i reciently bought a behringer vampire 112 modeling am and every thing worked great untill i tried to plug in headphones... so guitar it plugged in and volume is off i plug in my sennheiser headphone and the thing starts feeding back, everything goes back to normal when i unplug headphones. could it be leads are touching? or some sort of ground loop?
Strange.
*How* are you plugging your headphones?
Do they have an 1/4" stereo plug"
Do you use an adapter for 1/8" miniplugs?
Does any control have influence on the feedback?
headphones are using a 1/8" to 1/4" stereo adapter and it feeds back into the main speaker and not the headphones. no controls have any affect on the feedback.
I think you are plugging your headphones in the Power Amp In or Loop Return .
The "real" headphones jack mutes the speaker, hence, no sound.
heres the amp "phones" jack above guitar input..
http://www.behringer.com/EN/Products/LX112.aspx (http://www.behringer.com/EN/Products/LX112.aspx)
I have run into similar problems with using adapters
Check the length of the adapter with other stereo 1/4 inch jacks
I have run into adapters that are just a little short keeping the tip from activating the switch that cuts the speaker off
Now I believe you.
Amazing.
Only a MORON would fit the headphone jack (which handles the strongest signal possible in an amp: speaker level), of all places, just by the input jack, maybe even sharing grounds or al least being as close as possible.
Doubly so in a high gain amp. :trouble :grr
yeah its odd to say the least.. i will do some tinkering to see if i can isolate the issue. on a good note this thing actually has some legit tones some of the emulations are so close its unreal. :duh
I'd take Bry's advice and check that the length of the adapter is right.