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Old 30th April 2010, 09:34 AM   #1
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Default 35khz High Frequency AC

To build my magnetic audio amplifier, I need a 12v AC source running at a frequency of 35Khz. The input into such a circuit would be stepped down 60hz line voltage at 12v AC.

I looked all over the net, and I couldn't find a good simple circuit. I have explored the possibility of building a tiny spark-gap Tesla coil tuned circuit, but I was hoping for something more conventional.

Any ideas?
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Old 30th April 2010, 10:45 AM   #2
Mooly is offline Mooly  United Kingdom
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So your requirement is,

Input 12VAC 60hz
Output 12VAC 35Khz.

Does the output have to be fully floating ? What sort of output current ? Is efficiency a prime concern ? Is output waveform purity a concern ?

Options,
A DC DC convertor/amp with built in 35k signal source.
An amp feeding a custom transformer perhaps. Bridged amp feeding same.
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Old 30th April 2010, 12:32 PM   #3
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Originally Posted by Mooly View Post
So your requirement is,

Input 12VAC 60hz
Output 12VAC 35Khz.
Yes, you got it.
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Old 30th April 2010, 12:38 PM   #4
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Originally Posted by Mooly View Post
So your requirement is,

Input 12VAC 60hz
Output 12VAC 35Khz.

Does the output have to be fully floating ? What sort of output current ? Is efficiency a prime concern ? Is output waveform purity a concern ?

Options,
A DC DC convertor/amp with built in 35k signal source.
An amp feeding a custom transformer perhaps. Bridged amp feeding same.
I'd like the output current to be around 1-5 amps. That way I can control it later with an inductor if I need to.

it will be going into a circuit that will have rectifiers in it which will chop it up, to half-wave or something like that, it will pass into iron core transformers but being that it isn't full wave there isn't hysteresis heating in the iron.

This is the diagram I am working off of:
http://sparkbangbuzz.com/mag-audio-a...93-cr-33-l.jpg

This is for an audio magnetic amplifier.
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Old 30th April 2010, 01:19 PM   #5
Pano is offline Pano  United States
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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.
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Old 30th April 2010, 01:58 PM   #6
Mooly is offline Mooly  United Kingdom
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It is oddball isn't it. Never seen anything like that before
You might find faster diodes an advantage such as BY399 etc.

If you just want to play around with the circuit initially then an old ordinary amp would do to feed the 35 khz with a suitable input from a generator. Perhaps ensure the "primary" side isn't grounded etc and use a battery and a portable CD player/MP3 as a source.

Fascinating thing really... although I think I will probably stick to my Lateral FET amp

Go for it...
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Old 30th April 2010, 02:04 PM   #7
Pano is offline Pano  United States
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Now I remember where I've seen it - by the dozens. In a theatre in West London. They had a room full of magnetic amps used as the lighting dimmers. Tube circuit control, but the tubes didn't do the heavy lifting, the magnetic circuit did. It was 220V/50Hz that was controlled in this case.

Should be great fun to play with. I like your suggestion of using an amp for a test power supply.
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Old 30th April 2010, 02:28 PM   #8
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by CivicProtection View Post
To build my magnetic audio amplifier, I need a 12v AC source running at a frequency of 35Khz. The input into such a circuit would be stepped down 60hz line voltage at 12v AC.

I looked all over the net, and I couldn't find a good simple circuit. I have explored the possibility of building a tiny spark-gap Tesla coil tuned circuit, but I was hoping for something more conventional.

Any ideas?
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.
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File Type: gif Royer35K.GIF (53.1 KB, 374 views)
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Old 30th April 2010, 03:30 PM   #9
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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.
Thank you so much!
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Old 30th April 2010, 03:31 PM   #10
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Originally Posted by panomaniac View Post
Now I remember where I've seen it - by the dozens. In a theatre in West London. They had a room full of magnetic amps used as the lighting dimmers. Tube circuit control, but the tubes didn't do the heavy lifting, the magnetic circuit did. It was 220V/50Hz that was controlled in this case.

Should be great fun to play with. I like your suggestion of using an amp for a test power supply.
That's pretty cool, I have a few e-books on the mag-amp for anybody who wants them.
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