Whats that big cap do? (si II fuzzface)

[Joecool85]

What does the 100uF cap do?

[hank reynolds 3rd]

it's for filtering on the power supply ..it's present on most efffects,sometimes 47uf

[wampcat1]

If you are using a good power supply or battery power it is possible you won't notice much of a difference with or without it. Try using a radio shack 'selectable voltage type' adaptor and you'll notice it cleans up quite a bit of the hum! Alot of guys just use a large-ish cap depending on what they have on hand -- 10uf/22uf/47uf/100uf/etc.

Take care,
Brian

[Joecool85]

Ah.  Thats interesting.  So if you are running off a 9v or a good ps it probably won't matter then.  huh.  Thanks.

[bioroids]

I use normaly 470uF in parallel with a 100nF ceramic for RF noises

[wampcat1]

Ah.  Thats interesting.  So if you are running off a 9v or a good ps it probably won't matter then.  huh.  Thanks.

Well...I can't honestly say it "probably won't matter", but from my experience I haven't noticed a dramatic difference in Power supply noise or RF reduction by placing a large cap there off of the 9v supply, UNLESS I use a cheapy 9v supply. RF can be reduced quite dramatically by placing a small cap (500pf or less) from input to ground and output to ground.

Hope that helps!

Brian

[Joecool85]

k.  I haven't had any issues with RF or PS noise, but I use batteries.

[WGTP]

IIRC using that cap can prevent wierdness (oscillations) as the battery runs down and the impedence of it increases.   

[Paul Perry (Frostwave)]

IIRC using that cap can prevent wierdness (oscillations) as the battery runs down and the impedence of it increases.   

That's a hint if ever I heard one 

[puretube]

"A circuit is only as good as its power supply"

never a circuit without a low impedance across the rails...

[petemoore]

  I always stick a BFC there at PS input. I'm running adapters mostly, so I can stick a really BFC like 470uf there if I want, also sometimes a teeny cap parallel to handle the H.Freqs.
   A few extra caps, here and there, can certainly tame the wierd stuff down, smaller cap to ground at input Is a good one, just enough to take a touch off the high end, or touch smaller yet to just 'clean', but not really reduce HF's.

[no one ever]

I use normaly 470uF in parallel with a 100nF ceramic for RF noises

is there math behind that combination? i'm trying to kill the rf/power noise in my vibe, (640 KFI, traffic on the 1's) and i'd love a solution.

[bioroids]

In my case the math is in the cost: 470uf is the biggest capacitor I can afford for a pedal (and is not huge in size too) and 100nf is the most used ceramic so I have lots of them. Sometimes I use a 22nf. Normally I also put a 10ohm series resistor before the cap combination to increase the rejection (at the cost of dropping some voltage).

I don't think the values are too critical here, normally you just use the biggest you can.

For the real math, you have to consider the resistor and cap form a simple low pass filter, and the cutoff frequency is obtained by the 1/2*pi*r*c formula. Bassically you want that frequency to be very well below 20hz.

At least that's how I understand it. If anyone has better insight please post

Luck

Miguel

[Joecool85]

Bah, I wouldn't worry if it was at 20hz or even as high as 40 or so.  Guitars only produce down to 80hz or so.  On top of that, most guitar speakers can't reproduce noise below 50hz even if you have a nice 12". 

[puretube]

...I  do worry about noise below 20Hz - don`t wanna have my amp modulated by motorboating...

[Joecool85]

What I meant is that I wouldn't worry about trying to reproduce noise above that.  Cutting it out is fine.  Actually, thats what I was getting at.