I've get a Phaez amp that has 2 individual inputs, one for each channel. I decided instead of using an AB box that I'd install a switching circuit to route a single input to either channel. Originally the amp had each channel's preamp tube connected to its own input jack. I got a Granger optoFET channel select board: http://grangeramp.com/shop/index.php?main_page=popup_image&pID=493 I powered it off a wall-wart and hooked it up like this (all connections via coax): 1 NC - ground 1 Com - clean channel 12AX7 cathode 1 NO and 2 NC - input jack 2 Com - dirty channel 12AX7 cathode 2 NO - ground My only problem is that I hear a slight pop when switching from the clean to dirty channel. I've read that FET based channel select circuits should have quiet switching. Is there a pull-down resistor or something that I'm missing that could be causing the pops?