Switching power supplies are often noisy

[shredgd]

Hi,

I've been often experiencing noise problems with power supplies which use the switching technology (which are now the industry standard). First was a Visual sound 1-spot, which became noisy after a few weeks; then was a Line6 power supply, after only a few days! (I still have another identical Line6 one which is perfect and I regularly use, though). Today I received a Dunlop 9v power supply which I bought as a backup and... it is already noisy at first use!
The noise is typically a high pitched fastly-vibrating and continued noise, which I have read is inherent with the switching technology itself. However, this does not explain why some are good, some were good but then become noisy, and some are noisy out of the box... So my question is: why?
Also, how do you deal with it? I just verified that, in my setup, if I add a standard silicon diode in series with V+ (like many guitar pedals do) the noise is quieter but doesn't disappear, while a 100ohm series resistor effectively filters out the noise (from the audible range). But not every guitar pedal has this kind of additional resistor filter, and I also don't like to be obliged to modify all my pedals to get along with an imperfect commercial product. What are your thought and experiences?

Giulio

PS: I've previously built regulated power supplies with 7809 power regulators, but for this small pedalboard I have made, I wanted to keep things clean and compact with the straightforward ease of use of the compact commercial supplies.

[EBK]

A couple questions:
Are you powering all of your pedals from a single supply, daisy chained?

What particular pedals are you powering?

I suspect (guessing, really, pending answers to those questions) one or more of your pedals are making the power noisy for the rest of them and the switching noise is not caused by the power supply itself....

[shredgd]

A couple questions:
Are you powering all of your pedals from a single supply, daisy chained?

What particular pedals are you powering?

Not daisy chained, but "star-chained" (to minimize noise)

I am powering a bipolar buffer, two overdrives and a high gain pedal.

I suspect (guessing, really, pending answers to those questions) one or more of your pedals are making the power noisy for the rest of them and the switching noise is not caused by the power supply itself....

That's what I would have thought... if I didn't have a perfectly silent setup with one of the two line6 power supplies or one of my diy 9v regulated power supplies! 

[reddesert]

Some switching power supplies are literally noisy, in the sense of microphonic, in the sense of I can actually hear them.  Not through an audio chain, I can literally hear them making a high pitched whine. I unplugged a phone USB charger in my office yesterday because it was doing this. I have noticed that these can be intermittent, which isn't that surprising with microphonic vibrations.

I don't have a good answer for your problem as I don't have experience with a lot of commercial pedal power supplies, but you could build 100 ohm resistors into a star-chain cable if they solve the problem to your satisfaction.

[R.G.]

I would agree with the subject line. It takes a lot of work to make a switching power supply quiet. I can speak of this personally, as I have been involved for some years in making quiet switching power supplies for pedalboard use.

I've been often experiencing noise problems with power supplies which use the switching technology (which are now the industry standard).

That's not quite right. They're standard all right - countries have enacted laws requiring efficiency specifications that only switching power supplies can meet. They're standard because laws require them.

First was a Visual sound 1-spot, which became noisy after a few weeks;

I would really like to get more details on this, and even the noisy 1Spot if I could. I regularly perform autopsies on power supplies to find out what happened. If the 1Spot was quiet for some weeks then changed, the real question to be asked is - what changed? Was it an early part failure in the internal filtering or what? If it was once quiet, it could be again; more importantly, other examples of the same thing could be quiet for their entire lives, maybe.

then was a Line6 power supply, after only a few days! (I still have another identical Line6 one which is perfect and I regularly use, though).

Again, quiet to start, then getting noisy. What changed?

Today I received a Dunlop 9v power supply which I bought as a backup and... it is already noisy at first use!

I can almost guarantee that unless the switching power supply has had a lot of work put into making it quiet, you will hear the switching noise. But again, we do have examples of quiet switching power supplies, which have remained quiet in demanding professional situations for years. The devil is in the details - not in the glossy broad brush of categorization. Of course one horse can run faster than another one - but WHICH ONE?? Details matter.

The noise is typically a high pitched fastly-vibrating and continued noise, which I have read is inherent with the switching technology itself. However, this does not explain why some are good, some were good but then become noisy, and some are noisy out of the box... So my question is: why?

I do have personal knowledge that there are many thousands of switching power supplies of at least one brand/model that are quiet and have remained quiet for years. I can make guesses about what might happen, but some detailed post mortem work is needed in every case. This forum is not going to give you the answers, only general guesses.

Also, how do you deal with it? I just verified that, in my setup, [...] What are your thought and experiences?

My experiences are that there are many causes of noise issues. I have been involved with a lot of power supply noise complaints, and they seem to come down to either
(1) the power supply was not carefully enough designed or tested
(2) the power supply was quiet, then something failed
(3) the power supply was quiet, then something about the AC mains wiring changed
(4) something changed about the pedals being powered that interacted with the power supply to make noise audible that was not audible before.

Your experience with the 1 Spot and one of the Dunlop power supplies seems to eliminate them from (1).

I have seen instances where adding a new pedal with its own power supply can cause audible noise from the ground interactions.

What particular pedals are you powering?

Not daisy chained, but "star-chained" (to minimize noise)

Star-wired power eliminates common ground-current interactions, but not conducted EMI interactions. Better than nothing, but no panacea.

I also know of many, many pedalboards with pure daisy chains for power that are quiet. Daisy chaining by itself is not guaranteed to be bad, either. Details matter.

I am powering a bipolar buffer, two overdrives and a high gain pedal.

Which ones? (1) that's a lot of gain and (2) some overdrives and high gain pedals are more prone to noise conditions than others.

I suspect (guessing, really, pending answers to those questions) one or more of your pedals are making the power noisy for the rest of them and the switching noise is not caused by the power supply itself....

That's what I would have thought... if I didn't have a perfectly silent setup with one of the two line6 power supplies or one of my diy 9v regulated power supplies! 

Still could be. Which line6 power supply? Exactly the same as the first one that went noisy? And linear regulated supplies have a "frequency response" where they can eliminate noise better from the input than the output. Details matter.

[shredgd]

Hi R.G.,

now that I recall better, the noisy 1-spot was of a friend of mine (who goes through frequent changes of pedals in his pedalboard, so I can't tell you any details). Mine had another problem: you could "feel" the tension with the side of your fingers on the pedals chassis/ground. This happened with all the house warts, and if I recall well, even at my parents' home in another city. Then one day I touched an angle of a pedal with the side of my hand and I could even feel an hurting stinging  sensation, which stopped when I unplugged the 1-spot. If I used my Line6 M5 9v power supply for my pedals (model DC-1g), there were no "shocks". I was afraid, though sounding ok, that the tension I could feel with my fingers with the 1-spot plugged might hurt my pedals' circuits. So I bought two more DC-1g, one for me and one for my friend. Mine (the new one) started to be noisy after a few days, as I wrote. So, in the last months, I've been using the "old" DC-1g to power my diy pedals, and the new noisy DC-1g with the Line6 M5 (which isn't noisy with it!). No noise at all.

The pedals have always been the same: a fine tuned bipolar buffer (see a previous topic of mine), which is always on, inside a Rockett animal clone pedal; a double pedal which contains a JHS morning glory and a angry charlie clone; a microamp clone.
When using one of the "noisy" power supplies, the noise is there even if I connect just each one of my diy pedals (obviously you can hear it only when they are engaged); of course, the more the gain I dial, the more the noise.

As far as power supply filtering concerns, the rockett animal circuit is the only one to have a series resistor (56 ohm), but having the always on buffer before it, which hasn't got a series resistor, might let some power supply noise get through nevertheless, in that pedal. The two JHS clones have a standard 100uf cap to ground and parallel silicon diode. The microamp has a series protection silicon diode.

I KNOW that, from a "practical" point of view, adding a little series resistor to all my diy pedal will be the way to easily and cheaply solve the problem, now and in the future, with any commercial 9v power supply for guitar pedals use; it creates a low pass RC filter with the electrolytic cap to ground, and the voltage drop won't be any audible one. What puzzles me, though, is why can I have a perfectly silent setup with some power supplies, and why some would be noisy without that extra filtering (even same brand same model, as in the case of the DC-1g)?

Giulio

PS: To add even more ambiguity, after keeping it in a drawer for months, today I connected the 1-spot again: no "palpable tension" over the pedals, no problems. I didn't move, the house is the same, no changes to the electrical line!

Edit: I asked my friend and he reported to me that he had to dump two 1-spot power supplies, to date: one had become noisy, as I said, one for the same "palpable high tension on pedals" as mine

[shredgd]

Another little update:

As I wrote in my last post PS, my 1-Spot seemed to work nicely again. But I recently used it to power my pedals in front of my Triaxis lead2 channel, and it added a noise that my other power supplies didn't add. The 1-Spot goes back into the drawer...