# Frequency amplification

## Main Question or Discussion Point

How do I know, how big of a voltage gain for an amplifier do I need, if I want to increase the input frequency from 250 Hz to 50 kHz?
Thank you.

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Drakkith
Staff Emeritus

The purpose any amplifier is to use a small voltage signal as an input and generate a higher voltage signal with the same waveform.
Generally transistors are used for this but transistors vary in their optimum operating voltage range, and they also vary for input sensitivity.
Transistors which can guarantee to efficiently/accurately amplify higher frequency input signals tend to be harder to make, and at very high frequencies they get expensive.

NascentOxygen
Staff Emeritus
How do I know, how big of a voltage gain for an amplifier do I need, if I want to increase the input frequency from 250 Hz to 50 kHz?
Thank you.
It is very unlikely that you would be building a circuit to do what you seem to be saying. Perhaps you could explain what you would like to achieve, then we can tell you how to go about it?

Averagesupernova
Gold Member
Not making any sense. Voltage gain does not increase frequency.

It is very unlikely that you would be building a circuit to do what you seem to be saying. Perhaps you could explain what you would like to achieve, then we can tell you how to go about it?
Ok, I want to increase the frequency of an audio source from 250 Hz to 50 kHz so I can hear it via inner ear...Roughly speaking...

There isnt a circuit yet, because I dont have nearly enough knowledge to build one yet, thats why I want to know, how to go about it. I simply want to increase the frequency of an audio source from 250 Hz to 50 kHz so I can work with ultrasound, listen to it by using my inner ear.

Not making any sense. Voltage gain does not increase frequency.
Not going to argue, thats why Im here- to learn!

Do you want to increase frequency/amplitude?

Do you want to increase frequency/amplitude?
Yes, just that-frequency.

Then there are something called as frequency multipliers

Then there are something called as frequency multipliers
Thank you for the intel, any suggestions for one that would be relatively cheap and amplify the frequency 200x?

Yes, they are verily possible. We can double or triple frequency using some simple circuits. The doubled or tripled frequency signals can be used for various applications.
Take the case of microprocessors. A faster clock frequency(say twice or four times) means faster operation in sequential circuits.
But it is not much use of increasing frequency by 200 times( either for sine or square eaves).
Instead of increasing frequency from 250 Hz to 50Khz, you can generate 50KHz output itself.

Baluncore
2019 Award
The amplifier does not need a different gain for a different frequency. It needs a greater passband. Audio power amplifiers often have an ultrasonic filter to prevent parasitic oscillation in the output stage. That may block your 50kHz.

What type of transducer will you use? What is the frequency response?
To compensate for the frequency response of the transducer may need to change amplifier gain.

With 50kHz you will probably feel very irritated, but you will not perceive it as a sound.
How good were your ears. If you are not very careful you will probably damage your ears in the experiment.

Yes, they are verily possible. We can double or triple frequency using some simple circuits. The doubled or tripled frequency signals can be used for various applications.
Take the case of microprocessors. A faster clock frequency(say twice or four times) means faster operation in sequential circuits.
But it is not much use of increasing frequency by 200 times( either for sine or square eaves).
Instead of increasing frequency from 250 Hz to 50Khz, you can generate 50KHz output itself.
I do have a 50 kHz square wave generator, it would be possible to mix it with the audio source, but what would happen to the frequency of the mixed signal?

But, can we really hear 50Khz? Is 20Khz, not the maximum frequency we can hear?

The amplifier does not need a different gain for a different frequency. It needs a greater passband. Audio power amplifiers often have an ultrasonic filter to prevent parasitic oscillation in the output stage. That may block your 50kHz.

What type of transducer will you use? What is the frequency response?
To compensate for the frequency response of the transducer may need to change amplifier gain.

With 50kHz you will probably feel very irritated, but you will not perceive it as a sound.
How good were your ears. If you are not very careful you will probably damage your ears in the experiment.
http://www.topqualitytools.co.uk/atomiser-ultrasonic-liquid-1-65mhz-m165d25/?gclid=CjwKEAjwsMu5BRD7t57R1P2HwBgSJABrtj-RSZsII55UH4lAyheqgLOQGEeq2dm9l1Fi69zGYIMpKRoCuNnw_wcB
That would be the tramsducer I have in mind, the inner ear should be able to perceive it as sound...Im positive there is a way of getting this done and I will do so no matter how many people I have to ask for help...

What do you mean by the term "mixing"? does it mean voltage addition(adding function generator waveform and audio signal)?

But, can we really hear 50Khz? Is 20Khz, not the maximum frequency we can hear?
You are correct, but the inner ear is something we have in common with dolphins and a few other species who can perceive ultrasound, so it should be possible.

What do you mean by the term "mixing"? does it mean voltage addition(adding function generator waveform and audio signal)?
No, I meant by using an audio mixer of sorts to combine the two signals and create a third one, just that the third frequency most likely won`t be at 50 kHz.

What do expect the third frequency to be?

What do expect the third frequency to be?
I need a 50 kHz frequency, but I doubt that the third frequency will be such...

So, you want something like 50 Khz? If you want some mixing you can use the principles used in Amplitude modulation, where both the signals are multiplied. But, i doubt the usefulness of the method.
Leaving the circuit construction aside, how can you sense ultrasonic waves? Don't we need an ultrasonic sensor?

So, you want something like 50 Khz? If you want some mixing you can use the principles used in Amplitude modulation, where both the signals are multiplied. But, i doubt the usefulness of the method.
Leaving the circuit construction aside, how can you sense ultrasonic waves? Don't we need an ultrasonic sensor?
An ultrasound transducer can output sound in this frequency range and thus the inner ear can perceive it...Ok, then which one would you suggest a transistor amplifier or a frequency multiplier?

Baluncore