Brutewes

Senfinger was telling me about a thread that talks about wiring up this amp to 4ohm components and a 4ohm sub and still getting 75watts to the component speakers. However, we've been unable to find the thread.

According to JL tech support and the 300/4 manual, when you hook a 4ohm sub up bridged to the rear channels, it drops the power to the front channels to 38 watts each.

The only way to maintain 75watts to the fronts with the rear's bridged is to have an 8ohm sub. However, senfinger was saying that someone had posted a way around this.

Anyway, I'm stuck because I don't know whether or not to return my Polk MOMO 4ohm sub and get the JL 10W1 8ohm (about the only 8ohm sub I can find) or if I should just live with 38watts to the fronts and keep the Polk MOMO sub which should sound much better with my Polk db6500 components than the JL sub. Ugh

Please help, thanks!

senfinger

This is perfect... Please help us find the thread it was almost 2 paragraphs stating how/why that I ran across and cannot find the orig post.

s4play

The 300/4 amp is rated for 4x75 watts each. Each of these channels is independent and stable from 1.5 - 4 ohms.

When you brigde 2 channels of an amp for mono use, the amp will see half the inpedance of the actual load. For example if you have a 4 ohm sub, it will see 2 ohms. If you have an 8 ohm sub, the amp will see 4 ohms.

I do not see why the other 2 channels will drop in terms of power?

This is straight from their website:

Rated Power (4 Channel Mode): 75 W RMS x 4 @ 1.5 ohm-4 ohm (11V-14.5V)

Rated Power (Bridged to 2 Channel): 150 W RMS x 2 @ 3 ohm-8 ohm (11V-14.5V)


Thus in plain english with your setup:

Your components will see 75 watts per side and your subwoofer should be at 150 watts RMS.


rick

Brutewes

If you look at the manual for the 300/4 online you will see what I mean.

JL Audio 300/4 Manual PDF

Toward the back of the manual it shows charts for the ohm loads, and for a 4ohm stereo load on the front, and a 4ohm mono load on the rears, the output is 38x2 up front, and 150x1 in the rear.

It has to do with all four channels using the same power supply from what I have read and heard from JL tech support.

senfinger

Brutewes is correct. This AMP is not what you think; one of the senior people in the forum wrote an article possibly darkknight1999 regarding how to receive full potential out of this AMP.

Brutewes

I didn't realize that you can wire dual voice coil 4ohm subs to produce an 8ohm load. Thats good news, because the Polk db sub comes in a dual 4ohm voice coil, and its $20 cheaper than the momo.

I wonder how it compares as far as SQ goes.

Anyway, at least I can stick with Polk.

senfinger

I found this, but I saw something else in the past that showed how to hook it up to gain the full power of the amp.

QUOTE
Originally posted by scooby2
Correct me if I'm wrong, but I think there's some funky stuff going on because of the RIPS circuitry when you use the 300/4 with the Stealthbox. The Stealthbox is running a 3 ohm load, right? According the JLAudio specs, if you bridge the "rear" channels and it sees a 3 ohm load, and you're running 2 channels for the front speakers at 4 ohms, the output of the front is reduced to only 37.5 watts per channel, not the rated 75 watts if you were running 4 ohm loads front and back. Maybe a bridged 300/4 is not the best match for the Stealthbox.
ANSWER
I have the same setup and called JL tech support....they indicated that the wording in the amp documentation is somewhat misleading....I was assured that I would get the full 75wpc at a 4Ohm load to my BA separates in the front and the 150 bridged to my stealthbox....sorry...can't help much on the rationale...you might want to call them to get more info.....

NFRs2000NYC

Thats one of the things I hate about JL. Regulated power supplies. Really limits your use of their amps.