Bridging 4 channal amp in stereo?

10+ year member

I would like to bridge my JBL P80.4 amp to two channel for a full range speaker use (not sub use). Connecting the speakers wire to the amp in bridged mode is not a problem for me. My question is what do I do with the RCA inputs? Currently I have 4 RCA's (front L+R, rear L+R) plugged into the amp from when I was running in 4 channel mode. What do I do with the RCA's once I am running in two channel? Can I unplug the rear RCA's and just use the front RCA's or do I need all four plugged in? How can I hook it up so I have stereo not mono? I would still like to have stereo (balance left to right) mode running, not both front speakers outputting mono like it would be for sub use? The manual is not clear on full range speaker use in bridged mode and RCA hook-up.

Thanks in advance.

are you trying run 2 speakers off a 4 channel amp by bridging?

if so, you only need 1 pair of input rcas.

get 2 rca y-adapters (the 2 male, 1 female type)

from the left rca input, hook the y-adapter up to it, and hook the male ends of the y-adapter into the corresponding channels (either both 1&2 OR 3&4).

do the same for the right rca input.

so basically you end up with channels 1&2 getting only the left signal, and channels 3&4 getting only the right signal.

then when you bridge 1&2 or 3&4, the 2 wires from the bridged connection go to either the left speaker or right speaker.

also make sure amp settings for channels 1&2 and 3&4 are identical (gain, filters, etc)

Thanks, that's exactly what I am trying to do. I completely understand your explanation. Although, could I hook the left (front and rear) RCA into 1&2 and the right (front and rear) RCA into 3&4 and not have to use the Y-adaptor? That way I would not be trying to split the pre-amp power output and thus lower my gain settings? This would be assuming I didn't require the rear RCA's for anything else and I was running the fade between front and rear flat. Or is there a possible difference in the signal timing between front and rear RCA's that the amp could receive an out of phase signal?

My JBL amp has a mono/stereo switch. Should this switch be in mono mode when running bridged? My JBL owners manual does not explain in any way. The JBL P-4040 owners manual sorta does, which explains that this "sums left and right inputs". Or does it mater in this case as 1&2 would see the same signal anyway with the Y-adaptor. I assume this would be for sub use as you would want non-fading base as adjustments are made.

Thanks again

Using both F&R outputs from your hU would work fine, but using y cables will not degrade the signal to any noticable degree. What happens with y cables is the load on the HU increases, but V stays the same (or approximately the same). You can split pre-amp outputs 2, 3, probably 5 times before there would be any noticable decrease in Voltage.

I'm not sure on the stereo/mono switch, but since -electronically - each pair of channels would be operating in mono I would guess it needs to be set to that mode.

For an amp to be bridged one of the channels has to be inverted - which is probably what that switch does.

lol.. signal can be split up to 7 times safely (dont ask how i know this).....(technically i think you could do about 20 given you have a head unit that is well built)

// Thanks guys, the Y-adaptor was the missing information that I needed. Hooked it all up, sounds great, as I think I was under powering my components with only 40 watts RMS. 180 RMS is probably too much for my infinity 605cs rated at 90 watts RMS but I’ll turn the gain down.

As well, the Y-adapters give me the option to add fill on the rears using the deck amps and still having FADE controls.

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That amp does not have the RCA summing feature. You will have to use RCA splitters at the amp. If you already have that, then check the gains.
Bridging the amplifier Mono(LPF)on that sub will work just fine @4ohms
I talk about these boxes a lot, maybe cause Im biased, but they are just great boxes...

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