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Old 5th February 2010, 04:10 AM   #1
jdubs is offline jdubs  United States
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Default LM3875 gainclone gain in dB?

Guys, how much gain one of Brian Bell's LM3875 kits has? I haven't heard back from him and wanted to check in here to see if anyone knew offhand.

Thanks all,
Jim
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Old 5th February 2010, 05:46 AM   #2
ratza is offline ratza  Romania
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It's 30dB, but you can change the value by replacing the feedback resistors.
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Old 5th February 2010, 01:15 PM   #3
AndrewT is offline AndrewT  Scotland
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the dB gain is 20 * Log(voltage gain)

the voltage gain for inverting is Rf/Rb
the voltage gain for non-inverting is {[Rf /Rb] + 1}

You must also correct for the loss at the input. (-dB)
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Old 7th February 2010, 12:09 AM   #4
jdubs is offline jdubs  United States
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Thanks guys. ratza, which resistors are these and what values would I need to get to 26db of gain?

-Jim
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Old 7th February 2010, 08:36 AM   #5
ratza is offline ratza  Romania
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Replace the 680R resistor with 1k (27.2dB), 1k1 (26.4dB) or 1k2 (25.7dB).
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