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Old 19th May 2008, 03:05 AM   #1
carcomp is offline carcomp  United States
diyAudio Member
Join Date: May 2008
Default Help with RF 800a4 bridging issue

I've done a lot of searchingonline about this.... I can't figure out why when I bridge my Fosgate 800a4 as it says in the manual, with one left and one right channel i get hardly any power, but I get true stereo. Then if i bridge it the other way with both lefts and both rights connected, I get TONS of power, but no stereo separation and the gains affect both speakers simultaneously (both up = quiet, both down = quiet, one up one down = loud). I've tried both configurations with the 2/4 switch set both ways. None of these things works correctly, just comes close.

Right now i'm just using 2 channels of the four b/c that works correctly (I originally bought the amp to power front components and read 6x9s but now i know that the 6x9s are pointless.) I've owned the amp for a very long time now (since I bought it new). I just hope to get it to work right.

I've read that this amp doesn't work in 2 channel stereo mode. I can't believe that a 600 dollar amp would not be designed right. BTW, the amp is powering a couple of Focal Components, not subs. I have 1000a1s for that

Also I know that the 800a4 isn't an audiophile amp, but I believe that it *can* sound pretty good so I'd like to figure this out.
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Old 19th May 2008, 04:09 AM   #2
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
Try this...

Connect a single speaker. Use one left positive and one right negative speaker terminal. The positive speaker terminal goes to the left positive speaker terminal on the amp.

For that speaker, you use the two input RCA jacks for the terminals to which the speaker is connected. It's strange because you have to feed the left signal to one left jack and to one right jack. If it's confusing, plug into one jack at a time until you find the two that drive signal to the speaker.

Do the same for the other channel.

2/4ch switch set to 4ch.
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Old 19th May 2008, 12:58 PM   #3
carcomp is offline carcomp  United States
diyAudio Member
Join Date: May 2008
This works, but I end up with mixed stereo and the gains are all backwards. Also, there are only 2 gains on a 4 channel amp? what the heck? If you look at the 3 channel mode, this is how you are suggesting i set it up (look at how the sub is wired)

Click the image to open in full size.

This is how they suggest you create a 2 channel amp.
.Click the image to open in full size.
but it just DOES NOT WORK RIGHT!

I've actually got the amplifier apart right now and i'm going through the input side of it. RF did some crazy stuff when they built this. This amp doesn't have true independent power supplies for each channel. I doubt thats my problem, but it could be related. i've traced the inputs to a couple of ICs with my scope but then I lose it. This amp is pretty complex.

I should have bought just a normal 2 channel amp. If anyone has an 800a2 they want to trade for a 800a4 hey be my guest
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Old 19th May 2008, 02:28 PM   #4
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Join Date: Mar 2007
It is critical that you have the crossovers both set at the same frequencies, and both be on high or lowpass, or flat. It tells you to reverse the phase of the subwoofer if you are using high pass on front and low pass on rear. It sounds like the front and rear are out of phase.

Remember the 650?
If it ain't broke Don't fix it
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Old 19th May 2008, 06:13 PM   #5
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
If you connect it as I suggested, what is the problem?

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Old 19th May 2008, 11:49 PM   #6
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
After more research...

The suggestions I made earlier won't work because they don't use L+/R- like they do for most of their amps.

When bridging an amp, you have to have one normal and one inverted output for each speaker. The speaker connections in the manual are correct.

The gain controls are front/rear, not left/right so wiring it like they suggest won't allow left/right control. The gains would have to be set the same. This shouldn't be a problem. It's possible that the connections to the switch are wrong and that's causing the problem.

If you want left/right gain control, you're going to have to use the front channels for one speaker and the rear channels for other channel. The 2/4 switch will have to be set to 4ch.

Set the crossovers to flat for now.

This is what I'd suggest trying...

Right speaker:
Positive terminal to RR-
Negative terminal to LR+
You will feed the left signal to the LR+ and RR- jacks

Left speaker:
Positive terminal to LF-
Negative terminal to RF+
Feed the right signal to the RF+ and LF- jacks

You can reverse the polarity of the speakers if you'd like. These recommendations are based on the normal/inverted output of the actual power amplifier section.
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