Digitech 2112/2120 Stereo Effects Loop Mod
the relevant
portion of my board (rev B by the way)
Mark Gibson on the 2120-users mailing list brought
up the idea of adding another FX loop to the 2120,
after the distortion stages. After
evaluating this idea and my 2120, it seems that it
is doable quite easily.
Findings
- A/D = CS5335KS
- stereo inputs, 2 dual OPs (LF353) for anti aliasing LP filters
- install backdoor before dual LP filters
- adding SPDIF input != rocket science :-)
Applications
- pan tube and dist to the extreme left and right
- use dual or stereo effects, or even parallel
paths to process 2 mono signals in stereo.
- morph between dual mono signals!
- use tube or SS dist on one channel and
process it in stereo, insert external mono signal
e.g. guitar synth on the other channel and
process it in stereo, and mix both in the output
mixer stage (wow!)
- create the pitch/arpeggio which I have been
missing since I sold my SPX90, by using
pitch/delay w/o feedback, and looping it into one
or both inserts. This may require an external
mixer or loop switcher.
Caveats
- no SW inside the 2120 to control the backdoor
- you have to use an use external switcher &
DPDT relay / 4053.
- use 1 more dual OP to set line level to -10
dB or +4 dB (A/D converter takes 2V RMS for full
scale)
Options
- we can build the Fx loop circuitry to allow for
a 50/50 mix of the dist and external signals like
the GSP2101.
- The Fx loop can also be located between the
distortions and the normal Fx return, after the
signal is split for the 2 distortion paths. This
would allow to apply some distortion to a guitar
synth or something. Actually, I prefer this idea in
the meantime.
- If we manage to find the right traces, I'll
make a small PCB (100x80 mm approx.) with 3 1/4"
TRS jacks (Fx send 2-channel out, Fx rcv 2-channel
in, 2 footswitches) and the -10/+4 dB level switch,
pretty straightforward. The good news is if someone
fails to appropriately cut the traces you can
simply re-solder the cut traces and forget about
it. I like to make reversible mods :-) The other
good news is that the traces are very likely to be
located on the component (i.e. upper) side of the
PCB, i.e. they are easily accessible.
Please note that such a modification voids
your warranty! You have been warned.
Harald Milz
Last modified: Mon May 13 22:48:15 CEST 2002