Non-inverting amp with variable gain

Thread Starter

Dritech

Joined Sep 21, 2011
904
Hi all,

I would like to construct a non-inverting amplifier with variable gain (from 1 to 10)
The input of the amplifier will have an offset of Vcc/2, hence why R1 is connected to Vcc/2.
Is the circuit below theoretically and practically correct for obtaining this (is it good practice as it is)?
Is it OK to have 0ohms at the feedback loop when the gain is set to 1 ?

upload_2018-7-2_23-11-57.png
 

Hymie

Joined Mar 30, 2018
1,286
Hi all,

I would like to construct a non-inverting amplifier with variable gain (from 1 to 10)
The input of the amplifier will have an offset of Vcc/2, hence why R1 is connected to Vcc/2.
Is the circuit below theoretically and practically correct for obtaining this (is it good practice as it is)?
Is it OK to have 0ohms at the feedback loop when the gain is set to 1 ?

View attachment 155488
Varying the amount of feedback to alter the amplifier gain is not the conventional method.

Normally the amplifier gain is fixed (at the maximum required), fed into a wiper pot to attenuate the output signal to the desired level.

The disadvantages of varying the feedback include the fact that the feedback signal is normally at a low signal level – running this to an accessible pot invariably adds noise; plus the performance of the amplifier may vary with gain.
 

Thread Starter

Dritech

Joined Sep 21, 2011
904
Thanks for the feedbacks (no pun intended :p).

@Hymie , Do you mean connecting the output of the amplifier (with full gain) to a pot serving as a doltage divider? If so, I cannot do that as the signal is offsetted at Vcc/2.
@danadak , the op-amp datasheet stated that it is unity gain stable. Is this what you are referring to?
 

Hymie

Joined Mar 30, 2018
1,286
Thanks for the feedbacks (no pun intended :p).

@Hymie , Do you mean connecting the output of the amplifier (with full gain) to a pot serving as a doltage divider? If so, I cannot do that as the signal is offsetted at Vcc/2.
@danadak , the op-amp datasheet stated that it is unity gain stable. Is this what you are referring to?
Your output pot would be connected between the op-amp out and Vcc/2
 

crutschow

Joined Mar 14, 2008
34,689
Normally the amplifier gain is fixed (at the maximum required), fed into a wiper pot to attenuate the output signal to the desired level.
That's okay as long as the maximum input signal doesn't saturate the op amp at the desired maximum gain.
 
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