (1% THD, 2.7 Ω),
NC 252MP(Audiophonics) is rated 2x250W @ 4Ω, 2x180W @ 2Ω (hm...less power from NCore below 4Ω)

Anyway, for 460 € at Christmas sale (with shipping) its is very good sound quality + elegant case, gain control and auto on/off function as a bonus. Ok, measurement junkies will say, but Purify is just better... Yes I guess it is for 3X the price!

 

[fpitas]

View attachment 56159

It really is like technobabble Whack-A-Mole.

 

[HelgeH]

Friends, all the measurements and theories are very good, but see and hear here what some old school logic and simplification will do. The difference is total and it sounds now like a very good amp.
In all the classD threads I miss someone that actually listen, and try to optimize the construction. Like in analog audio. And then, if necessary, try to understand why the differences appear...!
That is how we learn.

Please see and listen to the whole video.