Passive AB speaker wire box

[Axe_34]

I'm currently playing two separate amp heads into the same mono cabinet (not at the same time). I'm getting tired of having to unplug the speaker wire from the back of the amp every time I want to play the other one.

Can a passive junction box like this be built? If so, could someone draw me a schematic? It would be greatly appreciated.

Again, I know you can't play the amps at the same time. And I don't need any LEDs or a switch. Just two jacks in and one jack out.

[pappasmurfsharem]

I would say this is a bad idea unless you are turning the amps of before switching. Most amps require a speaker load or it will blow.

[dirtysteev]

Are you manually unplugging your instrument to switch amps or switching dedicated instruments? What about just putting a parallel input in your cab and leaving both amps plugged in, switching the unused amp to standby (or off) when not in use. In general this looks like a clumsy application, chaining amps often leads to hum issues, and as noted above, you can easily damage your amps from improper loading.

[Axe_34]

I would NEVER have both amps on at one time. What I'm trying to avoid having to reach to the back of one amp, unplug the speaker cable that runs to the cab and then plug it into the other amp's speaker out jack.

Put another way, if I'm playing one amp it's got a speaker cable running from the amp to the cabinet. Later that day I want to play the other amp. I have to unplug the speaker cable from the back of amp 1 and plug it into amp 2.

This isn't about switching instruments.

I thought I could just have a box that would accept two speaker cables into it from the two amp heads and then run a single speaker cable to the amp. Seems like it would work if there was only one amp on at any one time.

[gcme93]

You're right it would work, but you really have to consider "papasmurf"s point. All it takes is for you to forget to hit that switch one time as you switch amps, and you'll have a dead amp. Furthermore, if its passive you'll have no LED to remind you which amp you left the switch on.

It sounds like a nice idea but im afraid it'll be worth doing it manually in the long run.

George

[PRR]

Amps can usually be switched with few precautions.



Amps must NOT be floating ground output. (1/4" jack is normally perfectly safe.)

Resistor shoud be speaker impedance and larger than the Watts of the largest amp. (If this leads you to 50 Watt resistors, note that many of these MUST be bolted to a Large heat-sink to actually survive 50W.)

With transistor amps, you could instead double the impedance and half the Watts. Indeed many tranny amps don't really need a load... or 100 ohms 20 Watts will cover quite large amps.

With tube amps, do not tease the switch! Flip it FAST! Preferably when NOT making any audible sound, certainly not when over-driving the power amp.

[Gus]

IIRC at Ampage in the 90's Steve Conner did some tests on higher value load resistors to keep tube amps stable.