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Old 3rd September 2012, 08:57 AM   #1
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Default the definitive opamp decouplig question

Hi, refered to decoplig the opa627, I searched in this forum about the best components for decopupling and I've found very differents opinions, + to ground, - to ground , and + to - 0.1 uf. so I'm still very confused:
0.1 tantal + 10 to 100 uf electrolytic
0.1 ceramic np0 + 10 to100 uf electrolytic
0.1 ceramic xr7 + 10 to100 uf electrolytic
0.1 film + 10 to100 uf electrolytic
only 0.1 tantal
only 0.1 film


Any definitive combination? Is important the quality of the electrolytic? (I have silmic, elna hfq, nichicon fine gold and muse in my stock)
thanks !!
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Old 3rd September 2012, 09:30 AM   #2
AndrewT is offline AndrewT  Scotland
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start with the datasheet recommended decoupling scheme.
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Old 4th September 2012, 09:02 AM   #3
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Cb1 = 50/pi*fc
primary bypass capacitor equals fifty divided by (pi times the op amp unity gain crossover frequency)

Cb2 = Lbp1
secondary bypass capacitor equals Cb1's parasitic inductance
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Old 4th September 2012, 10:53 AM   #4
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Quote:
Originally Posted by sofaspud View Post
Cb1 = 50/pi*fc
primary bypass capacitor equals fifty divided by (pi times the op amp unity gain crossover frequency)

Cb2 = Lbp1
secondary bypass capacitor equals Cb1's parasitic inductance
thanks I will check this
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Old 4th September 2012, 12:17 PM   #5
marce is offline marce  United Kingdom
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0.1uf SMD ceramic (smallest package you can find) next to supply pins Pos to GND and Neg to GND. X7R have the smallest cases so are best.
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Old 4th September 2012, 02:31 PM   #6
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Originally Posted by marce View Post
0.1uf SMD ceramic (smallest package you can find) next to supply pins Pos to GND and Neg to GND. X7R have the smallest cases so are best.
Thanks Marce, I will try this, I dont have measure equipment so I just use my ear to find the best combination. now I have 100uf + 0.01 ceramic np0 + to ground and - to ground. to my ear sounds exactly the same with just 0.1 uf film + to -. I'm a little surprised about how some people achieve "big sound improvements" with just different capacitor rolling in op amps. I barely find any difference even with differents opamps "upgrading" in 3 differents preamps, very subtle changes, maybe different coloration but I cant say better.
Thanks again
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Old 4th September 2012, 03:10 PM   #7
DF96 is offline DF96  England
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Quote:
Originally Posted by bernat123
I'm a little surprised about how some people achieve "big sound improvements"
I'm sure you have noticed that men never boast about anything, especially when it might imply that someone else is less skillful, less choosy or less observant. Men hate to hurt each other's feelings so tend to play down differences which they, rightly or wrongly, perceive to be present.
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Old 4th September 2012, 03:39 PM   #8
AndrewT is offline AndrewT  Scotland
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Originally Posted by bernat123 View Post
......................... I have 100uf + 0.01 ceramic np0 + to ground and - to ground. to my ear sounds ..................
This may be a bad combination.
The NP0 may be too close to a "perfect" capacitor with losses/parasitics that are too low to achieve sufficient damping of the transients.

You should check with something other than your ears to identify a properly cleaned line that is near enough glitch free when transients pass.
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Old 4th September 2012, 03:49 PM   #9
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Originally Posted by AndrewT View Post
This may be a bad combination.
The NP0 may be too close to a "perfect" capacitor with losses/parasitics that are too low to achieve sufficient damping of the transients.

You should check with something other than your ears to identify a properly cleaned line that is near enough glitch free when transients pass.
I'm sure I'm doing something wrong, I will try with 0.1 film, the opa627 is replacing the rc4560 but I feel the rc4560 still sounding more natural, I'm sure the opa627 is better than the rc4560 .
thanks for your support
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Old 4th September 2012, 03:53 PM   #10
AndrewT is offline AndrewT  Scotland
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Why are you using your ears to prove the non-existance of rail ripple when transients are passed?
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