Alpine head unit not putting out or amp not "seeing" 4 volts

[Corbin Dallas]

Caveat: This is an older school equipment quandary

I recently had some time and became re-interested in car audio again after an 8 year hiatus. Kids will do that. After reading the posts over the last week or so I felt motivated to finish some of the minor things I knew needed addressing in my truck.

Today I was tweaking my system by replacing the rear stock speakers with some old Rockford coaxes I had laying around. They run off the head unit and really do not see much signal as I really love my Focals up front.

I decided to button down the amp under the rear seat (Ext cab Silverado) because the kids have managed to salt, gum, candy and lollipop stick the top of my once beautiful Alpine Expert amp as it precariously sat on the middle hump and slid forward over time.

In doing this, I started to play with the settings on the amp as I noticed my subs getting full range. "That's weird", I thought, so I set the LP switch on the amp and the subs played as they should have and I was happy. I wondered if one of the kids may have inadvertently set it to full range in the past, but figured it was not likely.

As I looked closer, I saw that the amp had a 4v or nom setting (kids also tend to make you forget all the cool things your toys could do when you bought them) and it was set at nom. "That's weird", I thought again as I switched it to 4v because I have 4 volt pre-out on my head unit. Well, when I did, the bass dropped. Say it with me - "That's weird", I thought as I flicked it back to nom because it sounded better.

So I ask, why if my sub gain and fade control on the head unit work fine, would the amp see full range out of those pre-outs? And why would it drop in volume when I switch the amp input to 4 volt?

Alpine CDA-7894

Alpine MRV-F505

Click to read more...

 

[subzero 5,000+ posts]

4v is not a constant state. I am pretty sure 4v is max. NOM is basically a recognition of signal then match output properly. Most decks back then where 2v max so that would make minimum around .5v or something like that. As for the lp hp filters. you have to play with it and see why it was changed. Remember music is dynamic, so sometime it may seem awesome and a few days later you feel the sound is weeker for some reason.

Always install equip in a location that is concealed and protected from theft and falling chewing gum.

I miss my old school alpines. I can't remember what model I had though. I think 401's

 

[Corbin Dallas]

4v is not a constant state. I am pretty sure 4v is max. NOM is basically a recognition of signal then match output properly. Most decks back then where 2v max so that would make minimum around .5v or something like that.

I am going to play with it more today if I get the time (sick kids will take your time too). I have a Phoenix Gold PLD1 line driver laying in a box too. Maybe I'll drop that in and see if it helps at all.

I still don't get why my sub pre-out was sending full range either.

Thanks

 

[subzero 5,000+ posts]

I am going to play with it more today if I get the time (sick kids will take your time too). I have a Phoenix Gold PLD1 line driver laying in a box too. Maybe I'll drop that in and see if it helps at all.
I still don't get why my sub pre-out was sending full range either.

Thanks

Sub preout from the deck.? If so then most deck have an internal switch to go from fullrang to subwoofer. So if you soley relying the deck to do the freqxover for that then check it on the deck.... On the other hand, If you dont have sub out as and option in your deck then your primary freqxover would be in the amp OR you would have to get an active or passive xover as well.

 

[Corbin Dallas]

I'm on it. I must have it set at full range within the setup parameters or something. I have the manual. Thanks again.

Adjusting the built-in Crossover

The High and Low Pass Filters on this unit can be

adjusted to suit your personal taste.

1 Press and hold the X-OVER button for at least 2

seconds.

Repeat this procedure to select the desired parameter.

∗ When the subwoofer output of this unit is turned

OFF, LPF and phase are deactivated.

2 Press the DN or UP button to select the

desired setting.

1. HPF (Setting the High Pass Filter):

FLAT (OFF) ↔ 80Hz ↔ 120Hz ↔160Hz

Outputs all frequencies higher than that selected

according to your preference.

2. LPF(Setting the Low Pass Filter):

FLAT (OFF) ↔ 80Hz ↔ 120Hz ↔160Hz

Outputs all frequencies lower than that selected

according to your preference.

(Only available when using the subwoofer output from

this unit.)

 

[Corbin Dallas]

OK, I played a bit more with the amp and connections. I have deduced that while Alpine insists that my head unit has 4 volt outputs at least for the sub pre-out, I just don't think I'm getting it. The signal just drops too low when I select the 4v input on the amp. I am definitely better off with the nom setting. I tweaked the cross over freq's and played a bit more with the gains to fine tune it.

I also added the Phoenix Gold PLD1 and noticed a huge output difference in my sub channels. I then decided to switch the amp back to 4v to see if it liked the new voltage change. It may have, but to the detriment of the front Focals on the other two channels. Back to nom.

The amp did seem to get hotter than previously, so I will have to watch that. If it overheats, I will adjust accordingly if it's not too late.

Thanks all.