Broken Digitech Whammy WH-4...

[hairyandy]

Does anyone have a schematic for the WH-4 Whammy pedal?  It's the newest one, the reissue.  I'm trying to fix one for a friend who blew his up.  Two SMT components, one by the input (L12) and one by the output (L14) are fried and I'm not sure what to replace them with.  Would they just be protection diodes like 1N4001's?  Any help is greatly appreciated...

[hairyandy]

I was just looking at the schematic for the Digitech XP100 which is the 3rd whammy version I believe.  It's a completely different beast but it did have some components listed in the BOM as L1-L6 and they were SMT Ferrite Beads, 2.5k-ohms @70Mhz.

Is this what I'm looking for?  I have no idea what Ferrite Beads even do.  Ferrite is iron right?  I'm lost...

[Connoisseur of Distortion]

they are inductors.

i don't think you'll find a schemo of the Wh-4 any time soon... but maybe you can read the markings on the broken parts?

[Peter Snowberg]

Those are acting as filters. The schematic shows that they are specified to have 2.5K of impedance at 70MHz but you can replace them with lots of parts if you don't mind going outside the FCC approved circuit.

In an emergency you can just bridge over them with a wire, but it's much better to use a 10 ohm resistor and put a 47pF cap to ground in parallel with the jack.

Now the better question is why did the inductors fry in the first place? 

[hairyandy]

Those are acting as filters. The schematic shows that they are specified to have 2.5K of impedance at 70MHz but you can replace them with lots of parts if you don't mind going outside the FCC approved circuit.

In an emergency you can just bridge over them with a wire, but it's much better to use a 10 ohm resistor and put a 47pF cap to ground in parallel with the jack.

Now the better question is why did the inductors fry in the first place? 

Who knows why they fried?  The guy is a brilliant musician but he knows squat about gear.  Maybe he plugged in the wrong wall wart or maybe his cable touched something hot while it was plugged in.  The same part fried on the in and the out so I'm thinking that somehow some voltage was sent through his cable.  If I bridge them will the sound be different?  What are these inductors doing?  They're connected between ground and a resistor on both the in and the out.  At least that's what it looks like to me...

The broken parts were literally fried.  They crumbled when i touched them...

[Peter Snowberg]

They're part of an LC filter to stop RFI from leaking out of the computer that is that effect. They're commonly called RFI filters and you see them inside all computer gear where wires extend outside the shielding case. In effects we occasionally see a cap to ground and a series resistor on the input of a pedal to stop RFI from getting into the circuit.

I'm going to guess a ground loop problem if the inductors were in the ground wiring. There may be more fried than just the inductors so cross your fingers.

[Peter Snowberg]

Is there any way you can post pictures? I'm very curious about the circuit. 

[hairyandy]

Well, I crossed my fingers, bridged the resistors to the ground connection on the jacks and it seems like it works.  The horrible ground hum is gone and the effect sounds normal.  I'm going to continue to keep my fingers crossed though...

Peter,  I'll put up some pix when I get the chance tonight.  I'm doing about eight things right now including trying to eat dinner...

[Peter Snowberg]

I couldn't tell from your description, but be sure to use some small resistors and don't bridge the inductors directly. A 10 ohm 1/8 watt resistor will give similar protection in case the offending cable gets plugged in again.

Could it have been speaker output -> pedal input? 

I'm looking forward to pictures. Thanks!