having trouble with input sensitivity

[westikle]

hi, i'm sure this has been discussed a billion times and i've been reading everything i can, but i was hoping someone might shed a simpler light on my problem. i have a JVC KD-X50BT and a Kenwood KAC-8105D sub amp. I'm having a hard time figuring the input sensitivity, which i assume is what other amps label as "gain." My head unit specs state that the sub out level/impedance is 2.5V/20 kohm load. my amp input sensitivity ranges from .2(max) to 5V(min.) The amp is also 300W RMS at 4ohms and i'm hooking up to a 12" 300W RMS 4ohm speaker, so the match is good i assume. problem is i have to turn the sensitivity knob all the way to .2V to even get decent sound out of the sub and even then i'm not getting the 33.6VAC from the speaker outputs that i should be getting (used a calculator from another site) unless i turn my bass boost up halfway. does it sound like i've done everything right? am i missing something? i'm not used to this input sensitivity thing, just a gain knob on the amp. i feel like if the HU specs state a sub out level of 2.5V, then that is what i should set the amp to. but it just isn't working out.

thanks for any help

wes

Click to read more...

 

[VisceralSound 10+ year member]

Try turning up the "subwoofer level" on the headunit, then reset your gains and report back, should be lower on the gain if done right.

 

[westikle]

i had the subwoofer level on 8/8 even though i have read not to do that when setting up a system. but i figured the specs mentioned are when settings are at full potential so the 2.5V may only be achieved when sub levels are 8/8 and volume is cranked way up. i'm about to go take a reading and see what actual voltage i'm getting from my rca plugs.

thanks

wes

 

[VisceralSound 10+ year member]

Things you don't want up during this phase is Bass/Mid/Treb and bass boost.

 

[westikle]

i have the EQ on "flat" and bass boost all the way down. i just went outside and took a reading of my pre outs and with the volume at 45 out of 50, i was only getting .3 VAC. i guess it could be a head unit problem but all have done is swap out amps. i had a RF punch 300W RMS @2ohm that worked great but only pushed my sub halfway, whereas this one should push it to the max.

 

[maylar 10+ year member]

What source are you using when making these measurements? You won't get your desired voltage if you're playing music.

 

[westikle]

i'm using a 50hz test tone

 

[westikle]

Ive just read on the crutchfield forums that that HU is known for having weak preout problems. There is nothing they are willin to do about it. Would an inline RCA amp solve my problem?

 

[CrossoverOre 10+ year member]

its possible that the rca's could be the problem. If all you did is swap amps and not head units one could conclude that the issue is not the head but something else. I would suggest checking the pre out at the back of the head and at the end of the rca's verify they have the same output.

 

[maylar 10+ year member]

A preamp can help, yes. If you go that route get a good one - the cheap ones can give you turn-on or turn-off "thump" noises (DAMHIK).

 

[westikle]

it seems like i used to have one of those little preamps to turn my rear speaker signal into a line level RCA output. are all of these little preamps passive? or are there active ones that would be a better bet. i'd rather not use one if i can help it. i've contacted JVC about the issue even though i haven't checked output at the back of the HU yet. i did however go and check the gain on the amp i was using, and it was turned up maybe a quarter. maybe my new amp is bad?