Abomination! or Painting a Mustache on the Mona Lisa meets the Island of Dr. Moreau - Page 18 - diyAudio
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Old 29th December 2008, 10:56 PM   #171
AndrewT is offline AndrewT  Scotland
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Hi,
yes, post141 schematic is the one where both C4 & C6 are shown and you discuss the offset problem if C4 is omitted. Mixed AC & DC coupling with the unmatched resistances explains all.
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Old 30th December 2008, 01:07 AM   #172
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Quote:
Originally posted by AndrewT
Hi,
yes, post141 schematic is the one where both C4 & C6 are shown and you discuss the offset problem if C4 is omitted. Mixed AC & DC coupling with the unmatched resistances explains all.
Well Andrew, you motivated me to try again.
My fatal flaw the first time was running all of the simulations with the input unconnected.


Another rookie mistake. With the input grounded or connected to a signal, I have the offset down to 50mV range and with your suggested change to R15 (from 2.2K to 500R), 6-7mV.
Another lesson learned.
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Old 31st December 2008, 04:34 AM   #173
KLe is offline KLe  Australia
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Happy New Year everybody
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Old 31st December 2008, 12:02 PM   #174
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Default Abominable results for BAIN!

Happy New Year to you also KL!

I became restless last night and played around with this for a while:

Click the image to open in full size.

Many changes and if I'm not mistaken, slightly better performance than Abomination. More simulated testing is needed though.
Please look it over for obvious bone-headed mistakes.
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Old 31st December 2008, 12:14 PM   #175
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It looks like "proper" CCS's are popping up everywhere..
(reproducing) ...And hey ...a buffered widlar CM
(betcha it gets 70-80 db gain now)
and a CFP input . Whoaaa...
Happy New Year (NY) ...I used to live there
OS

Edit: U5 and U1 emitters need a 33R across them.. then you will
have a"leach" OP..
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Old 31st December 2008, 12:17 PM   #176
atiq19 is offline atiq19  United Kingdom
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any reason for not using thermal trak? tripple emitter follower instead of CFP?


HAPPY NEW YEAR 2009!
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Old 31st December 2008, 12:27 PM   #177
atiq19 is offline atiq19  United Kingdom
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in the spirit of new year,

how about bob cordell thermal-trak bias spreader and T-output? u need to modify the upper and lower CCS for VAS connection.

you could add mosfet flavour by swapping bjt driver over with low Ciss MOSFET.


keep up the good art works..


cheers.
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Old 31st December 2008, 12:31 PM   #178
atiq19 is offline atiq19  United Kingdom
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Mr Cordell's output stage

does not suffer from any (?) influence of VAS stage...
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Old 31st December 2008, 12:36 PM   #179
atiq19 is offline atiq19  United Kingdom
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Default Re post 174

Despite the fact that the amp is absolutely stable in simulator, I would still like to have a small phase lead compensation cap (1-3pf) from collector of VAS to fb loop.....
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Old 31st December 2008, 12:38 PM   #180
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Quote:
Originally posted by ostripper
It looks like "proper" CCS's are popping up everywhere..
(reproducing) ...And hey ...a buffered widlar CM
(betcha it gets 70-80 db gain now)
and a CFP input . Whoaaa...

Hi OS,
In for a penny, in for a pound...may as well go whole hog and throw more transistors at it. The ones that stick improve the design!

Just ignorantly playing around last night, so I may have some more work to do.

The CFP input was in the last version of this, several posts ago. I haven't examined the gain yet, but here's the simulated PSR. Better, by a long shot, than Abomination:

Click the image to open in full size.


Happy New Year!
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