Hey Dante, yes that's one way to go, but then if you didn't use the extension speaker the amp will see 8ohms from the internal and give you a bit less power.

But there is another way I thought up last night (when I should have been sleeping

) where you can use either jack and use 2 x 4ohm speakers using 2 x switching jacks.

So the switch bit connects to the +ve (tip) when no jack plugged in. So with 2 of these jack sockets, you can wire it to be series with 2 speakers (both jacks; 4 + 4 =8ohms) or either jack will work on it's own at 4 ohms or 8 ohms.

T= tip, m = middle lug (connects to tip when unplugged), S = sleeve (earth). Note: for this to work you have to make sure the jacks don't earth to each other (i.e. not use a metal plate unless you insulate the jack from it as the plate earths them together.

On each jack wire the m lug to the S lug, join j1 S to j2 T, wire j1 T to amp +ve, and j2 S to amp -ve (series when both jacks used but each jack will also work on it's own)

so:

amp +ve > j1 T

j1 m > S

j1 S >>>>j2 T

j2 m > j2 S

j2 S >>>amp -ve

A. So with a speaker plugged into just j1, j1 T connects to amp +ve, j1 m is disconnected from j1 T, j1 S conects to j2 T wich is connected to j2 m (as no jack) which connects to j2 S connects to amp -ve, all good amp sees 4 ohms

B. One speaker plugged into just j2, j2 T connects to j1 S which connects to j2 m which connects to j1 T (as no jack in j1) connects to amp +ve and j2 S connects to amp -ve, all good amp sees 4 ohms

C. (series) 2 speakers plugged in, j1 T connects to amp +ve, j1 S connects to j2 T (speaker 1 -ve > speaker 2 +ve), j2 m disconnected from j2 T (coz jack plugged in), j2 S connects speaker 2 -ve to amp -ve, all good amps see 8 ohms.

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D. (parallel) as you say just use 2 non switching jacks, wire j1 T to amp +ve and to j2 T, j1 S to amp -ve and j2 S, 2 8 ohm speakers amp sees 4 ohms (this option gives the most power).

Anyway, options.

MJMP, correct me if I'm wrong, but could Dante also wire a 4 resistor in series (inside the jack) for the 4 ohm speaker and make it 8ohms ??