# Frequency amplification

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.

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
2021 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.

Alpharup
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/at...UH4lAyheqgLOQGEeq2dm9l1Fi69zGYIMpKRoCuNnw_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 wont 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
2021 Award
Is that transducer designed to operate at 50 kHz or at 1.65 MHz ?
30 W of ultrasonic near your ears will be dangerous.

I don't think you really know what you are doing. What do you actually want to do and why ?

Alpharup
Is that transducer designed to operate at 50 kHz or at 1.65 MHz ?
30 W of ultrasonic near your ears will be dangerous.

I don't think you really know what you are doing. What do you actually want to do and why ?
30 W is too much, though. Some suggest that ultrasonic waves can be used to repel pests(including rats) but they also warn that higher power can damage humans too.

Is that transducer designed to operate at 50 kHz or at 1.65 MHz ?
30 W of ultrasonic near your ears will be dangerous.

I don't think you really know what you are doing. What do you actually want to do and why ?
Its designed to work up to 1.65 MHz, I intend to use it at 50 kHz...If youve heard about a neurophone, youll understand...

jim hardy
Gold Member
Dearly Missed
Hmmm let's compare cochleae....
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC389506/
In the dolphin Tursiops truncatus, the basilar membrane over its course its course from basal to apical ends shows a systematic variation in width and in the manner and rigidity of its suspension.

The suspension is by bony laminae on both the outer and inner edges in the basal region, and by progressively less rigid attachments in the more apical regions, until near the apex the membrane is held only by connective tissue.

The basilar membrane shows an unusual variation in width of 14 times, ranging from an astonishingly small value of 25 μm at the basal end to a value toward the apex of about 350 μm. This structural variation is in harmony with the extension of sensitivity of the dolphin ear into the very high frequencies, and suggests unusual capabilities of pitch discrimination in this high range.

human on other hand is

The parameters of the membrane at a given point along its length determine its characteristic frequency (CF), the frequency at which it is most sensitive to sound vibrations. The basilar membrane is widest (0.42–0.65 mm) and least stiff at the apex of the cochlea, and narrowest (0.08–0.16 mm) and most stiff at the base.[3] High-frequency sounds localize near the base of the cochlea (near the round and oval windows), while low-frequency sounds localize near the apex.
Not that different maybe , 3x in width ?

Before investing a lot of money, see whether you can hear that 50khz .

It will be interesting also to see whether you can hear short bursts of 50khz
when i was in high school a fellow built a 40khz sonar for science fair using a hi-fi tweeter and a parabolic dish to both send and receive. (All vacuum tubes of course in 1963....)
When he broadcast continuous tone for tuning it up one could not hear it
but when he switched into pulsed for ranging, wow was it annoying.

The guys are right - you want to amplitude modulate. Easiest way is just switch it on and off. A 555 timer's discharge pin could short the input to an audio ampilifier. If you use a LM386 it cant make enough power to hurt you.

I see same outfit you're looking at makes this gizmo
http://elcodis.com/parts/2881113/SRM400.html#datasheet

Sveral
jim hardy
Gold Member
Dearly Missed
If youve heard about a neurophone, youll understand...

Interesting !

https://neurophone.wordpress.com/2012/08/05/make-a-diy-flanagan-neurophone-with-a-tl494/

but i'd add a cap in series with transducer and connect both wires....
and set his TL494 for push-pull

Happy Experimenting !

Sveral and Alpharup
@jim hardy...This is the first time am hearing neurophone but the concept is cool. Thanks OP.

Hmmm let's compare cochleae....

human on other hand is

Not that different maybe , 3x in width ?

Before investing a lot of money, see whether you can hear that 50khz .

It will be interesting also to see whether you can hear short bursts of 50khz
when i was in high school a fellow built a 40khz sonar for science fair using a hi-fi tweeter and a parabolic dish to both send and receive. (All vacuum tubes of course in 1963....)
When he broadcast continuous tone for tuning it up one could not hear it
but when he switched into pulsed for ranging, wow was it annoying.

The guys are right - you want to amplitude modulate. Easiest way is just switch it on and off. A 555 timer's discharge pin could short the input to an audio ampilifier. If you use a LM386 it cant make enough power to hurt you.

I see same outfit you're looking at makes this gizmo
http://elcodis.com/parts/2881113/SRM400.html#datasheet

Ok, this was VERY helpful, thank you and one more thing...can you hook up an audio source to this device?

jim hardy
Gold Member
Dearly Missed
Ok, this was VERY helpful, thank you and one more thing...can you hook up an audio source to this device?
I dont know - never have seen one of these for real.

It's just an on-off device controlled by pin 1
see
http://elcodis.com/parts/2881113/SRM400_p2.html#datasheet
you'd have to amplify and clip your audio, make it drive pin 1 low to send tone burst
and to prevent it from hearing an echo, remove that rightmost 6.8K resistor

That's from just a cursory glance at the documentation,
most experiments don't go so smoothly
if it's inexpensive enough to buy one just for tinkering , you'll learn from it.

It seems to be set for 38khz not 50 though. Would that do ?

Don't risk much expense on my speculation, though.

old jim

I dont know - never have seen one of these for real.

It's just an on-off device controlled by pin 1
see
http://elcodis.com/parts/2881113/SRM400_p2.html#datasheet
you'd have to amplify and clip your audio, make it drive pin 1 low to send tone burst
and to prevent it from hearing an echo, remove that rightmost 6.8K resistor

That's from just a cursory glance at the documentation,
most experiments don't go so smoothly
if it's inexpensive enough to buy one just for tinkering , you'll learn from it.

It seems to be set for 38khz not 50 though. Would that do ?

Don't risk much expense on my speculation, though.

old jim
Yes, 38 kHz would do...

jim hardy
Gold Member
Dearly Missed
Again i'm speculating here

and i'll feel awful if you spend money on my advice that doesn't work.

If this thing costs not much,
you get a lower power transducer than that atomizer you linked
and a driver that's not powerful enough to hurt you
and a gizmo to experiment and learn with.

I've held an "ultrasonic tape measure" up to my ear , can barely hear faint clicks. Never dawned on me to try modulating it.

That TL494 IC in the other link is capable of a few watts output.
Datasheet for your proposed transducer does not say what voltage is needed to drive it.

This might work,
perhaps somebody here has more experience than me with ultrasonic transduers.

again - get a second opinion before spending money

old jim

jim hardy
Gold Member
Dearly Missed
This is the first time am hearing neurophone but the concept is cool. Thanks OP.
first for me, too. Thanks @Sveral