switching input sensitivity?

[rustydawwg 7]

Hi, there is a "high" level and "low" level sensitivity switch on my JL amp. The manual suggests to set at "high" but I almost get no movement from the sub until I turn the gain at least halfway. Setting it at "low" seems to boost the signal input and the sub bumps alot more with the gain at zero compared to halfway setting before? I usually set mode slope to 24db as it sounds better to me and center frequency 65hz and low pass around 80-100 depending on size/box the sub is in. Its a sealed 400w 10" that I've been fooling with, so should I keep input at "high" level setting and boost sub eq on headunit and gain more? Or just stick with what sounds best? I have 4v preouts, using store bought CDs, and checked rca connections to amp to make sure they were solid. Separate 4 channel speaker amp too so headunit amplfier is turned off. From what I've been gathering the Nak headunits sound very natural (very flat conservative eq factory eq settings). How does rca signal relate to sub level adjustment on headunit? It goes -10 to 10. I have it set around +5 right now.

So i guess the big question is, am I safe running "low" setting for rca input and setting conservative gains? (just under a quarter) Or a big no-no?

[Impious 1,476]

You just want to make sure you aren't overdriving the preamp input section of the amplifier or the output section of the amplifier, leading to clipping.  Otherwise it's a simply matter of setting it to whatever is necessary for your installation.  Without knowing your preamp voltage level or what level JL considers "high" and "low" I can't say for certain.  There is nothing wrong with a gain setting halfway up (or higher) as long as you are getting full power from the amplifier without clipping.  With the setting in "high" you will need more preamp voltage to drive the amplifier to full power output, so having a higher set gain makes sense.  There is nothing wrong with this.  Personally I would probably keep it in high and set the gain where necessary to avoid potentially overdriving the preamp section of the amplifier.  If having set to low isn't overdriving the amplifier preamp stage, then you can keep it in low as well. 

 

I would however not boost the EQ adjustment on the HU to make up the difference in output.  Increasing the boost on an EQ asks the amplifier to output more power at and around those frequencies, and can lead to clipping.  A +3db adjustment on the EQ asks the amplifier to double it's power output.  A +6db asks the amplifier to quadruple it's power output.  You can see how this can quickly lead to problems.

 

As for the sub level adjustment, it depends on how it works.  If +10 on the adjustments allows the HU to output full rated voltage than anything up to +10 is fine.  If it outputs full rated preamp voltage at a setting of 0, then increasing the adjustment means your maximum volume setting on the HU must decrease otherwise you will clip the preamp output.