What's the function of R1 resistor in this simple amplifier?

[myql]

Please refer to the attached drawing.

Why do we need R1 in the circuit? Usually we use 1kiloΩ for R1, but can we use below 100Ω?

Can somebody teach me how to design R1 correctly?

 

[oxide]

Re: Simple Amplifier

The C and R1 builds a HPF!
regrds,

 

[FvM]

Re: Simple Amplifier

Please check with OP circuit literature! The amplifier doesn't have a defined gain.

 

[Audioguru]

Simple Amplifier

The opamp circuit was wrong. It was amplifying Vref instead of amplifying the signal.
I corrected it.

 

[Kral]

Re: Simple Amplifier

Audioguru,
Do you have a question regarding the corrected circuit?
Regards,
Kral

 

[Audioguru]

Re: Simple Amplifier

Audioguru,
Do you have a question regarding the corrected circuit?
Regards,
Kral

I wonder why it was drawn wrong.
The corrected circuit is an ordinary single-supply inverting opamp circuit.
Rb is not needed. Connect Vref directly yo the non-inverting input of the opamp.

 

[myql]

Re: Simple Amplifier

Audioguru,

The reason why Vref is being put to the inverting input with the HPF is for the output will ride to the DC voltage which is Vref. I usually encountered this type of circuit in some of our experiments. I would like just to hear some good explanation why we need HPF in the inverting input.


Thanks,
myql

 

[Audioguru]

Simple Amplifier

The DC gain of the inverting amplifier is Ra/R1 times Vref. So if the gain is more than a little and if Vref is also more than a little and fed to the opamp's inverting input then the opamp's output will be saturated near ground.

The non-inverting input of an inverting opamp is almost always biased close to half the supply voltage if there is a single supply, and biased at 0V if there is a dual polarity supply.

The input coupling capacitor blocks DC (0V) from the input source. Then the opamp is a Vref follower for DC with no DC gain.

 

[smith123]

Simple Amplifier

you shoud concern with Amplifier designing

 

[abhityagi85]

Simple Amplifier

hey guys, you ppl are missing something very important here regarding the big circuit shown in above. its definately a gud one by a really gud designer
WHY? then have a luk below:
rest of things are ok about capacitor and other resistors BUT NO ONE DISCUSSSED THE NEED OF RESISTOR WITH DC VOLTAGE????
dude its for noise cancellaton : a problem with finitye CMRR of an opamp abhityagi85@gmail.com

 

[Audioguru]

Re: Simple Amplifier

A resistor in series with the non-inverting input of the opamp will not reduce noise and is not needed.

Rane make the MS-1B low-noise preamp. It uses almost exactly the same circuit without a resistor in series with the non-inverting input of an opamp. Except it uses a dual-polarity supply so its non-inverting input is biased at 0V.

 

[FvM]

Re: Simple Amplifier

BUT NO ONE DISCUSSSED THE NEED OF RESISTOR WITH DC VOLTAGE????

The resistor is sometimes used with bipolar input OPs when |Ib| > |Ios| for compensation of offset voltage contribution of input current. Some designers, that don't understand the principle are using it still with FET input OP or OP with input current compensation. Actually, it would cause higher offset voltage and additional noise anyway with most modern OP.