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Old 20th January 2011, 10:49 AM   #1
neazoi is offline neazoi  Greece
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Default lm387 made od discrete components

Hello This little amplifier is from a radio receiver.
I wish to replace the chip with an amplifier made of discrete components and achieving the same overal gain and maybe better noise, distortion and intermodulation characteristics.

The 120mH coil and associated caps form a high pass filter to cut off the 50Hz hum. I would like to keep this passive filter there as well as the mute switch, so I basically need 2 amplifiers made out of discrete components. One with gain 27dB for the front end and another one with gain 35dB for the back end.

Can this be done? any schematics?
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Old 11th September 2012, 11:46 PM   #2
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This is an old thread but I thought I would chime in too. I am building the same receiver that you were referring to in this post. I am looking for a better preamp then the LM387. Everything I read says go with the NE5534. Can I drop in a NE5534 in place of the LM387 or do I need to make some changes?
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Old 12th September 2012, 12:14 AM   #3
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never mind... looks like the ne5532 is a direct replacement..
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Old 12th September 2012, 01:14 AM   #4
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Just curious, which ARRL publication is that circuit from?
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Old 12th September 2012, 02:47 AM   #5
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Yep, its one written by Rick Cambell, KK7B - entitled "High Performance, Direct conversion Receivers." You can find it here
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Old 12th September 2012, 04:07 AM   #6
tomchr is offline tomchr  United States
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For lower noise, I'd recommend the LME49710 (LME49720 for the dual).

~Tom
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Old 12th September 2012, 05:49 AM   #7
djQUAN is offline djQUAN  Philippines
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Quote:
Originally Posted by jscherer View Post
never mind... looks like the ne5532 is a direct replacement..
No. The pinout is different and the LM387 is a unique op amp such that it is designed to work with only single supplies. The non inverting inputs are internally biased so that the output can work with single supplies without external biasing networks.

http://www.ti.com/lit/ds/snosbt7a/snosbt7a.pdf
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Old 12th September 2012, 07:10 AM   #8
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NE542 is a direct replacement for LM387.
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Old 12th September 2012, 07:27 AM   #9
neazoi is offline neazoi  Greece
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Quote:
Originally Posted by franzm View Post
NE542 is a direct replacement for LM387.
And which of the two is of lower noise?
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Old 12th September 2012, 10:18 PM   #10
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The NE542 is 0.7uV and the LM387 is 1.0uv so both are about the same. The LME49710 is listed as 2.5nV/Hz. So the LME49710 is it the lower noise winner which comes as no surprise. Given that bit of information, the bigger question I have is how should I go about reconfiguring the two preamps in the above circuits to use the LME49710.
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