Question about Jl Audio 300/4 Car Audio Amplifier

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Low ohm light on with no speakers connect??

I just hooked my 300/4 back up after about 8 months and when I started the car up the low ohm light came on and the right-rear speaker was hissing. The amp worked fine up until the day I took it out of mm old car. I figured there must be a short in the wire, but when I disconnected all of the speakers to narrow down the probelem the low ohm light stayed on. Someone PLEASE tell me how the amp can read low ohms when there's no speakers connected!!!

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  • Anonymous May 29, 2008

    Same problem here. I started noticing distortion at higher volumes, so i checked the amp and saw the low imp light on. Ended up unhooking all speakers, thinking one is shorted, and light is still on after all speakers unhooked.



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This can happen if the amp has an internal fault such as a shorted output transistor.

Posted on Dec 26, 2007

  • lovinlife792
    lovinlife792 Aug 13, 2012

    Where would the output transistors be located on the board?

  • Mantas Puskorius
    Mantas Puskorius Dec 18, 2012

    It is a bigest three terminal black things which is bolted to the radiator case, usualy in pair for one channel.



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My red light wont cut off

are they subs or door speakers? if they are subs, then speakers ohm load is too low for the amp. If they are speakers then again the ohm load is too low or one the speakers are blown are shorting out against the door. sometimes when mouting speakers in the door, the terminals are accidentally touching some metal inside the door.

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Y does my technics sug88 say low imp beside the a and b speakers

Because you've done something with the speaker connections that's too low impedance for the amp.

Amps need a certain level of resistance from the speakers otherwise there's a risk of the amp blowing itself up. Impedance is the name for resistance that varies with audio frequency. If the speakers you connected are any good, then there'll be label on the back telling you their impedance in Ohms.

When running a single set of speakers only then the amp would prefer an 8 Ohm load but it will accept a 4 Ohm load. If you plan to run speakers in both the A and B sockets, then both sets of speakers have to be 8 Ohms and no less. It also tells you this on the printing directly above the speaker sockets on the amp.

The amp is trying to protect itself from an overload situation where it would blow its output transistors and possibly kill your speakers too.

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Connecting a single 4 ohm speaker?

Gotta be careful here....the headphone output won't drive a speaker - if you already have all other speakers connected on the back as designed, you really don't have anywhere to connect a 4ohm speaker. The "front" speaker jacks have an "A" and a "B" section but they appear to be in parallel so you really shouldn't connect a 4ohm speaker to "B" for example if you already have speakers connected to "A". The combined impedance would be too low for the amp design.

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Jl audio 300/2 amp not working, yellow " Low Ohm" light on

Sounds as if you have the speakers hooked up improperly causing too low of a resistance. Re wire to increase resistance.

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I hooked up 2channel 500 watt amplifer and 1200 watt 300 rms subwoofer now the protection light comes on when i turn up volume

your speakers rating is too low for your amplifier. 300 watts RMS means the speaker can operate on an average of 300 Watts continuously. the 1200 watt rating is peak wattage input and meant for intermittent intervals only, a like a bass drum beat count. also , your speaker impedance must match your amplifier impedance or the speaker must be a higher impedance than the amplifier. Never lower than the amplifier's impedance output rating. If The amplifier is rated into an 8 ohm load, your speaker must be 8 ohms or higher. in other words you cannot use a 4 ohm speaker or you will damage the amplifier .

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Jl audio 300/4 low ohms light wont go off

If the low ohms light is on then you have your speakers wired to low. I need to know some more info like what type of speakers you have running on this amp and how many. Also was it working before and then it started doing this? Check the ohms with a volt meter if you know how, if not just get a volt/ohm meter and set it to the ohms setting and then take the positive(red probe) and touch it to the positive terminal on the speaker and then the negative(black probe) to the negative terminal and see what it reads. Make sure you check how low in ohms your amp is capable of handling. If you don't know just google the model of your amp and you will find a site that has a manual or just go to JL audios web site and you should find out there with no problem. Let me know what you find so I can assist you more if need be cause I also repair amplifires for a living and have many years experienc and I'm the cheapest amp repair business you will find any where. Good luck

Btw, I’m available to help over the phone in case u need at

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The MRD-M300 has speaker-level inputs so you can easily use it with any car stereo. Hook it up and hear what good bass can sound like!
  • 150 watts RMS x 1 at 4 ohms
  • 300 watts RMS x 1 at 2 ohms
  • MOSFET power supply and output stage
  • STAR Topology for cleaner sound
  • Bass Engine® features:
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    • variable subsonic filter (15-50 Hz in 5 Hz steps)
    • parametric EQ variable from 30-160 Hz
    • Bass Compensator enhances low-end definition
  • top-mounted digital control center with cover
  • time correction 0-10 milliseconds in 0.5ms steps
  • phase correction 0-180° selectable
  • digital readout
  • detachable front cover
  • blue power LED
  • delayed turn-on
  • requires 8-gauge power and ground leads — wiring and hardware not included with amplifier
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  • gold-plated terminals
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Most likely one of your subs are blown, or the Ohm's are too low for the ampliphier. Try hooking up one speaker at a time to the amp and see if it does the same thing. If it shuts off on one of the two speakers, that speaker is most likely blown.

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Legend Amp hook up manual.

Pretty Straight Forward get a 8 or 4 gauge amp wiring kit.

Run your hot wire to the +12V from the battery make sure to install the supplied inline fuse near the battery don't connect to the battery until installation is complete.

Run the REM to your stereo power ant. Wire. if available.

Run the GND to Metal Chassis Ground keep it as short as possible.

Run the RCA Cable from the back of the Stereo to the RCA Inputs or Low Level on the amp.

This amp is 2 Ohm Stereo Stable which means you can connect 2 (4 ohm) speakers in parallel to each channel or 1 (4 ohm) speaker on each channel or you can connect 1 (4 ohm) Speaker in bridged mode.

There are other speaker configurations you could use but you cannot drop the load below 2 Ohm in stereo mode and no lower than 4 ohm in bridged mode.

Hope this helps

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Disconnect the speaker wires from the amplifier's terminal block. If the low ohm light still comes on with no speaker wires connected, the amplifier will need to be repaired.

If the light no longer comes on, check the speakers and the wiring.

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