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Old 6th December 2012, 10:05 AM   #7771
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by nigel pearson View Post
.............I hope Andrew T is reading this .............
Not really, I pop in now and again.
There is so much to read and to understand that I found I could not spare the time that this Thread deserved from me. So I gave up reading all of it about 8weeks ago. There are three other Threads that I have had to give up with, simply due to lack of time.
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Old 6th December 2012, 10:08 AM   #7772
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I friend I made at the Frankfurt hi fi show who owns one of the USA's more esoteric speaker brands asked me which filter curve he should use for real music ? I said none , try Phi . He did and said it works correctly . He wrote to me recently and said life is grim in the real world of selling . Out of respect I better not say who .

Andrew . It proves coincidence is normal . The French define it as things that " will " meet if my understanding is correct ? That's the problem with English . We pirate words and never know quite of what we are saying ? Salty sea dogs all ( only the English perhaps ? )

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Old 6th December 2012, 10:44 AM   #7773
dvv is offline dvv  Serbia
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I read a paper that concluded that the minimum capacitance RATIO when paralleling an electrolytic with a film capacitor was 16:1
I did not understand all the maths but it did seem to make sense.
That was in the days before I saw what others are finding with ringing when doing such with low ESR capacitors.

If there is some truth in that conclusion, then 100:1 may well be a good ratio to use that gets one well away from the "ringing" condition
The trouble is, Andrew, when there is a minimum, there is also a maximum. The whole story would be to know both.

For example, I usually bypass a quality electrolytic cap of 220 uF with a metallized film Wima capacitor of 2.2 uF, or 100 times lower. So far, it has always worked.
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Old 6th December 2012, 10:55 AM   #7774
AndrewT is offline AndrewT  Scotland
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Originally Posted by dvv View Post
The trouble is, Andrew, when there is a minimum, there is also a maximum. The whole story would be to know both.

For example, I usually bypass a quality electrolytic cap of 220 uF with a metallized film Wima capacitor of 2.2 uF, or 100 times lower. So far, it has always worked.
Is this post telling us that if the ratio is much bigger than 100:1 then the ringing problem comes back?

I hope that is NOT what you are saying.
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Old 6th December 2012, 11:09 AM   #7775
fas42 is online now fas42  Australia
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An electro bypassed with a single film should never have a problem, no matter what the values are ...

Frank
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Old 6th December 2012, 11:11 AM   #7776
AndrewT is offline AndrewT  Scotland
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But I have seen many posts showing the ringing measured across the capacitors.
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Old 6th December 2012, 11:33 AM   #7777
fas42 is online now fas42  Australia
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Quote:
Originally Posted by AndrewT View Post
But I have seen many posts showing the ringing measured across the capacitors.
Could you give me a precise link to one of those posts, or some other way of tracking down the relevant material? I am interested in what the circumstances were in total: for example, if there was another film cap in the electrical "neighbourhood" of the first film, with a "bad" ratio match, then I would expect ringing.

Another mistake that is made is to have the leads of the bypass cap long, so that it physically fits in. This is bad in every sense; a rule of thumb is that the smaller a cap, the shorter its leads need to be. Otherwise, the exercise is close to useless ...

Frank
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Old 6th December 2012, 11:35 AM   #7778
AndrewT is offline AndrewT  Scotland
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memory no good.
Some are posted by our Member that claims to be a digital PSU and digital Amp designer.
I think Cordell did a circuit/test procedure to measure the effect of fast transients on the PSU caps.


And yes to lead lengths.
The straight through must be the smaller cap value. The high value cap then gets tacked on afterwards.
It's the same philosophy that is applied to the on board decoupling. The small caps must be right next to the power Pins (= short route lengths).
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Last edited by AndrewT; 6th December 2012 at 11:39 AM.
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Old 6th December 2012, 11:49 AM   #7779
dvv is offline dvv  Serbia
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Originally Posted by AndrewT View Post
Is this post telling us that if the ratio is much bigger than 100:1 then the ringing problem comes back?

I hope that is NOT what you are saying.
No, I am NOT saying that.

Please note that the ratio is not "much bigger than 100:1", it is EXACTLY 100:1.
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Old 6th December 2012, 11:56 AM   #7780
AndrewT is offline AndrewT  Scotland
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No, I am NOT saying that.
but you said
Quote:
............. when there is a minimum, there is also a maximum.
What do we do if there is a maximum (ratio)?
You have put the doubt in our minds.
I am asking you:
Are you saying that there is a maximum ratio?
I am not asking:
What ratio do you use?

Back to "what are you saying".

Are you telling us there is a maximum ratio to go along with the 16:1 minimum ratio? If the 16:1 ratio is right, it might not be.
What are the consequences of not knowing what the maximum ratio is?
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