Quick capacitor question - Bartolini Mid
 

The values shown here:
http://www.bartolini.net/pdf/Ntmb_918f.pdf
are marked in mfd.

Am I correct in assuming that's the same as µF, so 2 x 680nF and 1 x 100nF?

Also, does it matter what type these are, any types to avoid or any that would be preferred?

Actually, except for those stuck in the 1950's mfd would be milli-Farads but I am going to assume that Bartolini is stuck in the 1950's and so those capacitor values would be 680nF and 100nF using modern engineering units, as you surmise. Of course modern Americans tend to be stuck in the 1960's so they would say 0.68uF and 0.1uF instead. Any type could work but in my opinion paper/oil capacitors are also for those stuck in the 1950's and while you can get perfectly good ceramic caps you need to be careful about the dielectric and they can be hard to find that large so you probably want to go with any of the many available plastic film caps.

I think the give-away is that the proper modern abbreviation of milli-Farad would be mF not mfd which was the ancient abbreviation of micro-Farad. I can't imagine that Bartolini wants you to use 680uF and 100uF capacitors as their schematic would seem to indicate to modern eyes!

Ken

Thanks Ken

Think you got confused there... Maybe you meant nF? Mfd is for uF, so it's 680nF and 100nF.

No, I am not confused. The abbreviation of mfd for uF went out of style decades ago and if you see mfd today it looks like someone is talking about milli-Farads and just does not know the proper abbreviation, mF. In that case 0.68mfd would be 680 uF. But in this case I think Bartolini is just being that far out of date and that 0.68mfd means 0.68uF or more properly 680nF.

Ken

Yes you are confused. Who cares about "style" in giving capacitor values. Nobody EVER uses "millifarads". That's just spouting nonsense. Today usually the common units are Farads, microFarads, and picoFarads. Nanofarads are still a kind of oddball unit, but some people insist on it. The abreviations are F. uF, nF, pF. And the F is capitalized because it stands for a guys name: Faraday. And uF stands for microFarads and everybody also knows that mfd is also an abreviation for microFarad that has been used for a long time. Nobody is so electronically hip and "modern" that they think it's milliFarads! :-) And that "u" in microFarad isn't a "U" it's the greek letter mu which stands for micro. OK? We just use "U" because of keyboard limitations.

As for cap type, I'd recommend any high quality plastic film cap. Paper in oil are good too, but you don't need to go pricey. I'd avoid ceramic caps because in these values getting quality ones means you'd have to know what you are doing. Otherwise you could end up with nasty digital power filter caps. There is no reason to consider anything other than plain old cheap plastic film. Mylars are fine, but if you want extra quality hunt down some polysytrene caps. That's what I use.

Whoops, i think i read your post wrong.
"I can't imagine that Bartolini wants you to use 680uF and 100uF"

Missed that one. I though you were suggesting him to use a 680 uF capacitor, lol. Sorry for the misunderstanding. As for the abbreviation, usually when i see MFD people are talking about uF, and i often see MFD on capacitor themselves. Maybe it's an USA/Europe thing?

"MFD" or even just "M" was a very common abbreviation for µF. That was used before the µ (Mu) character was easily typed. Also "M" is the uppercase for Mu. µ is the lower case.

So Bartolini means 0.68µF and 0.1µF. Note that they are using two 0.60µF polarized caps to make a 0.34µF non polarized cap.

Some caps have mf or mfd written on them. Some use numbering like 104K, and most have µ.

Typing "uF" is not correct either, but I have some caps with that printed on it.

I remember caps marked mmfd - micro micro Farad (pico Farad).

mfd is the older designation for microFarad.

Yeah, I figured that, so I should be able to use 1 x 0.33µF instead of those two 0.68µF such as:
http://www.maplin.co.uk/metallised-p...capacitors-361 in the 0.33µF value and 1 in .1µF value?

Sorry but you are wrong. I am a professional electrical engineer and engineers use mF all the time. There are lot of electronic devices that have massive capacitor banks in them and none of us want to describe them as 150000uF, for example, they are 150mF. Using a bunch of zeros before or after a decimal point just leads to reading and transcription errors so smart people long ago devised the milli, micro, nano, pico, femto designations to eliminate these errors. And I have designed integrated circuits where capacitors are often sized in femto-Farads so that is not a useless designation either. I started learning electronics as a kid in the 1960's and mfd was already obsolete then. Anyone who has learned electronics recently, really learned it and not just picked it up from TB, could easily be confused by mfd for uF. In fact I am pretty sure the OP was uncertain about this very issue, otherwise why would the question have been asked??? If everyone knows beyond a shadow of a doubt that mfd means uF then there would be no need to ask. Seriously, no one publishing technical information in the 21st century should be using mfd, no one.

Ken

Correct. m=milli, μ=micro in everything else I've ever done with electronics but I was pretty sure they meant micro here, just wanted to be absolutely certain.

Thanks everyone.