Would you kindly elaborate a little bit?
Phase shift depends on frequency, we can hardly say that it is a "small error". For a complex system, phase response is pretty wild, and, what is worse, it is a nonlinear function.
Phase shift depends on frequency, we can hardly say that it is a "small error". For a complex system, phase response is pretty wild, and, what is worse, it is a nonlinear function.
PMA said:
Hi PMA,
Can you elaborate on the chart a little bit? It looks like you are driving a 741 op amp into slew rate limiting, am I correct?
PMA said:
PMA, note that we must be careful about how we use the word "non-linear" in regard to phase shift.
If the phase shift is nonlinear as a function of frequency, this a form of time delay distortion that does not cause new harmonics or IM products to be formed. It can result from a conventional linear passive circuit.
Note also that a small amount of phase shift from an LPF pole or two is a fairly good approximation to a fixed time delay at frequencies well below the pole frequency.
Finally, when phase shift is a function of signal amplitude, this is classic non-linear distortion that will result in the production of IM products. This is what has been called "Phase Intermodulation distortion" (PIM). It will produce IM sidebands in the CCIF IM tests, but the phase relationship between the upper and lower IM sidebands will be different than for a similar amount of Amplitude Intermodulation Distortion" (AIM).
Cheers,
Bob
Bob Cordell said:
No. Only the the highest amplitude is just at the edge of SR limit (0.5V/us). But, the phase shift depends on amplitude even below SR limit, exactly as expected.
Bob,
we had the amplifier not smooth step response issue, several posts ago. I did answer your questions 😉
we had the amplifier not smooth step response issue, several posts ago. I did answer your questions 😉
There's not a whole lot of difference between emitter degeneration vs. feedback off the collector. The collector signal is voltage amplified, includes more distortion, and has phase shift.
Trying to look at G NFB, isolating the differences, I come up with phase as a possibility.
I know, I know, phase is inaudible.
But something is being heard.
What if that slight phase shift is audible mixed with the original, as in NFB is audible?
It would seem to be testable in a circuit.
Trying to look at G NFB, isolating the differences, I come up with phase as a possibility.
I know, I know, phase is inaudible.
But something is being heard.
What if that slight phase shift is audible mixed with the original, as in NFB is audible?
It would seem to be testable in a circuit.
darkfenriz said:
Potentially you say "period doubling" which is a phenomenon
well known to chaos theory, which deals with non-linear
dynamics. I have looked for it a number of times in feedback
circuits, but it is quite elusive.
This phenomena can be easily found in Netzer preamp - discrete input differential stage, outputs of which are connected to the inputs of opamp.
google: subharmonic oscillation -pwm
(addthe -pwm because pwm/switching power supply control circuits do this too and the results drown out those directly applicable to linear feedback amps)
(addthe -pwm because pwm/switching power supply control circuits do this too and the results drown out those directly applicable to linear feedback amps)
Nelson Pass said:
Actually I was also suspecting flip-flop like behaviour, because the phenomenon was purely deterministic and repeatable, could be non-linear dynamics of course, the circuit was strange and wicked (although simple).
Bob Cordell said:
Did you ever see the paper where Paul Klipsh showed the PM of brand B--- vs brand K speakers?
darkfenriz said:
As described in chaos theory, this is repeatable and deterministic
- assuming that it really is period doubling.
Choice of small-value capacitors
Virtually all amplifiers using negative feedback employ one or more small-value capacitors in the compensation network, and often elsewhere as well. We're talking capacitances that often are in the range of 5pF to 100 pF.
We all know that it is important to pick good-quality passive components. The quality of the capacitor chosen for use in Miller compensation, for example, can be quite influential.
I'm interested to know what types of capacitors people are using in these small-value locations in power amplifiers and what their experience has been.
Thanks,
Bob
Virtually all amplifiers using negative feedback employ one or more small-value capacitors in the compensation network, and often elsewhere as well. We're talking capacitances that often are in the range of 5pF to 100 pF.
We all know that it is important to pick good-quality passive components. The quality of the capacitor chosen for use in Miller compensation, for example, can be quite influential.
I'm interested to know what types of capacitors people are using in these small-value locations in power amplifiers and what their experience has been.
Thanks,
Bob
Re: Choice of small-value capacitors
Currently I'm not using compensation capacitors, but when I need
something in low values I twist two strands of teflon insulated
wire-wrap wire together. It's very handy, as you can trim the value
down with a pair of snips as you test.
😎
Bob Cordell said:
Currently I'm not using compensation capacitors, but when I need
something in low values I twist two strands of teflon insulated
wire-wrap wire together. It's very handy, as you can trim the value
down with a pair of snips as you test.
😎
Re: Choice of small-value capacitors
Until now, I have used ceramics.
Simply because of I can easily find and buy such in my country.
Ceramics NP0 quality are also cheap.
For my next amplifier project, seems I would have to rethink!
MICA or better may be what we should go for ...
Thanks Bob 🙂
for bringing Compensation / Network caps Quality into our focus.
==============================================
Professor Leach, who I trust very much in audio amplifier matters
uses this for his The Leach 'LOW TIM' Amplifier. ( Low Inter Modulation Distortion ( 60Hz/4kHz test )
C8 - is in the Global Negative Feedback.
C9 - is the Feedback from Driver stage
C10, 11 - are VAS Base Collector (miller) caps, across 2N3440 / 2N5415
http://users.ece.gatech.edu/~mleach/lowtim/part3.html
http://users.ece.gatech.edu/~mleach/lowtim/parts.html
Regards 🙂
lineup
http://lineupaudio.freehostia.com/
🙂Bob Cordell said:
Until now, I have used ceramics.
Simply because of I can easily find and buy such in my country.
Ceramics NP0 quality are also cheap.
For my next amplifier project, seems I would have to rethink!
MICA or better may be what we should go for ...
Thanks Bob 🙂
for bringing Compensation / Network caps Quality into our focus.
==============================================
Professor Leach, who I trust very much in audio amplifier matters
uses this for his The Leach 'LOW TIM' Amplifier. ( Low Inter Modulation Distortion ( 60Hz/4kHz test )
C8 - is in the Global Negative Feedback.
C9 - is the Feedback from Driver stage
C10, 11 - are VAS Base Collector (miller) caps, across 2N3440 / 2N5415
Web References:
http://users.ece.gatech.edu/~mleach/lowtim/part3.html
http://users.ece.gatech.edu/~mleach/lowtim/parts.html
Regards 🙂
lineup
http://lineupaudio.freehostia.com/
Re: Re: Choice of small-value capacitors
Neat idea! It brings back memories of when I was in high school using a similar technique to trim some FM IF circuits. I think we also used short lengths of 300-ohm twin lead in some cases.
Thanks,
Bob
Nelson Pass said:
Neat idea! It brings back memories of when I was in high school using a similar technique to trim some FM IF circuits. I think we also used short lengths of 300-ohm twin lead in some cases.
Thanks,
Bob
Re: Re: Choice of small-value capacitors
I have always used silvered micas, but they have gotten very expensive - on the order of $1 to $1.50 each.
Thanks,
Bob
lineup said:
I have always used silvered micas, but they have gotten very expensive - on the order of $1 to $1.50 each.
Thanks,
Bob