How so safely parallel two BTL audio amplifiers ?

[Externet]

There is two BTL bridge tied load amplifiers on the same stereo LM4863 IC. Can they be safely operated in monophonic mode ?

Inputs tied together to the same signal. Can both outputs be safely paralleled for summing power/handling lower load impedance ? What about Rfs ? Any considerations ?

 

[audioguru]

The one with slightly more voltage gain will be overloaded since it will drive the load by itself while the one with slightly lower gain will do nothing.
An applications note for the LM3886 amplifier IC shows them paralleled with 0.1% tolerance gain-setting resistors and each bridged amplifier with two series 0.1 ohm 1% series output resistors.

Instead of paralleling bridged amplifiers with high accuracy extra resistors then why not simply use an amplifier IC for each pair of speakers?

 

[Externet]

Thanks, audioguru.
Could do the 0.1% resistors for gain setting, done that before. But perhaps you hinted a better 'normal' choice by using two speakers; one on each channel and simply parallel the inputs. The original intention was a single speaker driven by both channels...

 

[KeepItSimpleStupid]

The original intention was a single speaker driven by both channels...

That's what's used for some sub-woofers, The speaker has a dual voice coil.

 

[audioguru]

To make mono, you never connect the amplifier outputs together of a stereo amplifier that has stereo inputs, instead you mix the inputs of the amplifiers together with a mixer or two resistors.

 

[bountyhunter]

duplicate.