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Unusual amp from 1987
Unusual amp from 1987
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Old 4th August 2020, 04:54 AM   #71
kokoriantz is offline kokoriantz  Lebanon
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Unusual amp from 1987-russsian4-jpg
This measures 0.0006% on Tina but 0.002% on Lt .
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Old 4th August 2020, 02:26 PM   #72
minek123 is online now minek123  United States
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1) This sim is very 'fragile' in the sense that changing one transistor to a different,
reasonable type (E.g Q2/Q11 to KSA992/KSC1845) makes it unstable.
The same goes with other transistors.

2) Another observation: symmetry and DC offset depends on current flowing through R5/R11 (tolerances!).
How DC offset can be set/stabilized in real amp? Would a trimmer be sufficient?

3) I still don't see any difference with or without R13. Same sim results..
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Old 4th August 2020, 02:36 PM   #73
OldDIY is offline OldDIY
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An emitter follower is needed after the LTP.
(brother did in 1990)
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Old 4th August 2020, 11:49 PM   #74
kokoriantz is offline kokoriantz  Lebanon
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The bellow curves are the output impedance with R13 50k & 50M. You can see that the 50k keeps the output impedance to 1m ohm up to above 100khz what ever the input stage response. Here the circuit is not compensated with 20Mhz in closed loop.
The output stage in LT has different distortion than in Tina, I will investigate first the cause, after I deal with compensation. The offset can be resolved by adding a capacitor in series with R2 or a servo.
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Old Yesterday, 01:14 AM   #75
kokoriantz is offline kokoriantz  Lebanon
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Unusual amp from 1987-russian5-jpg
It looks the circuits has better performance when driven in push pull mode.
The idea of OldDiy multiplies the OL gain by the Hfe which is too much, perhaps reverse mounted with Hfe of 10 can work.
Hayk
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Old Yesterday, 06:45 AM   #76
kokoriantz is offline kokoriantz  Lebanon
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Unusual amp from 1987-russian-comp-jpg
This is compensated version.
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File Type: jpg russian comp.JPG (119.4 KB, 76 views)
File Type: jpg stable.JPG (88.3 KB, 17 views)
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Old Yesterday, 11:49 PM   #77
kokoriantz is offline kokoriantz  Lebanon
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Unusual amp from 1987-russianad844-comp-jpg
This is the compensated version of AD844 driven. It measures 0.00003%THD 10khz at 10w.
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File Type: jpg compensated.JPG (78.8 KB, 13 views)
File Type: jpg comp bode.JPG (82.4 KB, 12 views)
File Type: jpg russianad844 comp.JPG (154.5 KB, 50 views)
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File Type: asc russian ad844.asc (6.3 KB, 3 views)

Last edited by kokoriantz; Yesterday at 11:54 PM.
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Old Today, 05:32 PM   #78
minek123 is online now minek123  United States
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Hi Hayk, will play with this when my Internet service is back.
I'm down for over 2 days now, due to that stupid 'tropical storm'...
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