No sound in rear channel, GT-40 amp

[Michigan boarder]

I have a Boston Acoustics GT-40 amp powering 4 cabin Polk 651db's. Last weekend at some point the rear speakers stopped working. I put my ear to them with the radio on, and I can hear the bass tones coming out of them very quietly. Like if my volume is on 40, I can hear the bass at a level 5, but no treble or mid. RCA and all other connections are good.

?

Edit: front speakers sound great, no issues.

Edited July 9, 2012 by Michigan boarder

[jk13]

Swap front/rear RCAs and see if the problem remains the same. That'll at least tell you if it's the amp or something upstream.

If it stays on the rear, then swap speaker wires to see if it's the amp output channel that's bad. (could be input or output stage of the amp--just verifying which.)

Edited July 9, 2012 by jk13

[Michigan boarder]

Swap front/rear RCAs and see if the problem remains the same. That'll at least tell you if it's the amp or something upstream.

If it stays on the rear, then swap speaker wires to see if it's the amp output channel that's bad. (could be input or output stage of the amp--just verifying which.)

I'll try that (in a week), thanks!

[Michigan boarder]

So, I have an update. The Hi-pass filter on the rear speakers was on. I was monkeying around with it once after the install, and I must have left it on. I turned it off and sound came back, sounds great. Which leads me to some questions about the amp. Please bear in mind I know nothing about amps.

1. There is a stereo-mono switch for fronts and rear. I want stereo, correct? is there any reason I would want mono?

2. There is a subwoofer level on-off switch. I have it off. No sub yet, and when I do it's that Basslink that has its own power. Correct?

3. There is a high-pass filter switch for fronts and rears. Under that switch is a dial. That adjusts from 50 to 350. I have no use for this, correct? Just leave it off (and the dial is moot)?

4. There is an input sensitivity dial ranging from 0.2 to 5. I have it in the middle. Any reason to do anything different? It seems to sound the best in the middle.

Lastly, I have noise coming thru the speakers each time I turn on the blower, or in my case when it is automatically running. it is really loud. But, no noise with the bilge pump, and almost zero noise from the engine. Why does my blower make so much noise thru the radio? FWIW, the blower itself is actually very quiet. I have to put my ear to the engine cover to hear it when we are idling to make sure it is on.

[shawndoggy]

you should highpass at about 80-100hz. What that's doing is taking the lowest frequencies away from your cabin speakers. Those speakers can't reproduce those tones anyway, so don't ask them to.

Input sensitivity is probably the gain. You should turn the sensitivity all the way down, then you should turn your headunit up to 85% of its max, then slowly bring the sensitivity up until the speakers are as loud as they can go without breaking up or sounding bad.

Blower noise suggests a bad ground. Are the headunit, basslink, and amp all grounded and powered from the same place?

[Michigan boarder]

you should highpass at about 80-100hz. What that's doing is taking the lowest frequencies away from your cabin speakers. Those speakers can't reproduce those tones anyway, so don't ask them to.

Input sensitivity is probably the gain. You should turn the sensitivity all the way down, then you should turn your headunit up to 85% of its max, then slowly bring the sensitivity up until the speakers are as loud as they can go without breaking up or sounding bad.

Blower noise suggests a bad ground. Are the headunit, basslink, and amp all grounded and powered from the same place?

Thanks for the input Shawn. On the high pass that makes sense, cuz I turn it on (for the front speakers) and hear no difference, turn it off and hear no difference. The problem is in the rear speakers, though. When I turn it on for them, regardless of where the setting is, the rears sound goes down to nothing. There may be an issue with that adjustment knob, it was a refurbished amp, out of warranty now. Will it hurt to leave it off completely?

That sounds like a perfect approach on the sensitivity, I will do that.

The amp is grounded to the battery (3 ft or less). The sub is not installed yet (I know, I know). The HU is still the old one, grounded to whatever everything else is grounded to under the dash. Should I run a separate ground direct to the battery?