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Old 1st November 2013, 05:54 PM   #1
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Default DC servo for Sijosae Buffer

I want to build a buffer only without the gainstage but when i try with the sijosae buffer, i got about 200mV dc offset. Can someone suggest me a dc servo schematic to build . Here is the Sijosae Buffer:
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Old 1st November 2013, 06:25 PM   #2
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Here is a basic servo.
You will also need some resistance
to isolate the servo from whatever
is feeding the buffer.
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Old 1st November 2013, 06:33 PM   #3
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Quote:
Originally Posted by Avro Arrow View Post
Here is a basic servo.
You will also need some resistance
to isolate the servo from whatever
is feeding the buffer.
That mean i need to add some resistance to the output of the servo to the input of opamp? How about 10k? I see C1 and C2 is 10uf, is this value too high? I often see 0.47-1uF in other servo?
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Old 1st November 2013, 06:50 PM   #4
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Like this:
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Old 1st November 2013, 06:57 PM   #5
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R1/C1 and R2/C2 form low pass filters.
You want the F3 to be as low as practicle.
Too low though, and the time constant gets
too long.

1 meg and 1uF would yield the same time constant as 100k and 10uF.
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Old 1st November 2013, 07:01 PM   #6
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R3/R4 set the servos authority.
Less authority means less effect on the
incoming signal.
With 1k and 10k the authority is 10 to 1.
For every 1 volt of offset at the source,
you need 10 volts from the servo.
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