km said:hi.
pan i think you should hear some of the better pwm amps
im sure feedback after the output filter is way to go for all pwm amps , perhaps in some it doesnt give much improvement but i think this is due to other factors.
sorry if im repeating myself but i think that usable opinions about class-d ctr. class a or a/b is only valid from those who has a reasonable background to talk from , meaning those who have actually heard some of the better types from both camps , right?
my personal feeling is that this is perhaps 1-2 guys here at most
im gettting a little bored with the usual hear-say and the usual talk about good static thd specs, i have heard and compared boards with good (published) specs and the good specs didnt help much re. sound quality.
happy new year to all.
karsten madsen - www.cadaudio.dk
ps. the easiest way to get low thd numbers is simply to lie and imho this is also used quite often.....
Karsten,
I´d love to hear the better PWM amps
. So far I have only heard the ice modules in the B&O speaker but that didn´t tell me much at all. Are you saying my opinion is not worth much because I lack experience or becasue I have not heard PWM amps? Do you know what equipment I have used/listened at?
I don´t care much for hear-say but do read reviews, whatch specs and no1 listen very criticall on various equipment.
Would love to listen to your designs.
Regards,
/Peter
hi.
>pan wrote ; Are you saying my opinion is not worth much because I lack experience or becasue I have not heard PWM amps? Do you know what equipment I have used/listened at?>
im saying that imho listening experience comparing several good pwm amplifier designs preferably to one or more good class-a and a/b designs has a lot more value than posting reviews from magazines or posting hear-say from others who hasnt heard much either.
to give valuable opinions about the subject of this thread (class-d vs. class a and a/b) i think at least you should have listened to the better of each type.
i think that some of the beolabs use class a/b amps for the hf so please check this if you want to compare , imho again its a lot better to listen to different amps using same speakers and the rest of the setup , if you hear one set of amp + speakers and next week another set , hmm. i dont think it adds very much to the issue.....
rgds karsten madsen - www.cadaudio.dk
>pan wrote ; Are you saying my opinion is not worth much because I lack experience or becasue I have not heard PWM amps? Do you know what equipment I have used/listened at?>
im saying that imho listening experience comparing several good pwm amplifier designs preferably to one or more good class-a and a/b designs has a lot more value than posting reviews from magazines or posting hear-say from others who hasnt heard much either.
to give valuable opinions about the subject of this thread (class-d vs. class a and a/b) i think at least you should have listened to the better of each type.
i think that some of the beolabs use class a/b amps for the hf so please check this if you want to compare , imho again its a lot better to listen to different amps using same speakers and the rest of the setup , if you hear one set of amp + speakers and next week another set , hmm. i dont think it adds very much to the issue.....
rgds karsten madsen - www.cadaudio.dk
Karsten Madsen: I agree with your views completely! I never heard your PWM amp, but i would be very interested to switch sets with you for a week for a mutual comparison.
Last friday i went with a couple of friends to visit AV-Reality (Who are located at the local bowling alley, one kilometer (not to confuse with km from my office), and then later to a B&O shop in downtown Holstebro 2 floors below my appartment.
Before this day i had only heard Beolab 5 through the building and floor, the bass vibrations, of the Beolab 5's are really impressive even 2 floors up.
I must say it was an interesting experience. These two systems sound completely different to each other, even if they probably use more or less the same Icepower modules. The placement in the rooms were also very different, which may be a contributing factor.
I think the Icepower modules are good enough not to be the limiting factor in either system, but other things would more probably be the source of the system's 'own sound'. Only my own private guess.
A very interesting couple of hours
Last friday i went with a couple of friends to visit AV-Reality (Who are located at the local bowling alley, one kilometer (not to confuse with km
from my office), and then later to a B&O shop in downtown Holstebro 2 floors below my appartment. Before this day i had only heard Beolab 5 through the building and floor, the bass vibrations, of the Beolab 5's are really impressive even 2 floors up.
I must say it was an interesting experience. These two systems sound completely different to each other, even if they probably use more or less the same Icepower modules. The placement in the rooms were also very different, which may be a contributing factor.
I think the Icepower modules are good enough not to be the limiting factor in either system, but other things would more probably be the source of the system's 'own sound'. Only my own private guess.
A very interesting couple of hours
km,
I have listnened to a lot of gear thru same speaker in same room. Several times at different locations.
I have also listened to some of the really good amps you talk about but as I mentioned no PWM amps.
So, I have very good experience with top notch class A and A/B in very high standard setups. Never have I tried to judge PWM amps from what I read in papers. As I say, I read graphs and I do own listening tests in carefully treated room.
Of course I can´t compare PWM amps to A and A/B since I´ve never heard a PWM amp. (except from the B&O speaker).
Maybe you did react on my verdict on the B&O speaker... I believe the driverunits and the room was the casue of the less than impressing sound I heard. I did not in any way mean that it had someting to do with the amps.
I do agree with the message in your post.
What "bother" me with PWM amps is that they have a rising THD at the high range. Most A A/B electronics I have heard that have such characteristics have been affected of it IMO.
/Peter
I have listnened to a lot of gear thru same speaker in same room. Several times at different locations.
I have also listened to some of the really good amps you talk about but as I mentioned no PWM amps.
So, I have very good experience with top notch class A and A/B in very high standard setups. Never have I tried to judge PWM amps from what I read in papers. As I say, I read graphs and I do own listening tests in carefully treated room.
Of course I can´t compare PWM amps to A and A/B since I´ve never heard a PWM amp. (except from the B&O speaker).
Maybe you did react on my verdict on the B&O speaker... I believe the driverunits and the room was the casue of the less than impressing sound I heard. I did not in any way mean that it had someting to do with the amps.
I do agree with the message in your post.
What "bother" me with PWM amps is that they have a rising THD at the high range. Most A A/B electronics I have heard that have such characteristics have been affected of it IMO.
/Peter
This is of course true. But while it is quite easy to get a chance to listen to a lot of the good equipment, it is much harder to get a chance to COMPARE the stuff at the same place/time, at least for Joe Average.
That's what I also once read.
The way the sub-bass driver with it's heavy cone is mounted it is a suitable candidate for generating a lot of structure-borne sound.
Do you want to say that you got a chance to listen to AV's active speaker system ? (Does it also use class-d for the tweeter ? How did it sound ?)
Regards
Charles
Having done 3 PWM amps myself, I guess I have some
basis for an opinion. One of these even got a good comment
from Gordon Holt, but I think he was being polite.
So far, I've not heard one which takes on the better Class A
or AB types except in the bottom end, and I have to lay the
blame at inadequate switching speeds and inadequate input
comparators.
No doubt these issues will be resolved over time, but the best
engineering talent does not seem to be working on the
problem from the high-end audiophile viewpoint - they are
still letting their meters tell them what's good and what's not.
basis for an opinion. One of these even got a good comment
from Gordon Holt, but I think he was being polite.
So far, I've not heard one which takes on the better Class A
or AB types except in the bottom end, and I have to lay the
blame at inadequate switching speeds and inadequate input
comparators.
No doubt these issues will be resolved over time, but the best
engineering talent does not seem to be working on the
problem from the high-end audiophile viewpoint - they are
still letting their meters tell them what's good and what's not.
It seems that the output filters are a source for a lot of problems with PWM amps.
My understanding is that they exist to stop the speaker cables from becoming HF antennas.
So.... if the output stage of the amp was close enough to the speaker (like inside the box), could the O/P filters be removed?
My understanding is that they exist to stop the speaker cables from becoming HF antennas.
So.... if the output stage of the amp was close enough to the speaker (like inside the box), could the O/P filters be removed?
It would be interesting to se distortion measurements of a pwm amp with pre-filter feedback.... measured both before and after the filter..?
Is the filter really adding this "much" distortion? In such case a normal passive loudspeaker filter would be suspect to add "lots"
of distortion as well... does this explain why people report such great benefits from going active?
/Peter
Is the filter really adding this "much" distortion? In such case a normal passive loudspeaker filter would be suspect to add "lots"
of distortion as well... does this explain why people report such great benefits from going active?
/Peter
That is why I would avoid passive crossovers, even ones which are air core. I hope to try air core filters on a PWM amp even though the feedback is taken after the filter.
MWP, some manufacturers seem to do that already for cell phones, etc., at least according to data sheets which describe "filterless" class D circuits.
MWP, some manufacturers seem to do that already for cell phones, etc., at least according to data sheets which describe "filterless" class D circuits.
Texas Instruments have output filterless PWM chips such as the TPA2000:
http://focus.ti.com/lit/ds/slos328e/slos328e.pdf
However increasing power levels would make it difficult to keep EMI within regulations limits for this approach. But for at powered PC speaker, laptop, TV set or transistor radio, a chip like TPA2000 would be the perfect choice. On the other hand you can almost build a cheap analog amplifier of 2W without heatsinking as well, so the bucks you spend on the PWM would only give you extended battery life, and added 'cool effect'.
Speaker Wires as HF noise emitting antennas: in any PWM amplifier there are two different EMI problems: The switching frequency 300 - 500 kHz typical could give you problems in AM radio reception, on long wires, and the other is VHF - UHF remains from the switching slopes of the power stage. Both can be dealt with.
6 m. speaker cables have a good antenna effect at 12 - 18 MHz (quarter wavelength) , so to give any substantial transmission you need a lot more than 1 V rms. But if you want it can be removed simply by means of an output filter and subsequent parallel resonant circuit in series with the output. At the 500 kHz (Frequency has to be known), the resonant circuit has a resistance of 50 - 100 Ohms, while a 100nF has 3 Ohms. So the remaining carrier noise is attenuated 15 - 30 times. If you need more attenuation, simply add a choke to the grounding filter cap, to form a seral resonant circuit at the same freq. Typical output of this type is 0.5 - 1 V rms without filtering. After resonant circuits the remaining voltage will be 20 - 66 mV RMS. The serial impedance of the resonant circuit is low, as you only need around 1 uH and 100 nF (not exact values!!).
On the other hand if your speaker cable is 180 Meters long, then you might have a real problem with a 500 kHz carrier frequency.
VHF / UHF residuals mainly transmit from the power supply wires, and the output circuit itself. NOT the speaker wires (if just simple measures are taken to prevent it).´
The most effective way to get these emissions down is using ultra short (HF emitting) signal path, good fast power decoupling and a 4 layer PCB can help a lot too, as most of the HF energy gets caught in the ground layers.
AIR cores for output filtering, we started out with that in the beginning, thinking the low THD would benefit sound quality. But as it turned out the Ferrite cored ones sound much better, even if the THD is higher. Why the preoccupation with THD?
Further the air cores significantly adds to the HF emitting part of the signal path. You have something like 3 Meters of coil wire with 50 - 200 MHz slope energy on it.
Now that's what i call an antenna!
http://focus.ti.com/lit/ds/slos328e/slos328e.pdf
However increasing power levels would make it difficult to keep EMI within regulations limits for this approach. But for at powered PC speaker, laptop, TV set or transistor radio, a chip like TPA2000 would be the perfect choice. On the other hand you can almost build a cheap analog amplifier of 2W without heatsinking as well, so the bucks you spend on the PWM would only give you extended battery life, and added 'cool effect'.
Speaker Wires as HF noise emitting antennas: in any PWM amplifier there are two different EMI problems: The switching frequency 300 - 500 kHz typical could give you problems in AM radio reception, on long wires, and the other is VHF - UHF remains from the switching slopes of the power stage. Both can be dealt with.
6 m. speaker cables have a good antenna effect at 12 - 18 MHz (quarter wavelength) , so to give any substantial transmission you need a lot more than 1 V rms. But if you want it can be removed simply by means of an output filter and subsequent parallel resonant circuit in series with the output. At the 500 kHz (Frequency has to be known), the resonant circuit has a resistance of 50 - 100 Ohms, while a 100nF has 3 Ohms. So the remaining carrier noise is attenuated 15 - 30 times. If you need more attenuation, simply add a choke to the grounding filter cap, to form a seral resonant circuit at the same freq. Typical output of this type is 0.5 - 1 V rms without filtering. After resonant circuits the remaining voltage will be 20 - 66 mV RMS. The serial impedance of the resonant circuit is low, as you only need around 1 uH and 100 nF (not exact values!!).
On the other hand if your speaker cable is 180 Meters long, then you might have a real problem with a 500 kHz carrier frequency.
VHF / UHF residuals mainly transmit from the power supply wires, and the output circuit itself. NOT the speaker wires (if just simple measures are taken to prevent it).´
The most effective way to get these emissions down is using ultra short (HF emitting) signal path, good fast power decoupling and a 4 layer PCB can help a lot too, as most of the HF energy gets caught in the ground layers.
AIR cores for output filtering, we started out with that in the beginning, thinking the low THD would benefit sound quality. But as it turned out the Ferrite cored ones sound much better, even if the THD is higher. Why the preoccupation with THD?
Further the air cores significantly adds to the HF emitting part of the signal path. You have something like 3 Meters of coil wire with 50 - 200 MHz slope energy on it.
Now that's what i call an antenna!
"Why the preoccupation with THD?"
With the new high rez digital performance of very low distortion and very high dynamics, and also new generation speaker drivers with 0.1-0.01% THD at 90-96dB (mid and high fr.), it seems like it would be possible and beneficial with amps at least 1/10 the distortion of speakers, if not as low as the distortion of the digital sources.
Lars,
I remember reading some time ago, about you using 1MHz switching in the Zapulse... why not now, would it not be beneficial for the high frequency performance of the amp?
/Peter
With the new high rez digital performance of very low distortion and very high dynamics, and also new generation speaker drivers with 0.1-0.01% THD at 90-96dB (mid and high fr.), it seems like it would be possible and beneficial with amps at least 1/10 the distortion of speakers, if not as low as the distortion of the digital sources.
Lars,
I remember reading some time ago, about you using 1MHz switching in the Zapulse... why not now, would it not be beneficial for the high frequency performance of the amp?
/Peter
hi.
nelson i think it would be very interesting to hear what work you did on pwm amps in the past and what suggestions you have for further improvements , any chance you could share your thoughts with us here?
about thd i agree with you completely , one can focus so much on the thd meter one completely forgets to listen (no names mentioned but i think some of you have got the picture)
about emi i think we have a couple of good examples of "emi-disasters" , wasnt that a suitable describtion of your zappulse 1.0 lars?
lets see what we can do about listening tests and comparisons , we are looking at 2 projects with finished pwm amplifiers for the hifi market at this point , i think you should be able to hear one of them within reasonable time (and others of course too)
what drivers are you referring to with 0.01% thd at 96 db pan?
best regards - karsten madsen - www.cadaudio.dk
ps. i do not agree that active crossovers in hifi speakers is better than passive ones , long time experience says that the opposite is very often true....
nelson i think it would be very interesting to hear what work you did on pwm amps in the past and what suggestions you have for further improvements , any chance you could share your thoughts with us here?
about thd i agree with you completely , one can focus so much on the thd meter one completely forgets to listen (no names mentioned but i think some of you have got the picture)
about emi i think we have a couple of good examples of "emi-disasters" , wasnt that a suitable describtion of your zappulse 1.0 lars?
lets see what we can do about listening tests and comparisons , we are looking at 2 projects with finished pwm amplifiers for the hifi market at this point , i think you should be able to hear one of them within reasonable time (and others of course too)
what drivers are you referring to with 0.01% thd at 96 db pan?
best regards - karsten madsen - www.cadaudio.dk
ps. i do not agree that active crossovers in hifi speakers is better than passive ones , long time experience says that the opposite is very often true....
There is no real dispute that these amps are not as evolved as the more traditional design and I cannot see buying one for much over $1K it is surprising that the consumer can get adequate performance from the Panasonic recievers that are going for under $300.
I can't say they are as good as my reference gear,but they do very nicely for value orientated consumers that go to BB or CC. They outdo the run of the mill mass market AB class junk recievers for a clean presention and great Bass which is what I think they do good.No glare or strident sound. Not bad for 300US bucks.
I agree with the comments posted by NP
I can't say they are as good as my reference gear,but they do very nicely for value orientated consumers that go to BB or CC. They outdo the run of the mill mass market AB class junk recievers for a clean presention and great Bass which is what I think they do good.No glare or strident sound. Not bad for 300US bucks.
I agree with the comments posted by NP
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