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Non ADA Gear => Rack Gear => Topic started by: Chip Roberts on January 11, 2018, 12:26:56 PM

Title: Digitech GSP21 Legend
Post by: Chip Roberts on January 11, 2018, 12:26:56 PM
Just picked up one of these guys for dirt cheap $30 USD the other day to use as a backup rig.  This thing is pretty insane in terms of the parameters, too much, in fact.  My question to you guys is, how would you recommend setting this up?  Currently I have the MP1 going out in mono to the input of the GSP21, then into power amp; real simple setup.  The problem I'm having is that my MP1 is either overloading the Digitech, or there's an imbalance between the volume when bypassed vs. on.
Title: Re: Digitech GSP21 Legend
Post by: rnolan on January 11, 2018, 01:31:29 PM
I don't know much about the GSP21 except for a quick glance at the manual.  Seems it's a mono in, stereo out device so the best way to use it would be with a small stereo mixer and feed it from one FX/Aux send and bring the stereo returns into 2 channels panned hard left/right (and the MP1 A/B outs into 2 channels sending both to the GSP21 on the FX/aux send), mix that together (GSP full wet) and then into stereo power amp into 2 cabs.
Alternately you could use it in the MP-1 loop but it would be mono and you'd have to balance the wet/dry mix via the GSP's wet/dry mix knob. This would be mono and not sound as good as using a mixer.  If you are not running your MP-1 in stereo then you are seriously missing out on it's full potential. Also the reverb etc fx in the GSP will sound much better in stereo.
The overloading is most probably because you haven't got the gain structure (GSP input output levels right).  It will probably be capable of taking a line level signal (around 1 volt) or an instrument level (millivolts) signal on its input.  MP-1 out is line level, the MP-1 loop can be adjusted from instrument level to line level and then fine tuned with the GSP input and output levels.
Title: Re: Digitech GSP21 Legend
Post by: Chip Roberts on January 15, 2018, 03:36:07 PM
I guess a better question would be how do you set your levels?
Title: Re: Digitech GSP21 Legend
Post by: rnolan on January 16, 2018, 10:36:03 AM
The idea with the MP-1 loop is to keep it at unity gain, what goes in volts wise is what come out volts wise (albeit augmented sonically by whatever is in the loop).  You don't want to add or take away level but also the device in the loop needs to be driven with a good amount of signal (so you don't add noise).  So set the GS21 input about half way, turn the MP-1 loop knob so you get good signal but not clipping (red) on the GSP probably have the MP-1 loop knob about the middle  :dunno: , turn the GSP input up or down until you get good input signal, then adjust the GSP output so there is no volume difference when the loop is on or off.
It's trial and error until you get it right and remember as you increase the MP-1 loop send, you are turning down it's return (dual ganged opposing pot) and visa versa.
You also have to remember that the send level is affected by how "hot" the patch is, so set the loop and GSP input output levels using your loudest patch.  If the GSP input leds have the occasional red flicker that's ok on you hotest/loudest patch, the GSP will have a little headroom above what the clip light is set to activate at.
Title: Re: Digitech GSP21 Legend
Post by: Soloist on January 16, 2018, 12:59:51 PM
The problems with running the gsp thru the mp1 loop are:
1. the mp1 loop is awful.
2. Your running a preamp thru a preamp. Unlike a combo or a head where as they bypass the preamp section only using the power section.
The best answer is using a mixer, then you can A/B between the two, or mix them together. You can get a rack line mixer fairly cheap.