Boss GP-20 Amp Factory COSM modeler - bypass /variation switching mod

[sonic66]

This switching mod for the Boss GP-20 Amp Factory, allows the use of the 'bypass pedal switch' to switch the variation mode in or out.

This was inspired by  http://www.lynx.bc.ca/~jc/KenHammConcertDI.html however retains normal bypass mode

this allows now 4 easily available tones rather than two.....


First cut the traces at the from the bypass switch , then connect leads from the ends of the cut traces and the switch pins in pairs to a DPDT switch ,

then connect the pins from the variation switch.... wire them up as per  usual for effect in / out when doing bypass on a stomp box , the normal mode is now switchable with

the mod ...  Easy..... thought it took me longer than expected  ......  but so far every project i've attempted has anyway i.... 'm still noob to electronics.


When using the gp-20 in front of a tube P.A  with eminence beta 12's in a twin reverb style cab i find its really quite good sounding.... ,

( switch the noise gate  off  though as it is noisy and doesn't help the sound )



This worked for me ....please take all the usual precautions when working with this kind of equipment ..... static , heat etc ...but since , but should be ok as the work is on the

control board not the DSP part ...


Cheers


Sonic66



P.S   Does anyone know if the cosm in this pedal is similar to the two new boss / fender pedals








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[sonic66]

Hold on out there if your going to try this ........!

i seem to have knocked out the bass , treble , and presence controls somehow !!

the gain , master and mid  + all the others work ok  ?

so i'm going to undo the mod and see what happens......

wish me luck ......



Ok  disconnected the leads from the cut traces ......  ( thats the


and the controls work again  just as normal !!!!  will give it another go  now so hang on ....

[sonic66]

Ok .... swapped the leads  black for brown ( just the colors i happened to use ) on the pins just next to the connector to the main board


All working ! so  can anyone suggest why ? besides any shonky work on my behalf


funny when the controls were not working properly ... turning the mid down made everything muffled ... but turning it up made everything  brighter too,

more than you'd expect from a 'mid' control ..... almost as if all the bands were going through the one control?  ... was kind of not bad ... quite thick sounding

not very versitile ......


if you do this mod you can check  as in memory mode if you turn a pot the whole way ... the memory light should flash


all done . so can any one suggest some sort of other mod ... mid boost foot switchable comes to mind ... but the variation switch can do that for some

amp models anyway...


cheers


Sonic66