It's not global feedback anymore just local (degeneration). As I said the simplest case is the H-bridge input, it is a VFA the BW goes monotonically down with the amount of global feedback. The gm and Ccomp determine the GBW product at all closed-loop gains (in the simplest case).
Zero cmr? where did that number come from? I dont have zero cmr.
But same question as psr..... how much cmr is needed in a home audio system? How much of a cm condition do you have and what are the many ways to prevent and combat or minimize it?
THx-RNMarsh
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How else should we interpret
? Unless you use some tricks CMRR falls rapidly with an inbalance.
I can count 9 RF sources in my living room. Could probably find more quite happily. If you have a predilection for DC-daylight bandwidth in your amplifiers then EMC/EMI should be high on the list of things to watch for. But for domestic listening 30dB CMRR on the input should kill nasties. The Bill Whitlock THAT chips give 65+dB with a 600Ohm mismatch which I view as very cheap insurance for the signal as it makes its way around.
Other belief systems around interconnects exist 🙂
I'm afraid people retired from the sales force are not what I am looking forward as mentors, not even when it comes to DIY. 🙂
With 8-legs the distinction is obvious. If you have a small signal frequency response test telling the difference between a bipolar H-bridge with a 1K Ohm bridging resistor and a long-tail pair of JFET's biased at 1mS please show me.
No hard feelings at all, the concept has been so muddled about that further discussion has become pointless.
EDIT - Dados' amp bears little or no relationship to a general purpose block we're just talking apples and oranges.
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Back to basics..... has anyone measured CM signals in their systems? What level and what freqs did you find?
I do use fiber optics. I do use isolation transformers. I do use twisted shielded pair. But I dont have an EM issue to begin with. But if others have EM issues in their home systems.... what are they caused by and what did you measure?
THx-RNMarsh
I do use fiber optics. I do use isolation transformers. I do use twisted shielded pair. But I dont have an EM issue to begin with. But if others have EM issues in their home systems.... what are they caused by and what did you measure?
THx-RNMarsh
Yes I think something like that was part of the original joke.
As 42 is the answer to the Final Question about Life, the Universe, and Everything, it should also include a final solution to the CFA and VFA controversy. Once, that is, when we know the question.
I'd hazard the guess that the CFA has less
because there is at least 1 less junction for
the feedback signal to traverse ....
That was the punch line.
As to 42 I am tied up right now but hang on and when I can I will get back to you with the question.
CFA has the chance to be better since local feedback (resistors) is necessary on the input devices.
we do need numbers for the Otala PIM hogwash/debunking arguments
except for the niggling fact that high feedback reduces all errors measured by the input by the excess gain at that frequency
and the high gain also indirectly, but powerfully linearizes the input stage by making the "error V" diff input very small - for balanced diff pairs 3rd order distortion dominates, making the much feared distortion of the diff pair reduce by the square of the excess loop gain
it is possible to have feedback factors of a million to 20 kHz if you use "modern" output devices, advanced compensation - you know the stuff we've had for 30 years now?
with <100 uV diff input V you don't even need local degen for -120 dB distortion from BJT input gm modulation
but local degen, fet input, fast "VFA" amps have proven in hardware to squash "PIM" since Bob's 1982 (AES Conference Proccedings) MOSFET Power Amp CordellAudio.com - A MOSFET Power Amplifier with Error Correction
looks like even removing shoes won't be enough for some of us count that high - just my contributions: http://www.diyaudio.com/forums/search.php?searchid=13328685
except for the niggling fact that high feedback reduces all errors measured by the input by the excess gain at that frequency
and the high gain also indirectly, but powerfully linearizes the input stage by making the "error V" diff input very small - for balanced diff pairs 3rd order distortion dominates, making the much feared distortion of the diff pair reduce by the square of the excess loop gain
it is possible to have feedback factors of a million to 20 kHz if you use "modern" output devices, advanced compensation - you know the stuff we've had for 30 years now?
with <100 uV diff input V you don't even need local degen for -120 dB distortion from BJT input gm modulation
but local degen, fet input, fast "VFA" amps have proven in hardware to squash "PIM" since Bob's 1982 (AES Conference Proccedings) MOSFET Power Amp CordellAudio.com - A MOSFET Power Amplifier with Error Correction
looks like even removing shoes won't be enough for some of us count that high - just my contributions: http://www.diyaudio.com/forums/search.php?searchid=13328685
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