Strange "signal sag" when I plug my stomp box into power unit

[Blast9]

I've got a cheapie Danelectro phaser pedal:

Whien I use a battery, the pedal works fine:

When I plug it into my pedal power supply, if i hit my strings hard, the signal "sags" to zero volume, like its run out of headroom or something. Then it pops back up to unity. If i play soft to medium, no problem. NB this is when the effect is switched on, no problem in bypass.

i'd decribe the sound like when you switch off a tube amp and the volume decays as you keep playing, and the signal gets grainy/lo-fi

I've tried it with other pedals plugged in to the pwr supply unit as well as without...

The supply is a (5 pedals) multi pedal power supply (regulated 9 volts DC).

Any ideas?

[ulysses]

Yeah, I've got an idea:

Your pedal and/or power supply is busted. Get a new one.

Seriously though. It sounds like the power supply is delivering enough juice to charge up whatever power supply filter caps are in the pedal or in the output of the power supply, but the power must be encountering some kind of impedance on the way in. At idle, the pedal uses less current and the unit stays powered up. When you hit a chord, current consumption in the pedal increased. The power supply is failing to deliver the necessary current, but the pedal works for a few seconds while some filter capacitor drains. As this happens, the voltage drops and the pedal "browns out" until it goes dead. This is an exaggerated version of what happens when old fashioned Heavy Duty batteries are almost dead in a distortion pedal, and the thing sounds cool for a while until they finish dying. In fact, it's the same thing that's happening in an amplifier with a tube rectifier - the high impedance of the power supply causes the voltage to sag on loud notes, causing a kind of compression. It's desirable in some cases, but clearly not in your case where the pedal craps out.

Does the problem occur with other pedals too? I mean, when you use a different pedal with this power supply and do not use the phaser? If so, then the problem is the power supply. If not, then the problem is in the pedal. You probably deduced that for yourself. If the pedal is to blame, then it would have to be in the part of the circuitry that chooses between battery power and adapter power. Usually the jack for external power has a built-in switch, so that when you plug a connector into it, the battery is automatically disconnected. Some kind of corrosion, defective component, loose connection, etc. could be going on in this general vicinity and monkeying up your works. I wouldn't be afraid to open it up and look inside - unless it's a new pedal, in which case you should return it.

Be warned though - those Danny pedals are cheap, and they're built that way. I wouldn't be surprised if the thing is difficult to disassemble or - worse yet - difficult to reassemble.

I've never been inside of one of these Danelectro pedals, but I know a lot of pedals will have a protection diode to prevent destruction of the circuit in the event the power is applied with reverse polarity. It's possible that such a diode could be protecting the adapter input and not the battery input. If this diode was defective, or in backwards, you would probably get the symptoms you've described. Have a look and tells us what you find.

[Blast9]

Cheers Justin I'll have a look inside and report back... Thanks for the thorough explanation:

Its definitely the pedal and not the power supply:

I think the short answer is "get a nother pedal but not a cheap Dano!"