Gain of Non-Inverting Amplifier Does Not vary with Resistor ValuesMy simple audio amplifier circuit does not workNon-inverting amp GainHi-Fi Stereo Amplifier gain regulation with potentiometerNon-inverting and inverting gain of differential amplifierWhy not vary the opamp feedback resistor to change output levels?Output resistance of non-inverting amplifierProblems with setting op-amp amplifier gainPhotodiode non-inverting amplifier circuitNoisy non-inverting op amp with gain selectionactual formula for open loop gain in a non-inverting op-amp?
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Gain of Non-Inverting Amplifier Does Not vary with Resistor Values
My simple audio amplifier circuit does not workNon-inverting amp GainHi-Fi Stereo Amplifier gain regulation with potentiometerNon-inverting and inverting gain of differential amplifierWhy not vary the opamp feedback resistor to change output levels?Output resistance of non-inverting amplifierProblems with setting op-amp amplifier gainPhotodiode non-inverting amplifier circuitNoisy non-inverting op amp with gain selectionactual formula for open loop gain in a non-inverting op-amp?
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$begingroup$
I am trying to build a non-inverting amplifier using a LM7171 op amp, and I am implementing it with potentiometers as Rf and R2 so that I can smoothly control the gain of the amplifier (and easily check if its working correctly). I am applying +/- 15 V to the op amp. When I adjust the potentiometer's resistance the gain does not change as expected, or noticeably at all. Setup is shown below with traces when the resistances are Rf=Ri=540 Ohm and Rf=1.8 kOhm, Ri=540 Ohm, and as can be seen the gain/amplitude is the same for the different resistances used. The yellow output on the oscilloscope is the output of the amplifier, and the green is directly from a t-connector to the function generator's output.
I have used two different op amps and got the same behavior, so it is not broken, and all connections seem good. I measure the values of the potentiometer so am confident they are as described. Any ideas what might cause this? Thank you in advance for your help.
operational-amplifier amplifier potentiometer gain non-inverting
asked 5 hours ago
wondersmwondersm
113
$endgroup$
add a comment |
$begingroup$
I am trying to build a non-inverting amplifier using a LM7171 op amp, and I am implementing it with potentiometers as Rf and R2 so that I can smoothly control the gain of the amplifier (and easily check if its working correctly). I am applying +/- 15 V to the op amp. When I adjust the potentiometer's resistance the gain does not change as expected, or noticeably at all. Setup is shown below with traces when the resistances are Rf=Ri=540 Ohm and Rf=1.8 kOhm, Ri=540 Ohm, and as can be seen the gain/amplitude is the same for the different resistances used. The yellow output on the oscilloscope is the output of the amplifier, and the green is directly from a t-connector to the function generator's output.
I have used two different op amps and got the same behavior, so it is not broken, and all connections seem good. I measure the values of the potentiometer so am confident they are as described. Any ideas what might cause this? Thank you in advance for your help.
operational-amplifier amplifier potentiometer gain non-inverting
asked 5 hours ago
wondersmwondersm
113
$endgroup$
$begingroup$
You also have a large phase shift. Something odd going on. You have no DC path on the non-inverting input. That's going to cause the input capacitor to charge up or down until it hits one of the supply rails.
$endgroup$
– Transistor
5 hours ago
$begingroup$
The LM7171 has a very, very fast slew rate and 200 MHz at unity gain. I think your output is showing a gain of about 1.5 in the setup. This looks more to me about the breadboard's pF, which is getting well into the 1k zone with that frequency. Use dead-bug construction and see what happens.
$endgroup$
– jonk
5 hours ago
add a comment |
$begingroup$
I am trying to build a non-inverting amplifier using a LM7171 op amp, and I am implementing it with potentiometers as Rf and R2 so that I can smoothly control the gain of the amplifier (and easily check if its working correctly). I am applying +/- 15 V to the op amp. When I adjust the potentiometer's resistance the gain does not change as expected, or noticeably at all. Setup is shown below with traces when the resistances are Rf=Ri=540 Ohm and Rf=1.8 kOhm, Ri=540 Ohm, and as can be seen the gain/amplitude is the same for the different resistances used. The yellow output on the oscilloscope is the output of the amplifier, and the green is directly from a t-connector to the function generator's output.
I have used two different op amps and got the same behavior, so it is not broken, and all connections seem good. I measure the values of the potentiometer so am confident they are as described. Any ideas what might cause this? Thank you in advance for your help.
operational-amplifier amplifier potentiometer gain non-inverting
asked 5 hours ago
wondersmwondersm
113
$endgroup$
I am trying to build a non-inverting amplifier using a LM7171 op amp, and I am implementing it with potentiometers as Rf and R2 so that I can smoothly control the gain of the amplifier (and easily check if its working correctly). I am applying +/- 15 V to the op amp. When I adjust the potentiometer's resistance the gain does not change as expected, or noticeably at all. Setup is shown below with traces when the resistances are Rf=Ri=540 Ohm and Rf=1.8 kOhm, Ri=540 Ohm, and as can be seen the gain/amplitude is the same for the different resistances used. The yellow output on the oscilloscope is the output of the amplifier, and the green is directly from a t-connector to the function generator's output.
I have used two different op amps and got the same behavior, so it is not broken, and all connections seem good. I measure the values of the potentiometer so am confident they are as described. Any ideas what might cause this? Thank you in advance for your help.
operational-amplifier amplifier potentiometer gain non-inverting
operational-amplifier amplifier potentiometer gain non-inverting
asked 5 hours ago
wondersmwondersm
113
asked 5 hours ago
wondersmwondersm
113
asked 5 hours ago
wondersmwondersm
113
asked 5 hours ago
wondersmwondersm
113
asked 5 hours ago
wondersmwondersm
113
113
$begingroup$
You also have a large phase shift. Something odd going on. You have no DC path on the non-inverting input. That's going to cause the input capacitor to charge up or down until it hits one of the supply rails.
$endgroup$
– Transistor
5 hours ago
$begingroup$
The LM7171 has a very, very fast slew rate and 200 MHz at unity gain. I think your output is showing a gain of about 1.5 in the setup. This looks more to me about the breadboard's pF, which is getting well into the 1k zone with that frequency. Use dead-bug construction and see what happens.
$endgroup$
– jonk
5 hours ago
add a comment |
$begingroup$
You also have a large phase shift. Something odd going on. You have no DC path on the non-inverting input. That's going to cause the input capacitor to charge up or down until it hits one of the supply rails.
$endgroup$
– Transistor
5 hours ago
$begingroup$
The LM7171 has a very, very fast slew rate and 200 MHz at unity gain. I think your output is showing a gain of about 1.5 in the setup. This looks more to me about the breadboard's pF, which is getting well into the 1k zone with that frequency. Use dead-bug construction and see what happens.
$endgroup$
– jonk
5 hours ago
$begingroup$
You also have a large phase shift. Something odd going on. You have no DC path on the non-inverting input. That's going to cause the input capacitor to charge up or down until it hits one of the supply rails.
$endgroup$
– Transistor
5 hours ago
$begingroup$
You also have a large phase shift. Something odd going on. You have no DC path on the non-inverting input. That's going to cause the input capacitor to charge up or down until it hits one of the supply rails.
$endgroup$
– Transistor
5 hours ago
$begingroup$
The LM7171 has a very, very fast slew rate and 200 MHz at unity gain. I think your output is showing a gain of about 1.5 in the setup. This looks more to me about the breadboard's pF, which is getting well into the 1k zone with that frequency. Use dead-bug construction and see what happens.
$endgroup$
– jonk
5 hours ago
$begingroup$
The LM7171 has a very, very fast slew rate and 200 MHz at unity gain. I think your output is showing a gain of about 1.5 in the setup. This looks more to me about the breadboard's pF, which is getting well into the 1k zone with that frequency. Use dead-bug construction and see what happens.
$endgroup$
– jonk
5 hours ago
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
The phase shift is the give-away. You are bandwidth limited. You need a faster op-amp, or a lower frequency.
answered 5 hours ago
Mattman944Mattman944
55317
$endgroup$
$begingroup$
Yup, 18.88 MHz. I hadn't spotted that.
$endgroup$
– Transistor
5 hours ago
add a comment |
$begingroup$
I cannot add as a comment, my reputation is too low, but Transistor makes a good point, the +input of the opamp will drift up close to negative rail due to input bias current - connect a large ohm resistor from this pin to 0V.
Constructing high frequency circuits on breadboard is likely to be problematic, with multiple stray capacitances. If you have a signal generator, test again at a low frequency.
Also add some decoupling capacitors, see 8.1 of the TI datasheet.
answered 4 hours ago
InnovodesignInnovodesign
464
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
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2 Answers
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2 Answers
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$begingroup$
The phase shift is the give-away. You are bandwidth limited. You need a faster op-amp, or a lower frequency.
answered 5 hours ago
Mattman944Mattman944
55317
$endgroup$
$begingroup$
Yup, 18.88 MHz. I hadn't spotted that.
$endgroup$
– Transistor
5 hours ago
add a comment |
$begingroup$
The phase shift is the give-away. You are bandwidth limited. You need a faster op-amp, or a lower frequency.
answered 5 hours ago
Mattman944Mattman944
55317
$endgroup$
$begingroup$
Yup, 18.88 MHz. I hadn't spotted that.
$endgroup$
– Transistor
5 hours ago
add a comment |
$begingroup$
The phase shift is the give-away. You are bandwidth limited. You need a faster op-amp, or a lower frequency.
answered 5 hours ago
Mattman944Mattman944
55317
$endgroup$
The phase shift is the give-away. You are bandwidth limited. You need a faster op-amp, or a lower frequency.
answered 5 hours ago
Mattman944Mattman944
55317
answered 5 hours ago
Mattman944Mattman944
55317
answered 5 hours ago
Mattman944Mattman944
55317
answered 5 hours ago
Mattman944Mattman944
55317
55317
$begingroup$
Yup, 18.88 MHz. I hadn't spotted that.
$endgroup$
– Transistor
5 hours ago
add a comment |
$begingroup$
Yup, 18.88 MHz. I hadn't spotted that.
$endgroup$
– Transistor
5 hours ago
$begingroup$
Yup, 18.88 MHz. I hadn't spotted that.
$endgroup$
– Transistor
5 hours ago
$begingroup$
Yup, 18.88 MHz. I hadn't spotted that.
$endgroup$
– Transistor
5 hours ago
add a comment |
$begingroup$
I cannot add as a comment, my reputation is too low, but Transistor makes a good point, the +input of the opamp will drift up close to negative rail due to input bias current - connect a large ohm resistor from this pin to 0V.
Constructing high frequency circuits on breadboard is likely to be problematic, with multiple stray capacitances. If you have a signal generator, test again at a low frequency.
Also add some decoupling capacitors, see 8.1 of the TI datasheet.
answered 4 hours ago
InnovodesignInnovodesign
464
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I cannot add as a comment, my reputation is too low, but Transistor makes a good point, the +input of the opamp will drift up close to negative rail due to input bias current - connect a large ohm resistor from this pin to 0V.
Constructing high frequency circuits on breadboard is likely to be problematic, with multiple stray capacitances. If you have a signal generator, test again at a low frequency.
Also add some decoupling capacitors, see 8.1 of the TI datasheet.
answered 4 hours ago
InnovodesignInnovodesign
464
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I cannot add as a comment, my reputation is too low, but Transistor makes a good point, the +input of the opamp will drift up close to negative rail due to input bias current - connect a large ohm resistor from this pin to 0V.
Constructing high frequency circuits on breadboard is likely to be problematic, with multiple stray capacitances. If you have a signal generator, test again at a low frequency.
Also add some decoupling capacitors, see 8.1 of the TI datasheet.
answered 4 hours ago
InnovodesignInnovodesign
464
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I cannot add as a comment, my reputation is too low, but Transistor makes a good point, the +input of the opamp will drift up close to negative rail due to input bias current - connect a large ohm resistor from this pin to 0V.
Constructing high frequency circuits on breadboard is likely to be problematic, with multiple stray capacitances. If you have a signal generator, test again at a low frequency.
Also add some decoupling capacitors, see 8.1 of the TI datasheet.
answered 4 hours ago
InnovodesignInnovodesign
464
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 3 hours ago
answered 4 hours ago
InnovodesignInnovodesign
464
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 4 hours ago
InnovodesignInnovodesign
464
answered 4 hours ago
InnovodesignInnovodesign
464
464
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Innovodesign is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
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$begingroup$
You also have a large phase shift. Something odd going on. You have no DC path on the non-inverting input. That's going to cause the input capacitor to charge up or down until it hits one of the supply rails.
$endgroup$
– Transistor
5 hours ago
$begingroup$
The LM7171 has a very, very fast slew rate and 200 MHz at unity gain. I think your output is showing a gain of about 1.5 in the setup. This looks more to me about the breadboard's pF, which is getting well into the 1k zone with that frequency. Use dead-bug construction and see what happens.
$endgroup$
– jonk
5 hours ago