Hi James,

 

I have used a 741 in a couple different sensors and currently have one
sensor running with a 741.  It is not nearly that noisy.  What is your gain
setting?  Can you provide an FFT?  Is the noise in random spikes or a
constant hum?  What is the sample rate?  

 

I would look at a step by step troubleshooting process.

 

First increase the sample rate to 240 and look at an FFT for line noise or
harmonics of line frequency.

 

Put a resistor across the AD and get the AD noise using a high sample rate
such as 120 or 240 sps.  

 

Move the resistor to the amplifier end of the data line and look at the same
information without the amplifier connected.

 

Move the resistor to the input side of the amplifier replacing your pickup
and again check for noise while using battery power.

 

Next try this with your power supply operating.  

 

The steps will isolate the portion of the system providing the noise.   Also
be careful with 2 power supplies.  I have seen common mode voltages form and
I have had 2 supplies fight with each other so to speak causing extreme
conditions which fried my amp.  Simply reversing how one supply is plugged
into the wall can upset the entire balance from working fine to smoke.

 

 

Randy

 














Hi James,

 

I have used a 741 in a couple different sensors and
currently have one sensor running with a 741.  It is not nearly =
that
noisy.  What is your gain setting?  Can you provide an =
FFT?  Is
the noise in random spikes or a constant hum?  What is the sample
rate?  

 

I would look at a step by step troubleshooting =
process.

 

First increase the sample rate to 240 and look at an =
FFT for
line noise or harmonics of line frequency.

 

Put a resistor across the AD and get the AD noise =
using a
high sample rate such as 120 or 240 sps.  =


 

Move the resistor to the amplifier end of the data =
line and
look at the same information without the amplifier =
connected.

 

Move the resistor to the input side of the amplifier =
replacing
your pickup and again check for noise while using battery =
power.

 

Next try this with your power supply operating.  =


 

The steps will isolate the portion of the system =
providing
the noise.   Also be careful with 2 power supplies.  I =
have seen
common mode voltages form and I have had 2 supplies fight with each =
other so to
speak causing extreme conditions which fried my amp.  Simply =
reversing how
one supply is plugged into the wall can upset the entire balance from =
working
fine to smoke.

 

 

Randy