F5 power amplifier

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#4,421
bobodioulasso said:
Hi Nelson,
We were not saying that the F5 is a current feedback amp but discussing about the benefits of such an amp (CFB) driving ESL speakers.
Click to expand...

Sure knows that
But sound sounds more like you are not listening 😉
Me? I must admit I dont know what it means
Anyway, does F5 use feedback
I thought it didnt
 
#4,422
Thought I better read a bit 🙄
Low impedance feedback it seem to be:clown:
And says that its often wrongly named as current feedback

If I understand what Nelson says, we should not take it for a given fact whenever current feedback is mentioned, that it may not be that at all
I guess current feedback just sounds more fancy for marketing
 
#4,423
In the example from JM plantefeve the 0.25ohm resistor serial connected with the speaker develops across itself a voltage which is an image of the current flowing through the speaker. The junction point of this resistor to the speaker is returned to the inverting input of the amp through a 100 ohm resistor. This is current feedback.
 
#4,424
bobodioulasso said:
In the example from JM plantefeve the 0.25ohm resistor serial connected with the speaker develops across itself a voltage which is an image of the current flowing through the speaker. The junction point of this resistor to the speaker is returned to the inverting input of the amp through a 100 ohm resistor. This is current feedback.
Click to expand...


It is quite interesting design. And, looks like a non-inverting current feedback, doesn't it . . . :scratch:

🙂
 
#4,425
I have read somewhere that current feedback amps are less sensitive to cables and difficult loads
Is this true?
And is true current feedback really only a matter of a resistor?
I thought it was way more complicated
And also that current feedback introduce some complications, that may be less desired, despite its other theoretical advantages

So, what are the pros and cons?


Ahhh, now I know
I just realised that my very sweet Mirand amps are really current feedback design, which might explain a lot
 
#4,426
tinitus said:


... also that current feedback introduce some complications, that may be less desired, despite its other theoretical advantages

So, what are the pros and cons?
Click to expand...


A difference between voltage feedback and current feedback amps is:

  • Voltage feedback amp produces a low output impedance.
  • Current feedback amp produces a high output impedance.

Whenever the feedback voltage is proposional to output current, the circuit has current feedback.

In op amps, the non-inverting current feedback amp is called a "transconductance amplifier", and also called a "voltage-to-current converter" because an input voltage controls an output current.

🙂
 
#4,427
Babowana said:



[*]Current feedback amp produces a high output impedance.
[/list]
Click to expand...

Though I dont understand much of your informative post, I have looked at specs on my current feedback amps

output impedance doesnt seem high

at 20khz - 22mohm
at 10khz - 10mohm
at 1khz - 2mohm

Man please, its not to make it hard on you 😱
 
#4,431
Just received an Email from John @ Antek Inc. transformers.
He is still offering the DiyAudio GB of a 18v x 18v 400VA transformers........
TaTaTaTaTaDa $47.70 shipped to USA.

Thanks Mongo! for setting that up for us!
Yeah, I know, "Mongo just pawn in game of life". Well thanks pawn.

Ron
 
#4,433
Babowana said:
A difference between voltage feedback and current feedback amps is:

  • Voltage feedback amp produces a low output impedance.
  • Current feedback amp produces a high output impedance.

Whenever the feedback voltage is proposional to output current, the circuit has current feedback.
Click to expand...
Seems you mix up things:
http://en.wikipedia.org/wiki/Current-feedback_operational_amplifier

Point is, there is a difference between current feedback and current output, you are referring to the latter. Both have nothing to do with each other, you can make either current feedback or voltage feedback topologies to produce either current output or voltage output (or anything in between).

- Klaus
 
#4,434
Hi Klaus,

Let's think about a non-inverting feedback op amp.
When we give an input voltage to the noninverting input, we arrange noninverting feedback voltage to the inverting input.

When we get the feedback voltage from the output voltage-sampling, we call it a "noninverting voltage feedback". Meanwhile, when we get the feedback voltage from the output current-sampling, we call it a "noninverting current feedback".

So,
  • Noninverting voltage feedback: input voltage -> output voltage -> output voltage sampling (voltage feedback system) -> feedback voltage
  • Noninverting current feedback: input voltage -> output current -> output current sampling (current feedback system) -> feedback voltage
Isn't it?

🙂
 
#4,435
Do you see the difference?


🙂
 

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#4,436
A short drawing is better than a lon speach!
I see now why you call it: "non inverting...."
Mixed feedback can be nice when driving wideband high efficiency speakers or simply very light cones speakers which do not like high damping.
It permits to adapt precisely the amplifier output to the speaker.
 
#4,438
Babowana said:
When we get the feedback voltage from the output voltage-sampling, we call it a "noninverting voltage feedback". Meanwhile, when we get the feedback voltage from the output current-sampling, we call it a "noninverting current feedback".
Click to expand...
I perfectly see you point and all what you say (+ the drawing) is valid from the phenomenical standpoint, except that you chose to personally redefine the commonly accepted term in engineering that "current/voltage feedback" stands for. This only adds to confusion, especially for less experienced readers.

- Klaus
 
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