I recently purchased an Ampeg B500DR Programmable Head with a Hartke XL115 Cabinet. The amp delivers 500 watts into 2 ohms; 350 watts into 4 ohms and about 200 into 8 ohms. The Hartke cab is 8 ohms. I play a custom made bass with low impedence EMG pickups. They are active as I use a 9-volt battery. Strings are light guage round round by GHS. My last few amps sounded fine. Now, with this new rig, the low notes are thunderous and sound great. However, I can hardly hear notes on my G string, especially in the upper register. I've tried many different settings. What is the problem? Is it the cabinet? Thanks!