[MTVhike]

How easy is it to get more power out of a multichannel amp by bridging two or more of the channels? Specifically, I have a 6 channel, 65 Watt per channel amp and would like to convert it to a 195 Watt stereo amp. It's rated at 65 Watts per channel, all channels driven. Is that doable?

[RDavidson]

Amps that are bridgeable usually have switches on them to allow bridging. Something to note is that while output wattage increases with bridging, current will stay the same. Most speakers want current not watts. Using cars as an analogy, it's almost like the difference between horsepower and torque. Watts = horsepower. Current = torque. Generally, I don't think bridging is a great idea. If you want more power (both watts and current) get a bigger amp or use your multi-channel amp to bi-amp or tri-amp your speakers (if possible).

[opnly bafld]

Bridging an amplifier is best done with 8 ohm speakers since the bridged amplifier will see half the impedance of the speaker.
Also not a fan of bridging and agree a more powerful amplifier is better.

If you want more power (both watts and current) get a bigger amp or use your multi-channel amp to bi-amp or tri-amp your speakers (if possible).

Passive biamping doesn't really increase power.

[MTVhike]

Actually, I need more current, to feed low impedance speakers, so I guess that won't work!

[opnly bafld]

Actually, I need more current, to feed low impedance speakers, so I guess that won't work!

Correct, look for an amplifier that is rated at 2 ohms and provides an increase from the 4 ohm power.

Crown XLS xx00/02 series are an inexpensive option.

[RDavidson]

Bridging an amplifier is best done with 8 ohm speakers since the bridged amplifier will see half the impedance of the speaker.
Also not a fan of bridging and agree a more powerful amplifier is better.

Passive biamping doesn't really increase power.

The OP has a 6 channel amp. Each channel outputs 65 watts. Assuming his speakers have at least 2 sets of binding posts he can then hook up 2 of those 65 watts outputs to 1 speaker and 2 of those 65 watts outputs to the other speaker. This does increase the amount of power that each speaker receives to 130 wpc, BUT it is split 65 to the woofers and 65 to the tweeters (assuming the speakers are 2 way design). This is indeed not the same as feeding each speaker 1 channel at 130 watts.

[opnly bafld]

The OP has a 6 channel amp. Each channel outputs 65 watts. Assuming his speakers have at least 2 sets of binding posts he can then hook up 2 of those 65 watts outputs to 1 speaker and 2 of those 65 watts outputs to the other speaker. This does increase the amount of power that each speaker receives to 130 wpc, BUT it is split 65 to the woofers and 65 to the tweeters (assuming the speakers are 2 way design). This is indeed not the same as feeding each speaker 1 channel at 130 watts.

Not sure I follow the post (does get 130, but not the same as getting 130  ), but passive biamping doesn't work the way most people assume.

[MTVhike]

The speakers are Magnepan LRS ones, so they can't be biamped. When you say that bridging produces more power but not more current, that means they must provide more voltage, so I guess the two outputs are connected in series. I thought bridging meant putting the two outputs in parallel (and, of course, the inputs also in parallel).

[opnly bafld]

A bridged amplifier will see the LRS as a 2 ohm load and you are right a paralleled amplifier will drive lower impedance because it is shared between the two amps.

[RDavidson]

Not sure I follow the post (does get 130, but not the same as getting 130  ), but passive biamping doesn't work the way most people assume.

65 + 65 does add up to 130 wpc, but here's the thing : Let's say the tweeter can only handle 20 watts max. That means there's 45 watts that will never be utilized from one of the amp's channels. Conversely, let's say the woofer can handle 100 watts, but it is only being fed 65 watts, so the woofer may never reach max capability. It is potentially being underpowered. So you have a tweeter that is over powered and a woofer that is under powered. The speaker is actually only able to utilize 85 of those 130 watts. OK. Now think about if you have an amp that outputs 130 wpc. The speaker will be receiving all power from one large "pipeline" then distributed to the drivers via the crossover not split into 2 smaller pipelines ahead of the crossover per my example above. Hope this makes sense.

[opnly bafld]

We can agree to disagree about passive biamping and whether one gets up to 3 dB gain or no gain and why some might hear a difference between a single amp and passive biamping.

[Early B.]

Also not a fan of bridging and agree a more powerful amplifier is better.

I'm not a fan of bridged amps, either, but have two of them in bridged mode.

There's always trade-offs. The monoblocks I really want (Pass Labs) are many thousands of dollars more than I can afford, so I work with what I have. Regardless, my amps in bridged mode sound much better than running one of them as a stereo amp. But still, it's twice as expensive to do it that way. 

[opnly bafld]

The speakers are Magnepan LRS ones, so they can't be biamped. When you say that bridging produces more power but not more current, that means they must provide more voltage, so I guess the two outputs are connected in series. I thought bridging meant putting the two outputs in parallel (and, of course, the inputs also in parallel).

A higher quality 2 ch amplifier would provide more benefit IMO than the extra complexity and modest 3 dB gain of paralleled amp channels.

[opnly bafld]

I'm not a fan of bridged amps, either, but have two of them in bridged mode.

There's always trade-offs. The monoblocks I really want (Pass Labs) are many thousands of dollars more than I can afford, so I work with what I have. Regardless, my amps in bridged mode sound much better than running one of them as a stereo amp. But still, it's twice as expensive to do it that way.

The OPs muti channel amplifier is not bridgeable without modifications and (probably) will not work with 4 ohm speakers.

[mrhyfy]

This may seem crazy but in certain setups you can parallel amps.
I've done it  with an  inexpensive QSC amp with no problems.  I placed a 35 watt, one ohm resistor on the output of the amps  to provide some protection.
The amps must be identical, set to the same gain and receive identical signals.

[RDavidson]

We can agree to disagree about passive biamping and whether one gets up to 3 dB gain or no gain and why some might hear a difference between a single amp and passive biamping.

Wasn't disagreeing, actually. Everything you've said makes sense, except the part where you said that passive bi-amping doesn't increase power. It does increase power to the speakers. However it doesn't necessarily equate to a 3db gain (i.e. the increment of sound pressure level that humans can readily detect). I was just trying to help explain in more detail to the OP to be helpful. If I'm missing something or am not explaining something correctly, please share.

[opnly bafld]

This may seem crazy but in certain setups you can parallel amps.
I've done it  with an  inexpensive QSC amp with no problems.  I placed a 35 watt, one ohm resistor on the output of the amps  to provide some protection.
The amps must be identical, set to the same gain and receive identical signals.

Very true, and in this case a benefit is the amps will have an easier load driving the LRS.

The OP didn't identify his 65w multi channel amplifier, but I feel greater gain (pun intended) can come from a 2 channel amp of higher quality.