tuned amplifier which work at 20HZ only.

An ordinary amplifier and a band-pass filter?

Rockwell has one that they bought for the space station. Dosen't work and I am sure they will sell it to you real cheap.

If the only component of the input that gets amplified is the 20Hz component, then that component cannot change in amplitude, so the output of the amplifier must also have a constant amplitude. This makes the the notion of the device being an amplifier rather questionable.

You're asking for something that doesn't exist.

Sylvia.

Huh?

The OP asked for a tuned amplifier which only passes the 20 Hz frequency. There's nothing in that specification that restricts the response at that frequency. Admittedly a circuit with an infinitely narrow response is impractical but there's always the unstated bandpass requirement.

Norm

If the wave is not a constant amplitude sinewave, then it contains frequencies other than its fundamental. It therefore cannot pass through an amplifier that amplifies on 20Hz.

As you say, in practice, an amplifier will have some band-pass characteristic, but the OP's requirement was quite specific: 20HZ (sic) only. I suspect it's a case of trying to describe a problem in terms of a presumed solution. The OP needs to provide a clearer explanation of the real underlying purpose.

Sylvia.

other than its

Being of constant amplitude is of no import at all. Being a sine wave isn't significant either.

All it says is that only the 20 Hz component is going to be amplified and passed through the circuit. The degree to which that is true depends on the bandwidth of the circuit of course, so the precise results cannot be known without some relative indication of what the bandwidth it.

but the OP's

trying to describe a

explanation of the real

The answer is fairly simple. He merely needs to find an appropriate amplifier, of any bandwidth that will pass 20 Hz, and then put a tuned circuit between the signal source and the amplifier input.

The answer is correct, but obviously it is also just as ambiguous as the question. But, that *is* the beauty of it too! It is *precisely* as ambiguous as the question, and not one bit more or less.

The amplitude can vary in response to the input.

The amplitude can vary in response to the input.

"bushbadee" wrote

Pedantically, no. Not if the _only_ thing passed by the amplifier is 20Hz.

For the output to vary it must be modulated. The modulation frequency can not be 20 Hz and so can not get through the amp. (if it is 20Hz the result is attenuation not modulation)

Ergo: the output of the amplifier is frozen at either 0 or some 20Hz output, and has been since creation (of the amp).

This amplifier is, of course, an impossibility as a zero bandwidth filter is not possible.

It is possible to approach this pons asinorum though: As a filter gets closer and closer to zero bandwidth the output of the filter rings at 20Hz, and the less the bandwidth the slower the ringing decays, until eventually the output is nothing but ringing.

It is like the folks who try to actually measure by sampling at 2x f: doesn't work. The filters would have to be ideal -

100% pass and 0 phase shift at f, 0% pass at >f -- and that's impossible. And the output would be steady state at f as higher frequency is needed to modulate f, and that won't get through the filter.

This task is not impossible, however.

A 20Hz signal generator will work just fine. Connect the signal you wish to amplify to a dummy load - it is of no use.

In actuality the output of this amplifier is stuck at zero volts. Every time AeroJet General tried to turn it on, it blew it's output transistors.

But then again 300 volt devices do not work well with over 700 volts on them. This device was to be a 20 KC, 25KW converter that the company wanted to use aboard the space station. I told them it would never work and that make them very unhappy with me.

You have no idea of the problems involved in shipping 20KHz around a large space station. But then again, neither did they.

The OP said 20 Hz, you appear to be talking about 20,000 Hz.

Sylvia.

On Sat, 2 Oct 2004 23:45:09 +0200, Faris Alahmad put forth the notion that...

What are you making, a sound weapon?

No but that would be a good application. Attach it to a speaker and it will kill every dog around.

It was 20KHz as was pointed out,

It was thught that this would be a dandy way to route power around the space station and the transformers would be very small.

Didn't turn out that way though.

On Fri, 08 Oct 2004 22:59:23 GMT, bushbadee put forth the notion that...

The military has been experimenting with a sound weapon that will make you puke and/or crap your pants. I believe it was somewhere around 20 Hz. I'd love to have one.

Can't stand the taste of laxatives? :-)

j

I had a 20 watt amplifier in my hy fi set. I also had a Georgian speaker. A Georgian speaker is a series of Klipse horns. The largest in the Georgian is about 16 feet long (folded) A Klipse horn is 8 to 100 times as efficient in translating electrical to sound energy. One night at 2 am the people above me were celebrating very loudly and keeping me awake. I connected an input from an audio oscillator into the amplifier and at about 15 to 20 cps turned the dammed thing full on. Well the windows rattled and the floor shook. But the loud noise went away.

They never did that again. I guess the reason must have been they were celebrating because they were going to jail the next day. I do not know why or what they did, but the FBI came and fetched them the next day and we never heard from them again.

Bellieve it or not, true story. I wonder if they did do in their pants ???????

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