Bridging power amps

[emerth]

Noob question probably...

I understand how to bridge a pair of power amps: non-inverted input on one amp, inverted input on the other, and connect the speaker between the hot outputs of the two amps. Also that the power out scales by 4 not 2, thus I need to know the amps can handle that.

But I am not sure if I need to worry about the two amps' speaker ground outputs.

Should I connect the ground speaker outputs of the two amps or leave them unconnected? I *think* it does not matter but I am worried about whether ground would 'float' between the two amps, thus introducing a DC offset.

Thanks for any help!

[pacificblue]

Which speaker ground outputs?

[emerth]

Originally Posted by pacificblue

Which speaker ground outputs?

A speaker is connected to an amp between the output stage (hot output) and ground, which I have called "ground output". So if am bridging, do I worry about the ground "output" or speaker connections?

[sregor]

Speaker grounds on the amplifier side should go back to power supply ground and should already be connected at that point. The speakers themselves are not connected to any grounds, but should be connected between the two hot signals of the amplifers being bridged. Best if nothing is connected to the grounds externally.

[emerth]

Originally Posted by sregor

Speaker grounds on the amplifier side should go back to power supply ground and should already be connected at that point. The speakers themselves are not connected to any grounds, but should be connected between the two hot signals of the amplifers being bridged. Best if nothing is connected to the grounds externally.

OK, makes sense. Thanks for explaining it!

[SUZTEK]

I have a bridging circuit built in all my amplifiers with a switching facility for normal or bridge.The advantage is that you double the output power.This increases the bass and overrall response for a well designed amp.The result is well worth it.The speaker connections are between the hot (+) speaker terminals.Leave the (-) unconnected as these are connected to the star point on the power supply between the main smoothing capacitors.The input ground from the pc board should be connected to the same star ground of the power supply.Any other grounding should also be routed to the star point at the power supply.
wILLIAM

[AndrewT]

Originally Posted by emerth

I understand how to bridge a pair of power amps........................that the power out scales by 4 not 2,

No !!! Absolutely not.

The rule for a bridged pair of amplifiers is that the combination can deliver twice the power into twice the load impedance that the single amplifier can.

If you have a 100W+100W into 4r0+4r0 two channel amplifier then it can deliver 200W into 8r0.
It cannot deliver 400W into 4r0 and worse, it may not survive.

Do not believe the fools that tell you otherwise.
As a final comment, note that the total power delivered by that two channel amp is unchanged. as two channels it delivered 100W+100W = 200W to the loads.
As a bridged mono amplifier it is still able to deliver 200W to the attached load.

[AndrewT]

Originally Posted by SUZTEK

... switching facility for normal or bridge.The advantage is that you double the output power.

No !!!
the maximum total power that the amplifier is capable of delivering is exactly the same.
No magic, no extra power.

[emerth]

Hmmm, bridging doubles the voltage applied to the speaker other things being equal. A first approx says power dissipated is (V^2) / R, neglecting reactance. So if (bridged voltage) = 2*unbridged, the V^2 term causes the power to increase from bridging by a factor of 4, not 2. What is the flaw in this?

[SY]

Originally Posted by emerth

What is the flaw in this?

No flaw at all, as long as the load is the same AND the amplifier can supply the additional current. The real-world flaw is the last assumption.