Amp power question

mseller · Outlaw Joined: 05 May 2010 Posts: 220 City: Charleston

So this isn't getting answered in general discussion so i figured i'd bring it over to boat discussion...

I got the JL Audio MHD600/4 powering 4 JL Audio M770-TCS Tower speakers. I know the amp puts out up to 150w per channel and the speakers are rated for 100w RMS so I want to make sure I set the input so it doesn't blow the speakers. I got the amp set on 12db HP filter @ 100hz. I put a 170hz sine wave on my ipod to test the output voltage of the channels. The manual says that I want to measure 24.5V. Now if I want 100w output per channel I am assuming I need to measure 20V cause(correct me if i'm wrong) v=I*R and since speakers are 4 ohm then current would be 5 amps. And then P=V*I so power would 100W. However after all that I am only measuring about 5V per channel. I was scared to turn up the input more cause I didn't know if i was doing it right and didnt want to blow anything. I turned it all the way up for a brief moment and only got about 9V. Re-reading the manual I see that I should have played a 1khz sine wave and I shouldn't have had the speakers connected. Will have to wait till next weekend to get back to the lake to re-measure. But does anyone see anything else wrong with my logic?

PimpinD2 · Posted: May 04, 2011 7:09 am Post subject:

Disconnect speakers, turn off all the eq / bassboost on your headunit, turn all the levels to their "defualt" position. The JL amp manual should tell yoiu where that is, and turn the bass boost down.

Also it might be better to burn the sin wave to a CD and make sure it was not enhanced in anyway.

Brit Rider · Posted: May 04, 2011 2:28 pm Post subject:

Wow, never had anyone start measuring voltages to check speaker outputs etc... I think you might be overthinking this.

Truth is, I doubt you'll learn much from the multimeter. Simply tune the amp as the instructions tell you. If you begin to hear distortion, pull the gains back a touch and you're set. It is doubtful that you'll be blowing the speakers with that amp unless you have the gains ramped up a ton and are boosting the pre-outs between headunit and amp.

Remember, the 150watts RMS per Channel output is based on ideal/perfect conditions... You are very unlikely to have these... Plus you have access to the volume knob!

Hope this helps.

PimpinD2 · Posted: May 05, 2011 4:10 am Post subject:

those are the instruction from JL... ive never done them but ive watched my friends do it for hours =P

mseller · Outlaw Joined: 05 May 2010 Posts: 220 City: Charleston

PimpinD2 · Posted: May 05, 2011 10:27 am Post subject:

the manual will also give you good starting points for all the knobs on that amp. follow them, then raise your input sensitivity until you hear distortion.

Also make sure your headunit is about 3/4 of the way up. This is a good signal / noise ratio for most units and just know that whatever level your at is the max level you hsould be turning up the system. For me its 27 out of 35 and if needdddded i could go to 30...