Yes, a mixer allows you to loop "everything" on one Echoplex.
While I haven't seen Keller perform, I suspect that the button he was pressing on his mixer channel right after the loop was the channel mute button. If all of your channels are open (guitar, bass, vocals) all the time, whenever you press record or overdub, you'll capture the input of all three channels, which is often undesirable (guitar bleed into vocal mics, overall noise floor three times louder than necessary, etc.).
By keeping all the mixer channels feeding the looper muted EXCEPT when you're actively recording/overdubbing, you produce much cleaner loops. So, you'd unmute the guitar channel, hit record/overdub, play your part, end the record/overdub, mute the guitar channel, and so on.
On Wed, Sep 10, 2008 at 8:07 PM, Todd Chambeau <email@example.com>
I wish to loop live an acoustic guitar, bass, vocals and mandolin. Keller had a 16 track mixer with 3 echoplex's in his rack, all synched together.
His roadie told me he has 3 units because he needs 3 footpedals on different parts of the stage where his various instruments are setup.
1. If I purchase a 16 track mixer, will I be able to loop everything (guitar,bass, vocals) with my one Echoplex unit (without having to plug and unplug each instrument and mike during performance)?
2. I noticed Keller would play a part on an instrument, then press a button on one of his mixer channels right after the loop. What do you think he was doing?