I have an early 90's SR500 that seems to have lost it's "Shine". Had it looked at and tech found nothing unusual, but I have been playing it 20 years and know the sound is a little flat. Was wondering if the pre-amp is not working as should? Can i replace the pre-amp or pick-ups and get it's shine back or? also it has the P/J configuration, are they active or passive with active pre-amp?