wall wart supply questions....

[slotbot]

HI!

I have some questions about damaging pedals by using the WRONG ac-dc adaptor (wall wart, power supply etc etc).

Until recently I lived in the happy land of all my ppedals running off of 9 volts with center pin ground supplies.

But then recently i got a whammy 4 from Digitech. The power supply has an output of 9v AC and 1300 ma. Unfortunately the power jack is the same size as normal boss/digitech pedals that use 9V DC.

I was just wondering what the potential is there to damage my pedals if it is accidentily plugged into the wrong pedal. IE what will happen if i put the whammy 4 supply into say a boss or home made pedal expecting 9v DC?

and vice versa. (9v DC into a pedal expecting AC)

i jsut have visions of my friend (or myself) pluggin in 5 pedals off my power splitter cable and then sticking the ac adaptor in by accident. and blamo.

ANY info on this topic appreciated.

THANKS

scott.

[niftydog]

entirely dependent on the circuitry in each of the pedals.

It may be that the AC input is imediately rectified and filtered in the whammy, in which case, plugging in a DC supply to a pedal expecting AC probably won't do any damage, but the effect is unlikely to work properly if at all.

I can't say I've ever heard of anyone pluggin an AC supply into a pedal expecting DC! But, again it would depend on the specific circuitry. It could be ok, but generally 9VAC peaks above 9V... and it swings below 0V as well!!! It's kinda like plugging in a positive tip and a negative tip supply at the same time!! So it could do a fair bit of damage, even if the pedal has reverse-polarity protection.

I would be considering changing the DC jack in your whammy, but I gather it's fairly new and you don't want to mess with it? Sounds to me like you need a pedal board and custom power supply to save you the risk of connecting it up incorrectly.

[Mark Hammer]

One more time, as a public service....

IF IT CAN RUN OFF BATTERIES *OR* WALL-POWER.....

When a pedal CAN be battery powered, there needs to be a means to switch from battery to wall-power.  That MUST be done by the outside contact of the barrel plug.  So, the centre pin will generally be negative/ground and the outside positive.  If the design uses a positive ground then these will usually be reversed since one is switching between the negative lead of the battery and the negative lead of the wallwart.

If it can run off wall-power but uses a mini phone-jack for the adapter, the tip is ALWAYS positive, because the shaft is always unavoidably grounded to the chassis.

IF IT CAN ONLY RUN OFF WALL-POWER....

Then there is nothing to switch.  Since barrel jacks are generally plastic (hence isolated from the chassis) it then becomes the manufacturer's perogative to use either the outside OR inside connector for positive/ground.   In general, it's about a 55/45 crapshoot, with more instances of outside-pos.

Note that devices which run off ONLY wallpower will sometimes provide rectification/regulation on board.  So, the user will need an AC wallwart, not a DC one.  With any luck, the chassis will say AC explicitly.  I had the misfortune to stare at a chassis without any manual on hand and not realize that "10v~" meant 10vAC (the ~ signifies AC).  Nothing was damaged inthat instance, but the pedal didn't work, and I had bought a 10vdc wallwart I didn't need.

While replacing a 15vdc wallwart with a 10vdc one, for example, may result in a functioning pedal, note that AC voltages (and differences) are multiplied by roughly 1.414 once rectified.  So 15vac turns into just a shade over 21.2vDC and 10vac turns into 14.14vDC.  If the on-board regulation uses 3-pin regulators, such seemingly small differences in AC voltage can occassionally result in 3-pin regulators not functioning properly once things are turned from AC to DC. (3-pin regulators want at least 2VDC more at their input than they provide at their output).