16V Film Caps

[Rob Strand]

A reasonably approximation of a 9V battery, still series resistance ... but .. it's still an approximation,
https://www.diystompboxes.com/smfforum/index.php?topic=129995.msg1259217#msg1259217

[Phend]

Any ideas why the 1970's fuzz effect has a 33uF electrolytic cap across the battery ?

[FSFX]

Any ideas why the 1970's fuzz effect has a 33uF electrolytic cap across the battery ?

Because it most likely was designed by someone who actually understood electronics and audio electronics design as that is the correct way rather than miss off any decoupling capacitors like you see on a lot of DIY pedal schematics.

[antonis]

Hi-Fi design for a Muff Fuzz..??

[Phend]

Here is the circuit (example). My purchased Muff has a 33uF vs 47uF, whatever.
See C3. I resemble that remark.

[duck_arse]

Here is the circuit (example). My purchased Muff has a 33uF vs 47uF, whatever.
See C3. I resemble that remark.

interesting to no-one else but me, probably, that the single component of your interest in that schem, Phend, does not have the junction dot drawn as on every other juntion.

[Phend]

Maybe these ?  What is that cap across + / - for ?

[antonis]

@Phend: Place any cap you like and walk in peace..!! 

[FSFX]

What is that cap across + / - for ?

It is to provide a low impedance AC path between the +ve supply and ground so the +ve power supply appears as a ground to AC which will reduce the feedback of any of the output signal back to the input of the circuit. So it improves stability as well as any filtering noise on the power supply.

[Phend]

Re: Any benefit to having a power filter cap on a battery operated fuzz face??
« Reply #12 on: March 30, 2016, 08:53:11 PM »

PRR says:

"In the past, a nearly-flat transistor radio battery would increase in resistance and "crackle". In a many-stage radio, the increased resistance encouraged sneak-back from high level stages to low level stages, oscillation. We "always" threw 10-100uFd across the battery so we could use-up the battery right down to the nub.

I don't think it is a big deal in DIY pedals. The cost of a cap is small. You should probably leave space for a cap, in case some day a weak battery makes trouble. However many classic fuzzes will go sour for low voltage before the battery is really weak. And you should always carry a spare battery."


Re: Any benefit to having a power filter cap on a battery operated fuzz face??
« Reply #17 on: April 03, 2016, 03:07:58 PM »
   
A battery is already a f***ing giant capacitor alone

teemuc says:

"Within certain conditions I guess you could say that...

Theoretically the battery should be a DC voltage source with low internal resistance. If any AC signals happen to couple into such power source its low impedance effectively shunts them, similarly to what a filter - or "decoupling" - capacitor does when it provides a low impedance for AC signals above very low frequencies.

In nutshell, one wishes to "decouple" AC signals from the power sources because otherwise they effectively become feed forwarded or fed back into other gain stages, and if this feedback / feed forward happens to be positive you're probably in for a serious trouble considering overall stability of the circuit.

A battery with low internal impedance effectively behaves very well as "decoupling element". Problem is that when the battery charge gets drained the internal impedance of the battery starts to increase. Now it not only "sags" the supply voltage down but also becomes a much inferior decoupling element than a fresh battery. The thing could have charge left for hours of operation, but due to increased series resistance the circuit stability is compromised.

A cheap decoupling capacitor will prevent that. Its "filtering" effects for a pure DC supply are, of course, almost entirely negligible but (once charged) it retains constant low impedance characteristics and therefore works as a decoupling element. With a decoupling capacitor in place the power supply retains ideal decoupling characteristics even when the internal impedance of the battery starts to increase."

Anyway, great explanations from both PRR and teemuk, thanks.

And the new capacitor don't fit



I ain't walking i'm running