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Old 15th November 2011, 04:57 PM   #1401
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Finsihing the first PSU for Rod Coleman heaters
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Old 16th November 2011, 02:50 PM   #1402
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I have a doubt, due to the fact chokes are dual 2mH 1.5A, I suppose that I have to connect in parallel to reach 3A, right?
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Old 16th November 2011, 05:18 PM   #1403
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Yes, but the inductance will 1mH. Not sure what 1mH will accomplish though.
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Old 16th November 2011, 05:27 PM   #1404
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Quote:
Originally Posted by merlin el mago View Post
I have a doubt, due to the fact chokes are dual 2mH 1.5A, I suppose that I have to connect in parallel to reach 3A, right?

Felipe, they look like common-mode chokes.

Connect them like the top one in this drawing (taken from my application note) ........

...
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Old 16th November 2011, 06:04 PM   #1405
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Old crt monitors that people throw out have some nice common mode chokes at the very input of their power supplies. You can also find some in computer SMPSs. Those I've measured to be anywhere from 18mh to 33mH. Have a look what the effect of a few values is: 1mH 33mH 85mH 1H 3H, and this in the ideal world of the simulator. My point is, very little noise attenuation is to be expected from such small value chokes.
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Old 16th November 2011, 06:30 PM   #1406
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The old monitors use the CMCs to keep high frequency noise from getting OUT of the monitor (for emissions test limits).

In DHT filament supplies, the goal is to keep the mains-carried HF from getting IN.

And it is important to keep HF/VHF/UHF from getting in, since it's hard to predict what effects it will have. Most HF noise is AM or FM modulated, or more likely, both together.

HF noise can couple right through your signal chain, even backwards from the preamp DHT to your RIAA or DAC signal stages. If it gets this far, the risk of demodulation, and audio noise is very high.
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Old 16th November 2011, 06:39 PM   #1407
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Quote:
Originally Posted by Rod Coleman View Post
The old monitors use the CMCs to keep high frequency noise from getting OUT of the monitor (for emissions test limits).

In DHT filament supplies, the goal is to keep the mains-carried HF from getting IN.
Chokes are not directional, keeping the noise in isn't any different than keeping the noise out. Since they're easy to come by, you can put as many in series as you want/have. They are intended for high current, so they'd be fine for the dht supply.
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Old 16th November 2011, 07:17 PM   #1408
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Here's a sample of such choke. Two windings, 30mH with a Q of 10 each, physical size of about 28x30mm. Can be used as common mode choke, or with the two windings in series (cross connected); in this case it measured as 100mH with a Q of 24.

So, why bother though. What's the difference between a 1mH choke and a 30mH choke? The 1mH choke in the simulation example above makes the 1kHz noise 12.5 times lower, whereas The 30mH choke makes it 125 times lower.

Disclaimer: I'm not selling old monitors or such chokes. I'm merely saying that such chokes exist and you'll feel good about doing something good for the environment. Most old electronics end up in the landfill.
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Old 16th November 2011, 07:24 PM   #1409
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Quote:
1kHz noise 12.5 times lower
That's not bad is it? I'm suprised actually.
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Old 16th November 2011, 07:42 PM   #1410
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Don't know, all I'm saying is that if 10 times better is easy, why not do it?
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