I recently acquired my dream AMP, the Mesa Boogie Mark Five. I wanted to set up all of my song patches, effects, channel switching etc with the Helix via midi, and the 4 Cable method. Its been a few weeks of trial and error and lots of research and I finally have my dream rig sorted. I thought I'd share some of my key learnings here as it was hard to find everything I needed in one place. Here goes:
1. The helix won't enable effective channel switching via TRS cable as the Ext Amp settings only cater for Tip or Ring. The helix is lacking the third option and you can't assign these settings to snapshots, you can only use foot switches in stomp mode. This means you still need to tap dance like an old-fashioned pedal board. The SOLUTION is to acquire a midi interface for the Mesa MkV from EM Custom in Poland. It cost me 150 Euro and was delivered to Australia within 10 days. Take a midi cable out of the Helix, into the interface 'midi in' socket. Then run the standard Mesa foot switch cable out of the interface into the AMP. Download the midi interface manual from the EM Customs website, and use program control messages to control the AMP via midi. Just select your snapshot, goto the command centre, set an 'instant' command by simply calling up the corresponding program number to the setting you want from the interface manual. The black dot in the manual means 'on'.
2. I got a nasty Ground Loop the moment I plugged the channel switching cable into the amp. I got the same ground loop when I tried the 1/4 inch TRS cable as well. This resulted in a loud buzzing noise that was particularly loud in the higher gain channels. The SOLUTION is an EBTech Hum Eliminator that I purchased from bmusic for $150. I plugged the send 1 into the Hum Eliminator, then another cable out to the front of the amp, and followed the normal 4Cable method (amp fx send to helix return 1, 1/4 inch out to amp fx return). The Ground Loop buzz has completely vanished, the amp is quiet even in high gain mode at high volumes.
3. Noise gates, put one after the send/return block, and one at the the end of your effects chain. Tweak to suit. My highest gain channel is at -40.00db, 11ms
4. Ins /Outs, set ins outs as follows in global settings - 1/4 inch out "line", send/return "Instrument"
5. The amp's high gain channels respond really well to the Minotaur sitting in front with plenty of gain (7.4), tone (5), level (4).
Hope this helps any MesaHelixHeads out there.