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Power Supply filter capacitors
Power Supply filter capacitors
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Old 3rd December 2017, 09:46 PM   #1
ggidzinski is offline ggidzinski  United States
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Default Power Supply filter capacitors

I am working on my first gainclone stereo amp based on the LM3886. It looks like there are two camps on power supply filter caps. One is relatively low values such as 1,000uF to maintain the "magic" of the amp. The other is traditional large say 10,000uF filter caps with a snubberized circuit such as the Carlos Filipe design. What are the considerations and tradeoffs?

Thansk,

George
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Old 3rd December 2017, 09:56 PM   #2
scottjoplin is offline scottjoplin  Wales
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Why would you use small smoothing capacitors?
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Old 3rd December 2017, 10:20 PM   #3
bullittstang is offline bullittstang  United States
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I would go with the 10,000uF unless you have space constraints but wouldn't go below 8200, you will be glad you have them.
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Old 3rd December 2017, 11:25 PM   #4
ggidzinski is offline ggidzinski  United States
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Quote:
Originally Posted by scottjoplin View Post
Why would you use small smoothing capacitors?
I have read more than one thread that says to use small capcitor values or you destroy the "magic" of the amp.

One example from Decibel Dungeon/sticky above:

"How much capacitance do I use in the power supply? This subject is hotly debated topic amongst chip amp builders. If you are new to chip amp building I suggest the following arrangement. About 10-100 uF after the bridge rectifier, and 1000 uF on each (power supply) pin of the chip amp. If your speakers are a difficult load, you will need much more capacitance than this. But if you put say 10,000 uF after the rectifier, you will almost certainly notice that the chip amp loses some of its magic. It's another hi-fi compromise, trading some good mid-range, for better bass. There are a couple of ways around the compromise though. Either go for the snubberised supply as shown here, or a regulated supply as described here."

George

Last edited by ggidzinski; 3rd December 2017 at 11:35 PM.
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Old 3rd December 2017, 11:40 PM   #5
scottjoplin is offline scottjoplin  Wales
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I think what the author is getting at there is smoothing and decoupling, two different things which he is confusing with the help of the word magic
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Old 4th December 2017, 12:24 AM   #6
phase is offline phase  United States
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I have used a separate 1000uf after the larger caps, usually closer to the load.
Best of both worlds, and I canít believe it isnít common to do this on diy amps of any variety.
Why does it have to be one or the other?
I learned this from a guy here on another thread who has since passed on, and confirmed it with my own tinkering.

I always used a much larger case than typical, and raise the circuit board on 1Ē+ standoffs so additional parts can be installed on the underside of the board. Surface mount methods donít help this approach.
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Old 4th December 2017, 02:03 AM   #7
dotneck335 is offline dotneck335  United States
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/www.ebay.com/itm/High-current-dual-rail-regulator-kit-for-power-amplifier-or-bench-power-supply-/221251732452?hash=item3383a183e4:g:TkcAAMXQDDZR226 z
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Old 4th December 2017, 02:19 AM   #8
ggidzinski is offline ggidzinski  United States
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Quote:
Originally Posted by scottjoplin View Post
I think what the author is getting at there is smoothing and decoupling, two different things which he is confusing with the help of the word magic
I understand decoupling vs smoothing as well as ripple etc. No complete circuit diagram is provided and neither word is used in the tutorial. Also 10,000uF is discussed as an alternative to 1,000uF so I am going to have to do further research, this just is not clear enough.
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Old 4th December 2017, 04:27 AM   #9
PRR is offline PRR  United States
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You could buy and try both.
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Old 4th December 2017, 06:23 AM   #10
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by phase View Post
I have used a separate 1000uf after the larger caps, usually closer to the load.
Best of both worlds, and I canít believe it isnít common to do this on diy amps of any variety.
Why does it have to be one or the other?
I learned this from a guy here on another thread who has since passed on, and confirmed it with my own tinkering.

I always used a much larger case than typical, and raise the circuit board on 1Ē+ standoffs so additional parts can be installed on the underside of the board. Surface mount methods donít help this approach.
It is common practice to use decoupling caps close to the output devices, often in the region of 100uF and 100nF
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