pedal board power supply thoughts....

[darron]

i don't play guitar as much as i used to and don't even have a setup pedal board right now. i like using a power supply rather than batteries and haven't ever really had problems with noise or ground loops using a daisychain.

do we really need separately tapped transformers to make a power supply quiet? here's my thoughts:

AC into transformer > rectified > filtered > , then one regulator for every output to a pedal (even that's been unnecessary for me, but maybe some people need it). the first output supplies the +v and ground to a pedal on the chain. every other output only supplies the +v. There wouldn't be ground loops. The difference in resistance of ground from the first pedal to the rest I'd imagine will still be less than 1 ohm, so that's almost irrelevant.

Why do people not do this to solve problems? There must be something that I'm overlooking...

Thanks for your thoughts in return.

[R.G.]

i don't play guitar as much as i used to and don't even have a setup pedal board right now. i like using a power supply rather than batteries and haven't ever really had problems with noise or ground loops using a daisychain.

do we really need separately tapped transformers to make a power supply quiet?

Of course not. Hum is a strange thing. Sometimes it's there no matter what you do. Sometimes it's not there even if you do everything wrong. All of which is another way of saying that hum has many causes and is a complex issue.

I do have some practical experience with this. At Visual Sound, we have sold many thousands of the 1Spot power supply, often in the Combo pack with daisychain and power adapter plugs. We very, very rarely get complaints about hum with this. What this tells me is that many people have your experience - one power supply with a daisychain is good enough.

But sometimes it's not. I think that's what leads to the popularity of commercial copies of the Spyder, like the Pedal Power and its ilk, which did not exist before I published the Spyder.

here's my thoughts:
AC into transformer > rectified > filtered > , then one regulator for every output to a pedal (even that's been unnecessary for me, but maybe some people need it). the first output supplies the +v and ground to a pedal on the chain. every other output only supplies the +v. There wouldn't be ground loops.

Probably fine. In fact,  you probably don't need the independent regulators, as witness the 1Spot and daisy chain experiences.

The difference in resistance of ground from the first pedal to the rest I'd imagine will still be less than 1 ohm, so that's almost irrelevant.

Actually, it's not irrelevant. An LED often pulls 10-20mA. 20mA in 1 ohm is 20mV. A guitar signal is on the order of 100mV. So the LED drop is not trivial compared to the guitar signal.

What's wrong is your speculation about the resistance. It's probably less than 100millli-ohms, which means you get even less voltage caused by the ground resistance.

Why do people not do this to solve problems? There must be something that I'm overlooking...
Thanks for your thoughts in return.

People in general have no clue about ground loops and the issues of power supply wiring impedance and wiring order. Even those who do have some inkling miss the issue of it being both conductive loops and wiring impedance.

[darron]

thanks for your input R.G., you always give a very thorough breakdown.

all the more reassurance that i good high current power supply is sufficient in most situations. so go out and buy a 1spot! hehe.

yeah, the continuity should be VERY good from the first pedal to the last. much less than 1 ohm. so good in fact that it would be worthy of carrying an Earth! hmm 

i suppose i'm mentally trying to fix an issue that doesn't always exist, and those people who might use my solution are probably happier with the way that they are already doing things. i'll keep it in mind to try only if i ever have an issue.

[Paul Marossy]

In the two pedal boards that I have built and used, I found that the most significant factor in hum/buzz was where my wall wart(s) were in relation to things on my pedal board, especially in relation to any inductor based wah pedal. Pretty much in every iteration of my original pedal board, the wall wart was ultimately the culprit. And every once in a while, the physical location of the pedal board can even make a difference. I recently had a weird experience that showed me that. Doing testing with about 10 wall warts plugged in less than five feet away from your pedal board and at the same plane as your pedal board will cause some problems.

On my latest DIY pedal board, I have an LM317 voltage regulator taking care of the power supply. It's very quiet. On both of my pedal boards I am using a single power supply with a daisy chain. I have never had a problem with noise being caused by a dasiy chained power supply in the 10 or 12 years that I have been using them.

I think there is still a very tiny amount of hum in my pedal boards, which you normally can't hear. Where it comes out is with a super high gain distortion or cascaded dist/od pedals. But I really never use either scenario anymore.

I've concluded that nothing is bullet proof when it comes to hum/buzz in a pedal board or amp, but there are tried and true ways of dealing with it to minimize it as much as possible, and I have been pretty successful at getting rid of it in my own equipment.

[darron]

That's another good point Paul that the transformers are often located right on the pedal board! Especially with the multi-tap supplies. I've seen heaps of pedal boards where people run a 4 way multi-board which powers all sorts of things, sometimes even their amp. Might be more of a problem here in Australia where supply is 240V. The wattage consumed is the same of course, but I wonder if you get more noise from using transformers near sensitive lines.

My bench power supply I made uses a toroidal and a regulator, and it's pretty much dead silent when A/B'd with a battery, so that tells me it isn't necessarily always going to be a problem

If you are going to have the regulator with single or multiple outputs on your board, then I think you should get the AC mains as far away as possible. Even if you use a crappy transformer at the powerpoint and feed DC to a regulator on your board.

I've also seen people stacking guitar heads on each other, often blocking ventilation holes. Personally experience however tells me that is an excellent way to introduce unneeded hum!


But anyway... IF you did have a problem with ground loops, would it be a good idea to break the ground in the daisy chain that feeds all of the pedals except for one? Seems to me like it could just be a good practice anyway for the non-typical consumer who can remember what they have done and for what reason...

[Paul Marossy]

With the wall warts, I surmise that it's the field around them that radiates EMI a certain distance away from the transformer. The only thing that I have found that really cures that is distance from the pedal board.

The other half of the equation is ripple on the power supply, which can cause a 120Hz "buzz", which I think people many times call a "hum". Anyway, some wall warts can introduce a lot of noise because they are poorly filtered, or not filtered at all. That's why I like my LM317 power supply that I built into my latest pedal board - it regulates the voltage and at the same time filters whatever I plug into the power supply jack. Right now, I'm powering my pedal board with a thrift store wall wart that puts out 20.2V with no load on it. I can plug whatever I want into it and I don't have to worry about it.

[seedseed]

Has anyone used a ground loop isolator in there pedal line up to get rid of hum rather than use a dedicated power supply for each pedal?

[darron]

Has anyone used a ground loop isolator in there pedal line up to get rid of hum rather than use a dedicated power supply for each pedal?

that's one idea that you could break the earth to all pedals except one. I think people often use independant supplies to eliminate noise transfer between pedals, especially digital. One regulator shared can't always do the trick.

In most instances a quality power supply daisy chained is fine though...

[Eric H]

When I built my pedal-board 10 years ago I incorporated a very clean LM317 regulated power supply --one transformer and one regulator. I've had no hum problems, but I built it before RG's spyder articles and realize the lack of hum problems were partly serendipitous  I also haven't gigged that much in that period.
I think if I were building a pedal-board supply now I would probably use the lithium-ion power packs from my most recent drill/driver which recharges a 3 amp-hour battery in 45 minutes. Nice clean DC with no possibility of ground loops (from the power supply, anyway).

[simplypowersupply]

There may be another reason for the hum which you are discussing and it is all to do with the way in which switch mode power supplies rectify the mains (does not actually matter if it is 115Vac or 230Vac), the point is that they all have a certail switching frequency which may add hum to your amp. The switching frequency changes from power supply to power supply and so this may account for the way in which some people experience the hum and other not.

One way round this is to use a linear transformer, these are more expensive, heavier and bulkier than switch mode ones, but they don't have the problem of interference

We offer a range of units and can have units specially made also: http://www.simplypowersupply.com/Linear-Power-Supply/default.aspx. If you are not sure or if you don't see something you need then please get in touch with us via our feedback form and we will look into it for you

Thanks!

[darron]

thanks for bringing up this VERY old topic simplypowersupply. i'm glad that you have raised your concerns with switchmode supplies.



if we start a thread relating to switchmode supplied we can link back to this.



someone please ban that fkuctard?

[markeebee]

Eh?  Did I miss something??

I don't see the problem with simplypowersupply's post.  Ok, he's soliciting, but he's also offering help.

[Ben N]

In the two pedal boards that I have built and used, I found that the most significant factor in hum/buzz was where my wall wart(s) were in relation to things on my pedal board, especially in relation to any inductor based wah pedal.

Ditto--I've tried sticking a power strip with wall warts just below my board,  and it looks pretty, but sounds awful. I would add only that amp power transformers can the same thing, and if you wah is too close to a combo amp on the floor, that can cause objectionable hum as well.

Daisy chaining has worked well for me with the exception of one digital pedal (Line6 chorus). If you need more than that, what Darron is suggesting, or possibly something like the AMZ board should be helpful without going the whole distance to a Spyder-type supply, that as a practical matter pretty much has to be on board and could cause emission based hum.

[petemoore]

  One theory that often works is get it pretty good and that's good enough. Only problem with this theory is when noise all of a sudden is rediculous and there's no time to peel the noise-onions.
  Another is that noone knows how bad the hum is going to be until the hum is bad, do everything possible to eliminate noise at all times or wonder if there's a noise issue that could have been avoided by preparing the peeled onions in advance.
   One days noise is different than the next days noise.

[R.G.]

There may be another reason for the hum which you are discussing and it is all to do with the way in which switch mode power supplies rectify the mains (does not actually matter if it is 115Vac or 230Vac), the point is that they all have a certail switching frequency which may add hum to your amp.

I have some experience with this topic. 

I'd have to see a whole lot more explanation of that sentence, because it seems ambiguous to me. There are certain grains of truth embedded in it; actually, more of allusions to things that are true in some specific circumstances. However, it strikes me as a bit of exaggeration to say that these issues are significant causes of hum in pedalboards.

Switchmode power supplies rectify the AC mains in only two ways - half wave and full wave. It is *possible* under some circumstances for a half-wave rectifier to cause so much offset to the AC line by rectifying only one polarity to cause a DC offset that makes other power transformers on the same power branch see asymmetrical saturation. Generally this is only significant to toroidal power transformers, which are much more sensitive than EIs to offsets. Toroids are rare in guitar amps. I know of only two commercial amps which do/did this, although to be fair there may well be others, as I don't know the insides of all of them.

There are a couple of ways this gets filtered into DC, one is by simple capacitor filter and one is by means of a power factor correction circuit of some form. The simple capacitor filter causes spikes of current, which can cause both coupled/transmitted spikes and RF ringing from the main rectifiers. This CAN be the source of buzzy distortion sound in amps. However, the amp itself is doing the same kind of rectifying, and there's a lot less power in the spikes and RF in any small pedalboard adapter than in the amp itself. Again, there is a possibility here, but a little thought says it's going to be rare.

The switching frequency changes from power supply to power supply and so this may account for the way in which some people experience the hum and other not.

This strikes me as an oversimplification. First, it used to be that switching frequency was different from power supply to power supply. Today's energy conservation laws have forced switching power supplies to be variable frequency. So yes, the frequency is different from power supply to power supply. But it's also variable inside the SAME power supply depending on the input voltage and output loading. Yes, this could have an effect if you could hear the power supply switching frequency, but it's above audio; in fact, it's generally over 100kHz these days, so you can't hear the switching frequency if it does get into your pedals and amp. You *might* be able to hear heterodyne beating of the switching aliased back down into audio, but this requires a fairly special set of circumstances to happen. Generally, there has to be some oscillation going on in the pedal that's within 20kHz of the switching power supply's frequency to get a difference frequency that's within the audio range.

I think the operant word there is the easily-passed-over "may" which is so common in advertising, along with its brother "up to". If you construct the sentence very carefully, yes it MAY in some instances however rare, cause audible sound. Although even there, with variable frequency in the power supply I think it would cause more of a radio-tuning squeal instead of hum.

One way round this is to use a linear transformer, these are more expensive, heavier and bulkier than switch mode ones, but they don't have the problem of interference

Again, "yes, but...". This is indeed one way round it. They are expensive, heavier, bulkier, etc. than switchers. They don't have the *same* problems of interference as switchers, but because of the current rectification spikes which they DO still have RF ringing interference if you're not careful about rectifiers and snubbing, and they DO still have the issues of DC offset on the power line if they're toroidal for small size, and they DO still have rectification ripple problems which an active regulator would wash out.

Then there's the issue that they're banned in some place. The Republic of California and some other places have successfully forced all wall wart makers to go switching with carefully worded legislation that bans non-switching wall warts on efficiency issues.

So, again, I'd need to see a lot more technical information on real world situations to back up the posting in question. There are grains and nuggests and possibilities there. But there are literally tens of thousands of counterexamples where bog-standard switching wall warts work fine, and hum free. And that's just in my personal experience. May be; could be; up to...

And Paul and Pete are correct. Noise varies with time, place and physical arrangement. There's probably no power supply that's immune to causing hum if you place in an unfortunate place and at an unfortunate time. Including most especially non-switching transformers which are know to all emit magnetic power line frequency hum.

[darron]

Eh?  Did I miss something??

I don't see the problem with simplypowersupply's post.  Ok, he's soliciting, but he's also offering help.

Yes He's soliciting after one posts. He would have had to search specifically for this old thread to bring up a chance to put in the 2c....

The main issue is that we were not talking about switching frequencies at all. It's nothing to do with the original post or any following really.

Besides... There are a lot of people here who like their switching supply... Especially the smaller ones that don't take up much room....

Sorry for jumping the gun simplypowersupply if you legitimately wish to learn from and contribute from this site, but I have my doubts. if you wish to participate please read into the thread before assuming it's premise. this was an old thought about supplying the +9VDC to all pedals in a chain and only the negative to a single pedal and the PROS and CONS associated with the concept. i don't have an issue with hum at all and have a power supply that i have personally made to my liking.