Updating the Electric Mistress - No Send / Receive Loop Mod

Last week I posted an entry detailing my EHX Electric Mistress build based on the PCB Guitar Mania Electric Lover PCB. Overall I was pretty happy with the build, but I had noticed something a little unusual when I began the calibration process. In my first entry I mentioned having to crank the bias trimmer quite a bit to get a good tone (or any tone at all for that matter). On the PCB Guitar Mania Facebook group, another user posted that he was having a similar issue with his build, although his was apparently bad enough to where he couldn't get a reasonable calibration. Fortunately the long-time board users had a fix for him, and since I'd had a similar issue in my base-build, I decided to take a deep breath, pull the PCB out of the enclosure and try the fix on mine as well. 

The issue has to do with the optional Send / Return loop on the PCB. This is an optional inclusion so that you can add an extra effects loop that feeds back directly into the pedal. For many PCBs from many manufacturers, optional components are typically left out and the PCB is designed to work around it. In other cases a jumper or other work around is needed to make the board work normally. Apparently the latter is the case for this particular build. 

The feedback on the forum to the original poster having the issue was that they should run a jumper across the send / receive loop. This would ensure that all of the incoming audio signal was fed to the pedal as a whole as opposed to losing a portion of it in the disconnected effects loop. It was also suggested that R10 (normally an 82K resistor) be replaced with a 1K resistor or a jumper as well. So, I did just that. 

I had a lot of mixed emotions about pulling a nominally functional pedal out of the enclosure (as I have to disconnect the 9V plug) and making modifications. It's sort of the first rule of engineering - "does it work" and "did you mess with it" questions in the flow chart above. That being said, I was concerned that because I was pegged on the bias trimmer, I'd eventually encounter issues on this pedal - so it would fall under the "sorta" broke category in my mind. Getting the pedal out of the enclosure was straightforward as was adding the jumper to the send / return loop. I have some actual component jumpers I use (one black line) largely because I like the look of them. Snipping out the 82K resistor R10 was a little more troublesome because the capacitor I had to use for C23 was larger than normally specified because of what was available when I made my Mouser order.

Fortunately my de-soldering technique has improved and I was able to get all of the solder sucked out of the PCB around R10 - and I was able to do the same with the 9V DC plug. It was fairly straightforward adding the jumper (tan with one black stripe in the upper right) and the 1K resistor (next to the bias pot center bottom underneath the angled capacitor). Then it was a matter of re-running the full calibration. I immediately noticed that I had full functionality on the bias trimmer. I had sound at all levels and flanging once I dialed it in as per the normal calibration instructions in the PCB documentation. It took a little more work (as I had more actual knobs) but I managed to perform a full calibration and the pedal sounds excellent. It may be a bit better than before, and I now know if I run into any calibration issues down the road I actually have room to adjust it.