K, my new tenant has a beat up Beemer that somebody once loved... someone glassed three 10in. 4ohm PG subs into the spare tire well, with custom amp rack and whatnot. The rest of the car is in okay shape, lotsa kliks. Lotsa rattles & worn out parts, but still lookin' good.

So, buddy wants to get a system worthy again, not fixin' it right up, just get it operating.

He gave me three amps he had, a blown Xplod (typical), a tiny 2 channel PG, and a 4 channel "Majestic Axis MA7800". I've Googled the latter, found little info on it.

So I opened up the MA7800, all looks fine inside, nothing stinks, guess I'll try it. But it's four channel, bridgeable to two, not one.

There are three sub holes in the trunk, two subs, one completely missing. In my collection of old crap, I have a 10in Alpine 8 ohm sub. Was gonna drop it in, but it being 8 ohm, and the other two subs being 4 ohms each, they would end up frying the 8 ohm sub, yes? (it would get dbl the power the other two got, so user would pump up volume till the other two sound good, giving twice the power to the 8ohm'er, and *poof*). Right? Wrong? I'm just guessing logically here...

So, I was thinkin' of getting a used 4 ohm sub from my stereo shop. BUT, this is a 4 channel amp, bridgeable to 2, not 1. Three subs into 4 or 2 channels just won't work. I'd also have to get a different amp, and that'd put us over budget.

So I have some options, and remember, he wants to spend as little as possible on it, up to a hundred bucks, not including what he'll owe me.

a) Can I hook the two 4 ohm subs up to one side of this amp (to 2 of the channels, unbridged), and use my 8 ohm sub by itself on the other two channels, bridged, and still have a system that won't destroy itself? Theoretically, 2 of the channels bridged into an 8 ohm sub, and 2 channels unbridged into the two 4 ohm subs..... that'd be about the same amount of power wouldn't it, driving each driver about the same?

b) Plug the third hole with a board, or a dummy (blown) sub, and hook each of the remaining two subs to this amp, bridged to 2 channels.

c) Get a replacement sub for the missing PG 10in. 4 ohm (anybody have one they want to get rid of?), and then find another amp (since it's a 4/3/2 amp, it won't do a single 1.34ohm load, which is what three 4 ohm subs works out to) that'll handle the load... anybody have a simple amp that'll do this that they want to get rid of? Trade for this MA7800 and PG tiny amp?

[img]graemlins/jawdrop.gif[/img] Exasperating isn't it... Other ideas?

[ October 14, 2004, 05:20 PM: Message edited by: GrizZz ]

 

sound like a nightmare i once had ,but seriously... whats the power rating on the four channel amp, and what kind of head are you going to use? how many pre-outs, does the 4 channel have a pass thru?

 

Power rating on the 4 channel is 1200, but that's it's peak. I can't find specs for it, although inside it has four 25 amp fuses, presumably one for each channel, so that would make it roughly 75x4 I'm guessing...

Opened up the tiny Phoenix Gold amp... all looks very good inside, haven't tried it still though. Found it's specs at the PG site:

XS2300 SPECIFICATIONS:

Output Power:

4 ohm stereo @ 12/13.8 VDC
25/75 WRMS x 2

2 ohm stereo @ 13.8 VDC
150 WRMS x 2

4 ohm bridged @ 13.8 VDC
300 WRMS x 1

Crossover Frequencies
20Hz to 20kHz (Rnet factory set at 100Hz)

Crossover Slopes
24dB per Octave

That tells me that it would burn up if I tried hooking up the 1.34ohm load to it... so I can't use it.

He gave me three or four different HU's he had... I just gotta pick & test until I find one I guess... that's tomorrow though.

Ghetto... no kidding eh...

 

Hey, I dont really have a good solution for the subproblem. But an amp thats realatively cheap thats 1.33ohm stable is the Alpine MRV-100M will do like 240wrms into that. Not much, but for what the amp cost and the reliability of alpine, it was nice. (I used to run one at a 2ohm load and it got descently loud with 1 12").

If you got a used 4ohmer from the shop you could go with something like that.

otherwise id seal off the opening with a board, or if it isnt necessary ever, then fiberglass it.

 

that tiny pg amp you speak of is a veritable powerhouse. the xs line was a wicked line getting alot of its innards from the m series that make pg famous. i run and xs2500 an that sucker has been down to a .5 ohm before no problems. hook it up give it a whirl i bet you'll be pretty supprised. give it ample power tho like 4ga or dual 8ga in

 

I agree with option b). Plug the hole with a board and a 4" port

 

the xs2300 is stable at 2 ohms mono no problem, just dont cheat on the power connections, i would run it to two of the subs and run the 8 as a passive radiator and see how it sounds,i dont think that you should paralell all three,you can use the 4 channel to run the rest of the system

 

I agree with sux, existing two subs and port that box using the third hole somehow.
That little pg amp from what people are saying might do the trick at 2ohm mono.

 

The PG amp is toast. Hooked it up, and it "farted" the speakers, but that's about it.

So I hooked up the Majestic, one sub to each side bridged... (4 channel amp, bridged to 2, 1 sub to each side), and all seems to be working great. Plugged the hole with a 10in. circle of MDF. Had to run the sub out from the HU through a splitter to get this amp the 4 inputs it wants, but oh well. This amp has a remote gain module as well, trés chic!

The head unit is Panasonic's TOL for 2001, it has front, rear, and sub outs, built in crossovers, etc. All the factory speakers are hooked up to the head unit. One door tweeter is missing, guess I'll head to the "wanted" forums when I have a list of stuff he can get in the future.

So, we're into this for nothing... well, near nothing. The car was given to him for a debt owed, the electronics is stuff he's just collected over the years, two RCA line splitters, a little speaker wire, a piece of MDF, some screws, solder and connecters, and my time.

On a side note, the sub box in the trunk of this thing is a piece of art... one of these days I'll have to make something like that. A perfect fit for the spare tire well, made of MDF & fibreglass, and the baffle is all sloped and carpeted and sexy. Lots of miles on the box, but it was once very nice, and could be nice again with some cosmetic touchups. There's an amp rack on the front of it, and assorted covers for it all, you can't even see that there's subs in this thing when it's all in place.

It's the poo, just take a whiff! [img]graemlins/headbang.gif[/img]