Noisy Power Supply Question

[Ginsly]

Right off the DC jack, there's a schottky for reverse polarity protection. Drops .3v in most situations, which means basically nothing. From there I've got a ferrite bead feeding parallel caps - while RC worked fine, I found LC in this setup was significantly better at reducing modulated RF noise and didn't result in losing an additional 0.3-0.5v. 470uf is electro, 100nf is ceramic, ferrite bead is one of the little axial jobbies from Tayda. You absolutely could add in a <100R resistor after the ferrite bead if you didn't mind losing a bit of extra voltage, but some pedals I make require clean headroom so wanted to keep supply as high as I could.

I've also added in is a RC filter going to the PCB of 10k/100pf. It's so, so far out of the audio range it has no impact on sound even with some bad input/output impedances, but made a noticeable difference in noise (especially using a couple of lower quality leads I've got). You can definitely increase this to 22k/220pf or so, but I found 10/100 were components I always had thousands of.

This is great info, thank you! The Ferrite/Electro/Ceramic LC seems like a good idea to put on any power input, unless there's a downside I'm not considering. I have a VERY noisy city environment, with a power transformer out back, LED lights, Wifi, etc... And of course, I largely make higher gain fuzz pedals - doh!

I'm wondering if there's a "clean" way to incorporate your LC into existing pcbs and stripboard/perf layouts. I suppose you could do a lot of it right ON the DC jack lugs, but I'll have to take a look and see what makes sense.

It looks like the RC filter (lowpass, correct?) is more to address signal noise over power issues, and THAT is what I'm largely dealing with, to be honest. I've shielded my instruments as much as I can! Pretty much stuck with humbuckers, and even THOSE pickup environmental garbage sometimes.

I'm trying to figure out a systematic way to limit noise in a variety of fuzz circuits/situations, and I'm kinda getting in the weeds about it. I'm not exactly sure why some opt for a resistor/capacitor LPF over a lone cap-to-ground treble bleed at the input. I've also seen LPFs at the end of circuits (I believe Fredric Effects does that on their Percolator to cut some hiss..?). I'm hoping to gain some clarity about why people choose one over the other in certain scenarios.

I've also been trying Miller Caps on transistors, and they do help. I don't often leave them on all positions, but it's one of the first things I try. From there I try a Treble Bleed cap at input and modify Input and Output caps a bit. Some members here have posted about this, but I'm still trying to find a balance without throwing too much of a blanket over things.

 

[Ginsly]

@drew.spriggs Not sure if you saw my last post, but I’m constantly struggling with noise of all kinds and would love to hear a little more about your system. Haven’t looked at extra power-input filtering, and I’ve mostly tried treble bleed and Miller caps so far.

- how crucial is the 470uf value in your LC? That’s higher than I have, but can fix that of course. I take it a 220uf wouldn’t help as much.

- are there ever times when you’d put your RC filter at the end of a circuit instead? Looks like some do that with Harmonic Percolators to kill hiss, for example.

- have you incorporated both/either into existing boards?

 

[drew.spriggs]

@drew.spriggs Not sure if you saw my last post, but I’m constantly struggling with noise of all kinds and would love to hear a little more about your system. Haven’t looked at extra power-input filtering, and I’ve mostly tried treble bleed and Miller caps so far.

- how crucial is the 470uf value in your LC? That’s higher than I have, but can fix that of course. I take it a 220uf wouldn’t help as much.

- are there ever times when you’d put your RC filter at the end of a circuit instead? Looks like some do that with Harmonic Percolators to kill hiss, for example.

- have you incorporated both/either into existing boards?

• IMO anything from 220-470uf is fine.
• I have done pre/de-emphasis on EQ's, but typically wouldn't on most other pedals - even then I removed the pre/de circuit and found it made such a tiny difference I could have entirely omitted it and probably never heard a difference.

I have never found a need to do anything more than what I've listed, and I usually play a Tele into a 5w valve combo - not a combination that's known for being dead quiet. Everything is built on my own PCB's that have all the basics like reasonable trace spacing, a mostly unbroken ground plane, etc. I've also made a stack of very, very high gain stuff that hasn't been too noisy outside of what I'd expect.