Mailist to discuss all issues regarding the Digitech GSP-2101 Guitar FX Processor

The question of how to configure a DigiTech GSP-2101 in the effects loop of a modern guitar amplifier or another signal processor is one that gets asked every few months or so on this forum.  I've recently been using my 2101 with a Randall RM4.  The RM4 can accommodate up to 4 MTS pre-amp modules and has some features that make it a good companion for the 2101.  Although I use the RM4 as the companion here, the principles can be applied to any other piece of equipment being used in tandem with the 2101.

Whenever your analog guitar signal is fed through the 2101's digital effects section, it has to go though a couple of transformations; an Analog/Digital (A/D) converter prepares your guitar signal at the front end for the digital effects and, at the back end, a D/A converter translates the 2101's output back to an analog signal ready for your power amp.  Unfortunately, these transformations can relieve your guitar's tone of some of its warmth.

On the back of the RM4 is a pair of Parallel Loop connectors, a Send and a Return, and on the front is an Effects Control.  These features split your guitar signal into two parallel paths, allowing part of your guitar signal to pass directly to the RM4's Post Loop Output and the other part to be sent through the 2101's digital effects section.  Fortunately, the part that bypasses the 2101 does not suffer from A/D and D/A degradation.

You plug your guitar into the RM4's Input jack.  Use one jack-to-jack patch cord to connect the RM4's Parallel Loop Send to the 2101's FX Return Left / Mono.  Use a second patch cord to connect the 2101's Output Left / Mono to the RM4's Parallel Loop Return.  Connect the RM4's Post Loop output(s) to your power amp.  You use the RM4's Effects Control to balance the unprocessed guitar signal with the 2101's digital effects.

IMPORTANT: You must use the following settings in each of your 2101's programs or you'll wonder why the effects are not showing up back in your RM4.
(1) The 2101's External FX Loop must be set to "No Sum"
(2) The Stereo Noise Gate (immediately after the External FX Loop) must be set to "Bypass"
(3) The Wet to Dry Mixer (at the end of the digital section) should be set to "100% Wet"

I found the RM4's signal strength at its Parallel Loop Send is weak so I had to rotate the 2101's front-panel Output volume knob to maximum.

Finally, the above configuration bypasses the 2101's up-front analog section (its compressor, distortion, graphic EQ, and master volume) which is what you want if you prefer your amp's distortion over the 2101's distortion.  If you prefer to include the 2101's analog section in your signal path the first patch cord should be connected to the 2101's Input jack, its External FX Loop must be set to "Bypass" and the Stereo Noise Gate should probably be set to "On".

I hope some of you find this stuff helpful.  It was an interesting refresher course for me.  Let me know if any detail needs clarifying.