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Old 18th January 2015, 08:03 AM   #1
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Default Need suggestion of power supply filters and rectifiers

Hi

I need some suggestion of filters for the power transformer. My Acurus only have one 33000uF for each rail. I think I should do better than that. I am looking into CLC filter. I need suggestion of the values and suggestion in where to buy the parts particular the inductor L.

Also, what is the size of the rectifiers I need. The rail is +/-40V to +/-50V max. The amp is going to be 150W or under into 4 ohms. So max is 10Apeak/channel. Is a 30A bridge go enough for 2 channel? I am getting a 625VA transformer.

Thanks

Last edited by Alan0354; 18th January 2015 at 08:27 AM.
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Old 18th January 2015, 12:09 PM   #2
SY is offline SY  United States
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What are you trying to filter?
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Old 18th January 2015, 12:24 PM   #3
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Seeing as you want an L with very low DCR, you're better off winding your own. Use a Sendust toroid core (fairly high AL of 125) to minimize the number of turns you need to wind - handling more than 3 metres of wire stuck through a toroid gets rather tricky.
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Old 18th January 2015, 12:43 PM   #4
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Rather than just asking for parts and values describe what ripple specs you want under what operating conditions. CLC filters for 120 Hz ripple reduction generally cause more problems than they solve. the final LC value is far more useful filtering rectifier harmonics, besides AB audio amps generally contaminate the supply rails more than just the PS line related levels.
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Old 18th January 2015, 03:46 PM   #5
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Thanks for all the replies. To clarify, this is the filter for a 150W per channel stereo power amp. This is the filter right after the toroidal power transformer.

I already designed on the OPS board with a pair of 0.1uF parallel with 10uF close to the collector of each power transistor. Then I have a 2,200uF for each rail on the board. So I think I took care of the high frequency components generated by the Class AB noise of the OPS. I thought the main CLC should be straight forward!!!

The question is whether I even need CLC? I still plan to use smaller parallel C instead of one big C. I just want to see what people use for their filters and the values and what to look out when buying components.

Regarding to winding the toroid inductor, is toroid very bad with DC current? This is after the rectification, it is a bunch of half sine waves that has all the DC component in it.

Thanks
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Old 18th January 2015, 03:56 PM   #6
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most folks use 1.0 V rms baseline for ripple, which gives a useful rule of thumb 2,200 uF / A, for full wave 120 hz ripple. I think it's a linear relationship, so double up for each 6 dB reduction.

For other filters CLC CRC model on a spice type simulation tool is recommended. model small signal 1st then re-check on large signal. model the OP into a switched load. add parasitic esr and wiring inductances for each bypass.

sqRT(150W/4 ohm) ~ 6.1 A / channel + Ibias >
Class AB high bias uses 7 A / channel > 30,000 uF / rail for stereo
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Last edited by infinia; 18th January 2015 at 04:06 PM.
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Old 18th January 2015, 03:57 PM   #7
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Quote:
Class AB noise
What is "Class AB noise"?

More importantly, what's the s/n target and what's the PSR of the circuit?
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Old 18th January 2015, 03:59 PM   #8
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Why ask for "suggestions" for the cap values, when they can be calculated from knowledge of the ampliifer PSRR and your desired hum level? What other people use may be irrelevant, apart from being a plausibility filter to check your own calculations.

Toroids may be inappropriate for the choke, as you have substantial DC through it.
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Old 18th January 2015, 04:18 PM   #9
infinia is offline infinia  United States
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hummm we don't want no hum
line ripple is usually calculating Vrail operating limits , large signal stuff
PSRR at 120 Hz for modern / decent class AB is usually a large number anyways maybe what around > 70-80 dB on worst rail
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Last edited by infinia; 18th January 2015 at 04:28 PM.
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Old 18th January 2015, 04:42 PM   #10
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Guys, I have no idea. I thought this is supposed to be simple. I don't even know what ripple voltage I want!!! Is it that complicated? I saw my Acurus only has one 33000uF on each rail. I thought maybe I can do better.

What is good enough, I just want something a little better!!! I don't want to make it a design project. My head is spinning choosing parts, design and layout the OPS pcb already, have not got into the IPS and VAS yet!!!

Am I in the wrong forum? Maybe moderator should move this to "Power Supply". Thanks

Last edited by Alan0354; 18th January 2015 at 04:46 PM.
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