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New Bryston input stage measurable distortion < 0.001% (Audio Advisor)
New Bryston input stage measurable distortion < 0.001% (Audio Advisor)
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Old 26th March 2016, 01:10 AM   #11
bcarso is offline bcarso  United States
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The oddest part for me at first glance: why on earth does he return the input PNP collectors to the current source? Real CFPs will have the collector go to the emitter of the input device.

I threw this into sim with 100 ohm emitter Rs and 1k base-emitter R in the PNPs. 5mA tail current. I loaded the output of the mirror etc. with 10k to 25V and used a 30V positive rail. 0.392% with 10kHz to 9th harmonic.

With the more conventional CFP connection this drops to 379ppm, after adjusting the input drives to produce the same output voltages.
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Old 26th March 2016, 01:16 AM   #12
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by bcarso View Post
The oddest part for me at first glance: why on earth does he return the input PNP collectors to the current source?
Fine scale stability issues? All I know this has prior art back to at least 1968
(Barry Blesser's "super" transistor).
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Old 26th March 2016, 01:24 AM   #13
StephenR is offline StephenR  United States
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Anyone actually read the patent? there must be some tricks how he adjust the tail current, R6 and R7 for optimal value. I don't think you can just put in values and get the result.

Again, I am not at all defending the guy. I am just more curious than anything else and I am too lazy to do the work.
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Old 26th March 2016, 01:26 AM   #14
bcarso is offline bcarso  United States
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Originally Posted by scott wurcer View Post
Fine scale stability issues? All I know this has prior art back to at least 1968
(Barry Blesser's "super" transistor).
I don't see any hint of peaking or other anomalies in either the patent case or the more conventional (and indeed very old) differential CFP case.

The second stage is also odd with a similar departure from CFP. Maybe there is some sort of complementarity when the second stage is considered, although that sort of thing is only likely to be manipulable to reduce even order.

Puzzling and still pretty much anything but news. I guess we have to be reminded periodically of the broken patent system.
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Old 26th March 2016, 01:28 AM   #15
bcarso is offline bcarso  United States
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Anyone actually read the patent?
I skimmed through it, particularly the figures. As I remarked the approach to phase compensation is of some interest, although I suspect not really novel.
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Old 26th March 2016, 02:04 AM   #16
keantoken is offline keantoken  United States
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The transimpedance nonlinearity of the input stage is insignificant compared to the harmonics it absorbs from the VAS, because it only drives a few uA or so of current. Having the CFP collectors on the other side of the degeneration increases LTP gain (in theory) and thus total feedback.

BTW, the schematics in the patent are in fact LTspice simulations, complete with flawed simulator models, so the stability compensation values in the schematics are likely a far away dream. It's not stable when good models are used.
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Old 26th March 2016, 02:06 AM   #17
bcarso is offline bcarso  United States
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Yeah the more I read this patent the less appropriate referring to the circuit in places as a CFP is.

And I didn't see yet any helpful hints for setting resistor values. when I made some factor-of-two changes in sim it didn't matter much.
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Old 26th March 2016, 02:08 AM   #18
bcarso is offline bcarso  United States
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The transimpedance nonlinearity of the input stage is insignificant compared to the harmonics it absorbs from the VAS, because it only drives a few uA or so of current.
Yes, agree that the input stage nonlinearity in an overall amplifier is a relatively small effect. It would be mildly interesting to know what they told the AA blurbista.
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Old 26th March 2016, 02:27 AM   #19
keantoken is offline keantoken  United States
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Page 18 is the output stage. It has gain and it's own feedback loop.
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Old 26th March 2016, 02:36 AM   #20
AKSA is offline AKSA  Australia
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I used pretty much the same regime in my Lifeforce 100 in 2006. It was very linear and I achieved very low distortion with only 15dB of global feedback.
I'm with the skeptics; it is based on the Sziklai overlay on a LTP, difficult to argue it was not done years ago.
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