Minelab Big Signal enhancer

[Northoz]

Hi,I am new to the forum, and have a question about a Big Signal enhancer I recently bought,it seems to work fine on my F75,but when I hook up to my Gpx 4000,I only get a feint high pitched tone, it takes a 9v batt,the unit from what I can see,plugs directly into the 4000's battery,then the headphones plug into the unit,I understand the unit was made for an older GT 16000(I think that is the model)

Any help would be great,Thanks

ALL SORTED disregard above post..