Pros and Cons of current feedback amplifier. - Page 14 - diyAudio
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Old 20th March 2013, 12:15 AM   #131
Bonsai is offline Bonsai  Taiwan
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Agree - regulator can make an important difference. Both my VFA e-Amp (active ripple eaters in the rail) and my CFA sx and nx-Amps use heavy filtering in the rails. For the ripple eaters, you can kill both the LF and HF gunk. The simple RC filters get rid of the HF stuff - there's scope pics of both in the articles on my website.
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Old 20th March 2013, 12:29 AM   #132
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Quote:
Originally Posted by jcx View Post
"CFA" can be more linear at large diff Vin - in the extreme they can operate Class AB where long tailled pair would saturate

at very low level diff input V, corresponding to high loop gain, the input stage differences are more in implementation detail - not fundamental topology - everything becomes more linear with less signal
but the practical advantage of matching like type semi's may favor diff pair over complementary inputs
JCX,

Thanks I understand what you are saying, for purposes of this thread I was trying to dig deeper into differences between CFA and VFA.

The same question phrased somewhat differently, would the low frequency distortion of a CFA change (input stage distortion only) if the feedback impedance was lowered (same ratio and again ideal components) ?

Indeed the CFA would have much less distortion as it enters AB operation compared to an LTP clipping. At least for audio purposes I would think both of these extremes would be avoided and hence the inapplicability of the CFA slew rate characteristic.

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-Antonio

Last edited by magnoman; 20th March 2013 at 12:30 AM. Reason: Clarity
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Old 21st March 2013, 10:43 PM   #133
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Originally Posted by Bonsai View Post
Interesting how distortion (and noise for that matter) must blindly be as low as possible, yet slew rate and bandwidth only need to be 'enough'

Fascinating, isn't it?
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Old 21st March 2013, 10:55 PM   #134
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Quote:
Originally Posted by Bonsai View Post
Interesting how distortion (and noise for that matter) must blindly be as low as possible, yet slew rate and bandwidth only need to be 'enough'

Deaf guys rely on THD screen to be sure the amp is OK, others listen and are bothered if PRAT is not OK. Fascinating, isn't it?
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Old 21st March 2013, 11:00 PM   #135
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Superlative nonsense.
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Old 22nd March 2013, 02:34 AM   #136
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Quote:
Originally Posted by michaelkiwanuka View Post
Just why would you want more bandwidth or slew than you need?
Mikeks,

Same can be said for ultra low distortion also....
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Old 22nd March 2013, 02:36 AM   #137
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Quote:
Originally Posted by Lazy Cat View Post
Deaf guys rely on THD screen to be sure the amp is OK, others listen and are bothered if PRAT is not OK. Fascinating, isn't it?
THD specs on paper are more fascinating for some people....
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Old 22nd March 2013, 05:04 AM   #138
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Bonsai View Post
I am surprised you are so anti CFA Wahab. At least, they are symmetrical!

Ignore that false claims on both VFA and CFA sides and think about the additional scope you have in your design arsenal!
Yes , they are symmetrical , but not enough for my taste....

I m not anti CFA but rather against extraordinary claims.
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Old 26th July 2013, 05:44 PM   #139
lsheng is offline lsheng  United States
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Default VFA can also be considered as CFA but with a follower buffer

CFA is more direct feedback, just one transistor to realize the comparison of error signal. VFA is actually using a buffered copy of feedback to compare it with original signal. But VFA is more symetric, because the original and the feedback path is the same, even it is not required for amplification.

There are many circuit realizations, some even with both inputs buffered with follower(like LM3886). I like simple realization whereever posible. Simpler circuit mostly will have the wider bandwidth, if properly designed, have no worse linearity. Best of all, it can be more throughly understood. IC is usually more complicated to suit for cirtain specifications, they mostly have lots of sacifices made to make them safer to use, thus their performance are not at their best, otherwise their should be even better.


Quote:
Originally Posted by Lazy Cat View Post
Think it's important to present here the info from the other thread where "blameless" fans are gathered, blindfolded to the other's opinions. Again my statement follows: current feedback amplifiers outruns VFA in all parameters important for audio signals amplifying. This statement is based on years of experiences, testing and listening ready made amps from known producers as well as from all kind of DIY amps made from both topologies. Attached three steps describing what VFB actually is - to some "upgraded" current feedback circuit, while logical thinking will lead you to use wire only (fig1.) instead of nonlinear part (fig2.) if you pursuit an audio quality in power amplifiers. Case closed.
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Old 27th July 2013, 10:00 PM   #140
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