Troubleshooting a system

AFTER INSTALLATION

Setting up systems

after installation

for best performance

General:

As mentioned in the “General Installation Notes” section, the system should now be powered up, and working. At this point, all crossover frequency and input selection switches should be properly set for the application, and all volume, level and equalizer controls turned to minimum.

Level control setup:

Insert a CD or cassette that you are familiar with to use as a reference, and turn the head unit volume control to about 80% of its full setting. The system sound level will of course be very low, and the following procedures will help you to match the ampliﬁer input sensitivities properly to the head unit output signal level.

Single 2 channel ampliﬁer systems:

Turn the level control up slowly, till you hear distortion, then back off a few degrees on the control.

Single 4 channel ampliﬁer systems:

Turn the channel 1&2 level control up slowly, till you hear distortion, then back off a few degrees on the control. Repeat for channel 3&4.

2 or 3 way active systems:

Always start with the bass, or low frequency ampliﬁer as a reference, by turning its control up to the point where distortion is audible, and back it off some.

Now adjust the level control for the highs or tweeter channels in a 2 way active system, to balance the highs to lows.

In a 3 way active system, match the midrange level to the bass, and then the highs to the midrange and bass. It may be necessary to perform a few iterations of the midrange and highs level control settings to achieve a satisfactory sound balance.

Crossover frequency ﬁne tuning:

We had started off in the “General Installation Notes” section by setting crossover frequency controls to approximate positions, and now you can adjust these for best sound quality. Be careful not to stray too far from those crossover frequencies as recommended by the loudspeaker manufac- turer, as it is quite possible to damage midrange and tweeters with excess power outside their nominal operating frequency ranges.

Equalizer setup:

Once all levels and crossover frequencies have been set for a pleasant sound balance, we can start equalizing the system frequency response. It is important to remember that a boost applied at any frequency, or range of frequencies, will cause severe ampliﬁer clipping. The following comments apply to ALL equalizers and tone controls on the ampliﬁers, as well as those on head units and dash mount equalizers.

Use the head unit volume control to adjust the system to an intermediate level, and proceed to adjust equalizers and tone controls to personal taste. Now go back to the Level control setup above, and readjust all level controls.

Sit back and enjoy the music!

The key to ﬁnding the problem in a misbehaving sound system is to isolate parts of that system in a logical fashion to track down the fault.

Description of the Diagnostic system built into all MB QUART ampliﬁers:

The diagnostic system will shut down the ampliﬁer, until reset by turning the head unit off, and back on. This state of affairs will be indicated by the front panel PROTECT LED lighting up under the following conditions:

1 - A short circuit on the loudspeaker leads.

2 - An internal ampliﬁer fault that causes a DC offset on the loudspeaker output.

Should the ampliﬁer go into diagnostic mode, simply disconnect all RCA and speaker leads, while keeping +12 volt, power ground and remote leads connected. Now turn the ampliﬁer back on, and if the diagnostic LED lights, the ampliﬁer has an internal fault.

If not, plug the RCA cables back, and reset the ampliﬁer. If it goes into diagnostic now, the fault lies in the input, either with bad cables or source unit. If the ampliﬁer seems ﬁne with RCA cables plugged in, connect the speakers, one at a time, and if one of the speakers or its wiring is faulty, it will activate the diagnostic system.