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Run a single-ended stereo tube amp to a mono speaker?

lattiboy

lattiboy

Well-Known Member
Hi all,

I have an great little APPJ EL34 tube amp, but it doesn't have a set of speakers for me to use with it at the moment.

I also have a DIY Alpair 12p-based center channel speaker that is quite sensitive and sounds incredible. I think the APPJ would absolutely sing with this speaker. It's a single speaker cabinet, so the binding posts are just connected directly to the 12p.

So, what I'd like to do is feed the amp with a DAC from my PC in the office and power this single speaker as mono. I can easily send the same signal to both inputs using Windows, but how would I wire it?

Will I blow up the amp? Is there a way to do this without opening up the amp and re-wiring?

Thanks!
 
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What you never want to do is drive an unloaded tube amp into clipping. The rapid turn-off results in a "kickback" voltage that's extremely high, which can arc over tube sockets, fry the output transformer, etc.

If you connect an input to only one channel and speaker to the same channel, all is well. If you feed it a stereo signal (or get channels crossed) there is some risk (someone feeds it max volume with one channel unloaded). You could add a resistor across the unused channel (8 Ohm 10W, say) and risk is gone. In some cases, you can parallel outputs and get 2X power at half the impedance (two 8 Ohm outputs driving a 4 Ohm speaker)
 
Tom Bavis said:
What you never want to do is drive an unloaded tube amp into clipping. The rapid turn-off results in a "kickback" voltage that's extremely high, which can arc over tube sockets, fry the output transformer, etc.

If you connect an input to only one channel and speaker to the same channel, all is well. If you feed it a stereo signal (or get channels crossed) there is some risk (someone feeds it max volume with one channel unloaded). You could add a resistor across the unused channel (8 Ohm 10W, say) and risk is gone. In some cases, you can parallel outputs and get 2X power at half the impedance (two 8 Ohm outputs driving a 4 Ohm speaker)
Click to expand...

Thank you! That's was my main concern, and I will try it with only one speaker being fed by only one input.

The Alpair 12p is an 8ohm speaker, so I'm guessing no-go on the double power situation?
 
I am by no means an authority, but I'd put a shorting plug in the unused input and a dummy load on the unused output.
 
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