Aleksander Burd - the website of analog electronics
PRIVATE RESEARCH ON DISTORTION TIM
28-06-2022
The topic came from the discussion on the "Alek analogowy" - my channel on YouTube (for now, unfortunately only in Polish).
To investigate the effect of distortion caused by Slew-Rate (SR) I designed a special "research" amplifier.
The amplifier has been designed to reproduce the typical structure of
an acoustic power amplifier. That is, the circuit consists of three
common stages:
1) Error amplifier. Here I used a differential amplifier with the so-called dynamic load, i.e. a current mirror.
2) Classic control stage in a common emitter configuration.
3) The output stage in the form of a classical complementary pair.
The power of the amplifier does not exceed 5W, but
the point here was not to obtain high power (the structure would
potentially allow for a power of 15..20W), but to study the influence
of SR on the listening experience.
The error amplifier has been specially adapted so
that it is possible to consciously induce the Slew-Rate. SR can be
changed smoothly thanks to a specially constructed additional module.
Today (06/28/2022) I am publishing the first
research results. At this stage, I haven't used the SR adjustment
module yet, but I was adding and disconnecting the capacitance that
"turned on" and "turned off" the SR.
Below you can find files that were made after
passing through the amplifier the same test recording, created using
synthesizers especially for these needs (the author is Darek - thanks,
Darek!).
1) The file "1648-clear.wav" is the passage of the test recording through the amplifier without any distortions.
2) The file "1648-clipp.wav" is the passage of the test recording through the amplifier with slight clipping.
3) The file "1648-sr100nf.wav",
this is the passage of the test recording through the amplifier with
added Sew-Rate (SR capacity is 100nF). There is no cliping.
4) The file "1648-sr100nf&clipp.wav"
is the passage of the test recording through the amplifier with SR
turned on (again 100nF capacitance) and with clipping simultaneously.
Additionally - oscillograms
showing how the amplifier and its negative feedback loop work. The blue
trace is the output signal and the yellow trace is the error amplifier
output. If the feedback loop "pops out" of normal operation, the error
amplifier output (yellow) increases noticeably.
Provisional conclusion - but please note that this is just my personal and definitely provisional conclusion:
1) my ear can handle slight distortion (although I can hear it)
2) I don't hear anything special (at least on this recording) after adding Slew-Rate,
3) most important: only the occurrence of both phenomena at once is very unpleasant for the ear!
