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Old 13th October 2011, 03:23 PM   #541
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I think that I am going to withdraw what I wrote in post #524 about the language barrier !!! And Bruno has a lot of reason for being grumpy.

I don't know your topology but I guess it is a natural-sampling (i.e. the classic carrier -based PWM) amp.

There are some things that can go wrong when doing NFB in such a topology. And there is something called "ripple aliasing" that doesn't allow the same amount of distortion reduction from NFB - even when applied in very high amounts - as is achievable with a self-oscillating amp - unless special measures are taken. Maybe that is te reason for using no or low NFB factors combined with a regulated PSU. Just guesssing .......

Regards

Charles
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Old 13th October 2011, 03:38 PM   #542
AP2 is offline AP2  Italy
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Quote:
Originally Posted by phase_accurate View Post
I think that I am going to withdraw what I wrote in post #524 about the language barrier !!! And Bruno has a lot of reason for being grumpy.

I don't know your topology but I guess it is a natural-sampling (i.e. the classic carrier -based PWM) amp.

There are some things that can go wrong when doing NFB in such a topology. And there is something called "ripple aliasing" that doesn't allow the same amount of distortion reduction from NFB - even when applied in very high amounts - as is achievable with a self-oscillating amp - unless special measures are taken. Maybe that is te reason for using no or low NFB factors combined with a regulated PSU. Just guesssing .......

Regards


Charles
Hi,
DXA is selfoscillant ( pre-filter primary FB) after, use nfb as AB class.
scheme di modulator is absolute new. I do not want to discuss dxa ,if better or not (sorry for this).
I think that my last message have clare english,not absolute right, but very clean.
Independent of all, power supply is the soul of what you hear.
only the amp, should modulate the current. No Amp + PSU, especially at low power 40 50w.
Yes, entry-level use fixed carrier pwm (SDA-400). maybe if you listen this..understand all.

Last edited by AP2; 13th October 2011 at 03:41 PM.
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Old 13th October 2011, 04:23 PM   #543
ChrisPa is offline ChrisPa  United Kingdom
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Quote:
Originally Posted by AP2 View Post
Independent of all, power supply is the soul of what you hear.
only the amp, should modulate the current. No Amp + PSU, especially at low power 40 50w.
The PSU will be the soul of what you hear if the the amplifier is incapable of isolating itself from the supply (poor PSRR)
A more stable, higher reserve supply will make the task easier for the amp and make the most of its PSRR, but the end performance will be whatever it shown by the (measured) results.

I can't see why you have a problem - which is what your posts imply - with SMPSs and why you have a problem with the ncore producing its results when supplied by an SMPS.
An SMPS inherently contains regulation (the final specs. and performance will tell you how good it is).
It has to, because its job is to regulate a mains voltage directly down to a DC voltage

I, as an external reader of the specs and performance results that I have seen here - not as a 'Bruno fan' - have no problem in observing (from the results) and believing (from concept and theory) that an appropriately designed SMPS will match a linear PSU.

An SMPS is a form of class D amplifier. It uses switching topology to produce an output signal that tracks the input signal - a static DC value. It regulates AC mains down to a DC output signal.

A class D amplifier uses switching topology to produce an output signal that tracks the input signal - a varying value. It regulates the DC supply voltage to provide an accurate alternating voltage.

If you can accurately produce AC by switching DC then you can accurately produce DC by switching AC
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Old 13th October 2011, 05:54 PM   #544
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Quote:
I do not want to discuss dxa ,if better or not (sorry for this).
Maybe we can see some measurements or a link to them ? Or maybe you want your own thread ?

While looking for cover I'd like to add that topologies with mixed feedback (i.e. pre- AND post- filter combined) are not fashionable anymore.

Regards

Charles
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Old 13th October 2011, 07:06 PM   #545
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A good power amplifier is a voltage regulator in its own right. That's what power amps do. A power amp that is incapable of regulating its output voltage independently of its supply voltage has some serious explaining to do.
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Old 13th October 2011, 07:39 PM   #546
tengizk is offline tengizk  United States
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Bruno, although you somewhat covered it already (you basically said that good IMD performance for the input below 20 kHz range most likely results in good-ish IMD performance for the input within the power bandwidth), it would be really interesting to see the results of actual measurements.
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Old 13th October 2011, 07:43 PM   #547
AP2 is offline AP2  Italy
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Quote:
Originally Posted by ChrisPa View Post
The PSU will be the soul of what you hear if the the amplifier is incapable of isolating itself from the supply (poor PSRR)
A more stable, higher reserve supply will make the task easier for the amp and make the most of its PSRR, but the end performance will be whatever it shown by the (measured) results.

I can't see why you have a problem - which is what your posts imply - with SMPSs and why you have a problem with the ncore producing its results when supplied by an SMPS.
An SMPS inherently contains regulation (the final specs. and performance will tell you how good it is).
It has to, because its job is to regulate a mains voltage directly down to a DC voltage

I, as an external reader of the specs and performance results that I have seen here - not as a 'Bruno fan' - have no problem in observing (from the results) and believing (from concept and theory) that an appropriately designed SMPS will match a linear PSU.

An SMPS is a form of class D amplifier. It uses switching topology to produce an output signal that tracks the input signal - a static DC value. It regulates AC mains down to a DC output signal.

A class D amplifier uses switching topology to produce an output signal that tracks the input signal - a varying value. It regulates the DC supply voltage to provide an accurate alternating voltage.

If you can accurately produce AC by switching DC then you can accurately produce DC by switching AC
what measures? continuous signal with fft?
apart from that, listening to the problem is immediately apparent.
I remind you that we are talking about a high end amp, not a PA.
an audiophile feel immediately when the voltage moves. this is perfectly measurable by other measures (dynamic).
In this range, typically using a linear PSU up to 100.000 uF capacitors. NuForce use a good smps clean regulated psu and adjust the dynamic response with a table of capacitors.
I have developed a regulated power supply (SMPS) especially for this.
What are you talking about the PSRR?
I have nothing against the NCore. everyone is free to do and say whatever he wants.
I do not agree that over 20Khz does not make sense.(i start from this)
yes, if you extend the band, everything becomes complicated, I know. drivers, dt, bias, phase shift, delay, comparator and buffers. For this, the project is worth much more.

Last edited by AP2; 13th October 2011 at 07:54 PM.
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Old 13th October 2011, 08:00 PM   #548
AP2 is offline AP2  Italy
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Originally Posted by Bruno Putzeys View Post
A good power amplifier is a voltage regulator in its own right. That's what power amps do. A power amp that is incapable of regulating its output voltage independently of its supply voltage has some serious explaining to do.
Why you have capacitors oversized in your smps? for ripple? well, what is frequency of ripple that you adjusted with it?
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Old 13th October 2011, 08:10 PM   #549
AP2 is offline AP2  Italy
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Originally Posted by Bruno Putzeys View Post
A good power amplifier is a voltage regulator in its own right. That's what power amps do. A power amp that is incapable of regulating its output voltage independently of its supply voltage has some serious explaining to do.
I have no doubt, only 5 transistors for good amp, this amp Can be Amp or regulator. then your amp solves a problem of the regulator. response time?
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Old 13th October 2011, 08:36 PM   #550
AP2 is offline AP2  Italy
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Originally Posted by phase_accurate View Post
Maybe we can see some measurements or a link to them ? Or maybe you want your own thread ?

While looking for cover I'd like to add that topologies with mixed feedback (i.e. pre- AND post- filter combined) are not fashionable anymore.

Regards

Charles
yes,i know B&O con mixed FB...
DXA not use mixed FB. use two fb and other circuit for obtain a linear response in range 10Hz to 60Khz.
behavior is also different in audio measurements refer to an class D.
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