Dear Mr. Pass
The enclosed schematic is a simplified example of how a BCA output stage might look like. At least how I understand it. Otherwise I might just have made a cool invention
!
If the input signal is zero then both "switches" are on at the same time and off at the same time with a duty cycle of 50%.
If the input voltage rises then the upper switches on-time increases, the lower switches on time decreases according to the input voltage. For negative signals it is vice-versa.
As you can see, the topology is single-ended, i.e. the load is referenced to ground (O.K. one can also reference one leg of a bridge to ground but I assume you know what I want to say).
The three main advantages of this toplology are:
1.) No need to suppress shoot-through current by dead-time and the like (nothing to adjust !! )
2.) No problems with reverse diode turn-off times.
3.) Good supression (theoreticall a 100% cancellation) of the switching residual for low signal levels.
Having done quite a lot of thinking regarding switching amplifiers I must enviously admit that it is one of the coolest ideas anybody had, regarding switching amplifiers, so far.
Regards
Charles
The enclosed schematic is a simplified example of how a BCA output stage might look like. At least how I understand it. Otherwise I might just have made a cool invention
!If the input signal is zero then both "switches" are on at the same time and off at the same time with a duty cycle of 50%.
If the input voltage rises then the upper switches on-time increases, the lower switches on time decreases according to the input voltage. For negative signals it is vice-versa.
As you can see, the topology is single-ended, i.e. the load is referenced to ground (O.K. one can also reference one leg of a bridge to ground but I assume you know what I want to say).
The three main advantages of this toplology are:
1.) No need to suppress shoot-through current by dead-time and the like (nothing to adjust !!
)2.) No problems with reverse diode turn-off times.
3.) Good supression (theoreticall a 100% cancellation) of the switching residual for low signal levels.
Having done quite a lot of thinking regarding switching amplifiers I must enviously admit that it is one of the coolest ideas anybody had, regarding switching amplifiers, so far.
Regards
Charles
Nelson Pass Is Right...
....nothing impressive about class-d (pwm), amplification...at least with respect to hi-fidelity reproduction.
The singular failing of the pwm approach is the fact that the mandatory output RF filter permits a flat frequency response into one...and only one design load....which is probably why a class D device may produce low distortion, (~500ppm thd+noise, ref 1Khz, 80khz bandwidth, smpte ), into a dummy laboratory load, and deliver an absolutely horrendous performance when terminated with a loudspeaker system, whose impedance characteristics vary with frequency.....
This is the single greatest limitation of the new breed of so-called digital power processing amps. by grundig, texas instruments...etc....
Do not believe the hype.....linear power processing, (aka good old fashioned analogue amps), still remains the only way to produce true hi-fidelity....for the moment....i do'nt myself see the status quo changing in the immediate future...
....nothing impressive about class-d (pwm), amplification...at least with respect to hi-fidelity reproduction.
The singular failing of the pwm approach is the fact that the mandatory output RF filter permits a flat frequency response into one...and only one design load....which is probably why a class D device may produce low distortion, (~500ppm thd+noise, ref 1Khz, 80khz bandwidth, smpte
), into a dummy laboratory load, and deliver an absolutely horrendous performance when terminated with a loudspeaker system, whose impedance characteristics vary with frequency.....This is the single greatest limitation of the new breed of so-called digital power processing amps. by grundig, texas instruments...etc....
Do not believe the hype.....linear power processing, (aka good old fashioned analogue amps), still remains the only way to produce true hi-fidelity....for the moment....i do'nt myself see the status quo changing in the immediate future...
.....worse still, for anything approaching passable hi-fi, the switching frequency would have to be of the order of 100 times the highest nominal audible audio frequency....which means a 2MHz oscillator is mandated....this requirement can be watered down (20Khz switching freq.), if the design load is to be a single subwoofer driver...... operating at say 2 Kilowatts+....., and a 200hZ low-pass cut-off freq...
Charles, you've got the basic output stage concept correct as well as the key features of BCA. Somewhere on one of my mag optical disks I've got some papers Gerald sent me back in 1999/2000 when he was evaluating our CoolMOS transistors for the switching amp (these are charge compensation high voltage MOSFETs designed for much lower Ron and faster switching speed than standard vertical MOSFETS- Ron is about 1/6 of a standard device of the same chip area).
This is pretty humorous... from the reaction to my post above, it seems I'm perceived as an advocate of Class D amps...
My only point in posting was to explain why Gerald Stanley's invention has some sigificant advantages compared with a conventional half bridge or full bridge PWM switching amplifier. These advantages extend to robustness and freedom from the most common failure mode plaguing these designs, as well as extensibility which makes some incremental improvements in fidelity possible.
On the whole, for someone looking for a sound reinforcement amplifier, or perhaps a high power sub amp, the K series are decent well engineered products, for their intended market and applications.
Techron was producing amplifiers for the MRI market using this concept, with some significant success, as I understand.
Though I've had an on again, off again fascination with the class D amps since the seventies, and had a few papers published on the topic, including an AES paper, I'll readily admit you won't find one in my audio system...
my own tinkerings are non-loop feedback designs, and my current favorite endeavor is rebuilding Aragon amplifiers into something more listenable. You can pick up used ones pretty inexpensively, and the chasis, heatsink, and power transformers are an acceptable starting point, without the hassle of doing your own metal working-
Best regards,
Jon
This is pretty humorous... from the reaction to my post above, it seems I'm perceived as an advocate of Class D amps...
My only point in posting was to explain why Gerald Stanley's invention has some sigificant advantages compared with a conventional half bridge or full bridge PWM switching amplifier. These advantages extend to robustness and freedom from the most common failure mode plaguing these designs, as well as extensibility which makes some incremental improvements in fidelity possible.
On the whole, for someone looking for a sound reinforcement amplifier, or perhaps a high power sub amp, the K series are decent well engineered products, for their intended market and applications.
Techron was producing amplifiers for the MRI market using this concept, with some significant success, as I understand.
Though I've had an on again, off again fascination with the class D amps since the seventies, and had a few papers published on the topic, including an AES paper, I'll readily admit you won't find one in my audio system...
my own tinkerings are non-loop feedback designs, and my current favorite endeavor is rebuilding Aragon amplifiers into something more listenable. You can pick up used ones pretty inexpensively, and the chasis, heatsink, and power transformers are an acceptable starting point, without the hassle of doing your own metal working-
Best regards,
Jon
Re: Trouble with tribles
They do sound decent, but are kinda excessively priced. There are a couple companies getting good results with analog amps and switching supplies. Chord?
dave
Variac said:
They do sound decent, but are kinda excessively priced. There are a couple companies getting good results with analog amps and switching supplies. Chord?
dave
Variac said:
Linn starts by putting each half of the amp into its own very isolated solid aluminum well. And they must have spent 10 years & a lot of R&D dollars to get it to work. They aren't perfect, perhaps a little smoothed over sounding. Certainly not worth the asking price, but show that if you throw enuff time, money, and smarts at it you can get something decent.
dave
Hi All
Regarding switching PSUs and amplifiers there was already a discussion within another thread. I can only repeat that it IS possible to build a good sounding amplifier with a switching PSU but then you can't optimize your PSU for cost as it is done with your PC's and TV's PSU. They can even be built in a way that they send less garbage back into the mains than the best conventional PSUs (for DIY I would of course prefer the latter ones) !!
Just have a look at those CHORD amplifiers.
The lowpass filter issue is in fact one of the biggest problems within Class-D amplifiers.
But the statement that it has to be designed for a given load would be the least problem for me: I am into active speakers anyway
Apart from that, all the other amplifiers are also grateful if they can drive a resistive load (at least it doesn't hurt) !
The load related peaks and drops generated by the output filter are usually harmless compared to the response anomalities of some speakers (metal domes for instance).
The real culprit is the bandwidth LIMITATION and phase distortion which I don't like. There is of course a possibility to get around this by paralleling of a conventional and a switching amplifier but this is 1.) not an easy task and 2.) there is only about 85 % of efficiency left.
The class-D amp I developed back then was a lab power source and it's bandwidth was from DC to 45 kHz. It's THD was 0.44% and mainly k2. Carrier suppresion was 80dB. It could deliver up to 250 Watts.
We saw how THD could be improved but left it as it was because we already achieved the goal of THD < 1%. Apart from some faint treble noise it was quite pleasing to listen to it, although not intended for this purpose.
Because I have some demand I will once make another try to develop a better one but for domestic purposes I do also prefer to listen to conventional amplifiers.
But I am still convinced that the majority of applications could easily be covered by switching amplifiers because most people simply don't care about sound quality that much.
Regards
Charles
Regarding switching PSUs and amplifiers there was already a discussion within another thread. I can only repeat that it IS possible to build a good sounding amplifier with a switching PSU but then you can't optimize your PSU for cost as it is done with your PC's and TV's PSU. They can even be built in a way that they send less garbage back into the mains than the best conventional PSUs (for DIY I would of course prefer the latter ones) !!
Just have a look at those CHORD amplifiers.
The lowpass filter issue is in fact one of the biggest problems within Class-D amplifiers.
But the statement that it has to be designed for a given load would be the least problem for me: I am into active speakers anyway
Apart from that, all the other amplifiers are also grateful if they can drive a resistive load (at least it doesn't hurt) !
The load related peaks and drops generated by the output filter are usually harmless compared to the response anomalities of some speakers (metal domes for instance).
The real culprit is the bandwidth LIMITATION and phase distortion which I don't like. There is of course a possibility to get around this by paralleling of a conventional and a switching amplifier but this is 1.) not an easy task and 2.) there is only about 85 % of efficiency left.
The class-D amp I developed back then was a lab power source and it's bandwidth was from DC to 45 kHz. It's THD was 0.44% and mainly k2. Carrier suppresion was 80dB. It could deliver up to 250 Watts.
We saw how THD could be improved but left it as it was because we already achieved the goal of THD < 1%. Apart from some faint treble noise it was quite pleasing to listen to it, although not intended for this purpose.
Because I have some demand I will once make another try to develop a better one but for domestic purposes I do also prefer to listen to conventional amplifiers.
But I am still convinced that the majority of applications could easily be covered by switching amplifiers because most people simply don't care about sound quality that much.
Regards
Charles
Ice Power Indeed
Hi Peranders, I have had a 90 minute osr so listen to the IcePower modules on a isobaric sub and 8" 2 way active prototype system using 3 of the 100W modules, on music that is really not my favorite including some really old tracks on CD release.
First impressions are that they are utterly load independant, slewless, imd less, niceley accurate and unfussy, but strangely coldish and uninvolvingish - this I expect is a product of the load independance - really dirty old recordings were plainly presented as such without reduction or embellishment and tuneful resonance was sort of absent.
In the near future I'll get back to a proper longerer term listen.
I have held these modules in my hand and studied them closely - they look rather good, but perhaps a few little rearrangements are required in the layout and componentry.
Eric.
Hi Peranders, I have had a 90 minute osr so listen to the IcePower modules on a isobaric sub and 8" 2 way active prototype system using 3 of the 100W modules, on music that is really not my favorite including some really old tracks on CD release.
First impressions are that they are utterly load independant, slewless, imd less, niceley accurate and unfussy, but strangely coldish and uninvolvingish - this I expect is a product of the load independance - really dirty old recordings were plainly presented as such without reduction or embellishment and tuneful resonance was sort of absent.
In the near future I'll get back to a proper longerer term listen.
I have held these modules in my hand and studied them closely - they look rather good, but perhaps a few little rearrangements are required in the layout and componentry.
Eric.
Nelson Pass wrote:
I am convinced that (apart from curiosity of course !) Nelson Pass or Pass Labs will never be forced to develop/produce a class-d amplifier.
The highest quality segment of amplifiers will not be the main target of this technology (although there are very good class-d amps available).
The main application areas for class-d amps are:
1.) P.A.
2.) medium-FI applications (mass-market)
3.) applications with constrained space (active speakers, lifestyle systems, car audio........)
4.) active subwoofers
From a technical point of view I am a fan of class-d, but will definitely use conventional amplifiers for my active MSW project.
Regards
Charles
I am convinced that (apart from curiosity of course !) Nelson Pass or Pass Labs will never be forced to develop/produce a class-d amplifier.
The highest quality segment of amplifiers will not be the main target of this technology (although there are very good class-d amps available).
The main application areas for class-d amps are:
1.) P.A.
2.) medium-FI applications (mass-market)
3.) applications with constrained space (active speakers, lifestyle systems, car audio........)
4.) active subwoofers
From a technical point of view I am a fan of class-d, but will definitely use conventional amplifiers for my active MSW project.
Regards
Charles
hi.
how many of you have heard a pwm amplifier on a hifi setup?
it seems to me some of you are just repeating what they have heard about pwm amplifiers and later about switch-mode power supplies.
i have heard several high quality pwm amps and i have been involved in comparing several of these (including icepower , tripath and our own designs...)
and i have heard same amp with a normal power supply (toroid, fast diodes , ....) and with a switch mode supply , they do sound a bit different but i think i perfer the switch mode supply.
these tests were made on normal and on high efficiency hifi speakers ( 90 db and around 100 db) and the noise levels were completely acceptable (i.e. no noise at listening position and very little fine grain noise at high efficiency tweeter , an audax pr130 btw.)
so your statements that it will take long time before pwm amplifiers reach acceptable audio level and that switch mode supplies wont work in hifi are not verified in the real world.
if you want to discuss further about the quality (or lack of same) in pwm amps i think it wpuld be a very good idea to say what you heard and under what conditions.
i think its worth to say that there are in fact several good class-d/pwm amps around , spectron , belcanto, ps audio to name a few.
rgds karsten madsen - www.cadaudio.dk
ps. peranders good specs isnt always the same as good sound
how many of you have heard a pwm amplifier on a hifi setup?
it seems to me some of you are just repeating what they have heard about pwm amplifiers and later about switch-mode power supplies.
i have heard several high quality pwm amps and i have been involved in comparing several of these (including icepower , tripath and our own designs...)
and i have heard same amp with a normal power supply (toroid, fast diodes , ....) and with a switch mode supply , they do sound a bit different but i think i perfer the switch mode supply.
these tests were made on normal and on high efficiency hifi speakers ( 90 db and around 100 db) and the noise levels were completely acceptable (i.e. no noise at listening position and very little fine grain noise at high efficiency tweeter , an audax pr130 btw.)
so your statements that it will take long time before pwm amplifiers reach acceptable audio level and that switch mode supplies wont work in hifi are not verified in the real world.
if you want to discuss further about the quality (or lack of same) in pwm amps i think it wpuld be a very good idea to say what you heard and under what conditions.
i think its worth to say that there are in fact several good class-d/pwm amps around , spectron , belcanto, ps audio to name a few.
rgds karsten madsen - www.cadaudio.dk
ps. peranders good specs isnt always the same as good sound
Hi Karsten
I have only heard two high-end switching amplifiers so far, the TacT MillenniuM (digital PWM) and the Sharp SM-SX100 (delta-sigma) and I wouldn't hesitate to listen to all the others if the opportunity arises.
Both were very well sounding amps and also the build quality of both was very nice (especially the TacT). By that time they were extremely expensive compared to an ordinary amp with the same performance.
How does your amp compare to ordinary ones in the price respect (soundwise I've already seen some good reviews, congrats !) ?
I did never doubt that switching amps can be made well sounding and I must also admit that I am a fan of switching amplifiers myself.
But a technology does not only have to be small, efficient and sexy, it must be able to be good AND reasonably priced as well (cheap and mediocre is not a problem anymore with heaps of avaliable integrated solutions nowadays).
But I am still convinced that the absolutely highest quality amps will still be ordinary linear amps for some decades to come.
Regards
Charles
I have only heard two high-end switching amplifiers so far, the TacT MillenniuM (digital PWM) and the Sharp SM-SX100 (delta-sigma) and I wouldn't hesitate to listen to all the others if the opportunity arises.
Both were very well sounding amps and also the build quality of both was very nice (especially the TacT). By that time they were extremely expensive compared to an ordinary amp with the same performance.
How does your amp compare to ordinary ones in the price respect (soundwise I've already seen some good reviews, congrats !) ?
I did never doubt that switching amps can be made well sounding and I must also admit that I am a fan of switching amplifiers myself.
But a technology does not only have to be small, efficient and sexy, it must be able to be good AND reasonably priced as well (cheap and mediocre is not a problem anymore with heaps of avaliable integrated solutions nowadays).
But I am still convinced that the absolutely highest quality amps will still be ordinary linear amps for some decades to come.
Regards
Charles
I have "tested" the "Milennium"(TacT), over-rated, and much too expensive.
And the Acoustic Reality (icePower), also over-rated, lacking "body", but sweet and detailed.
And YOUR (CadAudio) version of Tripath, nothing special about them, but they were certainly less efficient than Tripaths own evaluation-board, wich I'm in the process of testing/tweaking now.
I thought you knew the difference of Class A and PWM...
And so-far, with DIY in mind, Tripath at-least has adjustment/tweak-possibilities, Not easily done with the other modules/amps, unless you start from scratch. Not easy...
Circlotron has done just that, and I'm filled with envy...
Arne K
NORWAY
BTW, All tests have been done on "better" versions of
AudioVector speakers.
And (IMHO) it's not difficult to get reasonably good sound with lousy spec's, the challenge lies in doing both good !
I have visited LC-audio's homepage recently and I have seen that they:
1.) got rid of the stupid sales-talk
2.) got rid of the air-cored output inductor in favour of an air-gapped ferrite one (like I did 12 years ago ).
To me these are two important steps. If the price will decrease to a more interesing level I might even think of getting two of these modules to play around with.
Regards
Charles
1.) got rid of the stupid sales-talk
2.) got rid of the air-cored output inductor in favour of an air-gapped ferrite one (like I did 12 years ago
).To me these are two important steps. If the price will decrease to a more interesing level I might even think of getting two of these modules to play around with.
Regards
Charles
hi.
"And YOUR (CadAudio) version of Tripath, nothing special about them, but they were certainly less efficient than Tripaths own evaluation-board,..."
just for your info , they are tripath boards , just a smaller footprint of their eval board.
we had the big footprint version for test too , it has same efficiency and other specs.
did you try to change deadtime? , efficiency (and audio quality) is related to that.
did you try to tweak other things ?
rgds karsten madsen - www.cadaudio.dk
"And YOUR (CadAudio) version of Tripath, nothing special about them, but they were certainly less efficient than Tripaths own evaluation-board,..."
just for your info , they are tripath boards
, just a smaller footprint of their eval board.we had the big footprint version for test too , it has same efficiency and other specs.
did you try to change deadtime? , efficiency (and audio quality) is related to that.
did you try to tweak other things ?
rgds karsten madsen - www.cadaudio.dk
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