# Is it safe to use 18V to power a device that uses 12V?



## Milkman

I have a wireless receiver I want to mount to my pedal board and it uses a 12v wall wart. The power supply built into my pedal board (Gator) has three 18V power outputs and three 9V. Would using 18v cause any damage to the wireless receiver?

If I can use the onboard power supply it will eliminate the need to run a second AC line just to power the wireless.

Any advice would be greatly appreciated.


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## Evilmusician

IMO yes! don't do it! what are the miliamp requirements ?


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## Jeff B.

There are a number of variable to account for before entertaining the idea.
Is it 12V AC or 12V DC it needs?
What is it's polarity? Negative or positive ground?
Will your power supply support the extra current draw? 
If it's current 12V adapter is an unregulated one it could be already putting out around 16-18V
Some capacitors inside may not be rated for much higher voltage

Best just to stick with the extra adapter and play it safe if you're not sure of these things and don't know how to check them.


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## Milkman

Problem solved. I mounted a small power bar on the bottom of the pedal board and simply plugged the power supply for the pedal board and the wall wart for the wireless into the power bar.

Now I need one AC feed to the pedal board as I wanted.

Thanks


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## mhammer

Though resolved, the query still demands a response in anticipation of the future. So, a response...

IT DEPENDS. There are many circuits/devices that are extremely flexible in terms of their power needs/requirements/tolerances. In some instances, pedals/devices can sometimes "work better" with a higher supply voltage.

A great many circuits in the guitar world, however, presume a 9v or 12v supply. So, for instance, many overdrive boxes that use JFET transistors bias the JFETs for optimum performance, _assuming a 9v supply_. That is, the value of the components used to bias them are dictated by the assumptin that they are using 9v. You could use higher supply voltages, but you'd have to know how to rebias the JFETs, and if the circuit uses fixed-value resistors, rather than adjustable trimpots, you'd have to overhaul the pedal just to do that adjustment.

Another aspect, though much less true today, is the voltage ratings of capacitors. Once upon a time, the ability of a cap to function at higher voltages and still maintain its specs, was more correlated with both size and cost than it is today. So, a manufacturer might use caps rated at 16v for a 9v circuit, because they were smaller, cheaper, and met the margin-of-safety (generally 1.5x the supply voltage). You could get away with feeding that circuit 12v instead of 9, but 18v would exceed the rating of the caps. So, not all components are necessarily guaranteed to work at voltages noticeably higher than what is listed in the manual. But, like I say, caps are cheap and small these days, and it is not uncommon to find pedals designed to run off a 9v battery that use caps rated for 35v.

A great many op-amps and transistors CAN work at higher supply voltages (often as high as +/-18v), but some things can't. CMOS chips are one of them. These tend to fry at supply voltages greater than 15v, and TTL (digital) chips need 5v, emitting "magic blue smoke" when you venture higher than that.

Finally, many devices assume all voltage regulation is done outside the pedal, but some take on the task themselves. If a pedal provides regulation of an input voltage *down* to 9v, it will generally want at least 2v more than that coming in. That is, the standard 3-pin voltage regulator has to see 2v more at its input than it is spec'd to produce at its output, or else it won't deliver. So, it is not at all unreasonable for a pedal to indicate use of any old 12vdc (outside pos) wallwart delivering 100ma or more, because the pedal is already designed to regulate that down to a stable and smooth 9v. That very same pedal may well easily handle an adaptor feeding it 15v or even 18v, because both of these meet the 9+2 requirement and aren't completely out of spec for what the on-board regulator can tolerate.

So, there ARE plenty of circumstances where throwing an 18v supply at a pedal that asks for 12v is not at all illogical or dangerous. Of course, the caveat is that you need to know a fair amount about the pedal/device, and you need to know what you're doing.

As an aside, I own a couple of old Boss BF-1 flangers. They require an adaptor and will not run off batteries. The *chassis *says 9v, but the service manual says 12v. They will "run" on 9v, but the performance at 12v exceeds that at 9v by a very noticeable margin, particular with respect to the width of the sweep.


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## Milkman

Thanks Hammer,

Actually I'll pass the tip about the Boss BF-1 on to my bassist. He uses one for a couple of tunes and I believe the wall wart he uses has switchable voltage.

I appreciate the detailed exlanation. I'm sure there are cases where it's not harmful and even advantageous to use higher voltages than specified. In my case I was able to find a practical solution without doing so.


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## mhammer

My pleasure. There's a lot of stuff out there subject to inaccurate or incomplete information. Music store people, and even those who write for magazines, can be clever folks, who know a lot and are eager to help, but extensive technical knowledge (or capacity to explain technical issues clearly) was never a prerequisite for working in either of those areas. And far too many musicians rely entirely on those two sources, and ad copy, for their info. There's a bunch of us old farts who are only too happy to fill in the gaps, because it makes for a more effective musical community.

Let me add to your comment that there are "_cases where it's not harmful and even advantageous_", that there are also plenty of cases where it doesn't make a damn bit of difference one way or the other. For instance, let's consider that case where the pedal includes onboard regulation. Many chorus and flanger pedals use a Panasonic MN32xx series delay chip. This 3rd generation series (MN3001 and3002 were series one, MN3004/7/9/5 were series 2) of BBD chips was designed to run effectively off lower supply voltages. 

The reason was pretty straightforward. In order to work properly, delay chips have to provide a DC bias voltage that the audio signal rides in on. If that bias voltage is too high or too low, you get a distorted sound, and if it lies a little further out from the bullseye than that, you simply get no output from the chip. The bias voltage is derived by "dividing down" the battery voltage by a given percentage, using resistors of a particular value. That's great if you have a new battery, but what happens as the battery starts to wind down? The bias voltage becomes less and less accurate, and the sound quality degrades quickly.

Panasonic solved this by developing BBD chips that could run off 5v. Remember I said a 3-pin regulator needs 2 volts more coming in than it spits out? That implies that a 5v regulator could provide a stable 5v from a 9v battery until such time as the battery reaches around 7v. (And by that point, there is precious little juice left anyway.) But what it also implies is that if you set your bias, based on a stable and unchanging 5v, then whatever you set the bias to remains "valid" for a long time, and won't drift, yielding more stable and predictable performance from the delay chip.

Here is the schematic from the venerable Boss BF-2 flanger. http://www.hobby-hour.com/electronics/s/schematics/boss-bf2-flanger-schematic.gif In the lower left hand corner, you will see a part labelled IC6. That is a 3-pin 5V regulator. The open upward pointing arrow to its left signifies 9v, and the closed upward pointing arrow to its right signifies 5v, which gets fed to the delay chips and supporting circuitry.

Why am I telling you all this? Because guys will hear stories about how using a higher supply voltage will increase your headroom. And while it does, if the circuit is set up for it, in this instance, the delay chips (which are the absolute weakest link in this chain) will *never* see more than 5v. True, the op-amps will see the 12v or whatever you feed them, but they aren't the portion where the greatest risk to signal quality lies. So bumping the supply voltage up doesn't necessarily hurt anything, but it sure as hell doesn't really help either.


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