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Massive Audio NX4 - protect mode when ran pretty hard.

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olds97_lss
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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?

Click to read more...
 
32 out 0f 35 is way to high. back it down to around 25-28, most likely 25. how did you set your gains. i imagine your amp is clipping and going into protect

 
Not to sound like an idiot... but then why have 35? If the HU clips at 30 then why can it go to 35? Pretty sure that just made me sound like an idiot though...

I didn't really "set" my gains. When I installed it, I put them at about 40% on the dial (hard to say since there are no numbers or anything). They are now at about 25%. I don't know how to set them properly without an o-scope. Even if I had an o-scope... it's been so many years since I used one, I might as well try to fly the space shuttle! lol

Read a lot of info here after doing some searching:

Massive Audio NX5 Going Into Protection - Page 4 - DIYMA.com - Scientific Car Audio - Truth in Sound Quality

Granted, the majority of that was discussing the NX5...

 
The problem with the NX4 and the NX5 is that they are both rather small for the amount of power they produce. 100 x 4 is pushing it for a class ab amplifier that measures 10" x 5.5" x 2.1" with no fan to cool it down.

 
you can use a DMM to set your gains. A simple google search "setting amplifier gains with DMM" will provide everything you need, and that is the safest bet. Sounds like you're running it too hot, which can be cause of too high of a volume, and an improperly set gain. So, use a DMM and set your gain properly. The reason your HU goes that high is because some source volumes are really quiet, you might need to turn it up extra. Among various other reasons... I have a Kenwood HU as well, and when I set my gains, I set them at Volume 28. And the loudest I'll ever go is Volume 30.

Also, your more powerful speakers should be up front, it produces a MUCH better sound stage that way. Many people will ONLY have front speakers. I have 300w running to my front stage, and have my rears powered by my HU, just for a little noise back there for the passengers.

 
I've read that a lot of guys do that with the front sound stage. Personally I like the sound all around me and with 6x9's in the rear deck, I at least get a bit of benefit out of the trunk for bass that isn't shallow sounding. I run the rears down to a lower frequency than the fronts as well to avoid the fronts distorting on me and giving me clean sound.

I did some searching for setting the gains using a DMM and am updating my thumb drive with a set of test sounds. Will have to fiddle with it this weekend to see what I can figure out.

Thanks for the help, I appreciate it.

 
For now, I adjusted the gains by ear. Turned my HU up to 75%, played the 100hz, 1000hz audio and adjusted from low to high until I heard distortion/clipping with either frequency, then backed the gains down a hair. Now... it just isn't loud enough to suit me. But I know if I push the amp much harder, it will be maxing it out and thermal on me again.

Since I like the size of the amp and realizing that without spending another decent chunk of $ for an amp that puts out at least 150W RMS for 4 channels, I'm thinking of an alternate approach of just getting another MA amp and bridge the 4 channel to 2 (200W RMS x 2 @ 4 ohm). That said, I don't want to have to buy more cable and have 0/1AWG power wire installed, which I think I'd have to do to run two NX4's bridged. So, I'm thinking of getting an NX2 (120W RMS x 2 @ 4ohm) for my fronts and bridging the NX4 for the rears. Then I'd have nearly twice the max RMS rating for my front and exactly twice the max RMS for the rears. That should give me plenty of power to drive the speakers, but yet keep amp temps/clipping well within safe ranges at a volume I want.

I may try this approach, but use my kenwood (bridged, 140W RMS x 2 @ 4 ohms) for my fronts and the NX4 for the rears just to see how it sounds and how it does before I spend more $ on another MA amp.

 
Well... not sure what the deal is with the NX4, but honestly, bridged or 4 channel sounds almost the same in volume to me. In bridged mode, it overheats and shuts down faster. So... the money on that amp appears to have been a waste already. The kenwood however, did push the fronts bridged far better than it did in 4 channel mode.

I have no idea what the issue is... Seems that the polks want big name brand power that I guess I'll have to cough up the $ for just to push them. What's funny to me is that I bought them due to them being reviewed as "factory replacement" speakers. Figured a lower wattage amp would push them fine. I guess it's either my bad luck, or polk's way of getting people to buy their stuff... then buy more to run it.

Or, do I just ditch the polks and go with something that has a lower RMS rating so I can run them with my NX4? Which is another thing I don't quite understand. MA sells 6x9's, but they are only rated 30W RMS less than my polks. Seems to me, the NX4 wouldn't push those either...

 
Were they ever making rated power? Talk about being slighted...100 x 4 really means 65 x 4... 35% failure?

Would explain why mine pushes the speAkers fine for a little while. Obviously if I had known before hand... I'd have bought something else.

I hope the used old school RF 800a4 works that I just won on eBay... Is old, but underrated. Hopefully it will work and this will be the last amp I buy for a while. 3rd times the charm, right?

 
Were they ever making rated power? Talk about being slighted...100 x 4 really means 65 x 4... 35% failure?
Click to expand...
It's not failure, but rather 65% efficiency. Here's a test report on the NX4 from Dec 2009. At 1% THD+N the RMS output at 4 ohms was 98W. Obviously this isn't the power it will put out all the time, as with any amp, but it looks a lot better than how the current NX4s and NX5s are performing.

DIYMA.com - Scientific Car Audio - Truth in Sound Quality

Here's a Russian car audio magazine's July 2010 review of the NX4.

original Russian language site : ×åòûð¸õêàíàëüíûé óñèëèòåëü Massive Audio NX4 - avtozvuk.com

Google translated site: Google Translate

You might need to log in to view that attachment.

 
In response to why the headunit goes up to 35: As you turn up the volume the headunit amplifies the signal being outputted. Around volume 30 is considered the 0dB point, or where the song is fully amplified. The headunit doesn't necessarily clip over 30 so much as it over-amplifies the output. In other words, if you were playing a song that was for whatever reason fairly quiet (sometimes downloading songs through youtube does this) you *could* turn up the volume past 30 or whatever you set the gains for in order to achieve the desired volume level, and you won't experience clipping nearly as much as if you had turned it up on a song that was properly amplified.

 
It's not failure, but rather 65% efficiency.... At 1% THD+N the RMS output at 4 ohms was 98W. Obviously this isn't the power it will put out all the time, as with any amp, but it looks a lot better than how the current NX4s and NX5s are performing.
Click to expand...
I was under the impression that RMS wattage was what an amp could sustain and peak wattage was what your kind of explaining. Seems that typical RMS ratings are half of peak. With that in mind, an amp rated at 100W RMS should not put out a constant of 65, to me, that's failure. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

In response to why the headunit goes up to 35: As you turn up the volume the headunit amplifies the signal being outputted. Around volume 30 is considered the 0dB point, or where the song is fully amplified. The headunit doesn't necessarily clip over 30 so much as it over-amplifies the output. In other words, if you were playing a song that was for whatever reason fairly quiet (sometimes downloading songs through youtube does this) you *could* turn up the volume past 30 or whatever you set the gains for in order to achieve the desired volume level, and you won't experience clipping nearly as much as if you had turned it up on a song that was properly amplified.
Click to expand...
Thanks for the explanation. I turned up my gains a bit, so what used to be 30 on the HU is 25. Seems to do better this way (ran it hard for about 45 minutes during my commute), but still heats up a lot. Didn't shut down though.

 
I gave up and got another amp. Seems like the new amp holds up. It's an old rockford fosgate punch 800a4. I ran it hard for an hour and it just kept going.

Will need to do some research though as it sounds a bit muddy compared to the other two amps. The MA was almost too bright on the highs (easily toned down via the EQ in the HU). The kenwood I had was pretty good on mids/high's, but lacked the power to drive the lows.

The rockford pounds hard on the lower frequencies, relatively mild highs (not shrill, but still pretty clear). The midrange is the muddy area. Hoping I'll find the right balance on the EQ of my HU to get the mids sounding better.

Definitely seems able to drive my speakers though. Gets warm to the touch, but not so much that you can't keep your hand on it.

 
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