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Old 23rd June 2010, 12:27 AM   #161
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When bypassing with low value, low esr capacitor it will only "throw" the noise back and forth between rails, so its better that the noise get dissipated somewhere like with a snubber together with the bypass capacitor. Like IRF does with their amp, 100nF bypass and 100nF + 1 ohm snubber.

Schematic on page 30 (C13+R31/C14+R32)
http://www.irf.com/technical-info/re...iraudamp4a.pdf

And i see on page 29 they use 100k resistors (R57, R58) between the rails to ground together with the 1000uF electrolytes. High frequency noise have no current (Ampere) potential, and will be dissipated by the 100k resistors.
Hope that helps (correct me if im wrong)
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Old 23rd June 2010, 06:48 PM   #162
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Hello,

Francis Ibre a very respected and famous audiophile in France explain that bypassing PSU electrolytics with film caps is a very good thing for sound quality but he laughs when he see schematics with little values (often less than 1uf). He says that to have serious effect you have to increase the value up to 20uf. I tested 2uf mkp capacitors and the quality of the music increased (more "airy") when I replaced it with 20uf mkp... whow it seemed like I changed the amp! The increase in quality was unbelievable!
You can thind on Ebay 20uf MKP for about 5 euros
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Old 24th June 2010, 01:09 AM   #163
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You could always try some of these:
http://www.wima.com/EN/WIMA_DC_Link_HC.pdf

JK

Large physical size should be avoided as much as possible, if not ESL is low.

Bypass film caps should be a larger value i think too, but i would not feed it with ac current when its purpose is to deliver ac current for the output. So i would use snubbers to get rid of frequencies above desired output bandwidth placed between the bypass film cap and electrolyte caps. And high value resistors in parallel with the electrolytes like IRF does, because electrolyte is too big physical (ESL) together with too high ESR to bypass high frequencies.
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Old 24th June 2010, 07:27 PM   #164
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After doing a bit of research...

Click the image to open in full size.

C1 - C4 - WIMA MKM4 1.0uF 250V
C5 - C10 - 1000uF 200V Nichicon KX
R1 - R4 - 3.3Ohm 5W Non Inductive
C11 & C12 - 2200uF 250V Panasonic TUP
L1 & L2 - 10mH 20A JW Miller Choke ( 5522RC )

The Cap Bank will be on a separate board and its gonna have 4 x 2.2uF 850V EPCOS Snubber Film Caps at the input and output of the cap bank which will be comprised of 12 x 10000uF 100V Chemi-Con KMH caps
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Old 26th June 2010, 06:00 AM   #165
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Snubbers with 1000uF capacitors will filter away 50hz into the resistors, making huge waste of power. 1uF maybe? Snubbers are there to remove transients, but in case of IRF amp its there to lower transients in supply voltage coming from buspumping in the output stage.

I did some simulations on powersupply with 50hz ac, and it seems like adding those 100k resistors at the electrolytes is a bad idea. Because they constantly draw currents from the electrolytes, and makes more noise in the supply voltage. So i would put the resistors and snubbers before the rectifier or transformer. Putting inductors in the curcuit with simulator made more noise also. Dont know how reliable simulator is, any comments?
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Old 29th July 2010, 05:26 PM   #166
Elvee is offline Elvee  Belgium
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Default Some more material:

Here are some actual and systematic data on the subject of paralleling a small ceramic cap (100pF - 1nF - 10nF - 100nF) with various types of electrolytics.

These are impedance plots between 0.3 and 100MHz, and in this particular set-up, the 0dB level is equivalent to 37.5 ohm.

A short executive would be: another myth is gone.
Basically, all the serious guys (and gal) in this thread are right.

A complete description of the test set-up and methodology can be found here (in french):
Tout ce que vous avez toujours voulu savoir sur les condensateurs de découplage sans oser le demande - Forum Électronique
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Old 29th July 2010, 05:28 PM   #167
Elvee is offline Elvee  Belgium
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Continued......
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Old 30th July 2010, 09:56 AM   #168
AndrewT is offline AndrewT  Scotland
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do those results show that there is insufficient damping of the two //cap resonances in the esr inherent in the two caps used for each experiment?

If more damping resistance is required, where should it be placed? In the path of the big electro and/or in the path of the smaller HF bypass?
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Old 30th July 2010, 02:32 PM   #169
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by AndrewT View Post
do those results show that there is insufficient damping of the two //cap resonances in the esr inherent in the two caps used for each experiment?

If more damping resistance is required, where should it be placed? In the path of the big electro and/or in the path of the smaller HF bypass?
The subject is not simple, and I remember Eva had given valuable advice about it, in this thread or in another one.

But basically, in most case, bypassing directly (locally) the electrolytic is not only useless, but harmful most of the times.
If damping has to be added, it has to be either in series with the small one (0.47R f.e.), or to be a RC network of his own, added to the two paralleled capacitors.
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Old 30th July 2010, 04:46 PM   #170
Elvee is offline Elvee  Belgium
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Here is the post (or one of them) in question:
Is bypassing PSU capacitors effective?
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