Can any stereo amp be bridged to mono ?

I came across some professional audio pdf's when researching a Yamaha P2200 amp. They state this is easily done ( with their amp ) with a splitter transformer on the input with one side out of phase with the other going into each channel; then connecting the speaker to the 2 positives. Would this work with any amp ?
The pdf is at this address - check section 6 page 17

Your expertise required, expected and I am eternally grateful
Yes, it will.
In response to the title of your post, no, not any amplifier can be bridged.
No. Not any amp can be bridged. It depends on the design. For example, some amps are already internally bridged by design and cannot be bridged again.

If you are interesting in bridging to increase output, please check with the manufacturer.
Yes, but only if the amp uses a common ground.

Also remember that a bridged amp sees 1/2 of the original speaker resistance. If your speakers are 8 ohm the bridged amplifiers only see a 4 ohm load. Make sure your amps are stable at the reduced load.
Well, I beg to differ. Using the technique described (making one input out of phase) will work with any amplifier. The correct terminology is actually "invert polarity of one input", not "out of phase."

As for amps that are already bridged, I assume you mean balanced amps where the + and - speaker terminals are of opposite polarity. You are correct in the sense that nothing would be gained in terms of power, but it could be done.

The point about a common ground is valid. For instance, amps that are transformer coupled to the outputs and where the outputs float would need to have the - terminals tied together.

I am not suggesting that you should try this unless you know exactly what you are doing or that there will always be a benifit in doing so, but the answer to the original question is yes.

You cannot bridge amps with balanced outputs. Assuming your amp is single ended, then yes, you could do so but whether you could do so safely is another issue.

Bridging doubles the voltage at the speaker inputs, which would double the current an amp sees at any given Vout. Another way to put this is the amp sees half the impedance it used to.

If you notice, most bridgeable amps limit the speaker impedance. For instance, maybe only bridgeable into 8 Ohms.

So, assuming you had a way to invert the signal by using a transformer or active circuit, AND your speaker impedance was high enough AND your amps were single ended outputs, then sure, no problem. :)


There's more than one way to do this.

If a solid state amp, and not a bridged output, then the first technique mentioned above will work. If a bridged output is employed I don't recommend it as the amp can be damaged.

If a tube amp with a grounded output, a Y adapter is installed at the input to drive both channels mono, and then a pair of jumpers on the output (one between the 16 ohm taps of the output transformer and the other between the Common connections) can be installed. At that point whatever your speaker load is, the amp output is half the impedance it was before, so if you have an 8 ohm speaker you use the 16 ohm taps, if a 4 ohm speaker you use the 8 ohm taps (and a jumper between the two is handy).

This will double the output power.

Our amps can be monostrapped too, despite having a bridged output. The technique is similar to above. The output power depends on the amp, but in the case of our smallest amp, the output power triples.

In all cases, don't expect the sound to be the same. Quite often it is degraded somewhat, so listen to the setup before committing to it- you may not like what you hear. Some cases it gets better....