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Amplifying an ac sin wave 1khz...

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devronious2009

New Member
Hi there, new to the forums. I have need to amplify an ac sine wave and perhaps square wave too, that runs at 1khz but might vary between 100hz to 1mhz. The input is from a function generator, probably in the millivolts, the output is 50volts at about 5 amps. Or 250watts I suppose. Any circuits designed for this? Can I just use a pnp and npn power transistor or something simple?

Thanks,

Devin
 

kchriste

New Member
Forum Supporter
That's a pretty tall order. What exactly are you going to need this kind of power for?
 

bountyhunter

Well-Known Member
Good luck with that 100Hz to 1MHz amp.... output is 50V @ 5Amps?:D

So all you really need is a basic wideband power amp like a stereo amplifier except you need about 50X the bandwidth.....;)

BTW: you want to amplify a 1MHz square wave? That really is impossible, at least impossible to do without severely distorting it. The rising and falling edges of square waves have frequency content that goes to infinty (pretty close anyway, if the edges are sharp).
 
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devronious2009

New Member
Wow I wasn't expecting such a fast response, thanks. Well even if its just for 1khz that's really all I need. I would like to use both a square and a sine. If there is some distortion in the square that's ok, like it turns into somewhat of a sine or something is acceptable.

Its for a physics experiment. 1khz is the target and that's what I need for now, I was hoping for some adjustability but I would be OK with just targeting 1khz for now.

Any ideas, simple as possible hopefully.
 

crutschow

Well-Known Member
Most Helpful Member
BTW: you want to amplify a 1MHz square wave? That really is impossible, at least impossible to do without severely distorting it. The rising and falling edges of square waves have frequency content that goes to infinty (pretty close anyway, if the edges are sharp).
The general rule is that a square-wave can be amplified with a frequency response of 10 times the fundamental square-wave frequency. That gives a good enough square-wave for most engineering applications.
 
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devronious2009

New Member
What's HHO?

Anyways, can't I just use some kinda transistor system?

OK how about if I make the target smaller? What I absolutely require to run the experiment is +-50v at 2 amps min. The wave can just be a sine wave only. Running at 1khz.
 
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kchriste

New Member
Forum Supporter
The wave can just be a sine wave only. Running at 1khz.
The simplest, non techical way, of dealing with it is to buy an audio amplifier with enough power (160W) to do what you want. Be sure to over rate the amp (x2 or more), because they are not usually designed for continous duty.
You could also build one if you wanted.
 
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devronious2009

New Member
Oh right, so I could just take a function generator and connect it to the inputs on a Rockford Fosgate amplifier and away I go? Adjust the input voltage and the gain to get the output voltage of 50volts?

But aren't amps built for like 4 ohms which would be an incredibly small voltage?

This is driving considerable load ohms. 50-300 ohms. But maybe I could modify the load to be smaller ohms or something.

-Devin
 
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kchriste

New Member
Forum Supporter
Pretty much. Just be sure not to drive the amp into clipping. An oscilloscope on the output would help.
But aren't amps built for like 4 ohms which would be an incredibly small voltage
No. To get 160 watts across 8 ohms you need 36Vrms which equals apx 102Vpk-pk.
This is driving considerable load ohms. 50-300 ohms. But maybe I could modify the load to be smaller ohms or something.
The amplifier won't care if it is one that uses transistors, ICs, or MOSFETs. As long as the load is the same, or higher resistance, than the spec, the amp will be fine. You just won't get the full rated power out of it. Only tube amps suffer from an open or too high impedance load due to transformer coupling/matching.
 

mneary

New Member
the output is 50volts at about 5 amps.
50/5 = Ten ohms.
This is driving considerable load ohms. 50-300 ohms. But maybe I could modify the load to be smaller ohms or something.
Check your math. Only one of these statements is correct.
 
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devronious2009

New Member
50/5 = Ten ohms.

I had thought about dropping the ohm rating to drive more amperage into the 5 amp area, but really I want some extra head room anyways.

Check your math. Only one of these statements is correct.

I had considered this range with that idea. But I can drop it to 8 ohms I think. It will take a redesign of the system which is something I wanted to avoid, the sweet spot for me is 150 ohms at the moment.
 

mneary

New Member
An amplifier in the US (you don't say where you are) that claims a particular RMS wattage has to specify the resistance into which that power is delivered. In other markets, trade regulations may be different.

If you're using an "8 ohm" amplifier (a very common specification point) and you need 50VRMS, then without any headroom at all it's a "312.5 watt" amplifier. The amplifier may have a data point at 4 ohms, but that's irrelevant here.

Now, if your load doesn't need to be "grounded", you can use a "stereo" amplifier in a bridged configuration. Two "8 ohm" amplifiers work out of phase against one another to provide double the voltage into 16 ohms (or more.) Each of the amplifiers only needs to provide 25VRMS, which requires a nameplate rating of only "76 watts" per channel (plus headroom).
 

devronious2009

New Member
But for simplicity and cost effectiveness sake, is there a simple schematic for amplifying an AC signal using a DC power supply? I'm sure there is, isn't there?

-Devin
 

mneary

New Member
You can build it or purchase it, but it's still going to look a lot like an audio amplifier. You can compromise on the specifications to save a few pennies, but not much.

If you want to build one, there are plenty of designs on the net. Many of us would be happy to evaluate proposals. I would start with a pair of LM3886's in bridge mode because I have some boards with chips left over from an old project.
 
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vortex2009

New Member
sine wave boost


Hi Dev,

what are you trying to do? I understand the sine-wave but swinging between 100hz to 1meghz?? eh??

is it a College project??
it sounds interesting but as the experts on here it's beyond me lol...

I wanted a sine-wave signal but at a high SPL level 140DB !!!
blow your ears off.
hope you get on with it though
Vortex..
:D
 

devronious2009

New Member
forget about the range of hertz. I just want to amplify 1 khz sine wave. I found a transistor design that was simple using a DC source. Any ideas on the transistor simple design?
 

vortex2009

New Member
amplify Sine wave..

Hi DEv.

1) Ok have you a Maplin store near you? If so get the TDA2030 its very high power amp, cant remember the Specs, but go a "Google" on it.. if thats not what your after 2) Maplin do a kit Amp 200watts /300watts, and they quite good price too...

Good luck.. hope I've helped a little, I do my own electronics at home for a hobby but I take it quite seriously.. & I've learnt the Maths side to it.. because if one dont, you will hardly get anywhere.. see it's 50-50
50, maths part 50 Practical work.. get me.. its taken me 7years to know what I know now..!!!
all the best
Vortex..
PS: So go here Maplin Electronics ? Website- 1TB Seagate FreeAgent External Drive
:)
 
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