tip polarity

[Beegeeboss]

newbie here!

I have a pedal with negative tip and positve sleeve, but I have a power supply with a negative sleeve and positive tip.  Can I just cut the cord and swap the wires to reverse the polarity?

thanks!

[jacobyjd]

If it's not also positive ground, then yes. Otherwise, you'll have to use a separate power supply.

[Beegeeboss]

Thanks...how can I tell if it is positive ground?

Adapter says:
Model A20920N
AC Adapter
Class 2 Transformer
Input: 120vAC 60Hz 5w
Output: 9VDC 200mA
then shows negative sleeve, positive tip

The pedal (DOD tec4x) shows 9v Positive sleeve, negative tip 200mA, and has a solid line above a 3 dash line

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[Paul Marossy]

Thanks...how can I tell if it is positive ground?

What pedal do you have?

[Beegeeboss]

...also the adapter does not have a polarized plug (i.e. both prongs are the same size)

[Beegeeboss]

Paul, it's a DOD Tec4x.

[Paul Marossy]

I'm pretty sure that is a negative ground pedal. Positive ground circuits are generally not used in pedals other than fuzz face type circuits.

In any case, you probably want that unit on its own power supply anyway since it draws 200mA.

[Beegeeboss]

thanks.  since the adapter was cheap, I gave it a try.  The pedal powers on, and some sounds come through, but there's a big hum, and not all the channels work.

The device draws 220mA, and the adapter is only 200mA.  The orignal adapter is 300mA.

Could that be the explanation for the hum?

[Mark Hammer]

Just because something says "DC" is no indication of the degree of regulation.  Heck, 2 diodes and a 47uf cap allows you to call yourself a DC adaptor.  The degree of AC ripple remaining, however, will be VERY different between that sort of adaptor, and one which uses a full 4-diode bridge and 2200uf smoothing cap.

What you are hearing is more than likely the result of insufficient smoothing inside the little sealed black box.

Since you have already cut the wire to flip the polarity around, get yourself a suitable 470uf cap, and connect the + side tot he hot lead, the - side to the ground lead, and give it a listen.  Chances are, the hum will be lower, though not necessarily eliminated.

And yes, having insufficient current delivery capability may be both undermining the performance of the pedal, and shortening the lifespan of any underpowered adaptor asked to power it.