PSN-L Email List Message

Subject: Re: Amplifier noise?
From: ChrisAtUpw@.......
Date: Sat, 23 Dec 2000 22:17:49 EST

In a message dated 23/12/00, mja6042@............. writes:

> When viewing the output with SDR I am getting about 80 to 100 counts of
> continuous noise. I don't know what the frequency of the noise is but the
> period is too short to see on SDR.
>  Is this noise level abnormally high and does anyone have any suggestions on
>  how to reduce the noise.

Hi there Mark,

    This noise level is much greater than I would normally expect. 

    Check your power supplies for noise with AC DVM. You aren't using the 
computer power supplies are you? They can be very noisy. Also check the earth 
connection. Do you have access to an oscilloscope? A quick look at the 
waveform, frequency, etc. can be very helpful.

    Check that you have the correct values of gain resistors in the feedback 
circuits. I have been sold resistors which are a factor of 10 out. Double 
check that you have made the circuits properly.

    Short the input to the ADC and check the noise level. Then check with the 
input to the first amplifier shorted, but everything else connected. If this 
doesn't cure it, you will need to short the input to the last OpAmp, check 
the level and work back chip by chip until you find the problem circuit. Look 
for mains / computer noise, oscillations, a dud OpAmp, dry solder joints, 
noisy resistors, faulty capacitors, etc. 
    Hope that these suggeations are of some help,


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Larry Cochrane <cochrane@..............>