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Old 4th March 2012, 10:50 PM   #1
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Default Op Amp

I was fooling around with Tina over the last couple of days after downloading some spice models for vacuum tubes. I got the 12AX7 and 12AU7. So, I came up with a little op amp. Distortion is 0.0003% @ 1kHz, 1Vp-p input. I'm sure this is probably already old, but playing around with Tina is fun.
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Old 4th March 2012, 11:47 PM   #2
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WAY too much "sand". Google Philbrick opamp.
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Old 5th March 2012, 12:50 AM   #3
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Originally Posted by Eli Duttman View Post
WAY too much "sand". Google Philbrick opamp.
Thanks!

I think mine is better...
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Old 5th March 2012, 04:05 AM   #4
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Originally Posted by dirkwright View Post
Thanks!

I think mine is better...
Except yours is AC coupled and cannot operate to DC like the Philbrick.

G
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Old 5th March 2012, 12:33 PM   #5
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Except yours is AC coupled and cannot operate to DC like the Philbrick.

G
I was joking! Horses for courses.

But yes, of course. He had to have DC response for his application. We don't need that. Response down to 1Hz is fine in my opinion.
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Old 5th March 2012, 02:47 PM   #6
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I tried replacing the CRD's with a 12AX7 CCS but the performance was worse. I'm not aware of being able to make a current mirror with vacuum tubes.
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Old 5th March 2012, 03:50 PM   #7
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This has small gain but is dc-coupled.

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Old 5th March 2012, 06:35 PM   #8
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Originally Posted by artosalo View Post
This has small gain but is dc-coupled.

Click the image to open in full size.
Yeah, he's throwing away gain with the voltage divider between the differential amp and the output stage. I haven't modeled this one yet. Thanks!
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Old 5th March 2012, 07:23 PM   #9
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Mirror mirror...

R5 and R13 could (should?) be CCS, got lazy drawing this up
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Old 5th March 2012, 07:56 PM   #10
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he's throwing away gain with the voltage divider between the differential amp and the output stage.
This was simplest way to level the output to zero DC-volts ( when input is zero too).
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