I had a Rockford Fosgate 100aII amp. It is a 25 watts x 2 channels amp. I had it bridged to a RF 12" sub in a sealed box. The amp got a signal through the high-level inputs. Though not perfect, this was not bad. I had 100 watts (bridged) to the 12, which was just enough to supplement the Bose system until I could afford components.

A month or so ago I bought some Infinity components and decided to upgrade to a 4 channel amp to run the whole system. My wife's amp was a RF 200a4 amp. According to Rockford this amp is just 2 of the 100aII amps in a single chassis. The plan was to use the 2 front channels to run the components and to bridge the 2 rear channels to the sub. Last weekend I swapped out the amps. I matched the gain and signal levels as closely as possible. I also left the front channels unused. I did not hook up the components. Only 2 of the 4 channels are being used, and those 2 channels are bridged in a manner identical to how the 2-channel 100aII was bridged. Now for the odd part:

At low listening levels things sound just like they did on the 100aII. As soon as I get up to moderate levels (such as what would be necessary to be heard with the windows down in mixed driving) the bass gets distorted and sounds like the sub is bottoming out or suffering from overexcursion.

Could it be that the power supply in the 200a4 is inadequate to support the current draw needs for all 4 channels? I know that although there is only a load on 2 channels, all 4 channels draw SOME current. BTW, like I said, everything but the amp is 100% identical to pre-200a4 conditions. The power cable is 8 gauge for 12V and ground. The amp is NOT hot to the touch following distortion periods, and the distortion is immedately evident upon start-up...there is not a warm-up or overheat period.

 

Sounds like you are out of phase. Try swapping the + and - speaker wires on the amp and see if it sounds any better.

 

I will definately try that...sometimes the most simple explainations are the right ones.

 

So true. When I first put my system in I was pulling out my hair because the left front speaker was so much louder than the front right. I was playing with the phase, the crossover, etc. Finally, I realized that I had only turned up the amp gain on the left side; a quick visual inpection looked like they were the same because one was at 0 the other at 50%, so the slot screws looked like they were in the same position. Boy did I feel dumb.

 

It was the polarity. i switched the wires @ lunch today and the bass literally went up by 100%. No bottoming out sounds, no problems. I was getting all worried. I love it when the culprit is stupitity (or carelessness) and the fix is FREE!