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Old 27th February 2009, 08:38 PM   #1
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Default Rectifier diodes upgrade

I'm about to make one of the basic mod procedures of my external DAC: the rectifier section is built by the regular 1N4001 diodes and the replacement are Fairchild Stealth fast and soft recovery (FSR) diodes. The goal is to minimize the switching ringing in the power transformer.
So far so good ,except one little detail: originally on the PCB every diode is paralelled by a small capacitor. The question is: in the case of new FSR diodes, should the capacitors in parallel stay or have to be removed? In general, a capacitor in parallel would make the diode at least not fast anymore...
Thanks for your advices!...
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Old 28th February 2009, 01:12 AM   #2
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I don't see any need for the caps since you are putting in fast, soft recovery diodes. If it were me I would remove the caps.
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Old 28th February 2009, 01:44 AM   #3
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Default Re: Rectifier diodes upgrade

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Originally posted by beauty_divine
I'm about to make one of the basic mod procedures of my external DAC: the rectifier section is built by the regular 1N4001 diodes and the replacement are Fairchild Stealth fast and soft recovery (FSR) diodes. The goal is to minimize the switching ringing in the power transformer.
So far so good ,except one little detail: originally on the PCB every diode is paralleled by a small capacitor. The question is: in the case of new FSR diodes, should the capacitors in parallel stay or have to be removed? In general, a capacitor in parallel would make the diode at least not fast anymore...
Thanks for your advices!...
Hi!
The caps across diodes in rectifier are not to make them any slow but that is called "snubber" -they can be simply capacitors value order :from some nano farads to 100 nF., and they can be series RC resistor and capacitor network across diodes In one only order to suppress high frequency parasitic oscillation caused when diode switch off, caused by own diode capacitance , capacitance of the pcb , wires to the transformer and capacitance of secondary windings, and Inductance of the each element mentioned before.
Few days ago I tried with some schottlys , in my case SB360 replaced standard bridge rectifier in my active two way filter (crossover) sub/mid high, with snubbers across each diode and the result for the first 2 minutes was O.K, I got cleaner sound , but when I listened a bit more simply I can not to stay and listen that sound, cos was very sharp with a lot of "air open images" but simply sound which makes me tired!
I switched again to the old standard bridge.
I have good results in the pre-amp with 1N5819 without capacitor or rc snubber across diodes.
You should test this by your own ears, I think it is the best.
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Old 28th February 2009, 04:49 PM   #4
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Default Re: Re: Rectifier diodes upgrade

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You should test this by your own ears, I think it is the best. [/B]
It would be finally tested by ears for sure, but I need to know the theory behind the operation of the FSR diodes as rectifiers. At least some measurements - oscilograms would reveal more technically detailed picture...
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Old 28th February 2009, 05:07 PM   #5
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Default Re: Re: Re: Rectifier diodes upgrade

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Originally posted by beauty_divine

It would be finally tested by ears for sure, but I need to know the theory behind the operation of the FSR diodes as rectifiers. At least some measurements - oscilograms would reveal more technically detailed picture...

Here is the link mentioned many times here:http://www.hagtech.com/pdf/snubber.pdf
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