4 Channel Amp, 2 Channels Not Working

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=109812
Printed Date: May 15, 2025 at 2:09 AM

Topic: 4 Channel Amp, 2 Channels Not Working

Posted By: roymcavoy
Subject: 4 Channel Amp, 2 Channels Not Working
Date Posted: December 16, 2008 at 8:36 PM

Hi how is everyone. I'm not much of an installer but thought i would take a swing at it. I bought a component set and 6 x 9's both 4 ohm and purchased a 4 channel amp. I can't get the 3rd and 4th channel to work. All speakers have been tested in the 1st and 2nd channels and work great but I can't get all 4 channels to work in unisom. I double checked my connections to everything but still nothing. Could anyone explain what could possibly be the problem? Thanks for your time!

Replies:

Posted By: i am an idiot
Date Posted: December 16, 2008 at 9:35 PM

What is the brand and model of the amp? Do they have any switches near the RCA jacks? Do you have the crossovers set to the proper settings?

Posted By: roymcavoy
Date Posted: December 16, 2008 at 9:54 PM

The amp is a Crunch 1800.4. It has a HP/FULL/LP on the side of the RCA jacks. I looked through the paperwork that I received with MB Quart and Crunch about the settings but it didn't say anything about it. Only mounting instructions. Do you know what settings I should set them to? The components are running on the first 2 channels and 6x9's on the last 2 channels. Where could I go to read up on what settings they should be set to if I have to figure this out on my own?

Posted By: i am an idiot
Date Posted: December 17, 2008 at 3:56 AM

AmpGuts has no pictures of that amplifier, some amps have 2 separate power supplies, it is possible that one of the supplies has failed. Could you remove the bottom cover and see if it has 2 transformers inside the amp.

Have you tried putting the front RCA cables on the rear jacks of the amp, and vice-versa to verify that you have signal on both sets of cables.

If you also have a subwoofer in the car, you need to set both crossovers to High Pass. If no sub 6x9s set to full and the separates to High Pass.

Posted By: roymcavoy
Date Posted: December 17, 2008 at 8:50 AM

Thanks for the info, it still is not responding. I'm going to call the manufacturer to determine if this amp is defective.

Posted By: paidnfull
Date Posted: December 17, 2008 at 11:22 AM

Some 4 ch. have a switch for 2ch.and 4ch. modes. Also Make Sure you are using 2 sets of RCA's for Front and Rear. Some people think a set will give you a 4 ch output for some reason. Also some headunits have the option of turning on/off the rear speaker and subwoofer outputs

Posted By: KarTuneMan
Date Posted: December 18, 2008 at 2:22 AM

You need an audio connection on ALL 4 inputs. If 2 of 4 are not working (as stated) switch them. If still nothing make sure the deck is set for high pass on the second set of audio outs (the rears)

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