In June 2007 I bought a new GTI 1500 and have used it with a Killer Bee headphone (only 1 earcup) I bought around 5 years ago for $90. The threshold of the detector would increase by itself from the level I had set, and then return after scanning another item or using Last Mode. I returned the detector for warranty work - what was done was not explained in the paperwork - but the threshold variations continued.
I recently spent $20 to buy Panasonic RP-HT227 stereo phones to use with my PC and radios. The phones have excellent fidelity. Today I used the Panasonics instead of the Killer Bees with the '1500. The sound was far clearer and the threshold oddity was gone! Maybe the Killer Bees have the wrong impedance to use with the GTI 1500, and somehow create a feedback loop in addition to muffling the sound. I'll use the '1500/Panasonic combo some more to see if the problem has been solved.
I recently spent $20 to buy Panasonic RP-HT227 stereo phones to use with my PC and radios. The phones have excellent fidelity. Today I used the Panasonics instead of the Killer Bees with the '1500. The sound was far clearer and the threshold oddity was gone! Maybe the Killer Bees have the wrong impedance to use with the GTI 1500, and somehow create a feedback loop in addition to muffling the sound. I'll use the '1500/Panasonic combo some more to see if the problem has been solved.