regarding my present setup

cjinphilly

I have a Grand Prix with the following setup:
Head Unit: Alpine 9981
Speakers : MB Quart 5.25 components in front and MB Quart 6x9 in the rear.
Amp: Polk c400.4

This was all installed by a professional company.

I have been considering buying a sub woofer to get more bass, so have started looking at the initial setup on the amp. The gains were both set at about 11 o'clock.

The Headunit is supposed to give 4 volt pre-amp out but the amp had been set to low "signal input". The manual states I should set the "signal input" to High, so I did.

Now I have to tweek the Gains to match the input of the amp.. I have set the gains to around 12 o'clock and have noticed a slight increase in sound, I will keep tweeking making sure not to set the gains past 2 o'clock.

2 questions...

1. Why are their 2 gain adjustments? Should they be set the same?
2. Does the "Crossover Frequency Adjustment" need to be changed in the gain is altered?

spwuinmk67

One gain knob is for channels 1+2, the other for 3+4. Like front/rear, or highs/mids, etc. The cossover tells the amp what frequencies to stop sending to the speakers, so that should stay the same no matter where the gain is. There is a tutorial for setting the gains floating around somewhere, I never saved the link otherwise I'd post it. When one of the others get on, I'm sure they will. Nice set-up though. What series quarts are they?

MacLeod

Setting the gains at noon is probably too high. The gain is not a volume control, is only matches the output signal of the head unit with the input of the amp. For example, you want your amp to be at 50% when the head unit is at 50%. If you set the gain too high you could have your amp at 100% with your h/u only at 50% and could end up clipping the amp which could destroy your speakers.

Here is a link to the gain setting walkthru.

The crossover filters out particular frequencies and you generally have 2 types, a low pass and a high pass. Say youre running a sub, you dont want anything above 80 Hz playing thru it so youd set the low pass for 80 Hz. And if youre running mids and you dont want anything below 80 Hz playing thru, youd set the high pass for 80 Hz.

The 400.4 has an excellent crossover network and you can adjust frequencies all the way up to 5.5 KHz but youd only need this if you were bi-amping your speakers (running tweeters off front channels and mids off rear channels). In this case youd only be concerened with the high pass and since you dont have a sub youll want to cross them over pretty low. Just play with this til you find the setting you like best cause midrange speakers dont play low frequencies well and will probably not like anything much lower than 70 Hz.

cjinphilly

1. Part of the reason for me asking this question was because of this older thread:

http://www.polkaudio.com/forums/showthread.php?t=31062&highlight=c400.4

The volume control on my CDA-9831 headunit goes from 0 -> 35
What I found with my amp set to high input, both front and rear channels, and the gains set at about noon, is that my headunit's volume does not increase after about 26 or 27... ???

2. Aslo, why are there 2 gain controls? My head unit does have 3sets of pre-amp outputs, 2 of which are used for front and rears, so should the gains be set equally since they are receiving from the same unit?

thanx

MacLeod

Keep it set to high input if that works best.

You have 2 gains because its a 4 channel amp. One gain is for the front speakers and the other is for the rear. You want to set them to the level that mixes them best. Generally youll want your rear speakers at a lower volume than your fronts to keep the soundstage up in front of you. Adjust the front gain according to the link above then adjust the rear gain till it blends in with the fronts properly.