Smeggy,
I use the same jack on my Dynalo, which is set up to also be a preamp, with the pre-outs wired off the switched jack. I have a modified e12 on it, with a muting switch, but of course this disables all outputs. When I tried it as a pre and listened to phones, I was also getting very quiet sound from the speakers (power amp stays on all the time). I haven't figured out why it is bleeding thru but it is. All three contacts do switch, so