Re: effects loop cable length?
Some effects won't work if you just plug them in to the amp. Delays, flange etc. The only effects I would plug straight in are distortion/OD, and Wah pedals.
As far as cable length it will depend on the quality of the cable. I use a MArshall 900 which has an effects loop. I use George L cables exclusivley. My pedalboard as well as the connections to the amps and Loops are run using this cable. It comes in a couple of thickness. .155 & .225, the thinner cable is what is recommended to use on boards, the heavier to connect board to amps, and guitars to amps. What is really nice about this cable is it gives the best transfer of signal I have had experience with, and I have had no degradation in tone or sound quality regardless of length. I use about 20 foot to connect my board to my amp and it works fine. I have heard good things about Monster cables as well. I have one, but have only used it a few times so I can't say how well they will hold up. The George L cables do not require any solder. The ends just screw on, so if a cable does break you can just trim it and reconnect the end. This means you can make a cable any lenght you desire. Even though this is very convieniant, I have yet to have a cable fail on me and I have used these cables over 3 years now.