Which capacitors?

[simonrichie]

Hey all,

I'm making a parts list for a D*A*M Red Rooster, and I think I've got everything figured out but the caps.

For the 47u and 22u I'm going for the BC Components Electrolytic 400-volt.

For the 10n, Ero Vishay Film: Mouser part number 75-MKT1813310405   

For the 2u2 I've narrowed it to BC Components Electrolytic 100v (Mouser has two. The main difference is their different operating temperatures. I assume I can go with the +85 C rather than the more expensive, higher temp one, right?) (Part numbers:  594-2222-021-39228 AND 594-2222-138-39228).

Does any of that sound off to anyone?

My main issue is the 4.7n. D*A*M uses the red Wima box caps, but I have no idea which of these 103 I should choose: http://www.mouser.com/WIMA/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?P=1z0zldhZ1z0x7x2

If someone can guide me toward which dielectric and voltage ratings I might want to narrow it down to, that'd help out quite a bit.

-SR

[PRR]

> 400-volt

It's a 9-Volt pedal, right?

16V or 18V cap rating is plenty ample. I can't see any reason to go over a 25V or 50V rating, which should be easily found in 47u and 22u values. A 47u 400V is BIG.

And electrolytics "need" voltage to keep the oxide healthy. In the past some 400V electros would die early worked at 2V or 15V. That's partly about impurities, which have improved. But there is no reason to over-over-over-spec your volts, and good reasons to right-size.

The 2.2u *may* only come in higher voltages... however 100V seems generous, I'd expect a 50V part is available.

Temperature also implies life. If you expect your grand-daughter to use it 20 years after you take your final bow, 105 C caps *may* be justified. If you are going to take it apart and mod it every week, use any cap, and replace it when needed.

For ALL these questions-- do not start at DigiKey/Mouser/Allied. They have WAY too MANY parts, some of them for applications you would never dream of. Start with folks like our host, Small Bear and other pedal-part vendors. They know what parts you need, and what you do NOT need (for pedals).

[GibsonGM]

+1,000   

A bunch of 25V electrolytic caps go a long way!  I buy 2.2u, 10u, 47u, 100u in bulk for all our projects.   

Many (most?) poly types are good up to about 100V; I never worry about their rating, put it that way.  Unless doing something for a tube amp, in which case on really SHOULD check.   But 9V?   All set.

+1,000 for starting with Aron, Small Bear and the like, who will have what you need and not get you messed up with 100 choices or more for a simple cap!

[simonrichie]

Well, the idea is to use the same parts used in that particular pedal, which are the 400-volt and 100-volt caps. I get what everyone is saying--those ratings are overkill--but people also seem to love that pedal. Would they love it with other parts? Maybe? I dunno.

I'd love to hear more thoughts on this. Why do so many builders use those larger rated parts? Is it just because they look cool? Or is that what the original pedals used?

And how about that red Wima? Anyone know what the values should be on that one?

[duck_arse]

my experience with wima caps is - if it is red, pick the lowest priced ones of the correct value. (it will most likely be the lowest voltage rating.) wima make excellent, expensive caps, whatever the dielectric, for a very long time now.

so many builders? be fresh, bold, original! don't follow the crowd. use the right part for the task at hand, a 9V battery powered audio circuit.

[edit :] their cheapest wima 4n7 shows as : Mouser Part #: 505-FKS24700/100/10, Manufacturer Part #: FKS2D014701A00KSSD
(if it fits, it's good enough)

[GGBB]

electrolytics "need" voltage to keep the oxide healthy

That reminds me of a related question I've always had but never worried about all that much to bother asking.

If an electro is used in the signal path of a pedal where no DC is present, and the AC signal is typically low for guitar, should we be using even lower voltage electros than the typical 25V or so that we typically use?  I've heard 10% of rated voltage as a minimum - should we go to 10V or try to find lower ones?  Do polar electros even work properly without a DC bias?

[PRR]

> Do polar electros even work properly without a DC bias?

Apparently they do, in many-many mike preamps.

[greaser_au]

Once was a time you could fix a good quarter of tv and video type things that came across your bench by replacing all of the 1uf 63V electros... 

davidt