# Wall wart weirdness



## Milkman (Feb 2, 2006)

I bought a Digitech Trio from a member here, who let me know in advance that he did not have the adapter.

No problem.

I went down to the surplus place and bought one that I figured should work.

I needed:

9 V DC
500ma
center ground (as indicated on the pedal).

I bought a multi voltage unit clearly marked with the right specs.










and then turned the package over.












So, as per the BACK instructions, don't use it right?


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## Sneaky (Feb 14, 2006)

You should be able to use it as long as you attach the tip as shown in fig. B.


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## Milkman (Feb 2, 2006)

Sneaky said:


> You should be able to use it as long as you attach the tip as shown in fig. B.



Polarity is not the issue.

"DO NOT use for devices requiring more than 300 ma."


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## Sneaky (Feb 14, 2006)

Oops, didn’t catch that. Does the pedal really use 500ma? Seems like a lot. Weird that it says 500 on the front.


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## Milkman (Feb 2, 2006)

Sneaky said:


> Oops, didn’t catch that. Does the pedal really use 500ma? Seems like a lot. Weird that it says 500 on the front.


Weird for sure. "Weird" wasn't exactly the word I used at first.

My inclination is not to risk frying the pedal but I'm happy to hear from some of our resident electronics gurus.


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## Tone Chaser (Mar 2, 2014)

My main concern is filtering questions. The introduction of noise from power supplies not intended for pedals.


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## chuck_zc (Dec 6, 2009)

I tried it with a 200ma EHX wall wart and it (adapter) ran hot after about 10 minutes. No issues running it with my Voodoo Lab Digital that has 400ma at the plugs


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## chuck_zc (Dec 6, 2009)

Pm sent bud


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## mhammer (Nov 30, 2007)

It's all about safety margin. As I may have noted in another thread, current-capacity recommendations are often predicated on what would likely maintain the power-supply on spec. If the PS is being asked to deliver ALL the current it is capable of, there is a pretty good chance that, as a sealed black blob with little or no ventilation to let heat out, the internal components may drift off spec and not supply the correct voltage or degree of regulation. Run that way for an extended period could result in damage to the step-down transformer. So the Digitech unit doesn't _need_ half an amp. But if you ran it with something that is capable of delivering half an amp, that power supply shouldn't be particularly stressed in any way. The wall wart can provide up to 500ma for a short period without any significant stress. BUt the unit will perform to spec for a lot longer if one doesn't ask more than about 300ma peak from it. The Digitech unit assumes this and makes its request accordingly.

This is one of the eternal shortcomings of wallwarts - they are sealed plastic boxes with no way for heat to escape. You can't look inside 'em to see what degree of regulation/smoothing they provide, and you can't even let them run cool.


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## vadsy (Dec 2, 2010)

buy a better power supply


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## Milkman (Feb 2, 2006)

mhammer said:


> It's all about safety margin. As I may have noted in another thread, current-capacity recommendations are often predicated on what would likely maintain the power-supply on spec. If the PS is being asked to deliver ALL the current it is capable of, there is a pretty good chance that, as a sealed black blob with little or no ventilation to let heat out, the internal components may drift off spec and not supply the correct voltage or degree of regulation. Run that way for an extended period could result in damage to the step-down transformer. So the Digitech unit doesn't _need_ half an amp. But if you ran it with something that is capable of delivering half an amp, that power supply shouldn't be particularly stressed in any way. The wall wart can provide up to 500ma for a short period without any significant stress. BUt the unit will perform to spec for a lot longer if one doesn't ask more than about 300ma peak from it. The Digitech unit assumes this and makes its request accordingly.
> 
> This is one of the eternal shortcomings of wallwarts - they are sealed plastic boxes with no way for heat to escape. You can't look inside 'em to see what degree of regulation/smoothing they provide, and you can't even let them run cool.



Much appreciated Sir, and I think I understand but in reading your comment, I still don't see a yay or nay.

Is there a risk? The adapter can deliver 500ma but maybe the pedal only needs 400 or whatever.

Should I just not be a cheapskate and buy a higher amperage unit?

And how do I know how much headroom to allow? if the pedal says 500ma do I need a 750ma or a 1 amp adapter?

Of course that's a moot point if I ante up for the manufacturer's recommended adapter.


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## chuck_zc (Dec 6, 2009)

The adapter shown might be able to burst 500ma but can't handle it constantly


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## mhammer (Nov 30, 2007)

A lot of folks will aim for a 50% safety margin. So if the device/s being powered will pull 300ma through the wallwart, then you probably want a wallwart rated at 450ma or more.

As Chuck implies, one needs to think of wallwarts as being a sort of slow-blo fuse. As long as the current passing through only surges briefly, the fuse remains intact. But if the current capacity is reached and things stay at that maximum for any length of time, they blow.

And yes, manufacturers will often insist on using their power adapter. Not because it's the only one that would work, but because it's a whole helluva lot easier to say "Just use this one", than it is to explain about plug polarity, current ratings, degree of regulation, etc. Given the packaging and shipping costs, the companies probably don't even make any money on them. But they DO save on having to provide additional tech support, take in repairs and ship them out, or take on the badmouthing that inevitably results from consumers who don't know enough to avoid mishaps and damage but pin all the blame on "shitty products" anyway.


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## Milkman (Feb 2, 2006)

Thanks to all who have replied. I'm going to buy the right one.

And a tip of the hat to Chuck, who is going above and beyond to help me.

I know people say this from time to time, but this site has many helpful and expert advisors.


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## greco (Jul 15, 2007)

mhammer said:


> A lot of folks will aim for a 50% safety margin. So if the device/s being powered will pull 300ma through the wallwart, then you probably want a wallwart rated at 450ma or more.


This is new to me and worth noting.


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## Milkman (Feb 2, 2006)

I just spoke to my local shop and the Digitech adapter is 1.2 amps.

He has one. I'll have it in my greasy hands by 5:00 PM.

Again, thanks for helping avert a pedal meltdown.


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## Milkman (Feb 2, 2006)

In my opinion, the needed adapter amperage should be reflected on the pedal. Why would 500ma be indicated if such an adapter could seriously damage the pedal?

It seems like a pretty easy mistake to make.


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## mhammer (Nov 30, 2007)

greco said:


> This is new to me and worth noting.


It's not a hard and fast rule, Dave. It's just something where you can rest easy that problems can be easily avoided, without having to go overboard.
Works the same way with electrolytic capacitors. That's why so many pedals use caps rated at 16VDC, even though the pedal uses a 9V battery. And if the manufacturer says the pedal can be used with 12-15V, the caps will be rated for at least 25VDC (the next rating step up).

It's all about making sure things remain true to their stated specification.


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## mhammer (Nov 30, 2007)

Milkman said:


> I just spoke to my local shop and the Digitech adapter is 1.2 amps.
> 
> He has one. I'll have it in my greasy hands by 5:00 PM.
> 
> Again, thanks for helping avert a pedal meltdown.


More and more wallwarts are switching power supplies, that use high-frequency switching to attain greater current-delivery capacity in a small lightweight package. Were this 1985, a 1.2A supply would weigh twice as much as the Trio pedal. It is less and less of a problem these days as more manufacturers anticipate and design around it, but the clock pulses riding on the power line from the switching supply can interact with digital pedals having their own internal high-frequency clocks, and create noise. However, that is more true of slightly older digital pedals of, say, 10-12 or more years of age.


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## ronmac (Sep 22, 2006)

Milkman said:


> In my opinion, the needed adapter amperage should be reflected on the pedal. Why would 500ma be indicated if such an adapter could seriously damage the pedal?
> 
> It seems like a pretty easy mistake to make.


The pedal will only draw as much current as required, so using a supply that supplies the correct voltage that is rated for a higher amperage will cause no harm.


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## mhammer (Nov 30, 2007)

Keep in mind that the power lines that come to your home are able to provide _many_ more amperes than you might use at any given time. When an AC adapter takes a small portion of all that potential current, and steps it down, whatever you have it plugged into doesn't necessarily have to use all the current available from the adapter either.


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## sambonee (Dec 20, 2007)

Low millamps causes stress on the unit and the adaptor. I’ve had that happen. 

Also the digitech Adaptor is medirocre.


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## keto (May 23, 2006)

Milkman said:


> In my opinion, the needed adapter amperage should be reflected on the pedal. Why would 500ma be indicated if such an adapter could seriously damage the pedal?
> 
> It seems like a pretty easy mistake to make.


When I rebuild my pedal board, I have to go to a bunch of websites and look at pedal power requirements, because I can’t remember what takes what, at least not all of them, and my power supply has a bunch of different ma outputs. Handy. I should write myself a list lol. DC ISO-Brick, btw, which has been excellent and flawless in about 18-24 months service I think.


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## mhammer (Nov 30, 2007)

sambonee said:


> Low millamps causes stress on the unit and the adaptor. I’ve had that happen.


That's confusing. How can using a fraction of available power cause "stress"? If the device draws far more current than it actually needs (e.g., _says_ and only needs 8ma, but _draws_ 100ma), I can see that happening. But that's a matter of lousy design, not a matter of "low milliamps". 

There's some information gaps here. Care to fill them in?


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## allthumbs56 (Jul 24, 2006)

No expert but I wouldn't use a power supply advertised as "good for your alarm clock" on anything where a clean guitar signal is required.


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## Milkman (Feb 2, 2006)

My main concern is to not damage the unit. My purpose for this device is jamming at home. I would never use such a toy for a live performance or recording so if I get a little signal noise, I don't really care.

Having said that I have purchased the correct Digitech unit and am awaiting delivery.


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## allthumbs56 (Jul 24, 2006)

Milkman said:


> My main concern is to not damage the unit. My purpose for this device is jamming at home. I would never use such a toy for a live performance or recording so if I get a little signal noise, I don't really care.
> 
> Having said that I have purchased the correct Digitech unit and am awaiting delivery.


Good idea. I have tried to use/build unfiltered/shielded wall warts before and the noise level is pretty unacceptable - home or otherwise.


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## mhammer (Nov 30, 2007)

A lot of that is in the degree of regulation and ripple-rejection. As I keep harping on, wallwarts are sealed black blobs tat you can't peer into. If you could, you might be able to see that it only uses half-wave rectification and a puny (e.g., 100uf) cap for smoothing, meeting the bare minimum requirements to be called "DC". Or, you might be able to see that it uses full-wave regulation, a nice big cap value, and maybe even a regulator with additional smoothing. But, as black boxes, we are - pardon the pun - left in the dark.

There is no real magic in making a quiet, stable supply, though. But if you don't know how, or what to keep an eye open for, it's smarter, easier, and probably cheaper to simply buy one that the manufacturer recommends.


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## sambonee (Dec 20, 2007)

mhammer said:


> That's confusing. How can using a fraction of available power cause "stress"? If the device draws far more current than it actually needs (e.g., _says_ and only needs 8ma, but _draws_ 100ma), I can see that happening. But that's a matter of lousy design, not a matter of "low milliamps".
> 
> There's some information gaps here. Care to fill them in?


My comment is a personal theory which could easily be debunked by anyone more knowledgeable than me. It’s the impression I got. When I used a 300mah 9v adaptor, the unit would shut down.


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## mhammer (Nov 30, 2007)

Yeah, something's not adding up there. I'm nt disputing the truthfulness of what you report. However the basis for it seems like something else is playing a role there that neither of us have a clear picture of. Just one of those things, I guess.


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## High/Deaf (Aug 19, 2009)

It sounds like the supply is under-rated to handle the load (pedal or whatever). 

Having a supply that can source more current than the pedal wants won't be a problem. The pedal will use what it needs and the rest will be surplus. 

Having a supply that can't source as much current as the pedal wants can lead to various problems with how the pedal works, some subtle, some not - and it may damage the supply but not the pedal. Same with using a supply with a voltage that is too low - it won't hurt the pedal, it just may not work well. 

Using a supply with a voltage that is too high or of the wrong polarity can definitely hurt the pedal. They will only take too much excess or incorrect power before some component is going to say "Uncle".


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## Guest (Jan 16, 2019)

I read once the adapter should have a 20% overage, so if the unit wants 500mA it would be wise to use a 600mA adapter.


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## knight_yyz (Mar 14, 2015)

The digitech is sensitive. I would look for for something at 1 amp oven though it says 500mA. My pedal board power supply did not have a 500Ma output either so I had to use the stock wart. I would have had to use a doubler.

You need 500 Ma but even if you get 5A it will still only draw what it requires


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