Power supply for pedals

[edde]

I'm going to build a pedalboard from scratch and have a few questions about power supply.

I need power to 8 pedals and most of them are analog (I've heard they use less power than digital). The very small and cheap plastic transformers allows 500mA of current and if i use a daisy chain cable i think it will cover all of my pedals. If that is the case, why do people use the 200$ powerplants with 8 x 9V jacks BUT also with a total current of 500mA?

[R.G.]

Part sound quality, part because they believe the advertising.

A small, cheap plastic (-cased) plug in transformer can give you 500ma. But unless it's carefully designed for pedals, it can also give you bad hum in your pedals, and may not be the right voltage. You need the right voltage and enough current.

Most pedals specify 9Vdc, largely matching what a 9V battery gives when it's new and fresh.Some pedals *tolerate* higher voltages. A few, mainly decades-old ones need lower, as low as 1.5V or 3.0V. some digital pedals need large currents and may need 9V*AC*.

You take a chance on killing your pedal if you don't give it the right voltage. If there is enough current available, it will take only what it needs. That's why you need to be careful. Not all "9Vdc" pedals are alike. Some are 9V only at fully current, and some are not filtered at all.

However, there are $20 power supplies specially designed to mimic an inexhaustible battery, and power tens or (literally!) hundreds of pedals while doing it. The company I work for does one of these. There are other brands. Why the gulf between these and the $200 many-output power supplies?

Two reasons. First, there are some pedals which need negative 9Vdc, not positive 9Vdc. The best illustration is the Fuzz Face and other germanium PNP pedals. It is handy to have an isolated output that can do this, although there are less-than-$200 solutions to the same problem. Second, there are some fairly rare situations where having isolated power supplies can make for less overall hum; the makers of $200 power supplies obviously will thump on these situations hard and long.

I show how to do a multi-output power supply on my personal web site, geofex.com. Look for the "Spyder". The whizzo isolated power supplies are largely flourishes and enhancements on that theme. I probably ought to go do the detective work to see if the whizzos predated the Spyder, or the other way round. I don't remember them before I published that, but then I was not looking.

Questions?

[oc disorder]

Saw these two sites which list the current consumption of some popular pedals.
Although you most probably don't need to, this enables you to add up the total amount
of current required.

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The Power List

[edde]

Part sound quality, part because they believe the advertising.

A small, cheap plastic (-cased) plug in transformer can give you 500ma. But unless it's carefully designed for pedals, it can also give you bad hum in your pedals, and may not be the right voltage. You need the right voltage and enough current.

Most pedals specify 9Vdc, largely matching what a 9V battery gives when it's new and fresh.Some pedals *tolerate* higher voltages. A few, mainly decades-old ones need lower, as low as 1.5V or 3.0V. some digital pedals need large currents and may need 9V*AC*.

You take a chance on killing your pedal if you don't give it the right voltage. If there is enough current available, it will take only what it needs. That's why you need to be careful. Not all "9Vdc" pedals are alike. Some are 9V only at fully current, and some are not filtered at all.

However, there are $20 power supplies specially designed to mimic an inexhaustible battery, and power tens or (literally!) hundreds of pedals while doing it. The company I work for does one of these. There are other brands. Why the gulf between these and the $200 many-output power supplies?

Two reasons. First, there are some pedals which need negative 9Vdc, not positive 9Vdc. The best illustration is the Fuzz Face and other germanium PNP pedals. It is handy to have an isolated output that can do this, although there are less-than-$200 solutions to the same problem. Second, there are some fairly rare situations where having isolated power supplies can make for less overall hum; the makers of $200 power supplies obviously will thump on these situations hard and long.

I show how to do a multi-output power supply on my personal web site, geofex.com. Look for the "Spyder". The whizzo isolated power supplies are largely flourishes and enhancements on that theme. I probably ought to go do the detective work to see if the whizzos predated the Spyder, or the other way round. I don't remember them before I published that, but then I was not looking.

Questions?

Damn good website you got!! It will probably be my new bible.

I post some questions if they dont get answered by you site.

[edde]

All my pedals are 9Vdc.

I have 240VAC at home so that will be a problem with the american standard.

I read your article about loops and interference. My loops will be very small if i use the daisy chain and small patch cables. I tested my very cheap plastic transformers and they produce 10.6V. If i put a resistor before the daisy chain, that could give me 9V right? I have four of them at home so sensitive pedals can get a power supply of their own.

What brand of power supplies did you recommend?

[Mark Hammer]

When power supplies are just "hanging there", with no load on them, you will virtually always measure a higher output voltage than their rating and what you expect to see. So if the only thing at the end of your power plug is your meter, it will read 10.6V or whatever, but if you were to plug it into a pedal or two, and measure the voltage provided to the V+ pins on any of the chips in there, you would read 9V (or close enough, given tolerances, to treat it as 9v).

So, no modifications or adaptation needed.

Ethics and modesty prohibit Brother Keen from using the opportunity to plug his employer so I'll do the plugging for him. He is referring to the Visual Sound One Spot. Fine product, though certainly not the only one of its type.

Some of the other reasons that people decide to go with a "brick", rather than something like the One Spot and a daisy chain include the following:

1) Not every pedal has the same footprint or form factor, and presents a convenient location for the power jack. Between wahs, and oddball pedals like the Damage Control pedals, the distance between power jacks, or the bizarre corners the cables have to turn to get there, can make conventional daisy-chain cables awkward. They will certaainly work like a charm for pedalboards that are all of one or two fairly similar form factors, and a great many pedalboards are like that, but not all are. So many users like the convenience of having multiple outlets from the brick that permit them to run multiple separate power cables to accommodate those inconsistent spacings and such, and keep cable lengths neat and short.

2) You mentioned that all your pedals are analog, so you won't have this problem now. But many companies are migrating to digital processing, because it allows them to do some things without necessitating huge boards, and because it often allows them to provide many more features for the dollar in a small package. It doesn't happen ALL the time, but many have noted that running two or more digital pedals off the same PS can result in a big increase in noise, if the power source does not feed those pedals in a manner that isolates them from each other. The problem is that digital pedals have multiple high-frequency clocks on them. On their own, they provide no audible noise, and no noise resulting from interaction with other analog pedals sharing the same power line. But if the clock signals riding on the power are free to move in both directions from digital pedal A to digital pedal B, they can interfere with each other to produce a great deal of audible noise.

I don't know that ALL brick-like units provide the necessary degree of isolation between outputs, and pedal manufacturers themselves seem to be paying more attention to the risks now that more players are using multiple digital pedals. But certainly the traditional daisy-chain cable will not provide the needed degree of isolation between pedals. Again, this is NOT a problem with analog pedals, or individual digital pedals, just with using multiple digital pedals off the same power source/supply. So some players need to use a supply that can assure optimal isolation between the outputs. And those will have multiple output jacks.

3) Not all pedals run off 9v. Some will want 12v, some 15, and some even more. Brick-type units that have multiple output jacks can do that, and single plug w/daisy-chain units can't. I wouldn't be able to provide a reliable estimate of precisely what portion of players have a 9v-only pedalboard vs a multiple-supply-voltages pedalboard, but the 9v users are likely in the majority, given that most beginners are going to have a small handful of fairly standard pedals (Boss, DOD, VS, EHX, Danelectro, Behringer, etc.) that one finds in the neighbourhood music store, and those are generally 9v.

[edde]

Thanks for the answer! I measured one of the transformers in action and it was 10V. If the voltage will cause issues i simply install a resistor.

I have a lot more transformers than digital pedals so i will be ok. If i need 18V i will just add a 18V transformer (which is probably included anyways)

[edde]

Is it possible to get 18V by connect two 9V transformers in serie?

And i noticed that the powerbricks have metal covers. Is that like a shield for electromagnetic waves? If it is, do plastic transformers produce such a field and if they do, is it possible to shield that of with some aluminium foil or something? My pedals will be just a plywoodboards thickness away from the transformers.

[Mark Hammer]

Your instincts are correct. Traditional wallwarts would usually be ocated at some distance from the pedal/s being powered. Since one of the purposes of power bricks is to provide for the shortest power cable distance possible, their intent is to be situated pretty close to the rest of the units on the pedalboard. In which case, it is useful to shield the transformer so that there is minimal risk of EMI from the transformer itself.

One way of generating 18v from a more standard 9v wallwart is to use what are called "charge pumps". You can read more about it here: New Page 1
Note that charge pumps, as wonderful as they can be, can be limited in how much current they can provide, and can also be a source of HF whine themselves if not used carefully.

[edde]

In my pedalboard the transformers will be located under some plywood so i will cover the inside walls with aluminium foil. Do you think that will do the trick?

[Mark Hammer]

You should probably turn to those who know more about such matters than I do, and I wouldn't treat this as gospel, but my gut tells me that shielding against RFI doesn't depend on the thickness of the shield, but shielding against EMI does. You may want to use something thicker, like maybe a sheet of aluminum or galvanized steel sheeting, like you find in a building supplies or hardware store.

[cjlectronics]

Shielding for EMI has always been a trial and error thing for me. In my day job, I design medical devices and radiated emmissions of EMI is critical in equipment and patient safety. Grounding plays a big role in squashing EMI. Copper tape works well. You can line the underside of the plywood with copper tape and make sure you ground it. Use a couple of wires or one big guage wire. But, this is where you get into the trial and error portion of EMI suppression.

[lowell]

I had to chime in here. I'm tired of 9v adapters and their ridiculously cheap cabling. One Spot included. The tiny (CHEAP) cable used from the transformer to the pedal jacks always tend to break internally after due time. Anyone have a recommendation on a more reliable manufacturer? And yes I need to power 4 or more pedals with identical voltage and current demands.

[R.G.]

I had to chime in here. I'm tired of 9v adapters and their ridiculously cheap cabling. One Spot included. The tiny (CHEAP) cable used from the transformer to the pedal jacks always tend to break internally after due time. Anyone have a recommendation on a more reliable manufacturer? And yes I need to power 4 or more pedals with identical voltage and current demands.

Since this is much the same post as over on diystompboxes, I'll chime in here too.

Lowell, didn't you say over there that you're using a Visual Sound 1Spot and it *hasn't* broken on you?

The tiny, (CHEAP) cable from the power unit to the connector plug is 18 gauge zip cord on the 1Spot. We deliberately started paying more (that is, un-cheaper) about five years ago when we upgraded the unit, and didn't increase the price when we put thicker cord on it.

I guess I could copy my response from diystompboxes back in here, too. That thread has before and after pictures of the 1Spot on it. I can't speak for any other manufacturer, of course.

As I mentioned over there, I'm going to ask the boss about bringing out a connector-ized version, where the pigtail can be replaced. That'll mean finding a connector that'll last longer than a strain-relieved cord, but, hey, it's worth a look.

As for powering more pedals, the office once called me to say they had low voltage coming out of a 1Spot they were using to test pedals. I asked a few questions and they sheepishly admitted that they had (accidentally, they said... ) connected up nearly 200 pedals with a nest of daisy chains.

The 1Spot pulling this train was happily producing about 9.4V at its terminals, but there was enough sheer length of wire and connections to drop the voltage over the length of the chains. "Doctor, it really hurts when I do ... this..." "OK. Then don't do that."

[lowell]

RG, yes I did say that. However the one spot cabling still looks similar to other adapters that I've had fail on me. Like the PSA from Boss. But yes it has YET to fail. To be clear. Maybe I'm not being accurate by saying One Spot included, as my One Spot is still working. Honestly though the cable doesn't strike me as being very thick... Especially the daisy chain.