Wire/re-Wire question

[steadygarcia]

Hey guys ... I have an Avatar 2x12 (16 ohm) cab that I want to use for my Dual Showman, so I'm thinking of converting it to a 4-ohm cabinet. I presume that it's currently two 8-ohm speakers wired in series. So to confirm, I'll need to run a wire from the +ve on the first speaker to the +ve on the second. Then I'll need to remove the wire from the -ve on the first to the +ve on the second. Then I add a wire from the -ve on the first to the -ve on the second. Is that it? I shouldn't have to change the wiring from the jack to the speakers, correct? Also, I presume I need to use the same wire gauge that's currently being used?

Is there any way to wire this cabinet up with a switch that can flip the cabinet from 4 ohms to 16 ohms? I can't think of any way to do this, but maybe there is?

[donnyjaguar]

Make it switchable between 4Ω and 16Ω, its easy. You'll need a DPDT switch. 3A contacts should be adequate.
Spkr 1+ to tip
Spkr 1- to centre of sw a
Spkr 2+ to centre of sw b
Spkr 2- to ring
jumper sw a left to sw b left
sw a right to ring
sw b right to tip

Rock on.

[steadygarcia]

Sweet -- thanks!

Just out of curiosity ... anyone know if the original 2x12 and/or 2x15 cabinets for the Dual Showman heads were made up of a pair of 8 ohm speakers in parallel? I presume they must have been.

[steadygarcia]

Originally Posted by donnyjaguar

Make it switchable between 4Ω and 16Ω, its easy. You'll need a DPDT switch. 3A contacts should be adequate.
Spkr 1+ to tip
Spkr 1- to centre of sw a
Spkr 2+ to centre of sw b
Spkr 2- to ring
jumper sw a left to sw b left
sw a right to ring
sw b right to tip

Rock on.

I just pcked up a DPDT slide switch at Circuit City. It's rated 3A at 250VAC. I presume this is fine?

[steadygarcia]

Bump on the switch question above ...

[donnyjaguar]

Yup! Just make sure it isn't one of those 3 position ones with centre off position.

[steadygarcia]

Perfect, it's not. Thanks!

[steadygarcia]

Another question ... my speaker cabinet has 2 jacks. As an alternative to donnyjaguar's suggestion above, is there a way to make one jack for 4 ohm impedances and the other for 16 ohm? If not, I notice that there is a short wire connecting the +ve's on one jack to the other, and another short wire connecting the two -ve's together. Using jaguar's technique above, do I still leave the short wires connecting the 2 jacks just the way they are?

[steadygarcia]

This all seems to have worked out. I rewired it with above information and put a DMM on the jack and I get a little over 3 ohms with the switch one way, and a little over 13 ohms with it the other way. I presume that's 4 and 16, since I know the impedance reading is always a little less. One thing I notice is that when I connect the DMM probes to the tip and sleeve of the jack, the reading often fluctuates all over the place before settling down. Other times, my DMM only reads "OL" and I have to keep moving the probes until I get a reading. Is that because I have a crappy DMM?

[donnyjaguar]

I do believe there is a way, but you'll need much more complex switching jacks to do it. And in so doing, I don't believe it would allow you to daisy chain cabinets. Hence, I'd just remove one jack and put the switch there.

[VaughnC]

Good luck with the speaker switch. Personally, any speaker switching on a tube amp scares me because if the switch goes bad (opens), that could cause output transformer flyback voltage...then good bye output transformer and possibly the tube sockets too. Too risky for me...I'd hard wire it.

[steadygarcia]

Originally Posted by VaughnC

Good luck with the speaker switch. Personally, any speaker switching on a tube amp scares me because if the switch goes bad (opens), that could cause output transformer flyback voltage...then good bye output transformer and possibly the tube sockets too. Too risky for me...I'd hard wire it.

Good point, I guess. I'll hunt around for a cheap 4 ohm (or 16 ohn) cabinet, and when I get one, I'll hard wire this one. For the time being, however, I think I've done a solid enough job with the switch. I'll be sure to check it from time to time.

[donnyjaguar]

I switch mine from 4Ω to 8Ω when its on. Not while I'm playing mind you. This is why I suggested a decent quality switch. The heavy duty toggles generally don't allow you to position the switch between one throw and the other so there's very little time indeed they are open circuit.

[steadygarcia]

Originally Posted by donnyjaguar

I switch mine from 4Ω to 8Ω when its on. Not while I'm playing mind you. This is why I suggested a decent quality switch. The heavy duty toggles generally don't allow you to position the switch between one throw and the other so there's very little time indeed they are open circuit.

Yeah, this little switch I bought seems pretty heavy-duty. Like you say, there's no position between one throw and the other. I don't have the need to switch it when it's connected to an amp, so that's even safer, I would say.

[VaughnC]

Originally Posted by steadygarcia

Good point, I guess. I'll hunt around for a cheap 4 ohm (or 16 ohn) cabinet, and when I get one, I'll hard wire this one. For the time being, however, I think I've done a solid enough job with the switch. I'll be sure to check it from time to time.

That's cool...but sometimes things like switches just don't let you know they're going to fail. They are mechanical devices and, one second they work, the next second they don't. I just wouldn't like to see anyone kill a good output transformer over a few dollar switch, when it could have been prevented by hard wiring in the first place.

Good luck .