Hi-
Just finished building a VFE Blues King.
The Switching Board is working fine (9.03 volts to effect board, bypass on and off fine, LED lights up with Effect on).
The Effect itself sounds very "splatty" and not much gain and volume not consistent.
I checked the voltages at the IC's and they are quite different on a couple pins each compared to reference voltages in build document (see below). Any thoughts on why Pin 3 would be so low on both ? I'm guessing that per the schematic Pin 3 of IC2.1 is fed by pin 1 of IC1.1 so the issue is upstream of IC2.1. Any other reference voltages I can check ? I'm kind of knew to troubleshooting using the schematic. Thanks for any suggestions.
IC 1.2 IC2.1 build doc
Pin 1 8.4v 4.6 4.55
Pin 2 8.4 4.6 4.55
Pin 3 0.8 2.3 4.14
Pin 4 0.0 0.0 0.0
Pin 5 4.5 4.5 4.44
Pin 6 4.5 7.1 4.44
Pin 7 4.5 4.5 4.44
Pin 8 9.1 9.1 8.88
Pin3 is almost at ground which is why pin2 and 1 has swung up nearly to the rail. That's your problem area. I think we'll need a nice clear pic of your build to review your component values and wiring to make sure nothing has gone wrong there.
Also, try removing both the 4580 ICs and measure that pin3 again in the bare socket and report your result.
OK thanks for the quick reply ... you guys are great ... I'll take some more measurements and take some photos and post tomorrow. :)
Ok here are voltages with the 2 chips pulled :
IC 1.2 IC2.1 build doc
Pin 1 0.0v 0.0 4.55
Pin 2 0.0 0.0 4.55
Pin 3 0.0 2.3 4.14
Pin 4 0.0 0.0 0.0
Pin 5 4.5 4.6 4.44
Pin 6 0.0 3.5 4.44
Pin 7 0.0 4.3 4.44
Pin 8 9.2 9.1 8.88
I double checked all the component values and they look correct ... I checked most of them with a Peak passive component analyzer before solderingg them ... I'm pretty anal about that too make sure nothing is way out of tolerance.
I also bent back the bigger pots a little and don't see anything funky under the chip sockets. I reflowed a couple of other joints that looked not great thru my magnifying glass. I really struggled with this board for some reason because the gromments are so small .... I've done hand work on SMD's before but still struggled with this one for some reason.
No change in output yet. Photos to follow.
Even with the ICs removed you should have some voltage on pin3 of IC1.1 because there is a resistance connected to VREF. This is pretty weird. It could be a bad IMPED trimmer or even a bad socket (rare, but it can happen).
I'll wait for the pic though.
Here is a picture of top of board.
Hard to get a clean shot at bottom with all the pots ... I bent them up as much I could and took a few side shots but not sure they help. The blob of solder at the front edge of the board is to jumper two of the 1N34's together ... one of the grommet pads pulled out somehow when I was tweaking it and since they are tied together anyway it was easiest just to run the lead over to the other pad ...
More pics
Last Pic
Brian-
Solved I think ... based on your comments I went back and looked at the trimmer ... the wiper connection looked questionable so I cleaned it up and reflowed. I'm getting 4.09 volts at pin 3 of the IC1.1 with the trimmer all the way down and the pedal works ! Still a little low at Pin 3 of IC 2 compared to build document (I'm closer to 3 v) but the pedal sounds good and plenty of gain.
Thanks for your coaching on what was giving me funny chip voltages !
Bob
Thanks for all the help. Couldn't be happier with the sound of this ... I'm more of an overdrive guy than a distortion or fuzz guy so this is great. Love the pots for blending the soft and clean clipping compared to selctor switches on most pedals with alternate clipping choices. Here is the finished pedal :
Looks great! And, good on you for sticking it out and solving the bugs :)