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Old 30th April 2010, 03:37 PM   #11
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Quote:
Originally Posted by panomaniac View Post
Well that's an oddball thing! I vaguely remember seeing something like that in an old amp book once, but only vaguely. Will be interesting to see what you come up with.

Where will you get the transformers?

EDIT: Never mind, I just read the article.
There is a new webpage that shows hot to build a simple mag-amp with off the shelf materials. The first was a mag-amp that controlled a 60 watt lightbulb, and the second was a very basic mono audio amplifier.
He used normal 110v to 12v transformers for the bulb, and for the audio amplifier he used hand wound toroids.

I see no reason whatsoever why the normal transformers won't work with the audio amplification.

About the need for 35 khz: you need the hf for audio. Lights and motors can be controlled with 60 hz.

My intention is to build a much more advanced audio amplifier. This was proof of concept, I'm making something I can use and anjoy, something hardcore.
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Old 30th April 2010, 04:07 PM   #12
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Originally Posted by Elvee View Post
A Royer converter is simple, robust and gives a good approximation of a sinewave.
It can be made to work from rectified and filtered 12VAC.
That will put out 35 Khz? Or is it adjustable.
I am not familier with such a circuit. Also the mag-amp doesn't nedd (in this case) a dead on freq. The old book I have says 30 khz, and the guy who replicated it used 35 khz.
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Old 30th April 2010, 04:36 PM   #13
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I imagine you need 35kHz so that it's supersonic.

The 35kHz driver circuit you describe is trivial to construct, and there are dozens of ways of constructing it. Most involve an oscillator and an amplifier, although an oscillator is an amplifier, so both functions can be combined. It's because the circuit is so general that you can't find one. It's the kind of thing anybody that with a grounding in basic amplifier electronics can build because the frequency is so low it's virtually baseband.

There are relaxation oscillators, resonant LC oscillators, crystal oscillators, YIG oscillators, more oscillator types than you could shake a stick at. You can probably build an oscillator with a magnetic amplifier. (!)

(Un)fortunately your chosen area of interest is leading you to ask broader questions than you suspected. Somebody can certainly post a circuit that will provide the drive you need, but in that case you won't learn much.

It's not a requirement that you learn anything, but one way that you could is to post your best guess circuit, or even a link to a circuit you think is capable of being adapted and wait for the comments.

w
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Old 30th April 2010, 06:35 PM   #14
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Quote:
Originally Posted by wakibaki View Post
I imagine you need 35kHz so that it's supersonic.

The 35kHz driver circuit you describe is trivial to construct, and there are dozens of ways of constructing it. Most involve an oscillator and an amplifier, although an oscillator is an amplifier, so both functions can be combined. It's because the circuit is so general that you can't find one. It's the kind of thing anybody that with a grounding in basic amplifier electronics can build because the frequency is so low it's virtually baseband.

There are relaxation oscillators, resonant LC oscillators, crystal oscillators, YIG oscillators, more oscillator types than you could shake a stick at. You can probably build an oscillator with a magnetic amplifier. (!)

(Un)fortunately your chosen area of interest is leading you to ask broader questions than you suspected. Somebody can certainly post a circuit that will provide the drive you need, but in that case you won't learn much.

It's not a requirement that you learn anything, but one way that you could is to post your best guess circuit, or even a link to a circuit you think is capable of being adapted and wait for the comments.

w
Oh no! I don't just want to get the job done, I want to learn as much
as I can about what I'm doing. I like learning.
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Old 30th April 2010, 07:00 PM   #15
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Try putting this into Google.

op amp oscillator circuit
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Old 30th April 2010, 07:36 PM   #16
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by CivicProtection View Post
That will put out 35 Khz? Or is it adjustable.
I am not familier with such a circuit. Also the mag-amp doesn't nedd (in this case) a dead on freq. The old book I have says 30 khz, and the guy who replicated it used 35 khz.
It can be adjusted by changing the capacitor value, or modifying the gap of the transformer.
The frequency is not particularly stable or accurate: it is a compromise between a pure LC oscillator and a multivibrator.
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Old 1st May 2010, 06:47 PM   #17
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As a transistor free direction, will this LC work?

http://img684.imageshack.us/i/circuit2t.jpg/

Last edited by CivicProtection; 1st May 2010 at 06:52 PM.
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Old 1st May 2010, 06:52 PM   #18
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Here is a tube version that will create a perfect supply for mag-amp.
But how do I substitute the tube and transformer for modern rectifier?
Imageshack - powersupplys.jpg
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Old 2nd May 2010, 08:31 AM   #19
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Any ideas in regards to the tube version?
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Old 2nd May 2010, 04:41 PM   #20
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Here's a simple logic-gate oscillator with a logic-level mosfet amp. The output is a square wave but the harmonics will quickly be attenuated. It'll probably be fine in this application. The output is never going to be hi-fi. You need the 5V for the TTL chip, I've made the mosfet supply 15V nominal. I think the values are OK for the frequency (~37kHz) but this is something you can check for yourself, and anyway the circuit will run at a wide range of frequencies, it's just a question of tweaking it.

Click the image to open in full size.

Click the image to open in full size.

w
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