PSU Keeps shutting down - why?

[simon111]

I have built a rangemaster +9v ground and have installed a dc jack, on it's own it is fine when using my dunlop dc powerbrick, but when I install my cry baby wah after it, if shuts the PSU down. Whats causing this folks? and is there an easy fix to get around it? Would using batteries in the rangemaster solve it?
Or am I stuck with that I can't use it with anything else in line with it?


Simon111

[LyleCaldwell]

Is the DC jack isolated from the chassis?

[simon111]

Yes the DC jack is isolated, but the jack sockets aren't as I use these to earth the box (+9V) I'm guessing it's because the chassis is at +9V and the wah is at 0V, and seeing that these are being powered from the same (non isolated) dunlop psu, it is shorting it out when I attach the audio leads. Wah=0v RG=+9V. Is this the correct thinking? And how can I solve it?

[George Giblet]

Let me guess you have a positive ground rangemaster (the normal PNP circuit)?

Here's the deal.

The range master is positive ground, that means the positive rail effectively connects to the ground lugs on the jacks.

The crybaby wha is negative ground that means the negative rail effectively connects to the ground lugs on the jacks.

The two devices are connected to the same power supply.

The two devices are connected together via the 6.5 lead, that means their grounds are connected.

So psu positive connects through the ground of the rangemaster, through the ground of the 6.5 cable, then to the ground of the crybaby, then to the negative lead of the PSU.  ie the positive lead of the PSU is shorted to the negative lead via the ground connection.

Basically you can't connect a positive ground unit to a negative ground unit if you use the same power supply - you always get a short.  There is a negative ground version of the rangemaster that uses PNPs on the web (you will have to search).  The alterative is to build an NPN with negative ground.

[simon111]

Cheers for the info George. One last question Would i be right IN saying that if the Rangemaster was powered by a separate PSU or by a battery then it would be fine when used with the wah?

[George Giblet]

Yes, no problem with separate power sources like another power pack or batteries.

[zachary vex]

if a power supply unit has multiple outs, often they're completely isolated (on different windings of the power transformer) so one can be used for negative ground effects and another can be used for positive ground.