Cabinet with DPDT switch to switch speakers?

itsGiusto

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I have a 2x12 cabinet. I want to use only one speaker at a time in it, but switch between them sometimes. Would it be safe to attach the speakers to the input jack by means of a DPDT switch? I assume it would be fine, but would I have to turn off the amp or put it into standby before flipping the switch?
 

Nicko_Lps

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would I have to turn off the amp or put it into standby before flipping the switch?
We all know operating a tube amp without a speaker cause catastrophic failure but in your case it will be like.. 0.5 seconds?
I dont think there is a problem but be sure your switch can carry your amplifiers current
 

printer2

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Yes 0.5 seconds (probably 0.05s though) could damage the amp. That is if you have a signal going through the amp. If you just have it idling and only a little hiss going to the speaker (or if you turn down the volume control so there is no sound, more or less) then switching the speaker will not hurt the amp. This does assume the amp does not mind taking a load that is half (double the ohms if they are the same) say a 16 ohm load as compared to 8 ohms.

You have to keep in mind the speaker that is being driven will be pushing air to the back also and some of this will move the non-working speaker around a bit. So it will not sound like just one speaker in a separate cabinet. But otherwise it is safe to do.
 

Paul G.

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I wouldn't risk it. You might get lucky the first 20 times, but the odds of doing damage are there every single time you flip. Probably not a big risk, but a risk is a risk.
 

wabashslim

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I put a on-on-on switch in my Plexi 6V6 with 2 speaker jacks to get either-or-both and I switch them all the time, sometimes in mid-chord for instant comparison. Been a couple years now and never had a problem. Transformers aren't that fragile, especially at bedroom volume or a bit above.

Now I do worry a little about the switch, since the only on-on-on's I've been able to find are minis. Rated 15 amps, but still...
 

printer2

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I wouldn't risk it. You might get lucky the first 20 times, but the odds of doing damage are there every single time you flip. Probably not a big risk, but a risk is a risk.
No, if there is no current flowing then there is no current to interrupt. And what damages the windings is magnetic flux in the core ending up with no where to go. If a significant current is flowing and the output winding goes open the magnetic flux in the core is converted into a voltage and that voltage can spike high enough to break through the varnish insulation on the wire. Then this causes a short and current at this point heats up the area and starts to melt more varnish. Things go bad from here.
 

RodeoTex

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IMG_20220522_123523079.jpg

I did this one a few years ago with a pair of mis-matched Weber 10s.
No problem as long as the amp is meant to handle the different impedances.
 

schmee

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You can do the speaker change with a switch. Or just have a jack for each speaker.
I have switched many times with the amp on..... as everyone says, the safest is to not do it. But I have never had an issue. Like mentioned, it's a split second. I have accidentally left an amp on for 10 minutes with no speaker connceted and didn't have an issue.. that was pretty lucky I think though.
When A/B ing speakers I often use an A/B switch to test them back and forth. That way you really get the subtleties.
 

KeithDavies 100

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Apologies if this hijacks the thread slightly, but would this idea give me a solution to my problem? I have a Fender heads that want 4 ohms, and Vox that want 16. Is it possible to rig a switch so that two 8 ohm speakers are in series one way - giving 16 ohms, but in parallel the other way, giving 4 ohms? I've now got about three different cabs!
 

schmee

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Apologies if this hijacks the thread slightly, but would this idea give me a solution to my problem? I have a Fender heads that want 4 ohms, and Vox that want 16. Is it possible to rig a switch so that two 8 ohm speakers are in series one way - giving 16 ohms, but in parallel the other way, giving 4 ohms? I've now got about three different cabs!
Yes. Using two jacks, NEVER PLUG INTO MORE THAN ONE.
8and16ohms.jpg
I'll see if I can find it with regular jacks...
 
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printer2

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You can do the speaker change with a switch. Or just have a jack for each speaker.
I have switched many times with the amp on..... as everyone says, the safest is to not do it. But I have never had an issue. Like mentioned, it's a split second. I have accidentally left an amp on for 10 minutes with no speaker connceted and didn't have an issue.. that was pretty lucky I think though.
When A/B ing speakers I often use an A/B switch to test them back and forth. That way you really get the subtleties.
A split second is an eternity electrically speaking. How long does it take to rise to the crest of a half wavelength of 5 kHz (picked it as many speakers roll off in the neighborhood)?

0.00005 seconds

Apologies if this hijacks the thread slightly, but would this idea give me a solution to my problem? I have a Fender heads that want 4 ohms, and Vox that want 16. Is it possible to rig a switch so that two 8 ohm speakers are in series one way - giving 16 ohms, but in parallel the other way, giving 4 ohms? I've now got about three different cabs!
It took a minute to draw it out and realize, this won't work. Might take a little longer than I thought. Took another shot at it and it and it was obvious.

Lu3Gv4p.png
 

itsGiusto

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You can do the speaker change with a switch. Or just have a jack for each speaker.
I have switched many times with the amp on..... as everyone says, the safest is to not do it. But I have never had an issue. Like mentioned, it's a split second. I have accidentally left an amp on for 10 minutes with no speaker connceted and didn't have an issue.. that was pretty lucky I think though.
When A/B ing speakers I often use an A/B switch to test them back and forth. That way you really get the subtleties.
Yeah, I've had my 72 Princeton Reverb on for like an hour or more while I was debugging it to find out why it wasn't making any sound. Turned out it was super easy and I just missed it - the wire going to the speaker came disconnected. But the amp still seems to work fine now, despite being run without a load for over an hour.
 




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