I just bought and installed a NX4 (100w RMS x 4 @ 4 ohm)amplifier in my car to replace a Kenwood KAC-8452 (70A RMS x 4 @ 4ohm) I was running. When run relatively hard/loud, it seems to heat up and the protect light comes on. I tried to match my speakers with an amp that was at least as high output RMS as the speakers can handle, which the NX4 is.
I'm using the following in a 2007 Mercury Grand Marquis:
Massive Audio NX4 with plenty of space all around it (except underneath it as it's sitting on the carpet in the trunk)
Kicker 4 AWG from battery (with inline fuse)
Kicker 4 AWG from amp to ground (18" or so using a 3/4" bolt to a sanded surface and appropriate connector
Kicker 4 AWG on top of stock battery cable to battery and to ground, pretty sure factory was 4 gauge to alternator and 2 x 6 AWG to ground (was odd, not sure why Ford did that)
Kicker 4 pair twisted RCA's from HU to amp (5/6 pairs for possible future sub)
Kenwood KDCBT945U head unit
16AWG wire from amp to speakers
2 x Polk Audio DB571 front speakers (70w RMS - 4ohm)
2 x Polk Audio DB691 Rear speakers (100w RMS - 4ohm)
It runs hard for about 30 minutes playing Ozzy then the light comes on. Is very hot to the touch. Will take my IR thermometer with me to work tomorrow so I can see how hot "very hot" is.
I didn't notice any headlight dimming when at idle when I had it running hard. I think my car has a 135A alternator and it's still running the factory battery.
I took a look at the manual and it just said that a blinking protect light means a fault. Guessing that means a shorted wire or something somewhere. Didn't see anything about a solid red light being on, which is my case. Assuming that means it's too hot.
Don't get me wrong, it does way better than the kenwood did, goes louder and runs longer. The kenwood running less loud shuts down into a sudo-protect mode of what sounds like 75% (maybe less) output volume after about 10-15 minutes, but doesn't shut all the way down. Was odd, but can't find any real info on it as it's an older amp. I can't believe how small the NX4 is compared to the older kenwood. Easily half the size. Maybe not enough heat sink?
As it is, I just turned my gains on the NX4 down a bit (probably at 10% from minimum now) and took note of where I had it on the HU (32 out of 35).
I'm not sure how to measure the RCA outs on my HU or where the gains need to be set to best match it. Do I just rely on the manual for the HU then adjust the gains by eyeballing after doing the math on .2-5V that the NX4 manual states?
My point is, according to my speakers (since they aren't on fire and/or are still working fine), I'm not running them too hard, but really if the amp puts out 100W RMS, then my front two (70w rms max) should have been distorting or something and they weren't.
It is stupid loud and sounds really good, but I replaced the kenwood because it appeared to have a thermal issue. I was hoping a bit stronger (and newer) amp would let me run it as loud as I want to tolerate with a little extra headroom so I wasn't running the amp at red line.
Or, am I just expecting too much out of a $200 amp and $150 worth of speakers?