The Steel Guitar Forum

I've got a 110/220VAC AC/DC Converter
(wall wart) with a 1.4vdc to 12vdc output
range. It's actually putting out 16.9vdc
at the 9v setting (with 110vac input), 22vdc
on the 12v setting. It puts out about half
that while plugged into 110vac with it's
switch set on 220vac in. I bought the
adapter in Uruguay, off-the-shelf in a
standard shrink-wrap package. I haven't used it since around the time I
bought it (about 3 years ago) and don't
recall noticing these anomalies then.
Weird, huh?

Is there any reason I shouldn't use this
thing to power my Matchbox and eliminate the
batteries?



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Rod Mason

It sounds like the output of the adapter is not regulated - that is, it does't have built in circuitry that will clean up the power and produce a steady 9V all the time. Even if you can get it to spit out somewhere in the region of 9V, you might get alot of noise & hum when used with the Matchbox if there's not alot of filtering going on in the adapter. Also, depending on where you use the adapter, you might get different voltage readings, since the power coming out of the wall isn't exactly 110V (where I live, it's more like 117V.) This might cause the circuitry in the Matchbox to blow.

Bottom line, if you can get it to produce somewhere in the region of 9V (say, +/- .5V) I'd try it out and see how it sounds. If it sounds good to you, go for it.

Given my somewhat limited knowledge of electronics, it seems to me that line voltage frequency (50hz or 60hz) would have an impact on voltage output. Could that be part of the inconsistency?

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Rick Richtmyer
users.erols.com/rickrichtmyer

Thanks guys, I think I'm going to go for it.
Hz not a problem as Venezuela is wired
110/60.

BTW, Rick, Hope to see you in late June. I'll
email or call when plans finalized.

regards



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Rod Mason

Rod, I would not do it. The device you are talking about is designed for battery operation. If you plug in a un-regulated power supply, which most wall-warts are, then sooner or later it will over voltage the transistor junctions. I guarantee it will do this. I make a device that runs off of either batteries or a wall-wart. Wall-warts do not regulate current or voltage, unless you buy a really expensive one, and will burn up your transistor junctions.

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Frequency is not relative to output voltage. Frequency basically affects devices that have a motor, such as a turntable, casette player, etc. e.g if you have a device that is designed for 60HZ (US standard) and you took it somewhere that had 50Hz it would run slow.

Voltage is another story and it is relative both to the input of a device and the output voltage. Running a device that is designed for 120 VAC on 220VAC, for example, will in most cases cause damage to the device.

Most non-regulated DC transformers, such as the one you have, may or may not work depending on the device you will be using it with. If the device is made for an external power source and has regulation (and filtering) internal to the device then the unregulated type will work fine.

However, if the device is designed for battery only, then you must supply a filtered/regulated DC power supply for the device to work satisfactory.

The Goodrich Matchboxes (or at least the ones I've seen) are only made for batteries and consequently you will need a filtered/regulated DC power source for the device to work properly. Using an unregulated power supply could damage the unit.

Thanks for the warnings, guys. That's one
brainstorm that won't get tested. Really
love that Matchbox and wouldn't want to take
any chances with it. I did put on a on/off
switch and pilot light after leaving it on
idle for about four hours the first day I
had it. Works fine. Switch is so much
easier than unplugging each time I get up.



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Rod Mason

Rod, I notice you said you put a switch and a light on the unit. Those LEDs lights eat up 20mili-amps of power. 2-9-volt batteries only have around 120 mili-volt hours in them. I would guess that the light alone will eat up your batteries in 4 to 6 hours, maybe sooner. So it is going to be an expensive light.

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Thanks, Keith:

I'll see how that goes. Maybe I can use that
info as ammo to persuade my wife I should buy
one of your pedals as it will amortize itself
in the cost of batteries in a very short
time.



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Rod Mason

Rod, Keith is correct on the current drain of an LED. It is a relatively big user of energy and probably uses as much (if not more)as the electronics in the matchbox.

I have a switch in my Matchbox and in my Matchbro. One of my pet peeves with Goodrich - no on/off switch. I put my switch in series with the original jack ground connector so that either unplugging the jack or operating the switch will turn the unit off. That way if I forget the switch or it gets bumped while its stored in my seat it will still be off. I had never considered adding a power on indicator light because of the current drain.

If you can come up with a regulated DC power supply then the extra power of the LED does not become an issue.

Depending on who did the LED and switch modification, the extra 2 to 20mA current draw could quickly chew up that 120mA-hour battery life that Keith states.

If you gotta have a battery powered "on" light, have someone buy the ultra-efficient and bright red LEDs from Hewlett-Packard. They give full brightness at 2mA draw and a 3600 ohm dropping resistor with the LED should make a fine 9volt battery on indicator.

Don, they must have finally got wise and added the switch. The MatchBox I have is an older one. Same with the MatchBro, it's one of the original models.