LM3875 gainclone gain in dB?

jdubs · 5th February 2010, 04:10 AM

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

ratza · 5th February 2010, 05:46 AM

It's 30dB, but you can change the value by replacing the feedback resistors.

AndrewT · 5th February 2010, 01:15 PM

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)

jdubs · 7th February 2010, 12:09 AM

Thanks guys. ratza, which resistors are these and what values would I need to get to 26db of gain?

-Jim

ratza · 7th February 2010, 08:36 AM

Replace the 680R resistor with 1k (27.2dB), 1k1 (26.4dB) or 1k2 (25.7dB).

5th February 2010, 04:10 AM	#1
jdubs diyAudio Member Join Date: Jul 2004 Location: NYC	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

5th February 2010, 05:46 AM	#2
ratza diyAudio Member Join Date: Dec 2007 Location: Sibiu, Romania	It's 30dB, but you can change the value by replacing the feedback resistors. __________________ Any solution is a compromise.

7th February 2010, 08:36 AM	#5
ratza diyAudio Member Join Date: Dec 2007 Location: Sibiu, Romania	Replace the 680R resistor with 1k (27.2dB), 1k1 (26.4dB) or 1k2 (25.7dB). __________________ Any solution is a compromise.

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5th February 2010, 01:15 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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)

7th February 2010, 12:09 AM	#4
jdubs diyAudio Member Join Date: Jul 2004 Location: NYC	Thanks guys. ratza, which resistors are these and what values would I need to get to 26db of gain? -Jim

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