One-Spots, Power Supplies

[timd]

I have a One-Spot power supply to power most of my pedals, and its rated at 9V 1700mA max. Some of my pedals connected to it are 300mA max. How does the One-Spot safely distribute the power?

Also, I have a small pedal board which was powered by a 9 volt adapter (gone) it has connections for 6 pedals and cables. I don't recall what that power supply was rated. If I use a 9V 200mA adapter to power all six pedals, do I risk damage to anything? 

[Bill Mountain]

I have a One-Spot power supply to power most of my pedals, and its rated at 9V 1700mA max. Some of my pedals connected to it are 300mA max. How does the One-Spot safely distribute the power?

Also, I have a small pedal board which was powered by a 9 volt adapter (gone) it has connections for 6 pedals and cables. I don't recall what that power supply was rated. If I use a 9V 200mA adapter to power all six pedals, do I risk damage to anything?  

The One-spot doesn't distibute current.  The Pedal's take what they need.

You could try the 200ma pedal but you really need to know the current draw of the pedals you will be powering.  You may not have enough juice.

[Bill Mountain]

Double post.

[Steve Mavronis]

Hi, I have a related question to add. I own a Visual Sound One-Spot w/daisy chain cable kit. My pedalboard has only 5 pedals consuming total current  draw of 126mA. The 1700mA that the One-Spot is capable of is overkill for my small Pedaltrain Mini rig and I got paranoid having 2 Boss pedals so I'm using their 500mA PSA-120S adapter instead. Figured I'd save the One-Spot for a larger rig. Since my understanding is R.G. designed the One-Spot, maybe he can answer this too: How does the One-Spot compare to the features of the Boss PSA-120S which includes a current protection module on its power cord? Not knocking the One-Spot as I think its great. If there is no practical diffrence between these two adapters (even though its overkill for my current needs) I'd like to go back to using the complete Visual Sounds kit instead.

Boss PSA-120S Adapter

[R.G.]

My pedalboard has only 5 pedals consuming total current  draw of 126mA. The 1700mA that the One-Spot is capable of is overkill for my small Pedaltrain Mini rig and I got paranoid having 2 Boss pedals so I'm using their 500mA PSA-120S adapter instead. Figured I'd save the One-Spot for a larger rig. Since my understanding is R.G. designed the One-Spot, maybe he can answer this too: How does the One-Spot compare to the features of the Boss PSA-120S which includes a current protection module on its power cord? Not knocking the One-Spot as I think its great. If there is no practical diffrence between these two adapters (even though its overkill for my current needs) I'd like to go back to using the complete Visual Sounds kit instead.

Good question. And it gets to the heart of the similar issue above. [Note: for readers who just want to know what the 1Spot does, skip the theoretical stuff and go down to "What the 1Spot Does"]

In theoretical electronics a "voltage source" is a thing that provides a constant voltage out no matter what current is necessary to make that happen.  So a 9V "perfect" voltage source would provide 1A into a 9 ohm load, 100A into a 0.09 ohm load, and 10,000A into a ... uh, whatever the number is that makes it 10,000. No limits at all. At the other end, with a 1,000,000 ohm load, the current is 9V/1M = 9uA and the voltage is still 9V.

There are no perfect voltage sources in the real world, of course. Everything gives up at some point. But power supplies can be modeled as a perfect voltage source in series with some resistance. So if you have a perfect voltage source of 9V in series with a 1 ohm resistor, the output voltage will sag by one millivolt per milliampere of loading.

A perfect current source is the evil twin of a perfect voltage source. A current source forces a specific current to flow in the load no matter what voltage is necessary to make this come true. If you had a current source of, say, 1A, it would force 1A out no matter what was connected. If nothing was connected, it would raise its voltage until a 1A arc formed through the air from terminal to terminal to make the current flow.

Pedal power supplies approximate a voltage source, not a current source. They have a (nearly) constant output voltage, and that voltage remains very nearly constant from zero current out until the maximum the power supply can do. How it handles more current than that is one of the distinctions between power supplies. Non-regulated power supplies have a lot of sag. They're maybe 10Vdc with no load and sag to 8.5V at perhaps 500ma (I'm making those numbers up, but they're representative) so they could be said to be  "9V" power supply, kind of. Actually, they act like a 10Vdc power supply in series with a resistor of (10-8.5V)/0.5A = 3 ohms. A regulated power supply like the regulated Boss supplies and the 1Spot provide about 9.4Vdc which doesn't sag more than a few millivolts right up til they hit their current limit.

So as long as the total current pulled out of a regulated power supply is between zero and the designed maximum, the voltage remains constant. The power supply is a pool of readily available current, and any number of pedals can "sip" whatever current out of that pool they need to work, as long as they're happy with the output voltage.

What the 1Spot Does
The 1Spot puts out nominally 9.3 to 9.4Vdc, depending mostly on the tolerances of the resistors inside that set the voltage. It is designed to be happy at zero loading - if you measure the DC voltage on a 1Spot with just the meter leads on the output plug, it's the same 9.4V with no load that it is for all loads up to 1.7A. We have (accidentally!) powered close to 200 pedals from a single 1Spot. It was humming along fine, output voltage was 9.4V. So the 1Spot is a dandy power supply for any number of pedals from only one, even if it's a low current pedal, up to as many as cause it to put out 1.7A.  There is no need to save it for bigger rigs. It's happy with very light loads.

Some power supplies get funny at very light loads. This issue was in fact one of the early ones that Visual Sound worked on when the first 1Spot was being designed. It HAD to be stable and happy with one low current pedal. In your setup, the 1Spot is capable of more current than your little rig absolutely needs, but there is no need at all to worry that it's too much.

(By the way, no, I did not design the original 1Spot. It predates me with Visual Sound. But I have been in on several of the updates we've done, and am responsible for any design or manufacturing issues that come up.)

I'm not all that familiar with the insides of a Boss PSA-120S. I guess I ought to go buy one and cut it open and look. But if it has a current protection module on its power cord, I'd have to dig a bit to understand that. The 1Spot doesn't need a current protection module, because current limiting is built into the main unit. It's that "what happens when they reach their maximum currents" I mentioned earlier. When you try to pull more current out of a 1Spot than it's happy supplying, somewhere above 1700ma, it decides "Uh-oh! Something's wrong, Timmy!" and shuts down entirely. The voltage and current drop to zero. It waits about one second, then tries to come back up to the proper voltage, and if it can raise the voltage to its preferred 9.4 or so, and the current is less than maximum now, all is well and the show goes on. If the load current exceeds the safe maximum, it shuts down again. This continues until it can come up safely again or until it's unplugged.

In the electronics biz this is known as "foldback and retry".

There are other current limit schemes. One is current limit, which causes the output voltage to drop once the max current is reached, but the max current is allowed to flow. A current limited power supply continues to provide its maximum current into a short circuit. This is what all normal 3-terminal regulators do. It's hard on the regulators, since they have to stand maximum current and also have the maximum possible voltage across their circuitry. They can get really hot. Normally, current limit is coupled with some kind of thermal shutdown, where if the thing gets too hot, it shuts down, cools down and trys to come back up. You wind up still getting foldback, but thermal, not current based.

If there's no thermal foldback, current limit is usually destructive if it goes on too long.

I don't know what the Boss unit does.

But I do know the 1Spot is not "overkill" in the sense of it being bad for either your pedals or the 1Spot to run even a single pedal. I use a 1Spot on my workbench to power test circuits all the time. It often stays on not connected to anything for days at a time. It always measures either 9.45V (mine happened to be a little high) or if it's overloaded, 0V with a little 'burp' of trying to come up every second or so.

The 1Spot is internally current protected.

[Steve Mavronis]

Thank you R.G. I'll switch back to the One-Spot then. I know it will handle more pedal than I can put on it. One of my pedals is a new Boss RC-3 Loop Station and they get you paranoid only use a Boss adpater or you void the warranty type scare tactic. My other Boss pedal is a NS-2 Noise Suppressor. Logically I know any 9V adapter with negative polarity will work with the pedals I'm currently using. Let me know if you get a chance to take apart a Boss PSA-120S. I'm curious about that cord piece. Other pedal manufactureres warnings get you psych'ed out, LOL!

[pinkjimiphoton]

fwiw, i run two complete pedalboards (the kind that have an onboard patch bay to power up to 6 pedals...i run 9 on each,..with one single one spot. sometimes i run more, and have no problem with it whatsoever, and have done so for over a decade.

i have even run 12 and 10 volt pedals on it with no problem.

[R.G.]

Thank you R.G. I'll switch back to the One-Spot then. I know it will handle more pedal than I can put on it. One of my pedals is a new Boss RC-3 Loop Station and they get you paranoid only use a Boss adpater or you void the warranty type scare tactic.

Be aware - that's probably not a scare tactic, it's just convenient. If you have warranty problems, it is a built in way to deny them. But if it's specified for 9Vdc, and has the proper polarity on the plug, the 1Spot is designed to run it. We do a lot of testing on the in-house "victim" pedals to see that we don't kill stuff, but there's no way to cover the entire pedal market these days.

We did have some boutique-y pedal makers who were warning not to use the 1Spot in particular. I've contacted some of them and worked with them on the issue, and to the best of my knowledge, no one is recommending not to use 1Spots now. Several of them got 1Spots to use to test their pedals out, etc as well as some free consulting, and we got things worked out technically. It's to no one's advantage to have pedals fry. 

Most of this happened back in the time when the problem with shorting the INPUT power to pedals was not recognized as a problem, or during the time when 9VAC into a 9Vdc socket was not widely known as an issue. Some of these got associated with a 1Spot, near as I can tell because the plugs all look alike and it's easy to either confuse 9Vac for 9Vdc, or with lots of plugs, it's easy to short one to a pedal housing or similar. Both of these can fry a pedal, even if the 1Spot is working perfectly. It's an almost unavoidable issue for the more complicated pedalboards we have today. I redesigned the power entry on all the Visual Sound pedals so they're immune to 9Vac, and any regulators on our stuff get immunity to input power shorting, but that's not possible for older pedals, so the exposure is still there.

While I'm blathering on about pedals and power supplies, there are two things that really help powering a complex pedalboard. These are (1) the colored "Plasti-Dip" tool handle stuff from a hardware store and (2) some kind of insulator for the unused plugs on a daisy chain power cable. Using the plasti-dip in bright colors on a 9Vac plug in the pedalboard lets you know it's dangerous. I like white/red/yellow/black stripes in imitation of the stripes on a coral snake (!) but just making them bright yellow or something works well enough.  Knowing that a plug is 9Vac helps with not plugging it in the wrong socket. Insulating unused plugs keeps you from killing regulator chips in unprotected pedals.

My other Boss pedal is a NS-2 Noise Suppressor. Logically I know any 9V adapter with negative polarity will work with the pedals I'm currently using. Let me know if you get a chance to take apart a Boss PSA-120S. I'm curious about that cord piece. Other pedal manufactureres warnings get you psych'ed out, LOL!

You have me curious about the lump on the cord now, too. I did see an earlier 120S, but it didn't have a lump, and I didn't get to open it up.

I have this knee-jerk reaction that lumps on cables are ferrite beads to suppress EMI transmission. It's possible that it is an add-on current limit, but if I was doing the design, I sure would want the output cable protected against shorts all the way back into the housing, not leaving a chunk that could still be shorted. That plus it's very hard to do a current limit out on the end of a two-wire cord that doesn't drop some voltage and mess up your regulation. But I'm just speculating.

[Cliff Schecht]

RG something I noticed recently (and I think mentioned in another thread) is that while 9V DC wall supplies typically use a 2.1mm barrel jack, all of my 9V AC powered supplies use a 2.5mm jack. If I plug in an AC cable to a DC input the middle conductor doesn't make contact and fry the pedal. From what I have seen from my pretty massive collection of wall warts this seems to be a universal thing, that is the DC supplies for musical effects is 2.1mm and AC is 2.5mm.

[Steve Mavronis]

You have me curious about the lump on the cord now, too. I did see an earlier 120S, but it didn't have a lump, and I didn't get to open it up. I have this knee-jerk reaction that lumps on cables are ferrite beads to suppress EMI transmission. It's possible that it is an add-on current limit, but if I was doing the design, I sure would want the output cable protected against shorts all the way back into the housing, not leaving a chunk that could still be shorted. That plus it's very hard to do a current limit out on the end of a two-wire cord that doesn't drop some voltage and mess up your regulation. But I'm just speculating.

It's hard to get an exact explanation for the "lump" on the PSA-120S cord but i found this from the BossArea product reference: "The PSA-120S is a replacement for the older PSA adapter. The old PSA adapter could only supply 200mA whereas the PSA-120S is able to supply 500mA." And a cached Google search entry from the old BossArea forum says "The plastic bit near the end of the cord is a housing for the rectifier and overload protection."

[R.G.]

RG something I noticed recently (and I think mentioned in another thread) is that while 9V DC wall supplies typically use a 2.1mm barrel jack, all of my 9V AC powered supplies use a 2.5mm jack. If I plug in an AC cable to a DC input the middle conductor doesn't make contact and fry the pedal. From what I have seen from my pretty massive collection of wall warts this seems to be a universal thing, that is the DC supplies for musical effects is 2.1mm and AC is 2.5mm.

Good bit of info to have - thank you. I have not done any concerted info gathering beyond plugging some randomly provided 9Vac warts into effects and test circuits.

If that's universally the case, the 0.4mm / 0.0157" of space, amounting to 0.2mm and 0.0078" of spacing in a perfectly inserted jack doesn't seem to be enough. It may only be the variable degree of misalignment that keeps this from being fatal in all cases.

I do know that the 9Vac adapters from a company there's no need to name here do cause the Death Of AC in some pedals. I didn't do the next step and go back to the pedals that use them and see if they specify a 2.5mm instead of a 2.1mm center post.

Could you look at how much misalignment is needed to make a 2.5 touch a 2.1 center post? I'll go do some further messing as time allows.

[Mark Hammer]

If that's universally the case, the 0.4mm / 0.0157" of space, amounting to 0.2mm and 0.0078" of spacing in a perfectly inserted jack doesn't seem to be enough. It may only be the variable degree of misalignment that keeps this from being fatal in all cases.

I do know that the 9Vac adapters from a company there's no need to name here do cause the Death Of AC in some pedals. I didn't do the next step and go back to the pedals that use them and see if they specify a 2.5mm instead of a 2.1mm center post.

Could you look at how much misalignment is needed to make a 2.5 touch a 2.1 center post? I'll go do some further messing as time allows.

Keep in mind that all of this will depend on whether you have a shorter or longer shank on the plug.  Shorter ones stand a greater chance of not making contact.

[R.G.]

Good observation. Also depends on whether it's inserted fully or just enough to catch the lip of the barrel contact.

[Cliff Schecht]

Yeah you can put a 2.5mm jack in at enough of an angle to make contact with a 2.1mm guy. The clearances as you pointed out are not very much (fractions of a mm). On an unprotected power supply this could cause instant death, or it could not hurt anything. Really depends on the power supply and how tolerant the IC's and electrolytics are of reverse biasing. I imagine effects using tantalums would become useless pretty quick.

Also the 2.5mm thing is merely an observation I've made fairly recently after revisiting my pedalboards power scheme. I noticed that my Line 6 FM4 has the same 2.5mm jack and that all of my AC adapters have larger plugs too. I highly doubt that this is a universal industry standard or anything but it's at least something for people to be aware of. I keep a known set of 2.1mm and 2.5mm plugs around so I can compare plug ends and see which is the right fit.

[Ronan]

Does anyone know the history of why negative center became the standard, was it implemented by Boss/Roland? I really wonder why it is so, there must be a historical reason?

[Govmnt_Lacky]

Does anyone know the history of why negative center became the standard, was it implemented by Boss/Roland? I really wonder why it is so, there must be a historical reason?

I believe it is to utilize the ability to switch between wall wart power and battery power easily.

[slacker]

That seems the most likely reason. I think the centre pin makes connection before the outer, that might have something to do with it as well.