I have an Ampeg SVT-III Pro which I just got used from GC. I run it through an Eden D-410T and an SWR Workingmans 1x15T, both 8 ohms for a combined 4 ohm load. The problem is that it works great with my P Bass (Seymour Duncan Quarter Pounders) or J bass (Fender Custom Shop 60s) both of which are passive pickups. However, when I use my EB Stingray or Dean Q5 with EMG HZs (Aguilar OBP-1 at 18 volts) the cabs sound fine for about 3 minutes and then sound fuzzy like they are blown, mostly with notes on the "E" string up to the octave (and also the "B" with the Dean). I used the -15db pad and cut back to 12 O'Clock on the gain for the active basses but the distortion is still there. Adjusting the tube gain and equalizer doesn't really help either. I have to practically remove all bass and low mids to lessen it but what's the point to having a Stingray then? I've seen in other threads that the SR sends a pretty hot output. It seems to do it a lot worse with the SR than the Dean. I never had this problem with my SWR 350 head that I traded in for the SVT-III Pro and I am convinced that it's not the cabs since they're fine with the Fenders. BTW, I also put new batteries in both actives just to be sure and use the same instrument cable for all of the basses. Could it be the preamp tubes? They seem to be good quality tubes and the amp is only 7 years old. Has anybody else ever experienced this problem. I've searched the other threads with no luck. I love the tone of this amp, but it will probably have to go back to GC if I can't figure it out. Any and all suggestions would be appreciated.