Ampeg Gemini speaker extension

[terryrocks]

My 65 ampeg gemini g12 came with a permanent 12" speaker attached. I want to add a 1/4" female jack to the end of the speaker lines so that I have the option of switching the speakers in the studio.
Is this as straightforward as it appears?
As long as I connect to speakers with the correct resistance it should be fine, right?[/img]

[Stevem]

If you get a Switchcraft 12A Female Jack you can wire it up so that when you plug into it the amps internal speaker will cut out and it will power the outboard one.
Or you can wire it to power both at the same time, but if the total load with both speakers is not kept at 8 ohms you will loose 1/3rd of the amps output wattage!

[Leo_Gnardo]

What stevem said ^^^, and I think it's a brilliant idea*. Your Gem wants to see an 8 ohm speaker, and max power level will suffer a bit if you drive a 4 or 16 ohm "guest" speaker. However if you keep the volume reasonably low so that the amp isn't driven to clipping into off-spec loads, you'll get away with it no problem. If you really must crank your Gem well into clipping, better stick with 8 ohm speakers.

I've fitted some combo amps with no output jack, with a bracket in the speaker chamber holding an output jack so no drilling into the amp chassis is necessary.

* So many folks stick with whatever speaker is in their combo & that's OK, but it does pay to audition other speakers and that's a pain to do unless the amp is fitted with an ordinary 1/4" output jack. Also eats up studio time listening and deciding, but if you come up with a combination that sounds exceptionally good it's worth the effort.

[pdf64]

If you get a Switchcraft 12A Female Jack you can wire it up so that when you plug into it the amps internal speaker will cut out and it will power the outboard one.

The potential drawback of this method is that jack socket switching contacts tend to be less reliable than the actual jack connector contacts.
If eg a dust bunny gets between the switch contacts when the ext speaker jack is used, then when it's unplugged, the OT secondary may be open circuit, leaving the amp vulnerable to flyback damage when next used in combo mode.
I think that's why combo speakers tend either to be hardwired, or use dedicated jacks, rather than using a switching jack socket as proposed above.

[Stevem]

Yup, and a Metor may come streaking out of the Heavens and hit my car as I drive myself to work today too! lol
If anything there's a much higher chance that the air moving around the Jack mounted near the speaker will kerp those dust Bunnys out of the switch contact area if you ask me!

[Leo_Gnardo]

If you get a Switchcraft 12A Female Jack you can wire it up so that when you plug into it the amps internal speaker will cut out and it will power the outboard one.

The potential drawback of this method is that jack socket switching contacts tend to be less reliable than the actual jack connector contacts.
If eg a dust bunny gets between the switch contacts when the ext speaker jack is used, then when it's unplugged, the OT secondary may be open circuit, leaving the amp vulnerable to flyback damage when next used in combo mode.
I think that's why combo speakers tend either to be hardwired, or use dedicated jacks, rather than using a switching jack socket as proposed above.

Good observation and if that's what's botherin' you Bunky just use an ordinary 1/4" jack, put a plug on wire going to the internal speaker, plug in either it or the external speaker, done. BUT then the amp user/owner has to remember to do that. Yes without a hard wired speaker you have to depend on the mental alertness of the person using it, always a hazard. That being said some owners of hardwired combos have asked me to put in a speaker jack so they can run their choice of external cab, I did as asked, & so far none of 'em have goofed it up. Yet.

[Stevem]

The simple 5 to 10 watt 250 ohm resistor( at a cost of less than 2 bucks )across the OTs output will protect the amp from the open switch section issue!