Class D is just Dandy!

 

 

Hi Erik, the big old ICEpower 1000ASP also had an output impedance of 1000… Perhaps that is one of the reasons why it outperformed the authority of the Boulder 2000 series in authority on Die Muzik…. Not sure of the damping factor of less powerful modules though.

 

The audible difference between an old ICEpower 1000ASP and an NCore NC1200 is that simple amps based on the old ASP1000 with little design around them did not sound terribly good, no matter how much they were broken in…. ASP 1000 gave the high current, the raw resolution, the compatibility with difficult speakers, but could sound quite harsh unless the designer created a solid input stage to raise input impedance and attenuate common noise….. The native power supply was somewhat weak in regulation…. The better amps used regulated custom SMPS, and at least in the case of M312 and M301 also an integrated power factor corrected rectifier to avoid any grundge contaminating the signal….. So much so that rowland created an external rectifier called PC-1 which could be used with some of his lower end ICEpower amps like M501, M201, and M102.

 

Here then comes NCore NC1200 with its companion NC1200/700 unregulated supply…. Turns out that a simple implementation of this module inan amp, even without the amp designer doing too much in custom active circuits, usually outperforms any sophisticated class D amps created round the older ICEpower 1000ASP modules. Then, if the designer does apply his more sophisticated input stages, power regulation, power supplies, and rectification to NCore…. Things sore.

Having said the above, I have not tried the latest generation of ICEpower 1000ASP, but I have heard that they are much more musical than the older ones.

 

Guido

 

 

I wanted to describe an additional benefit of good class D amps that I quickly discovered after switching from my former class A/B Aragon 4004 MKII amp to my first class D amp, a ClassD Audio SDS-440-CS stereo unit and is a quality of all 3 class D amps I’ve owned thus far: the latest 2 are an Emerald Physics EP-100.2 and a pair of D-Sonic M3-600-M mono-blocks.
It’s a benefit I never read about in my prior research on class D, still don’t read much about and that I believe is common to all good class D amps and not unique just to my 3 amps but I’m not currently certain.

As many of you already are aware, humans generally perceive bass and treble frequencies to be attenuated relative to mid-range frequencies when listening at lower volume levels. This means as volume is reduced, the less we perceive the bass and treble frequency extremes and the more the mid-range frequencies predominate; which flattens out the perceived sound since the mid-range frequencies are accurately perceived but the bass and treble frequencies are perceived as under emphasized. Some of you are old enough to remember ’loudness buttons’ on receivers from the 1970-1980s. These controls were used to boost the bass and treble frequencies when listening at lower volumes to compensate for this known deficiency in human hearing.

Okay, enough preamble. I’ll describe the class D benefit now even though I haven’t yet thought of a better short description of it than ’a consistent and continual loudness contour’. I began carefully listening to my first class D amp at a lower volume and immediately noticed the sound was much different than I was accustomed to with my class A/B amp at lower volume. There was no flattening of the frequency range, I perceived the entire frequency range of the music with seemingly no under emphasis of the bass and treble. This struck me as amazing since it was the best I had ever heard my system sound when listening at a low volume.

After a few days of listening I decided it was safe to experiment with higher volume listening levels closer to the levels I formerly listened to music at with my class A/B Aragon amp (probably in the 70 db and up range). As I began slowly increasing the volume, I was pleasantly surprised to notice the frequency range balance or perspective of the music remained constant while everything within this perspective just gradually increased in volume. The music sounded well balanced and enjoyable from low volume to high and all points in between.

This well balanced frequency perspective was also consistently maintained even at volumes well above my normal listening level.
Some of you with higher quality systems are probably thinking ’what’s the big deal’ about turning the volume up and the music just gets louder without the fidelity or overall frequency perspective within the sound stage changing but this was revelatory amp quality behavior in my experience. My former Aragon didn’t sound near as good at low volume levels and required volume levels in the 70 db plus range to sound its best in my opinion. Music at low volumes seemed to flatten out with attenuation in the frequency extremes.

I’m a bit embarrassed. As I’ve written this post, I’m thinking the quality of my former Aragon class A/B amp may have been lower than I thought or it was gradually aging and sounding worse just prior to the power supply caps leaking and it going belly up. Perhaps I was just hearing the difference between an older amp on its last legs and a brand new class D amp of good quality.

Well, at least I consider the good sound quality at any listening volume a class D benefit and hopefully others who may enjoy listening at lower or very high volumes will find this attribute useful as well.

Thanks,
Tim

So, let’s get into some meaningful spec-manship. Let’s compare the frequency response, and output impedance (8 / output impedance = damping factor) of ICEPower and nCore to see about what could matter with different speakers.

Here are the source docs I start with:

Ncore docs:

https://www.diyclassd.com/documenten/download/860

ICEPower :

http://www.icepower.bang-olufsen.com/files/solutions/icepower250aspdata.pdf

I’ll use a couple of examples. My own custom built speakers which have around 9 Ohms of impedance at the top octave, and ESL’s which are basically giant capacitors, and murderously low impedance at the top octave often near 0.3 Ohms.  I should point out most SS amps have coils at the output to protect from hyper-sonic oscillation. This coil acts as a low pass filter and will cause the frequency response to droop at the top octave. This is not by itself unusual or ONLY about Class D amplifiers.

Using a "normal" speaker like mine let's examine how the output impedance changes response at the 20kHz mark:

nCore: -0.003 dB
ICEPower: - 0.3 dB

0.3 dB isn’t inaudible.... but VERY subtle. Below this, in the bass where many speakers get difficult to drive, there’s only tiny differences in response. Certainly better than most tube and zero feedback SS amps. This is a small difference which fits well within the idea of "system matching" an amp to personal preferences, speakers and room tuning.

But let’s take an extreme case of an ESL which has around 0.3 Ohms in the top octave:

nCore: -0.08 dB
ICEPower: -6 dB

This is a case where the nCore could make a very significant, audible difference when playing the same speakers.

My point to this is, based on specs, both modules will perform very well with normal loads. Any differences in the top octave may be inaudible, or useful.

This is one example of where I think specs and technology can help us understand how to match an amplifier with our system better.

Best,


E

Following on, at 200 Hz the output impedance is 10x better with nCore, but the absolute figures are tiny. The difference in output between a high and low impedance speaker is less than 0.01 dB.

Most "normal" speakers get very difficult to drive in the bass, not the treble, so for these owners, I think nCore and ICEPower are equivalent and subject to personal preference.

If you have an ESL though, I would really expect the nCore to over perform.

Best,


E