Electronics > Beginners
AB-class amplifier schematic analysis & optimization
David Hess:
--- Quote from: magic on May 25, 2019, 08:55:29 am ---Say that I swapped a few paralleled NE5532 into one of those LM7171 amplifiers of yours, would you tell it apart?
--- End quote ---
I could; the LM7171 will produce noticeably more hiss because of its greater input noise. This might not be noticed in a noisy environment however.
magic:
I will add an LM7171 amplifying its own noise and mix it with the input signal, just for you :P
David Hess:
--- Quote from: magic on May 25, 2019, 11:34:43 pm ---I will add an LM7171 amplifying its own noise and mix it with the input signal, just for you :P
--- End quote ---
The noise (hiss) only bothers me (becomes noticeable) with no input signal.
Another configuration is to use the low noise audio operational amplifier, NE5532 or whatever, to drive the LM7171 which acts as the high current output stage. Now the LM7171 can operate at lower gain and its noise is suppressed by the excess gain of the NE5532's feedback loop.
The noise of an LM317 regulator can be suppressed using the same type of circuit.
Yansi:
317 is quite low noise by itself. Doubt it will have any major contribution to the amp output noise.
Zero999:
--- Quote from: David Hess on May 25, 2019, 10:52:36 pm ---
--- Quote from: magic on May 25, 2019, 08:55:29 am ---Say that I swapped a few paralleled NE5532 into one of those LM7171 amplifiers of yours, would you tell it apart?
--- End quote ---
I could; the LM7171 will produce noticeably more hiss because of its greater input noise. This might not be noticed in a noisy environment however.
--- End quote ---
With a gain of 23? Possibly if you have some very sensitive earbuds.
In all fairness the proponent for the LM7171, as a headphone amplifier, didn't give any details regarding their design i.e. the gain.
The LME49720 seems like a good candidate for a headphone amplifier, but has a relatively high input current noise, so will only be any good, if the source impedance is low. It also has a large enough bandwidth to cause problems, if insufficient care paid to the layout.
http://www.ti.com/lit/ds/symlink/lme49720.pdf
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