Inductor in the power filter?

[JackSkellington]

Hello, I talk here in the past about a problem sometime I got with some circuits: the whine caused by the power supply. It's useless to say that with the battery the whine is totally absent.
I have an old Boss PSU, a red label one, that I heard it's really good. Indeed, I never got problem with the pedal I built, and some original pedal (I never had a lot). Excpet rarely I solved eventually with common methods: 47R resistor or 1N5817 in line to the 9v or 100uF (or bigger) cap across the ground.

Now I have a pair of fuzz circuit with this annoying problme still unsolved. Woolly Mammoth and Ultimate Octave (Fox Tone Machine modified replica).

A schematic I saw time ago, I don't know where, shown an inductor (about 1000uH, but it was a random value) in line to the 9v, saying that's the better solution ever when we talk about voltage drop, impedance and noise filter. But I never see anyone used it, nor advice in any project.

I found even this now a bit different: http://www.muzique.com/news/dc-power-filter-box/

Did someone try something like that?

[WormBoy]

I used inductors of 100uH with great success as filters for generic switching power supplies. These are pretty cheap, deliver lots of current, but are by themselves way too noisy for pedals. Inductor plus big cap plus mlcc 100nF cap solves that (plus a regulator, depending on the power supply). Only thing to watch out for is the max current rating for the inductor. That way, I've been able to use various power supplies I had lying around the house.

If you have a deluxe pedal-specific power supply, you won't need this. Which is probably why most circuits don't include it. I just bought a nice pedalboard batterypack, and that also needs such a filter (the battery itself should not be a problem, its probably the circuitry for switching the thing on and off that's causing noise issues with, especially transistor-gain based, pedals).

[Aentons]

I believe the VFE switching board uses a 1mH inductor for filtering. It is discussed a bit in the build doc.

"The DC Jack inserts into +9v. Power is reverse-polarity protected via D1. It then passes through a 1mH inductor
which creates a low pass filter with the C1 decoupler. This helps reduce noise and minimize ripple on the DC power
(additional 100n decoupling caps are used on the audio boards). "

[JackSkellington]

To make it more clear: what about this schematic?
Correct me if I wrong. Thanks!



- The value of the inductor I guess can be 100uH, but what is the range of the value?
- 100uf has the negative side to thje ground.
- 100nF has to be ceramic or a film is enough?

[WormBoy]

Looks good to me  . The link you posted says "Component values are not critical" and used 330uH. I found 100uH advised somewhere else, and VFE uses 1mH. So that seems a reasonable range. I always use MLCC for the 100nF, but film is probably fine as well. I would choose the value of C1 based on how much ripple I expect, and how much current would be drawn. For most pedals, 100uF would be fine, but for an entire pedalboard, I would use something larger. However, my 'knowledge' all comes from scouring the internet for info and schematics, and my own experience ; I don't have the electronics background to make really intelligent statements here  .

[JackSkellington]

Well, I might include this filter in the circuit of a single pedal I got the whine/squeal. Just it. Indeed, I'm wondering if it actually do something about the whine/squeal issue. This thing is not very clear to me.

About the inductor valus in the page I found and then lost says that the valus was 1000uH, if I remember well, and it drops a bit the voltage, but not as a 47R or 100R. The result was good, but other values can be tested.

[WormBoy]

The resistance of an inductor will usually be quite a bit less than 47R. This circuit will help when the noise comes from the power supply (and it will be really effective), but things like whine/squeal will usually come from the effect circuit itself ... and then you'll need a different strategy.

[m-Kresol]

something to consider/my two cents: squealing is mostly high pitch, ie. frequency and the filtering you are describing is mostly concerning low voltage ripple (residual from AC/DC conversion) as far as i know.
I had some interferency of low budget power supply with pedals that used charge pumps. I think that your high gain circuits could have picked up some leftover high frequency ripple and shift that into audible range (some circuits are known to pick up radio).

I would encourage you to build the filtering section you talked about on breadboard and just insert it between power plug and DC input on the main pcb (double filtering will not hurt, only the minor voltage drop is doubled) and see if it helps. If yes, awesome. if no, you might need high pass filtering?

I could be utterly wrong here, just spitballing

[JackSkellington]

I can't be 100% sure, because I think in this DIY thing is almost impossibile, to me
But with my Woolly Mammoth on veroboard and on bredaboard I got the whine/squeal, I worked on it some months ago, but if I remember well the 1N5817 diode in line to the 9v slighlty tamed the whine, and a 220uF (original is 100uF) low the pitch of the whine. With battery no problem.
With the kind of Fox Tone Machine I got the same thing. Maybe with the Woolly Mamoth I didn't try, but here a 330R tamed the whine, but this resistor seems to me very oversized, and though I can't hear too much difference in the sound, it's hard to say (and to test well) if it sounds exaclty the same with no resistor. Also with this no problem with the battery.

Seeing the schematics are those, the filters should be strong, the layouts are verified, I got no issue with the battery, I'd say the circuits/schematic are ok and the problem is (oddly just for a few of effects) in the PSU.

[...]
(the battery itself should not be a problem, its probably the circuitry for switching the thing on and off that's causing noise issues with, especially transistor-gain based, pedals).

I got problem for the first time with the Echople Preamp and the Pharaoh Fuzz, but including necessaring a 1N5817 for the first one and just a 47R for the other one I solved. For those other two circuits I mentioned before nothing is enough to solve the issue.

I have to wait my next order, not so soon, to try it. Just I would like to know if the inductor placed there solves right this kind of issue.
Will be cool to know about somebody in the same "squaling" situation has tried it.

Thanks for helping me, guys!

[JackSkellington]

What's difference might have these two kind of inductors?

https://www.taydaelectronics.com/820uh-inductor-ec36.html
https://www.taydaelectronics.com/1mh-power-inductor-10-200-ma-radial.html

[WormBoy]

They at least differ in resistance and max. current rating, judging from the datasheets.