I just read something interesting in my PPI (2 channel) amp's manual that's news for me:

"....The ability to run stereo speakers while simultaneously running a
mono output from the same amplifier is accomplished by running the
stereo speakers normally and tapping into the appropriate wires for
the "mixed mono" channel (left channel positive for the positive
speaker wire and right channel negative for the negative speaker
wire). Speaker impedance should be no lower than 2 Ohms on the
stereo channels and 4 ohms on the mono channel.
NOTE: Passive crossovers must be used for "mixed mono" operation.
Choose a low pass crossover around 100Hz for your subwoofer, then
choose a high pass crossover for your stereo channels. The high
pass crossover must be at the same or slightly higher frequency than
the low pass crossover to maintain the correct impedance. See your
PrecisionPower dealer or call 1-800-62POWER for more information
about passive crossovers.
Mixed Mono Output......"

Has anyone ever tried it?

 

I'm not really sure what your question is...this is a pretty standard setup for bridging a stereo amp into a mono one.

 

It's the following part:

".....The ability to run stereo speakers while simultaneously running a
mono output from the same amplifier is accomplished by running the
stereo speakers..."

Remember, this is a 2 channel amp. What they are basically saying is to use the same two channels in stereo & bridged mono configuration AT THE SAME TIME. They even have a diagram showing the amp powering a set of components & a Sub all off of the same two channels.

I have since found that there are some amps that let you do this. I'm not sure if there's any catch in terms of sound quality, though?

 

yeah this is actually a pretty common solution now for many amps. it's usually called tri-mode.

the biggest sound quality type issue you might have with this setup is the use of passive crossovers. since they are wired post amplficiation, some power is lost to their function, and crossover points are typically dependant and fixed based on what passive crossover you purchase.

 

hmm impedance when you do that?

 

yeah, you'll have to calculate the proper values for the caps and/or inductors (coils) based upon what crossover frequencies you want and the impedance of the speakers.

you can find a quick calculation utility here that will help... plus there's lots more information available as well...

 

From the PPI manual:

"....Speaker impedance should be no lower than 2 Ohms on the
stereo channels and 4 ohms on the mono channel."

I'm actually not sure how the power is going to be "split" between the two stereo channels & the mono channels.

Here are the specs:
100 WRMS x 2 @ 4 Ohms
400 WRMS x 1 @ 4 Ohms bridged

So, is it going to be 100+100+200 or 100+100+40? EE guys?

I do have a seperate amp for my subs and the fronts but I'm tempted to try this out. It would be nice to save space & wiring for the 2nd amp, specially since I still haven't found a decent place to install it.

 

Let's see, if the amp is capable of producing 100WRMSx2 @4Ohms or 400WRMx1@4Ohms when bridged, we can easily see by visualizing the Thevenin equivalent circuit that......

I HAVEN'T GOT A CLUE!

At least not a real answer. My expectation would be that even in mixed/tri-mode, the amplifier will never generate more total power than it would in either bridged or stereo mode at the lowest safe impedance. I'm assuming 400x1 @4Ohms is the absolute max for bridged configurations, and that you could probably get 200x2 @ 2 Ohms in stereo. Both cases that's a maximum of 400 watts. If your mixed-mode scenario, these 400 theoretical watts assume you have the best combination of impedance (2 Ohm stereo, 4Ohm mono). In reality you probably have 4 Ohm stereo speakers and a 4 Ohm sub, meaning you'll probably get a bit less than 400watts available output, I'll guess ballpark of 300.

I don't know the actual circuit topology of the amplifier (nor remember much about microelectronics except that I hated calculating amp circuits, even with PSpice), so I'm not sure how the two amplifier channels are tied together and driving the mono speaker, so I'm kind of guessing as to the output levels, but I'd estimate you'd see something like
150 to the sub
75 each to the stereo speakers

Just a guess.....I'm sure somebody like MacGyver or Modifry will come along and rip my answer to shreds

 

Bumping an old thread...any definitive ideas on this?

 

Never got around to trying it but it should work. My car is in a body shop, once I get it back I can try it out without any xovers to get an idea. If it sounds like enough power then I may buy the passive xovers and get rid of my 2nd amp.