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Old 24th September 2003, 04:23 AM   #31
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By passing electrolytic caps must be done carefully so as not to set up a parallel resonant circuit. Even a little tweek in the higher registers can affect the sonics.
I did some testing on a phono RIAA section some years back by changing the -1db response from 200khz to 150khz, which made a noticeable sonic difference.

If electrolytic caps are that bad, do you really want one providing an AC path to ground so close to the signal tube? There are others too, but I will let you figure them out.
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Old 24th September 2003, 04:26 AM   #32
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I can add an ESR to the caps.

Here is one good link that I found:

Capacitor Model

But, I haven't found any means of computing the various lumped circuit elements here. If anyone can give me some decent values, I can make this model work.

In the meantime, I'll keep looking.

Next, however, I was planning to try to include some line side effects. I'm still noodling on this.
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Old 24th September 2003, 10:16 AM   #33
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The only measured values I could find for an electrolytic were for an Elna RSH 1000u 10V:

C = 765uF
ESR = 0.158R
L = 41.3n

These values were measured by a friend on a rather swanky HP component analyser. I have rather more data for 100n plastic capacitors. When I've been able to find data for electrolytics, the ESR has always been higher than expected. For recently made components intended for switch-mode PSUs, L has been lower.
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Old 25th September 2003, 12:24 AM   #34
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Hi,

Quote:
If electrolytic caps are that bad, do you really want one providing an AC path to ground so close to the signal tube? There are others too, but I will let you figure them out.

Hmmm...I guess that just like myself you know the answer to that one already....

Still, lets have a third party confirm it and have it out of harms way.

In that way we could both fall back on an independent measurement....

Sorry if it sounds like abuse to any of you, it really isn't.

Cheers,
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Old 25th September 2003, 01:24 PM   #35
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Electrolytics Models

Hey guys, I found that modern electrolytics are modeled using a series inductance/resistance and a ladder of RC pairs. Kemet actually has a nice program that you can download to see the frequency dependent ESR of some of their caps. Here is what one of the models looks like:

Click the image to open in full size.

I've simulated this and I don't find any resonances until up past 1GHz. This is a 330u low voltage cap. So I'm figuring that the high voltage electrolytics have different parameters. If anybody can provide me with more help here, I'd appreciate it.

More regulator analysis coming. . . . . . . .
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Old 25th September 2003, 01:57 PM   #36
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That's a remarkably low inductance, and much lower than my measured value. Rule of thumb is that the inductance of a straight piece of wire is 0.5nH/cm. I also find that ESR hard to believe.

In isolation, individual components look reasonably harmless. Due to falling open loop gain, regulators have a rising output impedance (as you've shown). Another way of viewing this is to say that they look like perfect regulators in series with an inductor. Add a capacitor across the output, and you have a resonance.
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Old 25th September 2003, 02:20 PM   #37
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Hi EC8010,
I am interested in thes values of inductance for different shape conductors. How about a piece of flat Cu pcb-level thickness with the same x-section same length: how does it compare to standard wire?
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Old 25th September 2003, 02:35 PM   #38
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The inductance seems low to me too. I'm assuming that this is a small capacitor.

However, if I simply use a series LRC model for the cap, here's what I have to do.

Assuming C=330u and R=.01 (low, I know), then L=3u to get a series resonance around 7K (where Steve put the earliest onset). This seems like an impossibly large inductance.

Increasing R, of course, will slowly turn this into a high pass filter.

If I use the parameters you provided above, I still don't get any visible resonances between 10Hz and 1MHz. I do get a very nice high pass filter that turns over at about 300KHz, but hardly effects the audio spectrum at all. Is this the heart of the issue?

I'm assuming that other folks have measured the series resonance features of aluminum electrolytics. Perhaps you all could point me to where to look.
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Old 25th September 2003, 03:59 PM   #39
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Default I find it oversimplified

Different capacitors and their sonic signatures, seems to me, to be different because the models are all different.

For instance, my source informs me that Hovlands (film cap) is complicated. The lead attachment is at one end of the foil and then the foil is rolled. Thus one has an infinite number of resistors and inductors and capacitors instead of one inductor and an infinite number of RCs. Electrolytics, I think are similar.

Infinis, on the other extreme, have the "metalized foil" deposited and the lead is attachmented on the entire edge of the whole roll. Thus the inductance is minimized and the resistance is in the the "metalized foil" itself from one edge to the other, which is where the wire is connected. I hope I explained it clearly.

"The Multicap" has ten sections of similar capacitance, I believe, yet it sounds different than the other two. I think each section is terminated at one point on the foil, so you have ten little "hovlands" so to speak paralleled in one package.

They sure do sound different, yet the specs seem to be similar.

ps. If you like, you might read "Picking Capacitors" by Walter Jung and Richard Marsh. Provides some interesting insights. I also have an article by a chemist on capacitor dielectrics.

pss. Remember, some electrolytics only terminated the foils at one or a few points, so you have alot turns.
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Old 25th September 2003, 04:10 PM   #40
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Default You asked for it!

Hello Grataku, I found this years ago in a Marconi manual. For a rectangular strip having dimensions in cm, where:

c = thickness
b = width
D = length
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