Iv used many of the razorback coils and they all run very smooth you may need to try another SPP with the same coil to try to find out if it's coil or machine'
It works fine at the beach etc I'm just having problems in the high mineralized gold area,
most likely my fault and not the detector or coil, next time I go i will use the Freq adjust before ground balance and not push the gain to high.
That's OK Bluey may be a member could post a video with sound on how to set up a spp on the mineralized ground on the gold fields ,I do not have one of those little movie cameras thingies , they are easy to use with the ground balance you just have to touch the knob just touch it they are very fine ,have a look on youtube there may be something there regards john