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Old 17th September 2012, 04:28 PM   #1001
bcarso is offline bcarso  United States
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Originally Posted by scott wurcer View Post
The 22K to ground was a nod to those that think 20KHz open-loop BW improves things, what I'm not sure. This should probably be left for listening experiments.
Those interested should also see Putzeys' article in Linear Audio for his take on having more gain at lower frequencies, and its effect on settling time.

It would be interesting to add overload behavior to the repertoire of tests in sim and in reality, including behavior under excessively high slew rate signals.

Virtually all conventional feedback amps (single-ended ones) will overload asymmetrically, the cure for which is making them faster, or bandlimiting ahead. Of course really poor slewing performance may require a lot of bandlimiting! But such performance is easy to avoid. According to Zanfino, Miller determined that Otala selected particularly poor designs to support his arguments about TIM. This does not invalidate the thesis, but it exaggerates a bit.

Once you make the bandwidth flat out to the highest frequencies of interest, does this guarantee equal distortion performance at all in-band signals? No, as there are other mechanisms besides those that the loop gain alleviates. One of the things I like about what linuxguru posts is the inclusion of the 1k resistor in series with the source, which is a reasonable start for what may be feeding the amplifiers. Those who omit any consideration of the source impedance are inviting sweet Spice lies.
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Old 17th September 2012, 04:37 PM   #1002
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Originally Posted by bcarso View Post
Those interested should also see Putzeys' article in Linear Audio for his take on having more gain at lower frequencies, and its effect on settling time.
You know, it depends. This example has no GNFB, and THD below 0.0005% in audioband. I suppose no one would also predict TIM problems
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Old 17th September 2012, 04:41 PM   #1003
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You know, it depends. This example has no GNFB, and THD below 0.0005% in audioband. I suppose no one would also predict TIM problems
When I said conventional feedback amps, I meant conventional feedback amps with global feedback.
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Old 17th September 2012, 05:00 PM   #1004
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Originally Posted by bcarso View Post
Those interested should also see Putzeys' article in Linear Audio for his take on having more gain at lower frequencies, and its effect on settling time.
Putzeys, in a later discussion in the John Curl thread here in DIYAudio, also made the point that the transfer function of the fedback signal differs above and below the open loop pole. Above has additional phase shift, of course, but this is a different transfer function.

Does this matter? And is it even possible to generalize? Dunno.

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Chris
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Old 17th September 2012, 05:03 PM   #1005
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Settling time of GNFB design depends on frequency compensation method used.
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Old 17th September 2012, 05:11 PM   #1006
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Aren't those p-channel FET's?

Thanks,
Chris
Yes, sorry PFET's were the only thing compatible so it's one flavor of each device.
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Old 17th September 2012, 05:21 PM   #1007
bcarso is offline bcarso  United States
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Default Wilson opamp

Hope these don't get Wiley's panties in a bunch, as they say. If so I'll take them down.

The spine is a little the worse for wear, but I've gotten a lot of use out of this book.
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Old 17th September 2012, 05:46 PM   #1008
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Settling time of GNFB design depends on frequency compensation method used.
Also, depends -- if CMF circuit - no Cdom.
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Old 17th September 2012, 06:19 PM   #1009
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Also, depends -- if CMF circuit - no Cdom.
Most of the circuits I've seen have ample junction capacitance to act as such.

Dick you would like the Wilson current mirror Wiki page. Barrie Gilbert and George had an overnight bet on who could make the best current mirror out of only three transistors, and George won.

I find it strange since given the first two there are not many ways to connect a third.
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Last edited by scott wurcer; 17th September 2012 at 06:23 PM.
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Old 17th September 2012, 06:51 PM   #1010
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Those interested should also see Putzeys' article in Linear Audio for his take on having more gain at lower frequencies, and its effect on settling time..
Bruno Putzeys lives here.

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