Distortion free amp

Greg,

The tittle of your thread obliges me to anticipate my views about distortion free amplifiers. Please consider the following though experiment.

Take the cheapest 100 watt amplifier you get - the only requirement is having a low impedance output.
Play your favorite music with it recording the output attenuated with a resistive attenuator with a decent 24 bit soundcard. Mathematically compare the two files and create a difference file between them .

Now play the two files simultaneously using two amplifiers - the first one and a low distortion, low power one for the error signal - connecting the speaker leads to the positive outputs, as if you were using a fully balanced amplifier. This subtracts the outputs of the amplifiers.

Do we get almost zero distortion playback for less than usd 100?

Same old question, 0% distortion of 60 HZ is a good sound ? try to get something doing better,may be loosing the others as well
tony ma

I am surprised about this tag line which seems to have been used elsewhere but doesn't reflect what Marten says itself about the amp:

"Max Power @ 8 Ohm, 1% THD / 550 W
Max Power @ 4 Ohm, 1% THD / 1000 W
Max Power @ 2 Ohm, 1% THD / 1700 W
THD @ 1 W, 8 Ohm, 20-20000 Hz / 0.0012%
THD @ 10 W, 8 Ohm, 20-20000 Hz / 0.002%
THD @ 100 W, 8 Ohm, 20-20000 Hz / 0.006%
THD @ 300 W, 8 Ohm, 20-20000 Hz / 0.02%
THD @ 400 W, 8 Ohm, 20-20000 Hz / 0.05%"

How could a distortion-free amp have THD?

Looking at the buzzwords used, it doesn't sound like anything special. While it is true that typical B&O Ice Amp runs at 380Khz so running at 600 Khz does show an improvement, it is still too low of a frequency for very clean output filter implementation. To wit, the Mark Levinson No 53 which is a class I amp (modification of class D) runs at effective rate of 4 MHz or almost 7X higher frequency. That amp retails for $25K each so it is only slightly more expensive.

The word "servo" essentially means feedback. It is with that feedback that they are achieving lower distortion than it would be otherwise.

Why are filters and feedback important concepts here? Because this is what typically comes out of a class-D amp before you apply one or both:



Doesn't look anything like a sine wave, now does it? All of those harmonics need to be filtered without impacting passband of the source frequencies we like to hear.

Here is the output of the Mark Levinson, again prior to filtering:



A hell of a lot cleaner and of course, easier to filter out.

Another issue with distortion measurement is the load. Class D amps are highly sensitive to load variations because the load becomes part of the output filter. In a subwoofer, you know the load so you can optimize the filter for that specific load. In a general purpose amp, you don't know the load and it takes far more skill to design the filter and the rest of the amp such that it still performs well. So in a general sense, the numbers spec'ed by Marten really have no meaning without knowing the load that was used. Indeed, the typical measurement setup for class D amps calls for using filters to get rid of ultrasonic distortion!

Here is the measured performance of the No 53 just done by Homethaterhifi magazine into a real speaker as noted:



You can read more about this topic in their review: http://www.hometheaterhifi.com/powe...levinson-no-53-monoblock-power-amplifier.html

Marten co-designed this amp with B&O. My recent experience with B&O modules even when paired with linear power supplies has been poor. I find them noisy and very harsh sounding. With an oddness that is hard to put your finger on. No doubt they have made improvements over their cheap modules they sell to everyone else to arrive at this product. But without more data as to what they have done other than mentioning terms like servo, it is hard to say where the innovation is. The amp certainly is not distortion-free per their own admission so right at the start, we have hyped up marketing which doesn't bode well in my book.

They are butt-ugly to boot. They kind of remind me of coffins and the more I look at them, the more they weird me out. I can almost imagine (there we go Amir) that if I took the top off there may be a body inside.

For you or for them Greg?

Amir,

Taken from the review you refer:
"With a 1 kHz sine wave and 10 volts into the Carver speaker, THD+N was a very, very low 0.002%. The second harmonic is the largest one, which is a good thing." Very interesting. I have tried to highlight this point in several posts, but is was always discredited or ignored.

Interesting that THD at power levels over tens a watt is between .02% and .05%. A similar thing happens with some other recent high-end amplifiers. One could imagine that using updated technology and semiconductors designers could easily reach levels below .01%. Why designers do not try to reach the minimum THD?

The easy path to lower THD is more feedback which is not in vogue these days. Alternative is more precision design and component selection. They may have reached what they can do here.

Amir, I like you, but you are mistaken as how ICE sounds. Nobody knows how ICE sounds better than I, and now my amp builder too who has my source duo inserted into his system as I write. I have talked on and on about how good my system is. My amp builder has a mirror system to mine as of now. He has the same speakers, ICs, amps, preamp, my speaker cables, and now my Flatfish/AN duo. Here is what he is saying"


"I have been listening all morning and YES!!! It is incredible. It is unreal how good the Flatfish and the Audio note sounds. It has the right amount of ambience, air, staging. Bass is beyond description. Very tuneful and meaty with right amount of pitch definition. Vocal is NIRVANA to listen to. Nothing is exaggerated. No wonder you have been screaming how good your system sounds, unfortunately mostly to unbelievers. Oh well, Too bad they missed out big time. Top end is so exxxxxquisite...."

Vince, I thought I sent out a smoke signal to get you back to the forum!

Note that I have been specific that class D amps interact with their loads unlike other amplifier designs. So it is entirely possible that you have found the magic combination of version of ICE amp, your wires and speaker. I could not in the two configuration I tested them.

BTW, if you put your ear next to your speaker, is it totally silent?

amirm said:

Vince, I thought I sent out a smoke signal to get you back to the forum!

Note that I have been specific that class D amps interact with their loads unlike other amplifier designs. So it is entirely possible that you have found the magic combination of version of ICE amp, your wires and speaker. I could not in the two configuration I tested them.

BTW, if you put your ear next to your speaker, is it totally silent?

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I just happened to pop in. I was so excited to hear back about my source duo. I am a lucky man. It seems finding the right stuff to make my speakers sound the best they came to me without hardly a deviation. I have no sound now without my source. Every time I have put my ear directly to the MRT of my speakers, all I hear is a microcosm of what I hear in the room, only just some clearer. Room correction for sound optimization is WAF weighted.

Gregadd said:

For anyone interested. In a distortion free. Amp

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Oh. I think they are out looking for a car which runs on water instead of gas!

Isn't Halcro supposed to be the record holder for lowest distortion? I must like some distortion because I can't stand them. Just stating personal preference here.

Vince, nice to see you back ...

Frank

fas42 said:

Vince, nice to see you back ...

Frank

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Thanks, Frank.

why are these amps so big if they are switching power supply/Class D?

they look like black tombs, as mep said.

i go by the adage---i don't buy electronics from a speaker manufacturer----nor do i buy speakers from an electronics manufacturer. some may disagree, but usually the designer is better at one or the other.

Class D amps can either use linear or switchmode power supply. Power supply design is a big deal in these amps. Any variations in the power supply directly translates into output distortion.

The Levinson monster "class I" am p I mentioned earlier use linear power supply and hence the big heat sinks on each side: