who can solve this amp problem

[scorpionss22]

microphonic capacitors

i did alot of project like spectrum analyzer and ultrasonic range metter
which is design by epe magazine
and all the circuit have operational amp like lm833 and tl082 lm741
and because of this operational amp i got a lot of noise in the output
(i mean at the output of operational amp)
i really feel like mad when i see the noise (i used oscilloscope)
so how can i over come this noise is there is any recommendation

thanks for u r cooperation

 

[IanP]

The noise that you "see" on the oscilloscope screen may come from two sources: input and power supply. The latter is reasonably easy to eliminate by using proper RC or LC low pass filter to the supply lines and/or de-coupling capacitors between + and - supply pins.
To eliminate the input noise you will have to try to limit the bandwidth of the signal (one or two stage low pass filters) or limit the banwidth of the opamp by adding C or RC tank between the output and the (-) input.

Are you sure it is noise and not oscillations?

Regards,
IanP

 

[scorpionss22]

yes the noise from operational amp
i tried to use battary but the noise remains

 

[IanP]

So, as I said, you can try to use a small (pFs) capacitor to limit the bandwidth and RC (or LC) low pass filter on the output of the opamp.
Regards,
IanP

 

[moda]

Limit your BW will reduce noise and your signal as well.

In what gain your opamp is working?
You can affect the noise with different gain.

Can you replace the OPAMP with different one?

Regards

Moda

 

[Borber]

I suggest first to analyze the noise voltage. How many Vpp it is, does it has any harmonic components? Is it like white noise? Is it hum. Try to answer these questions.

 

[wholx]

agree with Borber. IanP's ideas are to be used properly after the analysis of the noise you had.

 

[nemoium]

where is the noise from is important,
i think.
certaintly the method of measurement is sigificant too.

 

[scorpionss22]

thanks friends
i usrd LPF and coparator and its work fine
i clipped the noise by the comparator

 

[kwkam]

Can you specify more detail on the noise shows on output. Since, a opamp is just a amplifier. Output noise must come from input and then amplified.

 

[Kral]

Several Causes of noise:
. Poor circuit board layout. Ensure that the connections to the
. Op amp inputs are short and far from noise sources.
.
. The Op amp is inherently noisy. Look at the noise specs. There
. are several low noise op-amps, such as the OP-07 available.
.
. High input resistor values make the circuit susceptible to
. input current noise.
.
. Poor power supply decoupling (already mentioned in other posts)
.
. Microphonic capacitors. Ceramics are particularly bad.
.
. One trick that you can use in a pcb layout is to surroundt the summing
. junction (inverting input in an inverting amplifier) with track that is
. connected to signal ground. This is referred to as a "guard" band. This
. prevents noise current from reaching th NI input.
Regards,
Jon

 

[tecsiun]

In many cases, feedback is used to solve stability problem, and it can be used to modify the input and output impedence.