SE load mismatch, 8 or 6 or 4 ohms?

[flysig]

Looking at some SE output transformers, the Edcor only specify one impedance for the output load. There is only one set of wires on the secondary, compared to P-P transformers which frequently have multiple taps for 4 - 8 - 16 ohm loads.

So for this hypothetical situation, which way would you go? Or, is it even possible?

A 15 W SE guitar amp combo with a built in 8 ohm speaker. An expansion jack is there so that a second speaker cabinet can be plugged in, also 8 ohms. This would give a total load of 4 ohms. Normally the amp will run at 8 ohms with the included speaker, but once in a while it will be used with an extension speaker to increase projection during live performances.

Would you use a 6 ohm transformer and split the difference? Would you use the 8 ohm transformer and allow that the load will be lower than specified once in a while? Would you use a 4 ohm transformer to match the lowest impedance that might ever be seen?

If the 8 ohm transformer is used, will the sound quality or total power be badly affected when running a 4 ohm load?

[wakibaki]

I'd just use a txfrmr with 8 & 4 ohm taps and have some switching to allow you to switch in the second speaker and break the connection to the 8 ohm tap. You can leave the other terminal of the second speaker jack connected to the 4 ohm tap.

You might even be able to get a jack socket that will do the switch automatically when you plug in the second speaker, but I can't be bothered to think about that...

w

[flysig]

Looking at the Edcor site they only have single impedance transformers for SE designs, which is why I'm asking. A second tap using a switched jack would be a simple answer.

[wakibaki]

Originally posted by flysig
Looking at the Edcor site they only have single impedance transformers for SE designs, which is why I'm asking.

Buy elsewhere.

Another (somewhat less risky) sub-optimal solution, presuming an 8 ohm tx, would be to arrange it so that the speakers are in series, so you have 16 ohms nominal.

You will probably get away with running them in parallel for 4 ohms especially if you don't push it, but what are you really gaining?

w