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Old 21st September 2005, 08:26 PM   #1
Sander is offline Sander  Netherlands
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Default Rod Elliot's P3A considirations


Currently I'm building a Rod Elliot P3a, from Rods website My problem is that I don't have enough knowledge about capacitors to chose the right one for its purpuse.

There are many different types of capacitors such as, elctrolytic, MKP, cermamic, etc. Could you please help me deciding wich type I should use at which place? I would like to know the main purposes en performance areas of the different types. Thanks in advance!

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Old 21st September 2005, 08:46 PM   #2
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I'm pretty sure that Rod will send you a parts list along with the PCBs for the project

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Old 21st September 2005, 09:09 PM   #3
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Some suggestions for starts:

C1: MKP or some would like Black Gate lytics
pf values: Polyestirene or MKP, for lower values you can also use Silver Mica.
nf values: MKP or Mylar films.
uf values (other than C1) use electolytics

In any case check the footprint of your selections to see if they match your PCB.
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Old 22nd September 2005, 03:16 AM   #4
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Looks like C1 is polarized, doesn't that mean it has to be an electrolytic?

Oops, for the BOM

"C1 may be a standard electrolytic capacitor if desired. If a polarised electro is used for C1, the polarity is not shown on the overlay, but is clearly indicated on the overlay drawing.

Blessings Terry
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Old 22nd September 2005, 07:12 AM   #5
AndrewT is offline AndrewT  Scotland
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C1 should be a non polar electrolytic or back to back polarised of double the capacitance value.
It would be far better to use a film cap here instead but MKP will be much larger and cost considerably more.
The builder decides!!!
Ceramic would never be used in the audio stages due to variable capacitance as the voltage varies. However they are unbeatable in decoupling of the hi frequency rubbish on the PSU etc where they see an almost constant (DC) voltage.
The film type usually perform better than any of the electros even black gate. Some film are better than others. Polypropylene, polystyrene and teflon are of the highest quality,
Polyethylene and polycarbonate are the next level down. Then there are a few others.
Try a search for a much more full report on capacitor quality
regards Andrew T.
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Old 22nd September 2005, 08:16 AM   #6
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C1 simply isn't necessary as long as there's no DC coming from upstream! It's a case of best C is no C.

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Old 22nd September 2005, 12:18 PM   #7
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Here is my P3A BOM with part numbers from DigiKey.

I haven't built mine yet, but soon ...
Attached Files
File Type: zip p3a (2.5 KB, 220 views)
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Old 22nd September 2005, 03:43 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi Amplifier Guru,
the dc blocking cap C1 also stops bias from one amp interacting with the bias from another if more than on power amp is connected to the same source.
regards Andrew T.
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Old 22nd September 2005, 04:26 PM   #9
rushi is offline rushi  Finland
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Sander: Do _NOT_ use electrolytic as a C1. Use Polypropylene (Aydyn-Cap or similar) or better, Paper-In-Oil caps. It doesn't have to be 4,7F, 1...2,2F works fine. It won't fit on PCB, but who cares?
All electrolytics should (must, imo) be low-ESR types, Black Gate or something (OS-CON more preferably).
Mylar, MKP (Polypropylene), Silver-Mica or polystyrene for smaller ones.

That's how I would do it.
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Old 22nd September 2005, 05:01 PM   #10
paulb is offline paulb  Canada
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You can use a non-polarized electrolytic for C1. Or polarized. Disregard most of the hype about must-not-use, 99.9% of us can't hear the difference. Those that claim they can probably can't.
However, the output transistors can make a big difference.
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