bad amp?

Is it possible for an amp to be bad?  For the first time of any install I've done, I can't figure out why I've gone through 5 different subs using this one amp.  I've installed around 100 systems and never had a problem with tweaking it out properly.  I've been able to push subs before without burning them up or blowing them.  However, this one amp seems to be getting me.  The amp is a Phoenix Gold Xenon 600.1 rated at 612 watts rms X 1 @ 1, 2 or 4 ohms.

At first, I had the signal to the amp running off the amped signal from the factory sub and I blew the first sub that way.  I did it thinking if I turned the attenuators all the way down on the hi/lo converter, it would be cool.  Okay, so I was wrong.  That was also when I had the factory head unit in, knowing what I know now, I would have spliced the hi/lo converte into the rear speaker wires behind the head unit before it was amped.

Anyway, I replaced the head unit with an aftermarket Pioneer unit.  Okay, so I run RCA's directly from the HU to the amp, hook everything up and turn the system on.  With the gain control all the way down, the sub can't even be heard, nor do you even see it with any life.  Turning the gain up to about half, the sub is now audible, but very low...definitely not pushing the power it's rated for.  Now...if I turn the gain up to about 3/4's and activate the bass boost to about 6 dB's of boost...the sub is actually starting to sound okay.

The settings on the HU are still factory at this point, so I make some adjustments.  LPF set at 63 Hz and left on a level of 0 (+6 is the highest, -24 is the lowest).  The front speakers are cut off at 80 Hz (to bring some mid bass punchiness up front) and the rears are crossed off at 100 Hz.  With the volume at 10 or lower, the bass is nominal.  Once you turn the volume up past 10...say around 15, it starts kickin in.  There is no distortion in the sound, there was some flutter coming from the sub, so I backed off the bass boost till it went away.  This lasted all of 20 mins, then the smell of burnt electronics filled the cabin...the sub was fried.  Oh yeah, what sub you ask...Pioneer TS-W2501D2 (dual 2 ohm voice coils)rated for 800 watts rms.  I had it wired in series for a 4 ohm load at the amp so it would be most stable.

This amp also ate up a Phoenix Gold Xenon 10D2 sub rated for 450 watts rms (Pheonix Gold tech said would be perfect on the amp), an Alpine Type R rated for 500 watts rms, an Audiobahn Dub1000 rated for 600 watts rms, a Pioneer TS-W2502SPL rated for 800 watts rms (which Pioneer replaced after it burned out), it's replacement was the TS-W2501D2 rated for 800 watts rms as well.

Each sub was in a sealed box built to specs for each sub.  The PG sub was in .9 cu. ft.  The Type-R was in .5 cu. ft., the Audiobahn was in .5 cu. ft., the first Pioneer sub was in .85 cu. ft. and the 2nd one was in .7 cu. ft.  All of these are specs recomended by the manufacturers.

What is your take on all this???

I just wanted to get some input from others to see if there was anything I might be overlooking.  I just wanted to know if it were possible for an amp to be bad to the point it would cook subs left and right no matter what you try.  On one hand, with the low settings...the subs wouldn't perform at all, but when you adjust the amp to the point where the subs are performing...as soon as you go to crank up the music, POOF!!!

Eventually, I'll be sending that amp back to PG and let them look at it.  It is a great looking amp with awesome specs and I would hate to have to get rid of it.

Oh well!  Thanks for the feedback.