Power cap for fuzz box - diyAudio
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Old 24th October 2013, 11:27 PM   #1
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Default Power cap for fuzz box

I'm planning to build a small custom fuzz box for a musician friend. It will have quite a few components including six 2N2222 (or MPS6531) transistors, etc.
One thing I noticed was that it calls for a 100uf 10volt electrolytic capacitor across the battery terminals (rail to ground). I'm wondering would this be necessary at all if you are just powering it from a 9v battery? My guess is that maybe they are including this to smooth out the power in case someone was using a wall wart instead. In that case, wouldn't a wide range of caps be suitable, even a 4700uf 16volt cap for example? I'm trying to get all the stuff from the same supplier, and that's the closest they have.
A few other very simple questions for those who have worked with these before, but I'll post them later. Just want to make sure I work up the best design, as I'll have to to send it by mail to him.
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Old 25th October 2013, 03:05 AM   #2
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frank754
i might be wrong but the cap may be needed to prevent your circuit from oscillating it is after all an amplifier(with lots and lots of distortion!)so some stability i think would be desirable.
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Old 25th October 2013, 04:11 AM   #3
Enzo is offline Enzo  United States
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Please include it. It is a nice low impedance path to ground from the 9V rail. What you don;t want is the signal from one or more stages causing little variations in the power supply, which can then be amplified, causing instability or undesired audio artifacts.


What sort of supplier are you using that doesn;t have 100uf caps? if they don;t have it in 10v, go to 16v or 25v.
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Old 25th October 2013, 08:00 AM   #4
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Originally Posted by frank754 View Post
One thing I noticed was that it calls for a 100uf 10volt electrolytic capacitor across the battery terminals (rail to ground). I'm wondering would this be necessary at all if you are just powering it from a 9v battery?
Yes - absolutely essential - if anything it's perhaps more important than with an AC supply.

Without it you will get drastically reduced battery life (10% or less), instability and motor-boating. It may also prevent the circuit working correctly, as any circuit releis on that capacitor for it's operation.
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Old 25th October 2013, 06:34 PM   #5
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I usually use Antique Electronics, as they have a lot of parts for musicians and audiophiles as well, and carry a lot of tubes & supplies. My choices would be the 4700uf 16v (too high?), but they also have 25uf 25v, 47uf 35v (a lot in that range), also 220uf 50v (maybe that last one would be best if 50v is ok and 22 uf isn't too high.). I know that filter caps aren't always as critical, where the caps within the stages are finely tuned players. Within the circuit itself, it calls for eleven 10uf electrolytics but doesn't specify any voltage. I'm tentatively ordering 10uf 50v for these (that's the lowest voltage they have for 10uf). These are used interstage and also around a pair of clipping diodes. So I guess the voltage isn't critical on these since it's not specified? If not, I could go with Mouser or some place like that.
Anyway, thanks for your replies, I'm doing this for an out-of-town musician friend I've known about 20 years, and he's looking for certain vintage effects.
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Old 25th October 2013, 06:38 PM   #6
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Originally Posted by frank754 View Post
I usually use Antique Electronics, as they have a lot of parts for musicians and audiophiles as well, and carry a lot of tubes & supplies. My choices would be the 4700uf 16v (too high?), but they also have 25uf 25v, 47uf 35v (a lot in that range), also 220uf 50v (maybe that last one would be best if 50v is ok and 22 uf isn't too high.).
Considering 100uF is probably one of the most common values it's a bit strange they don't have those?.

220uF would be fine, or the 47uF - you don't need a 4700uF, and it wouldn't be a good idea.
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Old 25th October 2013, 08:45 PM   #7
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Thanks, I think I'll just put 2 of those 47 uf caps in parallel, and that should be darned close to the original spec
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Old 25th October 2013, 09:48 PM   #8
sreten is offline sreten  United Kingdom
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Originally Posted by Nigel Goodwin View Post

Yes - absolutely essential - if anything it's perhaps more important than with an AC supply.

Without it you will get drastically reduced battery life (10% or less), instability and motor-boating.
It may also prevent the circuit working correctly, as any circuit releis on that capacitor for it's operation.
Hi,

Care to explain any of the above utter nonsense ?

rgds, sreten.

Any reasonable value could be used, 100uF is just a standard
value you typically use on board rail to rail, but its no big deal.
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Last edited by sreten; 25th October 2013 at 09:59 PM.
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Old 25th October 2013, 09:52 PM   #9
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Hi,

Care to explain any of the above utter nonsense ?

rgds, sreten.
I was wondering the same thing. Thanks for posting, sreten!
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Old 26th October 2013, 08:14 AM   #10
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Originally Posted by sreten View Post
Hi,

Care to explain any of the above utter nonsense ?
In what regard?, no nonsense there at all.

Quote:

rgds, sreten.

Any reasonable value could be used, 100uF is just a standard
value you typically use on board rail to rail, but its no big deal.
I never suggested the VALUE was critical, only that a suitable capacitor is.
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