The Steel Guitar Forum

Several have e-mailed me and asked the following: "I have a old AC to DC adapter that I would like to wire up and use. How can I tell if it is regulated or not regulated?" I have been thinking how a person with only a volt meter, and limited electronic knowledge could determine if his AC to DC adapter was regulated. A un-regulated AC to DC adapter will "usually" read much higher voltage than the voltage written on it. For example; A un-regulated 12 volt adapter when tested with a volt meter will register in a range from 15 to 19 volts, and sometimes more than that. Why? Because un-regulated power supplies are usually run to a device that has voltage regulators. Voltage regulators usually require at least 2 to 3 volts over the listed voltage, or they won't work. That is why the un-regulated adapters read so much more voltage. There are special low drop out regulators that only require 1/2 volt over to regulate. If you get a adapter that says 9 volts on the outside of it, and it reads exactly 9 volts on your volt meter, more than likely it is a regulated supply. Likewise, if it has 12 volts printed on the outside, and reads almost exactly 12 volts, then it is probably regulated. If it were a un-regulated supply it would more than likely read quite a bit more volts, on a volt meter,than the volts printed on the outside. Be advised that this simple test does not prove beyond a doubt that an adapter is ,or is not ,regulated.
This test only indicates that an adapter "MIGHT" , or " MIGHT NOT" be regulated. To avoid ruining equipment, it is best to use adapters that originally came with the equipment. <FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Keith Hilton on 14 January 2001 at 12:29 AM.]</p></FONT>

Wow, thanks, Keith:

I awoke this morning and remembered that I had left my Matchbox switched on last night for the umpteenth time and the thought that I just gotta get an alternative to battery power for that thing. Remembered your discussion on the subject a couple months ago here on the forum. It's back to the testing bench for me. Thanks, again.



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Rod Mason

I would think most all small power supplies are regulated, nowadays. To get reasonable filtering by just brute force, you need large capacitors, chokes, and resistors. And, solid state devices are cheaper today than most of these.

One way you might be able to tell if it's a regulated supply supply would be to hook it to a speaker for a couple of seconds. A very loud hum would indicate the lack of filtering (regulation). A low hum (or none at all) would indicate good filtering.

Just remember, speakers hate DC.

"I don't disagree with Donny too often" (this makes it even and you don't have to send the Balimer crabs)
but most of the common wall warts are unregulated. A regulated power supply has the same (or nearly the same) voltage whether its "no load" or under load. Most of the wall wart power supplies have a substantial higher voltage with no load and usually very poor filtering, if any. Connect one to an oscilloscope and you'll see a lot of ripple or measure the "dc" voltage out with a voltmeter set on "ac" and you'll find they have a lot of ac.

The device it is connected to has to provide filtering and voltage regulation, if necessary.

Most of the stomp boxes only require an unregulated power supply. There are some that require a regulated power supply, such as some of the older Ibanez units (I had an Ibanez stomp box type analog delay unit and it had to have a regulated power supply).

Jack is correct.

Also filtering (or the lack thereof), is not analogous to the terms "regulated vs unregulated".

You can have near perfect filtering and still be "unregulated".

Filtering means from a practical sense, NO hum. Poor filtering always has some hum. More or less.

This is why you can take a lot of Boss devices and be dissapointed in the hum you get when you buy an off the shelf Power Supply at Radio Shack even though the voltage/current is identical. Yet you go an plunk down a premium price at the music store, and have NO hum when it is made by Boss for that device. The Boss simply has better filtering.

"Regulated" means the voltage will remain quite constant over various "designed" loads that may be powered by a given power supply.

Not too many devices we use require a regulated power supply. But many WILL require good filtering.

carl <FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by C Dixon on 15 January 2001 at 07:45 AM.]</p></FONT>

Carl,

I have to admit that I'm baffled. I have a Boss DD-2 that hummed with any power adapter that I tried, even the high end Roland one from my GR-1. I have a Heathkit bench supply. I built a super filter for the unit with big caps and inductors. I got a near perfect DC trace on my scope. Still it hummed with the DD-2. I finally gave up and spent $15 for the Boss wall wart and, viola, no hum. . .

Go Figure,

Bill

Bill, that sounds more like a ground loop hum than a power supply hum. Were any of the power supplies grounded??

Perhaps some of you could look at this circuit I found on the net this morning and let us know if it could solve the problem, i.e., safely power our Matchboxes and similar devices:
http://ourworld.compuserve.com/homepages/Bill_Bowden/page4.htm#ps3.gif



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Rod Mason

That's a nice regulated circuit, but it's overkill to power a couple of stomp boxes.
If you have units that all require the same voltage then the circuit will work for several units. But if they require different voltages then this particular adjustable power supply would not work as it only has a single voltage output.

Most only require an inexpensive ungregulated power supply.

Correct, Jack.

I just want it for my Matchbox. I think I'll try to build it when I get back to the U.S. I'm happy to say that our tour here is almost up and I could be packing out before I got halfway through the project. Hallelujah!!


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Rod Mason

I thought Bill Rowlett's reply was interesting. Bill, if there is one thing I have leared, it is big capacitors alone won't get all the noise out of DC all the time. Even if you seem to have no ripple in your DC ,on a scope, you can still have noise in audio. You can hear a lot of stuff in audio you can't see on a scope. Hang .1uf capacitors right at every power pin, on chips, since the distance a power supply is from a chip can alone cause problems. Go across from plus to minus with .1uf and .01uf capacitors, where you are filtering with big capacitors. If you are using dual polarity power supply hang .1uf capacitors to ground from the plus and from the minus. On linear power supplies, I think a lot of the noise comes in on the ground, due to ground loops. Guys have so many things hooked up in line, each with it's own power supply. Each power supply has it's own ground potential. Switching power supplies have taken a "bad" rap, because they used to be difficult to built. With the parts available today, they are easier to build. In my humble opinion, the beauty of the little switching power supply is that you can isolate signal ground from power supply ground. This is usually done with a LC network. LC meaning a inductor and capacitor network. To still maintain safety, with isolated grounds, you can fuse a device where it can cause no harm. Just my opinion.<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Keith Hilton on 15 January 2001 at 09:08 PM.]</p></FONT>

Switching power supplies were banned by NASA because of the radiation potential, when I worked at a Manned Space tracking station and at Goddard space flight center.

They didn't want anything interferring, or potentially interferring, with the weak downlink signal from a spacecraft.

Don't forget that there are devices which have the rectifier as well as the voltage regulator inside the unit, so they use an A/C wall wart PSU.
I seem to remember that Lexicon units do this.
There are lots of exciting ways of getting it wrong!

Jack/Keith,

I wondered about the ground loop potential, but never got the time to really trace for it. None of the wart units that I tried were grounded. The heathkit bench supply was, but I tried isolating it with a ground lift.

Hanging the small caps across all the power feed points in a device is certainly a good idea. That will bleed off a lot of the AC (and RF) that somehow gets past the filter caps. I haven't tried to reverse engineer the Boss units, but I'm still baffled that they can build a unit without hum when I can't. Or.. . Maybe that they can design it to hum with any supply other than their unit. I was very surprised that the hefty Boss GR-1 supply also hummed with the DD-2. Since Jack uses an aftermarket supply with his DD-3, maybe it is only a problem with the DD-2 or maybe just my unit has a problem. Seems that I had heard about this with other Boss units though.

Bill

I have gotten rid of hum a couple of times by taking the wall wart apart and putting a resistor in line between the transformer and filter capacitor. How big of a resistor depends upon the current draw of the device, since the resistor will drop some voltage and make less available at the output. I've got some effects that only draw 5 ma, but I have a Boss PN-2 tremolo that I believe takes about 20 ma.

The warts are usually glued together but with a little careful effort you can usually get them apart and tape them back together. Of course if you have a pedalboard you could just make an RC circuit and mount it in an external box, but then you might as well just build an IC regulator circuit.

This should only be done if you have a basic knowledge of electronics.

Has anyone taken apart one of the Boss adapters to see if there's anything special inside?

The good news is that by doing this you should be able to use any wall wart that is the correct voltage. The bad news is that it may just be easier to buy the $15 Boss adapter and be done with it.