guitar processor smells like burning

[burgiedanny]

I have a boss gx-700 guitar preamp. I started smelling something burning and traced it back to my gx-700. I opened it up and pluged it in. The big square chip with the pins coming out from all four sides (I think it's the processor) got really hot after about 5 min. with power and the burning smell got stronger. I've only been useing this preamp a short time and this is the first time I've smelled this burning smell. This preamp requires a power adapter putting out 14v ac 800ma. The adapter I'm using puts out 14v ac 1220ma. As I understsnd it this should be fine. The only other thing I've done is wire in another power input jack to fit the adapter I'm using, I soldered + to + and
- to -. If I had wired this in backwards, would'nt it not work at all? or burn out a fuse right away? The processor still works but what would cause it to get so hot and smell like it's burning? Any help would be appreciated, Thanks.

[Steve Conner]

Are you sure it's AC? You mentioned + and - markings, but an AC system shouldn't have any, because AC doesn't have a polarity. Maybe you used the wrong wall wart, though if the unit works, that's unlikely.

Also, these warts are not very well regulated, the "14V" of your new one may be higher than the "14V" from the old one, causing the regulator inside the BOSS unit to run hotter.

A friend once brought me a fried DJ mixer. He lost the wall wart and took it to the local electronics store to get a replacement. Somehow they ended up selling him a 24V DC wart even though the mixer clearly said "10V AC" on the back...

[burgiedanny]

What I did was solder the new input jack to the old, thats how I wired + to + and - to -. There were no actual "markings", but your right, it's ac so the polarity would'nt matter. I'll try measuring the output on my wall wart, thanks.

[Jag]

Darn Steve, I was going to steal that tag line!!!

[Sweetfinger]

A friend once brought me a fried DJ mixer. He lost the wall wart and took it to the local electronics store to get a replacement. Somehow they ended up selling him a 24V DC wart even though the mixer clearly said "10V AC" on the back...

I believe the Line 6 stuff that is normally AC can be powered by higher DC, but that is probably the exception that proves the rule. I can't tell you how many people will just cram any plug that will fit into a guitar pedal...and the result almost always has 'that' smell.

A seriously hilarious example of that happened a few years back when we repaired a customers pedal after he plugged in a 9V AC adaptor and fried the protection circuit. He pays for the repair, then goes into an amp demo room to see if the pedal is working. As we are helplessly watching, he grabs the first power supply he sees and jams it in the pedal.....a Line 6 power supply! You just can't buy entertainment like that.

Had another customer one time who complained that a pedal we sold him 'blew up' all his other pedals(all Boss or Ibanez standard 9V DC using a daisy chained power supply). The pedal, of course, had 'the smell'. When questioned if he "might have possibly plugged in the wrong power supply", he yelled "I'm not an IDIOT! I know what I'm doing!" OK, he didn't so much yell, as loudly SLUR the words while tiny gobs of foamy spittle shot out of his mouth while looking like the poster warning you not to abuse drugs..or fashion. We still use this phrase around the shop to describe 'operator error'.

[Mark Black]

The Boss GX-700 does want an AC power source, and I don't think it takes kindly to a DC substitute. I don't remember the particulars, but at one time tried to figure out how I could power mine from easily-found supplies before finally hunting down an AC unit of near-correct specs.

Boss will provide a schematic/service-manual for reasonable money - worth having if you are going to keep the unit even if only to provide if/when you take it to a shop.

The processor (or whichever big logic chip that is) getting hot doesn't sound good...

[Enzo]

Pedals often use AC when they are going to make both polarity DC inside from it. If you connect a DC to where AC belongs, it won't hurt it. The DC will go right through the rectifier to where it belongs, but the reverse polarity won't be there for the other DC rail. The net effect is that for example the +5 for the logic works and the +9 for analog, but the -9 for analog will be missing so no sound out.

On the other hand, cram AC in where DC is expected, and at least half the waveform will be the wrong polarity and will likely burn out something.