Class-D amps - a different re view

I think Kijanki is right: Martin Colloms' statements about the 17 weak points of class D have no solid scientific foundation. I wonder where he gets such information.

Chris

No I am not from Denmark. Nielsens doctorate is available on internet. I own Rowland 102. At first sound was a little "lean" and sharp but over time it mellowed. It needs a little more "chestiness" (lower midrange) - improved after switching speaker cables to Acoustic Zen Satori. Transparency and Clarity is great. Bass performance is outstanding. Stereophile, 6Moons and others had glowing reviews of different class D amps - also Channel Islands D100 (based on Hypex modules - and no I am not Dutch either). The very best class D amps are probably Kharma (not Icepower) and Red Dragon (both too expensive for me). Sound is a matter of taste (so to speak). There is no rights or wrongs. Tube amps producing/exaggerate even harmonics sound wonderful on guitar or voice but horrible on instruments with more complex harmonic structure like piano. Piano structure is a little like percussion instruments that not follow simple harmonic structure and often sounds "out of tune" on warm amps. I prefer neutral amps. The question also should be "what is best for the money" - class D is difficult to beat.

Elberoth2, I don't know where Kijanki is from, but would I be in my more waring moods, my argument would parallel his, for the most part. I live in California.

Not having heard ICE ASP module, I can't comment. Their 500A, mated with a great linear power supply can put your system in just this side of heaven made.

Kijanki - ok, fair enough. I would like to know though, why do you think that:

1. Pushing broad band radio frequency noise into the power supply outlets
2. Pushing broad band radio frequency noise out of the line and ground connections

is considered OK by you. Those are just two first Colloms points. You said they are rubbish.

Eleberoth2 - let me follow on this.

In point 3 he mentiones up to 2V of 50kHz frequency on the speaker cables - complete nonsenese - unless he talks about normal audio signal (my Rowland ha -3dB at 65kHz).

Point 4.
"Make the output impedance, a passive filter, variable with frequency and dependant on speaker loading."
I design electronics for 30 years but have hard time to understand how passive filter is variable with frequency. There are common mode chokes and capacitors on the output (zobel network) but they are present in most of other amps. This filter is set to about 65kHz (-3dB). Filter is within negative feedback and damping factor for Icepowe is about 4000. Early amps on Tact modules had output filter outside of feedback - but he makes general statements.

Point 5.
"Allow the amplifier to be marginally or completely unstable with high or open circuit output loading"
Complete nonsense - since switching amp is constantly unstable (cannot become more unstable - big advantage) being analog modulator/oscillator.

Point 6.
"Employ soft compressor clipping circuits prior to full power clipping"
Yes it does - (big advantage) designed in on purpose to protect tweeters from high energy during overdriving input. Many amps (like NAD) have this advantage

Point6.
"Employ high order negative feedback to improve in-band distortion figures"
Every amplifier does this either with global or bunch of local feedbacks. I know about multiple feedbacks in Icepower but suspect them to be shallow since output is pretty linear. I don't know how he knows about high order but Class D is different creature and has different feedbacks. He might be implying deep negative feeback - usually bad because of TIM distortions but there is no need for deep feedback and even if they put one in it cannot cause TIM. TIM comes when feedback cannot react fast enough and output transistors go to saturation getting charge trapped at their junctions becoming immune to following signal for a while. In Class D output transistors work differently (switching) and are respodning to time not voltage.

Point 7.
"Use feedback to provide numerically high damping factor at low frequencies and claim that this guarantees fine bass.(regardless of the interface to the loudspeaker)"
Isn't he implying by word "numerically" that this damping factor is not real and manufacturer is not honest. That is what I call manipulation. He makes impression of poor bass performance of Class D - this won't fly either. Enyone who listened to Class D amp knows tahat bass performance is its best feature.

Speaking od damping factor - my Icepower has 4000 and probably unnessesarily since inductor in series with woofers has obout 80mOhms and limits DF to 100. At 20kHz similar limitation is imposed by about 0.2uH imductance of the speaker cable. DF of 200 would be plenty.