Inductors to get rid of clock noise?

[commathe]

I have a crappy chinese digital delay that has serious clock noise issues. I was wondering though, if modded in a small inductor (say 1-2.2mH) somewhere between the delay chip's path to ground or between the 9v in and the board, would I be able to snub the noise? I'd probably have to add a kickback diode also. I was just wondering if this would help of if there is some issue with a large voltage drop across the inductor that I am ignoring or something like that?

[Jdansti]

I'm not sure about the inductor solution, but I've used a large electro capacitor with + side tied to the clock's + power pin. I had to get the cap as close as possible to the chip to avoid having a long + lead, which would defeat the purpose. The clock was a 555 timer.

[Seljer]

If it's high frequency noise then yes, you effectively create a 2 pole filter instead of a 1 pole order RC filter

for example, a 1MHz:
Z_L = 2*pi*f*L = 2*3.14*1000000Hz*1millihenry = 6280ohms
while at DC it's effectively a short

and if you add a capacitor (say 100uF)
Z_C = 1 /(2*pi*f*C) = 1 /(2*pi*1000000Hz*100uF) =  0.0015ohms

Looking at the amplitude as if it were a voltage divider: theres no way a 1Mhz signal is getting through there at all
But the thing is, the capacitor already looks like a short at any frequency over a couple of kilohertz.

If that current draw of the circuit isn't too bad you can get away with a couple of 10ohms of regular resistance without losing too much voltage over the resistor and still get good results.

I've never seen a kickback diode over a filter inductor in such a setup. You're not chopping up the signal with PWM or anything that extreme.


Also, I'm not sure if its more effective to filter the clock, or to filter the supply to the audio portion of the circuit. PCB layout issues also come into play (i.e. make sure the noise isn't coming in through the ground rails)

[R.G.]

Some questions have to be answered before you can do anything useful.

(1) You say " serious clock noise issues"; are these inside the pedal itself or when used in combination with other pedals?
(2) Does this happen with battery power, external power, both, and if not battery, what kind of external power supply?

[puretube]

I'm not sure about the inductor solution, but I've used a large electro capacitor with + side tied to the clock's + power pin. I had to get the cap as close as possible to the chip to avoid having a long + lead, which would defeat the purpose. The clock was a 555 timer.

Small can help too, sometimes...
@ some places, @ some frquencies, a few mH don`t hurt...