what happens to voltage when I add a good choke
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 17th July 2013, 05:21 AM #1 cyclecamper   diyAudio Member   Join Date: May 2010 Location: Chicago IL, Long Beach CA, Vienna VA what happens to voltage when I add a good choke If I add a reasonable-inductance but enormous choke with very little DC resistance before the capacitor filters in the main B+ supply, it should be easier for the power transformer to deliver current thru more of the wall-supply cycle, but what is the end result for the resultant B+ voltage? Will it always drop? I guess I should model but what's the rule of thumb?
 17th July 2013, 05:28 AM #2 KatieandDad   diyAudio Member     Join Date: Nov 2011 Location: UK The L should be between the C's ie CLC. You will get a small drop in voltage.
 17th July 2013, 07:53 AM #3 Enzo   diyAudio Member   Join Date: Sep 2004 Location: Lansing, Michigan Look up any basic tutorial on power supplies and read the differences between capacitor input filter versus choke input filter. The cap input filter charges to peak, or about 1.414 times RMS voltage of the AC. The choke input filter will charge to about 0.9 times RMS. Chokes
 17th July 2013, 10:23 AM #4 DF96   diyAudio Member   Join Date: May 2007 An ideal choke input supply gives you a DC voltage equal to 2 sqrt(2)/pi of the secondary AC RMS voltage. This is 90.03%. The derivation requires calculus and trigonometry - the maths you learnt in school does have its uses!
Nigel Goodwin
diyAudio Member

Join Date: Jul 2005
Location: North Derbyshire
Quote:
 Originally Posted by DF96 An ideal choke input supply gives you a DC voltage equal to 2 sqrt(2)/pi of the secondary AC RMS voltage. This is 90.03%. The derivation requires calculus and trigonometry - the maths you learnt in school does have its uses!
So does building it and bunging a meter on it!

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Nigel Goodwin

 17th July 2013, 03:07 PM #6 DF96   diyAudio Member   Join Date: May 2007 A meter will tell you what it is doing, but only after you have built it. A meter won't tell you why it is doing it, or what to change to make it do something different.
 24th July 2013, 04:42 AM #7 cyclecamper   diyAudio Member   Join Date: May 2010 Location: Chicago IL, Long Beach CA, Vienna VA Thanks! Very useful rule-of-thumb. ...and thanks especially for not ridiculing my ignorance.
 24th July 2013, 05:01 AM #8 cyclecamper   diyAudio Member   Join Date: May 2010 Location: Chicago IL, Long Beach CA, Vienna VA Thanks again Enzo, I remember reading that link from aikenamps.com before but apparently neither the math nor rule of thumb stuck in my brain. Unlike what Katie & dad posted, a CLC is still basically a capacitor input filter, and a choke input filter like I asked about has a choke immediately after the rectifier. But either way, I'm not talking about a small choke between B+ and grid supply & preamp either. I'm cooking up another single-ended guitar amp and picking out a power transformer, and I have some very nice chokes. So I'm just deciding what to do with them, if anything.
 24th July 2013, 07:23 AM #9 Enzo   diyAudio Member   Join Date: Sep 2004 Location: Lansing, Michigan That is why they are called capacitor INPUT filter or choke INPUT filter. it is about what the rectified AC sees first. What comes after a cap doesn't change that.
Nigel Goodwin
diyAudio Member

Join Date: Jul 2005
Location: North Derbyshire
Quote:
 Originally Posted by cyclecamper Thanks again Enzo, I remember reading that link from aikenamps.com before but apparently neither the math nor rule of thumb stuck in my brain. Unlike what Katie & dad posted, a CLC is still basically a capacitor input filter, and a choke input filter like I asked about has a choke immediately after the rectifier. But either way, I'm not talking about a small choke between B+ and grid supply & preamp either. I'm cooking up another single-ended guitar amp and picking out a power transformer, and I have some very nice chokes. So I'm just deciding what to do with them, if anything.
Chokes were used historically to reduce hum, because decent sized capacitors weren't available, so there's little reason to use them these days - unless you're going for the extra distortion as the HT rails comes down lower?.
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Nigel Goodwin

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