Not slew ...
After trying for a perfect match between VFA/CFA performance ,
the "pitchfork villagers" are still preferring CFA designs.
Perhaps the sub-par PSRR , lack of V/I at FB , (TIM/IMD) ... or
other factors are at play ?
PS- in this case the more "clinical" ... (5ppm) amp was NOT
preferred. 😕
Wonder if they - (villagers) will like a "Gilbert cell" amp ?
OS
After trying for a perfect match between VFA/CFA performance ,
the "pitchfork villagers" are still preferring CFA designs.
Perhaps the sub-par PSRR , lack of V/I at FB , (TIM/IMD) ... or
other factors are at play ?
PS- in this case the more "clinical" ... (5ppm) amp was NOT
preferred. 😕
Wonder if they - (villagers) will like a "Gilbert cell" amp ?
OS
Do you mean a Gilbert for the LTP? Also, I think a Gilbert type thing could be done with the OPS too, giving the parallel outputs different bias voltages. Might have bad thermal behavior unless you used ThermalTraks.
The answer is very, very easy. You will get nothing faster from CD than the attached rising edge. Keep the time and scale the Y axis according to amplifier's output voltage swing. To make it simple, let's assume 20V/div scope division and the swing (with ringing) of 130.7Vp-p. Then the SR would be about 80V/0.8div, i.e. 80V/16us, i.e. 5V/us.
Attachments
Should we design to a limited number such as 5v/usec or should we design to be maybe 10 times better? Should we design a ss amp to have a freq response that falls off at 20KHz (without filters doing it)? Should we design an amp whose low end response goes to 40Hz (-3dB) .. few speakers go lower. And, S/N ratio based on typical listening room background noise level. Etc etc. If we did ALL those things based on minimal requirements, would it sound better? Or even as good as designs which are 10 times better or more?
Then there is the point that what can we design without boundaries and limits... which is my interest. And, I am still gathering info re listening as to any difference between CMA and VFB amps. if there is a consensus on that - by listening - then what in the design makes a difference?
THx-RNMarsh
Then there is the point that what can we design without boundaries and limits... which is my interest. And, I am still gathering info re listening as to any difference between CMA and VFB amps. if there is a consensus on that - by listening - then what in the design makes a difference?
THx-RNMarsh
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I prefer to use what it started out being called. But for all to note: CFA can be CMA also. Or CFB. All same or similar.
CFA has caused confusion as to the operation and topology combo.... operating in Current-Mode nails it down, IMV.
Besides that, what are you confused about?
-THx-RNMarsh
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Thats all you will get from me. Emphasis on what I think is important to look into and discuss and SIM. I use the emoticons to indicate what I think is an import statement or view rather than a lot of words. As well as, pasted pages of CFA designs/ers, patents, etal. I know your MO, Waly. I am confident in my knowledge and place in the world. I've proved myself to others who are far more knowledgeable under difficult and trying conditions.
This is only a hobby for me... not the most important thing in my world. Others have their opinions about this, too. I get PM and phone calls about you but I dont bring it into this. I try to not be personal by an attack on others. This is for everyone to voice their opinions and say what they want to contribute and how they want to express it.
Back to My point..... we cant IMO design to such ridiculous minimal limits, as described, as it does Not produce better results. There should be nothing confusing about that opinion.
The biggest surprise for me here in DIY-Land is that a non GNFB amp can have as good numbers as a GNFB amp... I never thought that could be done. Congrates to Dadod to being the first or one of the first to do it.
Carry On, Waly.
THx-RNMarsh
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To answer these questions, you conduct Double Blind Listening Tests. In fact at least some of these questions have been investigated using DBLTs including some of my own eg bandwidth limitation (extensive) and speaker LF extension.
I've posted several suggestions of DBLTs on Bandwidth Limitation using CFAs.
I'm not sure why the Moderators have removed them. These proposed DBLTs are entirely on topic as the DBLTs of Bandwidth Limitation are possibly the only concrete evidence of the need for zillion V/us slew which CFAs provide with ease.
Are we not interested in WHY CFAs may sound better? If we knew more about this, it would help us design better amps instead of chasing new topologies which provide no practical or audible benefits.
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That is what OS is doing .. a spin-off from this thread. making both types with options for IPS and OPS etc so everyone can try them to help determine any listening characteristics which could be assigned to either and what designs affect that results, as well.
THx-RNMarsh
That's an easy question. Nobody has here the material and time resources (except perhaps Mr. Marsh, but his interests appear to lie elsewhere) to engage in any serious DBT. Besides, I doubt that even the most careful conducted difference and/or preference DB test will ever move an inch the staunch CFA (and VFA) sacred cows from their positions. We all know that, when it comes to audio, any DBT is inherently flawed, isn't it?
That's a rule of thumb that our instruments should be 10 times faster if we want to measure or transfer anything reliably and 'unaffected'. Anyway, 50V/us is not any strict or tough to get parameter for a 200W/8 ohm amplifier. Quite easy to get, isn't it?
then why not VMA...for voltage mode...?? We're talking about different types of feedback, so I think we should call it that.. VFB and CFB.. or.. (I now i wrote CMA. that was a mistake)
I believe CMA, is vider and broader than CFB,
I believe CMA, is vider and broader than CFB,
It has limitations, when it is simple. No global NFB amp with good parameters is pretty complex.
a few more posts have been deleted and Waly has earned himself two weeks in the sin bin for failing to follow moderators directive not to troll in this thread.
Do we still do not know why there should be any preference for the latter?
I would have thought that the answer was by now at least somewhat apparent to all or even ubiquitously self evident; although the definite relevance of extremely high slew rates could still be called into question.
Looking at the matter of slew rate in audio amplifiers from my own personal perspective as a professional designer of instrumentation for semi-conductor functional and parametric testing systems then the answer to to the connundrum of why such a preference may exist seems obviously not to lie directly in the harmonic and temporal content of the media itself i.e. music; but moreso perhaps in the many additive and subtractive compound misdoings within the messenger i.e. those circuits and components which perform the amplification thereof.
By this what I mean is that given the need for audio amplifiers to employ at least RF input filtering then; the advantages of a higher internal slew rate are primarily of benefit in the amplifiers correction of itself rather than being of any real relevance to the actual input and output signals per se. Even a cursory examination of the spectral content produced by these internal amplifier circuit non linearities can be seen to give rise to higher frequency components beyond those present at the input.
As it is well known that below a certain threshold of distortion there is almost no correllation whatsoever between percieved sound quality and conventional single frequency THD test results and with the same holding true for IMD and even multi tone burst testing.
My first question is: How realistic is it for us to expect that any single solitary slew rate parameter would be in any way a better indicator?
Therefore, my second question becomes; not what slew rate should be targetted, but: How do we determine what internal slew rate target should be set for any given internal circuit configuration?
P.S. My thanks to all the contributors of this very interesting thread
I would have thought that the answer was by now at least somewhat apparent to all or even ubiquitously self evident; although the definite relevance of extremely high slew rates could still be called into question.
Looking at the matter of slew rate in audio amplifiers from my own personal perspective as a professional designer of instrumentation for semi-conductor functional and parametric testing systems then the answer to to the connundrum of why such a preference may exist seems obviously not to lie directly in the harmonic and temporal content of the media itself i.e. music; but moreso perhaps in the many additive and subtractive compound misdoings within the messenger i.e. those circuits and components which perform the amplification thereof.
By this what I mean is that given the need for audio amplifiers to employ at least RF input filtering then; the advantages of a higher internal slew rate are primarily of benefit in the amplifiers correction of itself rather than being of any real relevance to the actual input and output signals per se. Even a cursory examination of the spectral content produced by these internal amplifier circuit non linearities can be seen to give rise to higher frequency components beyond those present at the input.
As it is well known that below a certain threshold of distortion there is almost no correllation whatsoever between percieved sound quality and conventional single frequency THD test results and with the same holding true for IMD and even multi tone burst testing.
My first question is: How realistic is it for us to expect that any single solitary slew rate parameter would be in any way a better indicator?
Therefore, my second question becomes; not what slew rate should be targetted, but: How do we determine what internal slew rate target should be set for any given internal circuit configuration?
P.S. My thanks to all the contributors of this very interesting thread
Yes, not super hard esp for a 50W amp... 200-300W I think would be better if the SR was higher. The thd numbers which members here have achieved at 20KHz and near full power are pretty amazing results, also. At least in SIM.
I am waiting for built units now to see if they measure even close to SIM... that would change my mind about a lot of things -- especially stability/comp methods. It's all been very good so far. I am not trying to be the judge and jury.... but like others... been down this road before and the dblt road before... lets not mix them in one thread, though.
One of the expressed reasons for investing in a A-Precision 2700 which I added IM is to do multi-tone tests on individual equipment and then on an entire system. First playback and then recording system. I said this was important on JC's place (Lounge) a year ago. Now, when I can get to it... maybe this summer, I'll get to do that. It is closer to reality than a single tone or even 2 or 3 tone test.... you'll see the grass grow a lot on some gear and that is what we hear as we listen to music.
I hope some of you can jump the gun and go directly to such tests to see how a system looks and where the weak links are.
THx-RNMarsh
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