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Old 26th June 2012, 03:43 PM   #2571
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Originally Posted by Esperado View Post
Listening experience confirm the measurements.
I wanted to add that most of the controversial aguments about CR here where right. And easy to understand why not contradictory when we understand the feedback principles.

Studying that from the early beginning of Analog Devices experiments on CF topologies, my religion, about audio amps and preamp design, can be resumed in a single attempt: "Speed" ;-)

Because the SSA feedback topology is (all along with "Error feedback" topology) the best way to get this speed (an most simple than Error feedback) , and can be applied to most of the power amps schematics: Go for SSA.

And to add that it is interesting to consider that, in my experiment about SSA, we have a fantastic increase of the slew-rate, while we do not change a lot the open loop schematic neither the active parts ;-)
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Last edited by Esperado; 26th June 2012 at 03:54 PM.
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Old 26th June 2012, 04:09 PM   #2572
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Originally Posted by alex mm View Post
...... few minors changes , and you can see the new PCB rev.1.1
It was my plesaure to do this board , but can be layout again if not ok
Alex.
What utilisas program?
for relizar these "PCBs"
EXAMPLE: Eagle, proteus, pcb wizard. What do you use? : Confused:
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Old 26th June 2012, 04:11 PM   #2573
mikelm is offline mikelm  England
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I agree with you about using CF because it is a fast topology and this sounds best but having chosen this topology I think it is best to avoid using too low value resistors in the FB circuit to try to speed things up even further - In my experience the opposite sounds better.

Do others have the same experience ?
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Old 26th June 2012, 04:17 PM   #2574
sonnya is offline sonnya  Denmark
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Okay i am stupid
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Old 26th June 2012, 04:36 PM   #2575
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Originally Posted by alex mm View Post
.... thanks to all for helping me to layout the correct PCB and kinds words , I do my best , learning something all time .....
Alex.
Hi, Alex MM
I just wish the "PCB", without components
to do with the method of the pplancha, "heat transfer"

"Post number 158"
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Old 26th June 2012, 04:52 PM   #2576
mikelm is offline mikelm  England
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Quote:
Originally Posted by Edmond Stuart View Post
Sonnya, Apart from propagation delays of the medium at use (e.g. copper or whatever), the onset of the response isn't delayed. If you keep thinking in terms of delay instead of phase lag, you will never understand why NFB works as it does work.
Sounds like semantics to me. Whatever you choose to call it the voltage rise is delayed so there is a delay - even though it is called current feedback in fact the i/p transistor compares voltages. So if the voltage rise is delayed, there is a delay before the signal gets back to the feedback transistor. - end of story.

Last edited by mikelm; 26th June 2012 at 04:55 PM.
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Old 26th June 2012, 07:13 PM   #2577
MiiB is offline MiiB  Denmark
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less devices less delay... and for current feedback the IP device is the feedback device. That is why the speed increases and why it sounds better... feedback applied this way is simply less intrusive than the typical LTP...where separate devices with different impedance's handles the feedback..
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Old 26th June 2012, 07:29 PM   #2578
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Originally Posted by sonnya View Post
Okay i am stupid
Who said that ?
What you said about delay is true. But the problem does not fully rely on that. First Nyquist law will never let-you run an amplifier with a 180° phase shift if any gain ;-)
Second, delay matters with fast changes in the signal, right ? And delay will bring overshoot Agree ? Slew rate limitation and good compensation avoid that. So the real concern is just final slew rate of your amp and flat response with no overshoot..
Where the delay/phase problem is your is when you are working on poles optimization / harmonization.
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Old 26th June 2012, 08:18 PM   #2579
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Default delay time (or latency) vs phase lag.

Quote:
Originally Posted by mikelm View Post
Sounds like semantics to me. Whatever you choose to call it the voltage rise is delayed so there is a delay - even though it is called current feedback in fact the i/p transistor compares voltages. So if the voltage rise is delayed, there is a delay before the signal gets back to the feedback transistor. - end of story.
A time delay, IOW a latency (caused by long transmission lines or so) is mathematically expressed by: exp(-sT). It delays the arrival of signal at the receiving end by an amount equal to T without altering the amplitude. Thus the onset of the step response is also belayed by T seconds.

OTOH, a phase lag (caused by a LP filter or capacitances of a tranny etc) are expressed by e.g. (1-exp(-sT))/s, which does alter the amplitude, but it does NOT delay the onset of a step response or so.

If you call these crucial differences just semantics, you've missed my point (and fundamentals of FB theory).
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Last edited by Edmond Stuart; 26th June 2012 at 08:20 PM.
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Old 26th June 2012, 08:22 PM   #2580
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Quote:
Originally Posted by MiiB View Post
less devices less delay... and for current feedback the IP device is the feedback device. That is why the speed increases and why it sounds better... feedback applied this way is simply less intrusive than the typical LTP...where separate devices with different impedance's handles the feedback..
Hi MiiB

Exactly, could not tell it better even if I tried.

Regards to all
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