Is it possible to have a dual power amp into a single speaker?

[markmalin]

Hello, all!


This is kind of a funny question, but someone was asking me about a way to have individual power tube sections for a dual channel amp.  So you'd have 2 preamps each with their own power amp, but into a single speaker output and have it switchable.  I'm not sure this can work because you have a specific impedance requirement on an OT for a given set of power tubes into a given impedance for the speaker.  But the idea would be:


[preamp 1] -> Phase Inverter 1 -> [Class A/B power amp section 1] -----\
                                                                                                            -------> [single speaker load]
[preamp 2] -> Phase Inverter 2 -> [Class A/B power amp section 2]------/   

[st]

In theory you could, as long you don't run both amps together but instead switch between them (and provide dummy load to the unused "channel". In practice, no.

[jjasilli]

It appears that you intend for only 1 power amp at a time to be connected to the speaker.  Assuming the power amps are tube amps, the disconnected amp should be switched to a dummy load, at the same time that the other amp is switched to the speaker.  I think some years ago PRR proposed a circuit based on an automotive hi/lo beam floor switch.  There are more sophisticated A/B amp switches for this purpose; or it could be a DIY project.


For impedance matching: if a power amp does not match the speaker's impedance rating, a matching transformer could be used.  Weber sells them.

[thetragichero]

sounds very inefficient partswise