Bridging outputs with separate PSU's?

[MBK]

Hi,

I'd like to build a 4 channel / side chip amp. I plan on keeping the channels separate (separate PSU's and signals) because I have seen how the woofer channel peak output can influence the mid channel sound - which invalidates the whole point of bi- and tri-amping.

I'd like to have the option however to bridge the outputs so as to use just 2 channels at higher power. I see a problem though on the PSU side. Basically any speaker current would have to make it to the "other" transformer, and the circuit would close at the line AC side only.

Now,

- is this a problem (I strongly assume so)
- option 1 to fix that: connect power grounds of the pairs that may be bridged. Could be done permanently or with a switch in case of bridge use. Potential problem, any current would have to cross each side's filter caps to close the circuit, and strong currents would pass the power ground
- option 2, have a switch that parallels both PSU's for bridge operation. I somehow loathe that option because I'd have to switch 6 channels (+, gnd and - for both amps, either "open" or "connect" to common lines for bridged operation) - higher complexity, layout and reliability questions...

Any comments?

[maylar]

I wouldn't worry about it. Tie the power supply grounds together. The whole idea behind bridging is sharing two circuits.

p.s. Remember that you need to invert one channel. The + output of that channel is ground when not bridged.

[MBK]

Yeah, I'll likely use balanced inputs, so all it takes is to mute one input and cross connect the hot and cold wires.

MBK

[MBK]

... til I start building and blowing things up?

MBK