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?
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?
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.
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-amp/ns2093-cr-33-l.jpg
This is for an audio magnetic amplifier.
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...
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...
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.
Should be great fun to play with. I like your suggestion of using an amp for a test power supply.
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.
Attachments
That's pretty cool, I have a few e-books on the mag-amp for anybody who wants them.
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.
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.
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
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.
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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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
But how do I substitute the tube and transformer for modern rectifier?
Imageshack - powersupplys.jpg
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.
w
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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