Ground resistor on AB box

[Outlaws]

I built an A/B box a while ago, but for fun I took a peek at this schematic of a DOD box.  http://www.generalguitargadgets.com/diagrams/ab-dod.gif

What purpose does the 51ohm resistor serve?

[Alex C]

This design grounds (essentially) the currently unused output depending on the switch state.  I would guess that the 51 ohm resistor serves to "soften" this transition so that the input of whatever follows the AB box does not experience a sudden direct connection to ground when switching away from that signal chain.  That's just my guess though, I'm wondering along with you.

[Leston Braun]

Almost with the topic here, but I'm building an A/B switch for my brother to be used with a Vox AC30. The amp has two independent preamps driving one power amp, and the idea is to use the amp channels as clean and crunch. To me it would make much sense that the unused channel input is grounded. That's easily achieved with 3PDT switch, but will that produce hum and other problems, as the ground between the 2 cables going to the amp are connected at each end, thus creating quite large loop?

Other option is to leave the unused input non-grounded, but will that be even worse?

And back to the topic, could this resistor have something to do with the subject? It's like a volume pot turned down for the another channel when the other is used, but still isolates the grounds, so a ground loop doesn't exist?