D.C. Jack Filtering for wah

[soupbone]

I was looking at this 9v filter for a d.c. jack for a wah from the gallery. http://www.aronnelson.com/gallery/main.php/v/Xaviers-shrine-of-noise/Layouts/9V_filter.gif.html I saw this other link from electosmash. http://www.electrosmash.com/images/tech/crybaby/cry-baby-wah-gcb-95-power-supply.png In the electrosmash schematic,there's no 1k resistor.In the layout there's a 1K resistor.Is that resistor supposed to be there or no?Thank in advance.

[whoisalhedges]

I can't answer your specific question re: the CryBaby, as I don't have one - but a series resistor is quite common in power filters. My question pertains to the capacitors: why is there a film cap (.1u in the electrosmash example, 1u in the DIYS gallery layout) in parallel with the 220u electro? I know some people like to bypass electrolytics in the signal path, but this is just power filtering, just between +V and gnd....

[duck_arse]

the electro is good wit der boom boom boom, whereas the film/ceramic is better at tweet tweet tweet. these technical terms apply to the hum and noise that appears on the DC supply line, through various mechanisms.

[whoisalhedges]

the electro is good wit der boom boom boom, whereas the film/ceramic is better at tweet tweet tweet. these technical terms apply to the hum and noise that appears on the DC supply line, through various mechanisms.

Hahahahaha... I suppose I figured that big caps passed all AC frequencies - but the smaller value helps extra more for any RF missed by the electro? That is to say, a massive 220uf cap will shunt any AC ripple to ground, but we're not just talking ripple - the cord is an antenna too, and the wee l'il cap takes care of that?

[PRR]

The resistor improves the cap's action tremendously.

[MrStab]

i'd guess that that 1k resistor was removed to allow for a higher voltage from low batteries or low-current power supplies. generally-speaking, you shouldn't take 1k as a standard for all pedals.

using Ohm's Law, 9 volts divided by 1000 ohms will only give you 9mA of power - fine for the original CryBaby, but not for an LED on top, and definitely not for more power-hungry pedals (or a whole bunch of em).

ideally, you should work out the current draw for each pedal and base the resistor value on that, but if you DO want a "one-size-fits-all" value, most people round here seem to settle for 100 ohms. that'll lessen the impact of the filter itself, but usually not an issue if the power supply has decent filtering. there's the actual filtering and current reservoir to worry about too, but i figure that's for another thread.

AFAIK the smaller cap also helps because it charges faster, so collectively they both recover from sag more quickly. from a decoupling standpoint, anyway.

[EATyourGuitar]

there is something in electronics called an RC low pass filter. RC is Resistor and Capacitor. without the resistor you have 1 Ohm before the cap, using the power hookup wire as a resistor. adding a 100R resistor gives an order of magnitude more ripple attenuation as the impedance of the cap is getting to be around the same as the resistor.

https://en.wikipedia.org/wiki/Low-pass_filter

http://www.muzique.com/schem/filter.htm

[soupbone]

Thanks everbody for the responses.Much appreciated!

[ficelles]

Has anyone who has made this filter found that it eats about 250 millivolts?

[davent]

Has anyone who has made this filter found that it eats about 250 millivolts?

That all depends on the amount of current being drawn through the resistor, ohms law, V=IR.
dave

[anotherjim]

If you have a LED, power it before the filter. The LED won't mind.
1k series it great for a Crybaby filter.
Caveat. A Wah often gets blamed for noise. In a high gain situation, the noise often jumps up when the Wah is engaged. The trouble is often a ground loop if another pedal runs off the same common supply. You can put 100R in the DC power negative (also after a LED). That ought to break the ground loop. It should still have the filter on the +supply.