Plugged in AC Power Adaptor... Oops...

[KerryF]

Hey guys.  I just got back from Samash.  I had brought a pedal there with an adaptor for it unknowing that it was an AC adaptor because i haddnt used it before.  So I plug in my pedal and no worky, just hum.  So then I just get home and plug it in with the correct adaptor and now theres no sound at all.

Any ideas of what may have blown?  Maybe some electrolyte capacitors?  JFET?  Op Amp?  Any information at all would be great!!!

Thanks very much,
Kerry

[Rectangular]

this happened to me once, does the pedal use a voltage regulator inside ? that's what blew on mine, a LM7809

just follow the voltage from the input with a Digital Multimeter,  and see where it stops. I'd suspect a diode, or electro cap, if you don't have any regulators in there

goodluck
rec

[Paul Perry (Frostwave)]

If you are lucky, there is a protective diode at the power input that is fried.
If you are unlucky, one or more op amps are fried (they hate reversed power).
I expect any transistors will be OK.
If there is a 4066 switching section, that will be gone, probably.

[markm]

Chances are there's a protection diode in there that's blown.
Maybe some other stuff but, that'd probably be the first to go.
What pedal is it with a "different" AC adaptor??

[KerryF]

Thanks you two.  Theres no protection diode.  I am an idiot and didnt expect this to happen so I didnt add one.

I suspect the Op Amp too.  Its an LM386.  I will change that and possibly change the Electros. too just in case.

Thanks guys!!!
Kerry

EDIT: Just changed the OpAmp.  Works like before!  Thank god and all of you.  You guys are the greatest!  That gave me a huge scare.

[R.G.]

Probably the single most destructive thing you can do to a pedal short of pounding it with a sledge hammer or melting it in an electric arc is to hook it up to one of the 9vac adapters. This is one of the few things you can do that a reverse-shunt diode will not protect against.

If there is a reverse-shunt diode in there, what happens is that first the diode is shorted, then burned open, and then the rest of the pedal is scorched. This happens pretty quickly, although sometimes people will interrupt the chain of disaster before everything is toast. Often, the burning is so bad that the reverse protection diode chars a hole in the PCB material under it.

Let me tell you exactly what to replace: everything that has a polarity associated with it.  All ICs, diodes, transistors, and polarized caps. It is possible that some of them are still OK. It is also possible that some of them that seem OK are just not quite dead yet and will fail as soon as something pushes them one fraction further over the edge.

There are a few pedals which use this kind of adapter; I think the Line 6 Tone Core, a few others. They're primarily digital and high power user pedals. The adapters are similar to other adapters in size and have the same physical plug on the end, so they plug into any pedal that uses the Boss-style 2.1mm barrel connector.

Only a series-style protection circuit which opens the incoming power line on wrong-polarities will protect against these things. The MOSFET polarity protector and the Cheap - And Good protector circuits at GEO work for this, as does a series diode. But shunt diode protectors only hold off death for a few seconds.

My condolences. Either replace a lot of parts in the corpse or give it a good burial.

[KerryF]

Wow RG, thanks.  Great info again.  I was expecting you to give me a lot of info since you are with Visual Sound with your Noiseless or whatever adaptors  .

Like I said, I changed the IC Chip and to my luck it it back and running at its full potential again.  I have tested it a lot while sealing it up just to make sure its all still fine and yes it is, no more problems.

Thanks all!

[sfr]

I often have several different adaptors in my rig.  It's easy to do, if you're at the pedal end of things plugging in tips and the power strip end if somewhere else.  I now put color coded shrinkwrap on the ends of my adaptors, and mark the pedals. 

(I also mark the wallwarts with coloured tape too, makes it easier to find the one 12V adaptor in a drawer full of different wallwarts when you know you're looking for "the blue striped one" and not "the black one that's a little bigger than all the other black ones")

[R.G.]

Hmmm... how about putting masking tape over the business end of the plug, then dipping it into that plastic coating stuff they sell at Home Depot for tool handles? Comes in raspberry red, lemon yellow, orange orange, and other colors. Or just painting it onto your plugs with a brush?

The real answer is to replace the plug and jack with something that physically won't go into every other pedal on earth.

[KerryF]

I marked the wall part of the adaptor labelling in red sharpie with "AC".  Then I just threw it into my red bag of backup cords and crap.    Well it wont be used again.

[Meanderthal]

I marked the wall part of the adaptor labelling in red sharpie with "AC".  Then I just threw it into my red bag of backup cords and crap.  Smiley  Well it wont be used again.

Jeez, get rid of the damn thing, unless ya have some use for it. If ya don't have it , it can't happen again. If ya do, somehow it might wind up getting used... regardless of what ya wrote on it. Ya never know, some 'helpful' soul might come along and do you a favor by hooking yer stuff up for ya...(you'd be surprised how many 'helpers' there are out there. They come outta the woodwork at gigs)

That being said, I have a drawer full of all kinds of wall warts... that probably won't ever get used. I just don't throw the damn things away... cause ya never know...
But I only use 1 for all my pedals, and it's a line wart, so it won't get mixed up with any others. I think it was for a laptop or something.

[petemoore]

Probably the single most destructive thing you can do to a pedal short of pounding it with a sledge hammer or melting it in an electric arc is to hook it up to one of the 9vac adapters.
  And why hasn't this been made completely impossible?
  For stompbox use, it seems perfectly feasable that some 'leaderco' could put some odd plug on all the AC supply connectors for stompboxes, eliminating the chance for over or reverse voltage applications. ..lol, while at the same time offering a brand dedicated accessory, I'm not saying it hasn't happened, just not to where I'd see it up close.
  It's a little bit silly IMO that we're still using DC type connectors for AC, there's gotta be 1000's of connector types being made, there's always room for one more. It's not like dedicated connectors haven't been figured out for just about everything else.
  For a time there might be a market for aftermarket DC to Dedicated AC type connector adapters.
  Just thought I'd vent a bit for you, call1800ksmyazz, and the person posting with a 'blown by AC' debug post last week. I hope you guys get your pedals repaired.

[Paul Perry (Frostwave)]

An ICL7660 voltae doubler/inverter makes a fine fuse, for when you apply 18V AC.
It's worked for me, more than once...

[KerryF]

Just thought I'd vent a bit for you, call1800ksmyazz, and the person posting with a 'blown by AC' debug post last week. I hope you guys get your pedals repaired.

haha thanks for the care.  I got it back working by just switching out the Op Amp.  I had taken it to Samash and when I plugged it in and it didnt work and was all hum, I instantly said "its the power supply" to them.  I haddent tried it before so I figured it must.  The guys went into their cabinets, the back, and even into their wearhouse to find the correct power supplies!  I have never seen someone that works at a guitar store look so hard.  Well at least they still like the other pedal that I brought again. 

Kerry

[sfr]

Hmmm... how about putting masking tape over the business end of the plug, then dipping it into that plastic coating stuff they sell at Home Depot for tool handles? Comes in raspberry red, lemon yellow, orange orange, and other colors. Or just painting it onto your plugs with a brush?

Interestingly enough, was exactly what I planned on doing today, as I'm making some longer power cables for my Gator G-Bus (kind of like those isolated Voodoo power supplies), one for one of the 9V taps, and one for one of the 18V taps, to power my two multi-FX units I'm wrapping up. 

I was thinking of just cutting the extra rubber off after it's cured, but the masking tape idea is probably better - might not be an issue with the mini phono plugs on one end, but with the boss-style plugs on the other, now that I think about it, I imagine getting the little plug of rubber out of the inside of the plug is bound to be a pain.

Speaking of plugs and jacks, I'm thinking of rigging up a bipolar power supply for a few projects - what to people use for a jack/plug in this instance, where you need three conductors?  Stereo mini plugs?