Hi everyone!

Question: Why does my amp keep cutting out? It alternates from normal to protect mode when I have the volume high on my HU.

Any help is greatly appreciated!

Background: I have a JL e1200 mono amp pushing a single 12" Alpine S-Type Sub (dual 4 ohm, wired for 2 ohms).

So I have a y adapter on the inputs and I'm bridging the channels on it to the speaker. Theoretically I should be hitting somewhere in the range of 200 W RMS.

I measured the voltage at the amp's + and GND and it averages 13.8 v, with the car idling and the HU turned up just before clipping (nearly all the way up). So it seems, even with the full draw of the the system, the car can maintain pretty high voltage levels. So I sit there and watch the voltage on the multimeter while music is playing and it remains steady while the amp just switches from normal to protect mode.

When I turn the gain down, the problem dissapears. Here's the issue...with the gain turned down so that the amp doesn't cut out...I'm hardly getting any output. I'm quite certain my e2150 with the sub wired for 8 ohms was putting out better bass.

Any ideas? I'm about ready to try the e1400d, or maybe I'll just go with a 250/1. I don't need a ton of power, just clean, steady power (making the slash a logical choice but mounting dimensions are an issue for my custom amp rack, which wont take a slash amp without modification).

THANKS!

 

Correction: I'm not bridging the outputs to the speaker. There is one set of + and one set of -. I'm using a + and a - to the speaker since this is a mono amp.

 

I have a 'slash' not an 'e' series, but the only reasons it would go into protect mode (according to the manual) are low voltage, a short, or wrong ohm load. Of course, there could be a problem with the amp, but I would check those things first. You've already ruled out inadequate power, so double check the wiring and make sure the sub is at 2 ohms. You could do both at once by measuring the resistance with your multimeter.

 

What size box is the sub in?

 

Enclosure size: estimated 1.5 ft3 (peanut method) without the sub in there. I did tightly pack (not just lined but pushed rolls of it in there) a bunch of polyfill in an attempt to reduce the volume more. Should I remove that?

Checked:

Ohm Load: on the back of the sub, I jumped the two +'s together and the two -'s together. Then I put my multimeter across the outside + and -....it read a steady 2 Ohms.

Short: all wiring appears to be intact, it's brand new...no apparent short.

Voltage: Already ruled that out with my other MM test.

 

I would have expected it to read lower than 2 ohms, but so long as it doesn't read 0 ohms, then the sub is cool. I only suggested checking the wiring and sub in one shot for simplicity. If you disconnected the wiring from the amp and measured the resistance you should get the same value as the sub alone (maybe 0.1 ohms higher depending on the length of wiring and multimeter), then you know for certain that everything downstream from the amp is cool. Curious to know why box volume might play a role in your problem...

 

Thanks Spoon...I'll double check it using your method. Yeah, I'm wondering about the enclosure volume factor as well...

 

Measures 2.1 ohms from the amp's output terminals.

 

OK, looks like I got it fixed. Thanks for all the suggestions guys.

Turns out that I was overdriving the amp pretty good. Wasn't so apparent at first but I decided to start over and zero out every setting and disconnect my sub.

Then I played a 0 db, 50 Hz tone (at about 80% volume on the HU) that I burned to a CD, and I hooked my multimeter to the output terminals of the bass amp. I turned the gain on the amp up until the DAC voltage read 20.

Then I reconnected the speaker...turned up the HU to check for clipping. I can get the HU to 30 out of 33 without any audible distortion. Bass amp doesn't clip either. I spent about a half an hour trying out all kinds of music from all different sorces (ipod, CD, DVD, Sirius)...all works well.

Output is the best it's ever been and ironically the gains are all lower. No gain increase necessary on my HU, just a small volume boost. Amp runs much cooler, and is working reliably.

I'm very satisfied! BTW, that was the procedure recommended in the JL owners manual for properly setting input sens. It works!

 

That's cool you got it working. Setting gains with a DMM is the way to go, unless you have a oscilloscope of course. One thing I picked-up from another forum though, is that unless you have a true RMS meter, unlike my basic RadioShack one, you should always use a 50 Hz signal, even though JL says to use 1kHz for mids. A basic meter is designed for household AC and is most sensitive at 50-60 Hz. My RadioShack meter significantly underreads the voltage as frequency increases.