Speaker load box type thing

bandmaster188

Just found out that my new blues junior sounds much better using an external speaker cab. It would be nice though to be able to combine it with the on board speaker. The amp is 8ohm and has only 1 speaker Jack. Just wondering is it possible to have a small box in the bottom of the amp that plugs into said jack socket so that when an extension cab and the on board speaker are connected into the box it matches the 8 ohm load of the amp by using a dummy load. Or is there such a thing on the market?

ICBM

Weber Z-Matcher.

It's not a dummy load, it's a matching transformer to make the amp see the resulting 4-ohm load as an 8-ohm load. (Or any other combination of impedances.)

To be honest you could probably get away with just a splitter. Most valve amps are tolerant of a too-low load like that, and although you will wear the valves faster there's no other serious risk. (Unlike with a solid-state amp!)

bandmaster188

If I could make a connecty box thingy would my theory be correct. Both speaker leads from on board speaker and extension cab connect into the box in parallel with each other creating 4 ohm load and then have a 4 ohm resistor connected in series to make it back to 8 ohms again. Then a speaker lead exits box to speaker jack. The webber thing looks like its a bit of a lump!

ICBM

It would work, but you would be wasting half the power in the dummy load - worse than the power loss from just running at a mismatch (which is typically only about 20-25%), so fairly pointless.

If you want something that's less of a lump than the Weber I might be able to build you something - I have a couple of impedance auto-transformers somewhere I think.

bandmaster188

Ah, power loss not factored in! Cheers for that offer ICBM, I might try rigging up a splitter box to see how it sounds with both speakers and if I like it,I'll get back to you on that. If you was to be able to make something up, would it be small enough to live inside the amp? It sounds like such a bigger amp with the 1x15 extension cab. I'm gonna bring home my 4x10 at the weekend to see how that goes too. Thanks again!

ICBM

Yes, the transformers I have - if I still have them! - are about 2" cubes, so in a minimum size box with a couple of jacks and a cable connection, easily small enough to sit in the bottom of the cabinet.

They're actually the output transformers from old Marshall solid-state amps that I scrapped years ago...