Hi Mike,
I’m wondering something about the addition of a preamp output to the WA6-SE, that you may want to ask Woo about. If instead of using my approach no. 4 you were to use that output of the WA6-SE, connecting it to the input of the power amp section of your LM integrated amp, you would of course be using the WA6-SE’s volume control to control the volume when listening via speakers. So in order to silence the headphones when listening via speakers, and possibly also to prevent overdriving the headphones when listening via speakers, I presume you would have to unplug the headphones from the WA6-SE. Which creates two possible causes for concern:
1)1/4 inch headphone jacks are not exactly the most robust connectors in my experience, and I would have some concern that eventually frequent plugging and unplugging would loosen the grip of their contacts.
2)As you may be aware, tube amps having output transformers, or at least such amps that are used to power speakers, should not be operated without a speaker or equivalent load connected, particularly when a signal is going through the amp. Otherwise damage to both the output transformer and the output tubes can occur, as a result of what is called "inductive kickback." I’m wondering if the same thing could occur with the WA6-SE when it is operated with a signal going through it but without the headphones being plugged in, since the WA6-SE utilizes an output transformer to drive the headphone jacks. Perhaps it isn’t a concern in this case because of the much lower power capability of the WA6-SE compared to most tube amps that are intended to drive speakers, or because of the relatively high impedances the WA6-SE is designed to drive, but I’m uncertain. And perhaps it isn’t entirely coincidental that nearly all of the headphone amps described at the Woo site as providing pre-outs in their standard configurations are the OTL models, which of course do not have output transformers.
With approach no. 4, of course, those issues would be avoided since the headphone amp could be turned off whenever you aren’t listening via the headphones.
As I say, you may want to present those questions to Woo, before deciding to spend the extra money to have the pre-outs added.
Regards,
-- Al
