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Old 25th June 2012, 11:09 PM   #1051
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The BC560C VAS needs no more than say 1V Vce, you could probably get away with less.
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Old 27th June 2012, 04:44 AM   #1052
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VAS, which VAS? As-if it were nailed down to one location.
The one that pulls up against constant current for half the cycle
Or the entirely other one that pulls down against constant current
in the opposing half cycle?

If the common mode loop is disabled, you have no less than five
transistors that could be VAS Q 5,6,7,8,16...

Last edited by kenpeter; 27th June 2012 at 04:47 AM.
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Old 27th June 2012, 05:08 AM   #1053
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I described it as the "BC560C" VAS... And I was referring to the cascode voltage.
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Old 27th June 2012, 03:09 PM   #1054
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I havn't seen a schematic of this thread with BC560, at least not lately.
Also havn't seen where I can pinpoint a solitary VAS. Cascode voltage
could mean anything outside the context of a specific schematic and
reference designator that you have neglected to reference.

It certainly makes no sense in the default context of the most recently
posted schematic #1049. Please post your current schematic or link to
past required to make sense of your statement.

Last edited by kenpeter; 27th June 2012 at 03:16 PM.
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Old 27th June 2012, 03:40 PM   #1055
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Quote:
Originally Posted by kenpeter View Post
The output cannot swing very low with that cascode in the way. Have you considered the existing negative rail for cascode base? You would have to provide an extra negative rail for circlophony. But it needn't be anything elaborate since the common mode is
strongly controlled by quadrature anyway, a 5v wart might do.
I don't know what it means without seeing the difference between two options. Could you post a schematic, so I could see?
Quote:
Originally Posted by kenpeter View Post
I havn't seen a schematic of this thread with BC560, at least not lately.
That is doable. See attachment.
Attached Images
File Type: gif CircloBuffCascode.gif (32.8 KB, 337 views)
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Old 28th June 2012, 06:17 AM   #1056
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I love the way you use BC560 as both an NPN and PNP.

Last edited by kenpeter; 28th June 2012 at 06:23 AM.
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Old 28th June 2012, 06:39 PM   #1057
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Quote:
Originally Posted by kenpeter View Post
I love the way you use BC560 as both an NPN and PNP.
That was a fluke. Hopefully someone would use BC550 when it comes time for the NPN. Point taken--BC560 vas did look a bit odd. So, anyway. . .
Quote:
Originally Posted by kenpeter
The output cannot swing very low with that cascode in the way. Have you considered the existing negative rail for cascode base? You would have to provide an extra negative rail for circlophony. But it needn't be anything elaborate since the common mode is strongly controlled by quadrature anyway, a 5v wart might do.
How is your demonstration schematic coming along to explain that extra negative rail to fix the cascode? I just can't quite imagine it from the words, but a schematic or even a sketch would be great.
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Last edited by danielwritesbac; 28th June 2012 at 06:54 PM.
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Old 28th June 2012, 09:11 PM   #1058
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Actually, using PNP for Q3 and Q4 is an interesting idea. This would reverse frontend and servo phase, making it an involving change.
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Old 30th June 2012, 07:57 AM   #1059
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Quote:
Originally Posted by keantoken View Post
Actually, using PNP for Q3 and Q4 is an interesting idea. This would reverse frontend and servo phase, making it an involving change.
I tested the idea. It seems to work, but with a THD figure approximately doubled, which is consistent with the degeneration of 4 junction resistances in the VAS, compared to two in the regular Circlophone.
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File Type: jpg CirCas.jpg (177.8 KB, 266 views)
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Old 30th June 2012, 08:26 AM   #1060
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But, now there is indefinite drive available from the VAS. An important difference WRT harmonics. Furthermore, the increase in distortion could be compensated by doubling R4 and R12 in your schematic.

It's interesting anyways.
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