Well, I just wrote a long post and lost it. Ugh. Here we go again.
I've never been able to get a really usable tone from my old big-box Q-tron+ and last night I cracked it open to have a look inside. Nothing noticeably wrong, for better or worse. While I was in there I poked around a bit and ended up modding the red LED light that's always on to just come on when the pedal is engaged, but no fix for the muddy tone.
Then I woke up to a thought this morning...the TRIMPOT! While I was in there I noticed a little trimpot about dead center of the board. What if the guy before me had messed with it and screwed up the envelope somehow? This morning I put the theory to the test as follows:
1) I put the settings in Jerry territory (cribbed from a pic Waldo posted in another thread):
2) Flipped it over, removed the back cover to reveal the backside of the circuit board:
3) Zeroed in on the trimpot, little white arrow in pic below:
4) I took a tiny screwdriver and started dialing the pot back...it was at about 2 o'clock when I started, currently at about 8:30 or so. EDIT: if picture is posting sideways, imagine a turn counterclockwise so arrow tip is at 8:30
I still don't have it dialed in but I think this is the whole problem I've had. Dialing back the pot reduces bass mud and allows the envelope to open at higher frequencies so you can play past the 12th fret. A little turn goes a long way and it's very sensitive, but I'm getting close to something usable, finally! Clip below has two sections, one at 5-8th frets and second at 12-15th frets, both with a little clean tone to establish a baseline.https://soundcloud.com/lunasparks/2013-06-28-qtron-test1
I exchanged some PMs with Waldo this morning and he thinks this may be the fix for issues a lot of people have with this unit and the original big-box Qtron. In any event, hopefully it helps someone else!