Use with a single speaker (e.g., monaural)

[Dr. Toobz]

A simple question (which I think I know the answer to, but I'll ask anyway): Is is possible to use the S.E.X. 2.0 (updated to 2.1 standards) with a stereo input, yet a single, summed speaker output, without interrupting the ability to use stereo headphones?

Once rebuilt, I plan to stick the S.E.X. amp in a 60's modern, sort of "console cabinet" for use in a small bedroom. The cabinet has two sliding doors. One side will house the amp, the other side would house a vintage box speaker, or something I put together with a large single driver speaker. (One door will have an opening underneath the doth to let sound pass through). Since I am looking to use this as a single-point sound source, such as for listening to radio shows, yet want to have the option to plug in headphones when wanting to do more serious listening, my thinking is that I could wire the outputs in series for a single speaker (using the 4-ohm taps to get 8 ohms total). Since the headphone jack shorts the speakers before the output posts, I shouldn't run into any problems with headphone use, correct? I do wonder if cancelation between two channels summed to one speaker would be an issue, but then again, this arrangement would be intended for mostly radio use anyway, not listening-room fidelity. (Again, that's what I would plug the headphones in for). Will this work?

[Paul Joppa]

Sorry, but the problem is that both channels use the same ground on the headphone jack, which prevents placing them in series. You will have to add a switch to put the outputs in series for a speaker.

[Paul Birkeland]

The tough part about doing this will be dealing with the grounds, as the headphone output relies on both output transformer secondaries being grounded, while the speaker connection you are interested in will lift the ground on one secondary in order to series wire them.

IMO, I would just parallel the secondaries to get your mono output.  Other than ensuring that you have the headphone jack wire as a SEX 2.1 instead of the 2.0, you would just wire both speaker outputs to the same speaker. 

[Dr. Toobz]

If wiring the secondaries in parallel at the speaker vs. in series, what will be the outcome in terms of power and impedance? My understanding was that with a single 8 ohm speaker, the 4-ohm secondaries could be wired in series for a total of 4W out at 8 ohms. What happens when each secondary sees the same load, however?

The amp is currently in pieces right now, but when rewired, I am indeed going to use the 2.1 headphone jack wiring. I understand this to be the same Neutrik jack, wired to short the speakers, without the previous 120 ohm resistors on each leg. With the combination of the 4 ohm taps and my 300 ohm HD650's, the self noise of the amp shouldn't be a problem, so I am leaving the resistors out this time around. They really make no difference with the Senns, per past experience.