At about ~£70, Behringer's 1002B is great value - 5 mic inputs, two with inserts, a pre- and post-fade pair of aux channels and actual real faders, not just pots. Build quality is classic Behringer - scratchy faders and way-too-bright-"signature" power LED are the order of the day here. I've done small gigs on it, and use it for bedroom mixing - very happy overall.
However, it has a fairly annoying flaw - the headphone output comes after the master fader, meaning you can't check anything in the phones without it coming out of FOH. After several hours of reverse engineering the circuit, I finally worked out how to mod it so the headphone amp's signal came before the master fader.
I had some assistance from a schematic of a similar desk, which I found online. The website doesn't look terribly legit - you've been warned:
Between the vaguely right schematic, a magnifying glass and a multimeter I mapped out which opamp was which (NB: These are LM4560s - not exactly amazing) and how the tracks ran between them (shown in white below).
The actual mod ended up quite simple - cut the two input legs of the headphone pot (breaking their connection to the mix output buffer, marked Mout above) and solder link wires to the outputs of the mix input buffer, marked Min above.
You can just about make out the two legs of the pot cut above - this was the easiest place to cut the signal path, and makes it quite easy to reverse, should I need to.
Some spare bits of SC-stage 22 served as link wires, as that was the nearest wire I had to hand. I doubt audio quality would suffer from just using some 7/0.2 though...
The final step was soldering the other end of the link wires in - I put them after the capacitor, as that seemed the way everything else was hooked up, and was easy to solder to. From what I can tell, it's just blocking DC, but I'm willing to offer point to anyone who can explain further.
With that, I fired up the desk, bareboard style, and checked everything worked - it did! There may be slightly less gain available of the headphones now, but it didn't seem to be enough to cause a problem - I might consider altering the feedback network as part of a future mod, but that's a lot more involved.
Space at the bottom of the mixer is actually very generous - a good 15mm or more, which is enough space for a whole nother PCB/veroboard. Future mods want to put in this space include:
- Adding PFL/AFL switches to the all the channels - I now have a place to solder in a PFL bus, so half the legwork's already done
- LED meters for each channel - a meter circuit is actually quite simple, and just requires a few comparators
- Integrated, low noise mains PSU (pipe dream...)
- Integrated USB sound card, possibly of my own design
I'd also like to upgrade the faders and opamps, but that will start to get expensive quite quickly - it would seem silly to spend Allen & Heath money upgrading a Behringer!