Hi All,
I just recently started building guitar pedals and have been doing pretty well so far. I built an MXR Blue Box (
http://johnkvintageguitars.homestead.com/Effects/Fuzz-ODs/BlueBox/MXR_BlueBox-Final-Verified.png) and Mad Professor Snow White Auto Wah (
http://tagboardeffects.blogspot.ca/2013/04/mad-professor-snow-white-autowah.html) as my first pedals, and they worked great the first time around. Unfortunately I've been having a lot of trouble with my third pedal, the DBA Robot.
I'm using the rotary knob layout from here:
http://johnkvintageguitars.homestead.com/Effects/Fuzz-ODs/DBA/01-DBA_ROBOT_VERO.png and have added a momentary switch to ground to toggle on and off vibrato (based on the spec sheet for the HT8950 I was pretty sure this should work).
Anyway, I've attached the pedal to all the controls and plugged it in. The LED works, the bypass works, but the actual effect is very very very quiet. Unless I set the gain at maximum I can't hear anything. When I turn the volume knob I get some sound at around the half way position, but then turning it further in either direction makes the pedal get quieter again. I can hear the effect doing some pitch shifting and fuzz, and my momentary switch toggles the vibrato on/off as expected, but the loudest I can get the effect is about 1/5th of the bypassed guitar volume. The rotary switch seems to go through different sounds as expected.
I have been over the board layout about four times now, and am pretty certain all the components and connecting wires are in the correct location. I've tried swapping out the HT8950 with a spare, with the same results. I've measured the values of all resistors on the board and they check out as well. I've measured the values of the pots, and they check out, and sweep as expected. I re-heated each solder joint on the board to try to rule out bad solder joints.
I put one probe on ground and measured the following values on the legs of the TL072:
3.27 3.82
3.27 3.26
0 2.29
0 0
And these values on the legs of the HT8950:
3.55 3.56
0 3.55
3.55 3.55
0 3.55
1.37 1.3
1.37 1.35
3.8 1.25
0.01 3.8
3.70 1.35
Anybody have something I should try next? I'm kinda out of ideas at this point. Sorry for the long post!
Crappy pics of the board (sorry I've only got a crappy camera):
http://www.flickr.com/photos/52081428@N03/11208746166/http://www.flickr.com/photos/52081428@N03/11208823585/http://www.flickr.com/photos/52081428@N03/11208845836/
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