Stereo Upgrade and Alternator Questions

Couple questions for you stereo guys.

Every time we go out about 15 minutes into our session my stereo volume decreases by about 25% -its very noticeable when it decreases and its been doing so throughout the summer -I'm only running two amps and two batteries as of right now, but I'm completely re-doing my system and I definitely do not want that problem with new system where I'll have 3 amps running.
I don't know if my volume problem attributes to the batteries getting old, or the stock alternator being too small...so, I've decided to replace both.

I have a 2007 SAN 210 -I have no idea how many amps the current alternator cranks out, but any advice on what alternator to step up to would be great (my mechanic will do the alternator install). I know there are plenty of battery threads on WW, I just have to figure out which one to go with (I'll be running about 2,000 watts with the new system).

Any help/ pointers/ suggestions would be great.

Thanks!

A) do not replace your alternator, try new batteries first.

B) it's probably your amps getting hot, or losing voltage.

With an 07, I would definitely get the batteries tested. They are probably reaching then end of their life span and therefore not taking a full charge. Do you have charger or are you just relying on the alt?

If the system is stock, then I bet the amps are wired with 8ga wire and wired to the "C" post of the battery switch. Id also bet you have two starting batteries. I think your OEM alt is a 90A output. If so, I would hold off on replacing it until you find a root cause for the reduced volume. 3 amps pushing 2K RMS is not over the top by any means, so I see no reason for a 90A alt and proper battery bank keeping up. If you have an means of plugging into shore power, I would spend my money on a battery charger and not an amp. A quality amp that is capable of actually recharging depleted batteries will cost $$$.

Thanks for the input.

I do have a pretty good deep cycle charger, sounds like I should use it more.

TigeMike -I'm pretty sure my stock battery cables are 4 gauge, I will check tomorrow though.
Is it common to rewire the stock battery set up? I do know that I have the stock perko panel and switch in the boat and it has not been rewired. I'm running zero gauge from 1 battery (the closest to the amps) to the distribution block, then 4 gauge out of that to the amps.
What would you suggest as far as rewiring the batteries?

Also, both batteries are interstate, and I'm not sure how old they are because the dates are not punched in.

C) it could be a rilla fart

So I got the batteries tested and they were both fine, and for good measure I got the alternator tested and it was find as well.
Since I just put in new Wetsounds amps and still experienced the volume lowering problem, I tried a new Gel Battery on the stereo side, the problem stll happened.
I'm completely stumped as to why the volume lowers by about 25% after playing for about 15 minutes.

Any suggestions would be great.

Some speakers like Apline marine coaxials for example have a protective device on the tweeter. When you lose the tweeter you lose volume.
The problem could be with the HU since that has been common all along. Don't buy any more electronics until you have isolated and confirmed the source of the problem. Temporary substitution is a very primative trouble shooting technique. An ipod directly into the amplifier would be effective in circumventing the HU. Unplug any remote control in order to bypass and eliminate that possibility. Start at one end of the signal path and by the process of elimination proceed in sequence with one component at a time. Its not very complex and it sure isn't an easy shortcut but it works every single time.
Also, for any kind of diagnostics you have to begin with the supply voltage with a simple multimeter to check continuity, resistance and voltage. Its essential. You have to check the complete circuit...the voltage and the ground. And you have to check it under load at the audio equipment terminals when you are encountering the problem. If your audio equipment is misbehaving then the voltage at the battery terminals under static conditions might be meaningless and misleading.

David
Earmark Marine