Opamp Gyrator Question

[ronnyelectron]

Greetings!

I'd like to use a opamp as a gyrator inductor for a audio filter.

The audio signal can get to 30 volts.

I know when using opamps as normal you should have the supply voltage double of your signal.

Does this apply to a gyrator in a audio filter?
I'd love to use the available 5 volt supply.

Thanks in advance!!

 

[crutschow]

Is this going to a speaker?

Opamp Gyrators are only for low level signals such as in active filters, not high power audio.

 

[ronnyelectron]

No, not to a speaker. In a negative feedback loop.

 

[MrAl]

Hi there,


Gyrators are pretty old now and there is most likely a better circuit for doing what you need to do, so the question is what are you trying to do with the gyrator? Is it a filter?

 

[crutschow]

Why is the signal 30V? Is it in a tube circuit?

 

[ronnyelectron]

Why is the signal 30V? Is it in a tube circuit?

yes sir! I'd like to use a opamp as a gyrator instead of a inductor. cost/ noise.

 

[Roff]

This looks like another one of those cases where the OP, instead of telling us the big picture, has already decided on a "solution" which may be unnecessarily complex, or maybe won't even work.
Ronny, why don't you tell us what you are really trying to do.

 

[ronnyelectron]

This looks like another one of those cases where the OP, instead of telling us the big picture, has already decided on a "solution" which may be unnecessarily complex, or maybe won't even work.
Ronny, why don't you tell us what you are really trying to do.

Yeah, you are right , it does look like that.


Application is a simple resonant circuit. Basically a inductor/capacitor in series draped across the signal line to ground. A broad notch at 100hz for example. Inductors are expensive and they pickup hum. I'm looking for a cheaper/less noisy solution.

As I've read, the gyrator is a great replacement for a inductor. Obviously I suck at OPamps. Requirements are that the signal cannot go through the opamp.....meaning this filter cannot be in series.

Thanks

 

[crutschow]

It may be possible to use a gryator, but the op amp would have to withstand the full signal voltage, so would require a high voltage op amp.

Is that 30V rms, 30V pk, or 30V pk-pk?

 

[ronnyelectron]

It may be possible to use a gryator, but the op amp would have to withstand the full signal voltage, so would require a high voltage op amp.

Is that 30V rms, 30V pk, or 30V pk-pk?

It is max 30 volts peak to peak.

Back to my original Q..... does supply voltage have a relation to how a opamp works as a gyrator?

 

[Roff]

I don't believe we have really gotten to the root of your problem yet. What kind of signal are you trying to filter, and why?
The op amp in your gyrator will have to handle Q times your p-p input signal. for example, if you set Q=10, the op amp will have to handle 300V p-p! And yes, the voltage across supply rails must be greater than the signal the op amp has to handle.
Again - tell us what you are really trying to do.

 

[MrAl]

Hello again,


You should really tell everybody what you really want to do here.

Also, it's been a long time since i have created a gyrator, but dont the inductor simulators mostly simulate inductors with one end connected to ground?

 

[ronnyelectron]

I don't believe we have really gotten to the root of your problem yet. What kind of signal are you trying to filter, and why?
The op amp in your gyrator will have to handle Q times your p-p input signal. for example, if you set Q=10, the op amp will have to handle 300V p-p! And yes, the voltage across supply rails must be greater than the signal the op amp has to handle.
Again - tell us what you are really trying to do.

see attached pic please.

What I'm trying to do is replace the coil with a opamp. this is in a 100 watt guitar amp using tubes.the signal is coming from a 16 ohm tap on the transformer speaker load. This is a negative feedback loop into a phase splitter.

Feel free to recommend a different approach for this circuit. I have 5volts DC. I thought it would be nice just to use a opamp instead of the coil. I'm here to learn and I appreciate your input.

 

[crutschow]

Below is a gyrator circuit with an equivalent inductance of 10.6H. The gyrator has to be at ground so the capacitor and inductor are reversed in sequence from your schematic but that makes no difference to the circuit operation.

The circuit input is connected to the junction of the 220kΩ resistor and 1µF cap in your circuit. LR8, the 0.1µF cap, and the A50 pot are also part of your circuit. The gyrator circuit is the circuitry to the right of A50.

With the 220KΩ resistor in series and the 6.8kΩ resistor to ground in your circuit, the 30V signal should be attenuated sufficiently to about 1V so the op amp should work ok at a 5V supply.

The op amp should be a rail-to-rail type such as a TLV2374. I added the resistors and capacitor to provide the pseudo-ground at 2.5V for the op amp input.

Edit: Changed op amp number

 

[ronnyelectron]

Below is a gyrator circuit with an equivalent inductance of 10.6H. The gyrator has to be at ground so the capacitor and inductor are reversed in sequence from your schematic but that makes no difference to the circuit operation.

The circuit input is connected to the junction of the 220kΩ resistor and 1µF cap in your circuit. LR8, the 0.1µF cap, and the A50 pot are also part of your circuit. The gyrator circuit is the circuitry to the right of A50.

With the 220KΩ resistor in series and the 6.8kΩ resistor to ground in your circuit, the 30V signal should be attenuated sufficiently to about 1V so the op amp should work ok at a 5V supply.

The op amp should be a rail-to-rail type such as a TLV2374. I added the resistors and capacitor to provide the pseudo-ground at 2.5V for the op amp input.

Edit: Changed op amp number

View attachment 46127

Thanks Carl! I will give this a shot and learn as much as I can. Thanks!

 

[crutschow]

Attached is the Excel program I use to design gyrator circuits. Use it if your are interested.
View attachment Gyrator zip.zip