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Old 23rd June 2013, 07:18 AM   #1
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Default whats worng with this circut

i am try to simulate it and it dosn't work at all
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Old 23rd June 2013, 07:24 AM   #2
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The non inverting opamp input needs biasing to the "midpoint" voltage.
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Old 23rd June 2013, 07:27 AM   #3
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There are some other problems too. The midpoint voltage (junction of the 100K's) need to be at a low impedance to AC which means adding a cap across R2, in practice something like 10uf)

Why not set your simulation to have a mid point voltage created by using another voltage source rather than two resistors. That takes the time constant of the cap out of the simulation.
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Old 23rd June 2013, 07:33 AM   #4
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Like this,
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Old 23rd June 2013, 07:46 AM   #5
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not working the output is steady line
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Old 23rd June 2013, 07:50 AM   #6
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Remove the voltage divider network formed by the two 100K resistors (posters ORIGINAL circuit) from the bottom of R1 and relace with an earth . Place the 100K voltage divider network at the + input after Cin to set the midpoint and bias the + input then the notes still hold good .
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Old 23rd June 2013, 07:56 AM   #7
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i quit
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Old 23rd June 2013, 08:05 AM   #8
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Dont you need to have an earth connection at the oscillator to generate the signal across the input to the amp .
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Old 23rd June 2013, 08:13 AM   #9
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The circuit in post #5 looks correct although 5 volts is to low for a TL074
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Old 23rd June 2013, 08:21 AM   #10
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It definitely works. Just tried it in Spice.
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