Soundcraft 400B Balanced Line Input Mod

Help Support GroupDIY:


Well-known member
Jan 10, 2005
Since I'm stuck inside and bored I decided to upgrade my Soundcraft 400B line inputs.  I love the sound of this board (especially after my extensive upgrades) but never liked the line inputs.  It uses a pad at the line in jacks and then into the mic pre.  I purchased 24 DIYRE 124x balanced line input pcb's from OSH park, and new 4PDT switches.  Its a relatively simple mod but is a bit time consuming to implement due to the wiring.  The 1243 is pretty efficient and I've already upgraded the power supply.  I remove the pad, replace the DPDT line switch with the 4PDT.  The mic/line switch (no metal work required) now switches the line in to the THAT 1243 and injects it back in at R12.  Mic pre works exactly as it did before.  The only down side is not having a line trim.  I considered adding that but it would be a more involved modification and the benefit was not worth the extra work/cost for me.  When a +4dBu signal is input, the level with channel fader at unity is only 0.5dB down.  This can be made up with the channel fader.  Now I can run my converter outs into the console for analog summing and still have the full use of the channel EQ.  I already modified my summing amps to my custom discrete opamps with Jensen output transformers (I may try Jensen 990's soon).  The photo attached is my first one done.  I'll see if I can refine the mod to be neater for the rest of them.  So far its good.  I'll update as I do some console checks.

P.S. the picture shows a 1240 installed.  All channels will be a 1243 instead. The 1243 was a better choice as it was within 0.5dB of the designed console gain structure.



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