A few of my pedals have terrible RF noise. I fixed it. Help me understand how?

[Rob Strand]

Ahh small update, a few of the pedals don't like the 1nf to ground - in particular, the SHO loses -all- top end.

Back to experimenting!

There was a problem with some of the MOSFET pedals oscillating due to the wiring inductance in the source lead.  The oscillation was suppressed using the same tricks as RF filtering, except for a complete different reason,
https://www.diystompboxes.com/smfforum/index.php?topic=123251.msg1165029#msg1165029

In short add the gate resistor and reduce the cap.  The cap is on the gate side not the input side of the added gate resistor.

[GibsonGM]

If the caps are chosen properly (small values), they shouldn't have undesirable effects. In fact, I'd encourage the OP to try the smallest cap possible (100p?) that will stop the RF.   The frequencies involved are above the audible range...

It depends on preceding effect out pot value/setting, Sir..

Of course!   Since I have those R/C bypasses on mine, I don't think of this often enough.

This is why using the smallest cap on the input that stops the RF is best practice!       I would try 47pF-100pF, even.  Anything that shunts the RF is 'enough'.

[drdn0]

More testing: FA1 clone using a 4580. HORRENDOUS RF noise. Way worse than anything else I've made, even on battery. 1nf is too big and loses a little top end, 470pf is too small to be effective.

I've just ordered some boards with pads for adding the filter, so fingers crossed i can find a good mid point for all the different pedals.

[GibsonGM]

It doesn't seem right to me that a few of your builds have this problem, inside a shielded enclosure.  Are you near a radio station??  I wonder if shielding your guitar would help (sorry if you mentioned this in a previous post or something).   

[drdn0]

It doesn't seem right to me that a few of your builds have this problem, inside a shielded enclosure.  Are you near a radio station??  I wonder if shielding your guitar would help (sorry if you mentioned this in a previous post or something).

5km or so from a radio tower, and I do have a house that's pretty old. If some were just a bit noisier than others it would be totally understandable, but I'm not sure why some are absolutely dead quiet and some are just unusable.

The guitar is pretty well shielded as I wired it myself - humbuckers, copper foil enclosure, star grounding. I don't think I could get lower noise through the guitar unless I went to actives.

[GibsonGM]

Wow, that's really unfortunate   I get nothing, and haven't even when playing in bars and stuff that have old, crappy wiring.   If anyone can solve this for you, it's these guys, though!  I really expected that a small (pF) cap would send the bad stuff to ground, but I guess not.

It's in the enclosure with a small cap, also?  (not out on your bench?)

[Phend]

check all solder joints for cold.
have copper water pipes ? , temp connect a wire to box and then a pipe.
hail mary

[Rob Strand]

More testing: FA1 clone using a 4580. HORRENDOUS RF noise. Way worse than anything else I've made, even on battery. 1nf is too big and loses a little top end, 470pf is too small to be effective.

Adding or increasing the resistor before the cap can help get the thing to work with a smaller cap.   Somewhere from 1k to 10k, 10k will be more effective for RF.  The resistor needs to be before the cap.   Say for the FA1, there is a 10k input resistor already, so put the cap from the JFET  gate to ground.   Drop the cap value back to find what size cap you need.

5km or so from a radio tower, and I do have a house that's pretty old. If some were just a bit noisier than others it would be totally understandable, but I'm not sure why some are absolutely dead quiet and some are just unusable.

Because of that you will need to do more than what most people do.

[drdn0]

Wow, that's really unfortunate   I get nothing, and haven't even when playing in bars and stuff that have old, crappy wiring.   If anyone can solve this for you, it's these guys, though!  I really expected that a small (pF) cap would send the bad stuff to ground, but I guess not.

It's in the enclosure with a small cap, also?  (not out on your bench?)

Yep, in the enclosure. My biggest confusion is why AC coupling the chassis works so,.so much better than direct coupling it though

I'll keep playing around with the filter until I get it somewhere that works for most things