amplify 40kHz audio signal using TL082: first two stages are fine, but high noise from the third stage

From: for_idea (zhiyang_at_gmail.com)
Date: 03/16/05 

Date: 16 Mar 2005 12:19:26 -0800

Dear friends,

I am making an ultrasound signal receiver. The transmitter and receiver
is apart from each other about 6 meters. The circuit is powered by a 9v
battery. I used three amplifiers from two TL082. The reference voltage
(about 4.5v) is generated from voltage divider (two 100k resisters in
series). All amplifiers are in inverting input mode. First and second
stages are configured as: 10k input resister and 500k feedback
resister. The signal output in the second stage is very good. However,
the signal from the third stage (input res.= 10k, output res. = 200k)
is significantly corrupted by noise. Please give me some advice to
clean up the amplified signal.

Thanks,

Zhi Yang

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