sub amp tuning steps

[Tobeit]

I am about to tune my mono amp/sub setup...I can't find a simple description how to tune the amp w/o having audio test equipment.

Amp has

• Gain control cont adjustable
• Crossover: 50Hz-200Hz, -24dB/oct. (Low-Pass)
• Bass Boost (fixed at 50Hz): 0 to +12dB
• Subsonic Filter: 15Hz (Fixed), -24dB/oct.

Box and woofer have a resonance frequency (on paper) of 48Hz. I would guess to set the crossover to something around 80Hz-120Hz, boost can be adjusted last according to taste, but how to make sure to get the correct gain setting to match the rest of the system (8 channel JBL OEM) and to avoid any clipping (I can't hear moderate clipping...)?

[Jigg007]

Does the amplifier have a peak light on it? You should be able to hear any distortion fairly easy, and when you hit that point, just back the gain down a little bit.

If you do have a peak light, you set the amplifier gain right before it starts lighting the lamp, this would be done with the stereo at its maximum output.

But really what you should do is flatten out the EQ and any sound enhancements, and tweak the gains to where it sounds realitivly balanced.

If you cant get the gain out of one amplifier, bring the other amplifier down to match, and bring the overall system volume up.

[Tobeit]

Thanks, no peak light, just power LED (Alpine MRP-M500)...

[bigloubumpin]

If ur talking about setting the gain w/o a DMM,turn the volume up 3/4 on the HU then turn up the gain knob slowing til u hear the sub stressing(bottoming).Remember to go SLOW doing this step.If u want to do it properly then u will need a Digital Multi Meter(DMM) & follow the steps in this link... http://mobile.jlaudio.com/support_pages.php?page_id=143

[Tobeit]

Originally Posted by bigloubumpin

If ur talking about setting the gain w/o a DMM,turn the volume up 3/4 on the HU then turn up the gain knob slowing til u hear the sub stressing(bottoming).Remember to go SLOW doing this step.If u want to do it properly then u will need a Digital Multi Meter(DMM) & follow the steps in this link... http://mobile.jlaudio.com/support_pages.php?page_id=143

Yeah, I could use a volt meter to test...oh, btw, how did you decide between adjusting the LOC output vs amp gain control? My first guess would be to adjust them both to be at the minimum setting while achieving the desired results? Both do practically the same...

[bigloubumpin]

LOC & amp was adjusted by ear,I 1st adjusted the LOC 3/4 of the way(PITA b/c the set screw is VERY small) then I adjusted the amp's gain accordingly.

[Mr Marv]

Here's something I posted on another forum recently that may help you out.

It appears you are setting the gains on a sub amp and if so here is a simple method I use that only requires a cheap piezo tweeter from Radio shack etc and the 50hz tone. Wire the Piezo to the amp in parallel with your sub(s) (due to the design of a piezo tweeter it will not change the load on your amp), set your sub level control to max with the main volume at 3/4 or so (check below for more accurate setting of the headunit) and play the 50hz test tone. Slowly raise the gain on the amp until you hear the piezo buzz which tells you clipping has occurred (since clipping increases the high frequency content in the signal the piezo will not make any sound until this occurs).

If you want to find out exactly where your headunit clips (I find most Pioneers clip in the 54/55 range out of 62) all you need is a 1khz test tone and a self amplified computer speaker. Connect the self amplified speaker to the headunit, play the 1khz tone and turn the volume up until you hear a sudden change/volume increase in the tone which will be the point it clips. Also, be sure to set the computer speaker volume low so you are not clipping the amp in there.

[Tobeit]

Thanks for all the help - I got the amp mounted (needed to build more custom boxes etc) and the sub is in the new box as well. Started to wire up the loc when I got hung up trying to find which wire is + on the rear speakers. Both rear speakers have red/yelllow pairs but I can not find the wire color map for my gen6 (the one in this forum does not apply for Gen6 w/ JBL).

[bigloubumpin]

Look for the '+/-' symbols by the speaker terminals

[Tobeit]

Originally Posted by bigloubumpin

Look for the '+/-' symbols by the speaker terminals

I did but the JBL speakers don't appear to have any symbols. Their is just that mini PCBA on w/o any identifier...I will look again though.

[MrGiggles]

Take a 9v battery, connect it to the speaker. If the speaker pops outward, then the polarity is correct. If it pops inward, then it is backwards.

[Tobeit]

Originally Posted by MrGiggles

Take a 9v battery, connect it to the speaker. If the speaker pops outward, then the polarity is correct. If it pops inward, then it is backwards.

Thanks. I figured out the "brutal way" - connected both direcstions with same amp setting. If wired incorrectly, the bass basically disappears. I did that after checking with a PAC tech if that could damage the LOC - he said no problem.