Bluesbreaker ain't bluesbreaking

skrattadu

Member
I'm just built a Bluesbreaker and it's not working. Both the volume and drive pots are acting as passive volume controls, so there isn't any volume boost at all with the volume knob all the way up, it's the same volume as when it was being bypassed. I know Bluesbreakers don't give much of a volume boost anyway, but there's usually some volume increase (I've built more of them than I can count, which is why I'm so confused as to why this one won't work). Did all the normal stuff, reflowed solder joints, make sure nothing was shorting out, blah blah blah. Still, all I get is two knobs acting as volumes. Tone knob works and I can here the slight bass cut when I turn it on. I thought it might be an op-amp issue, but I had two TL072s at my disposal so I tried both of them and it didn't make a difference. Maybe the socket I used is bad. Also, I just moved and my multimeter seems to have run away so I can't measure anything until I stumble across a new one.
Any help would be greatly appreciated.
 
Here's some pics, wanted to upload with the post but my camera was dead at the time.
 

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The resistors (R10:1m R8:1k) below the opamp are reversed.

C1 calls for 10n..was this intentional?
Holy smokes, that might be it! I'll check and report back. I changed C1 to 68n to give it some more bass... I think it sounds much better that way, especially if you play single coils.
 
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Holy smokes, that might be it! I'll check and report back. I changed C1 to 68n to give it some more bass... I think it sounds much better that way, especially if you play single coils.
I figured it was a tone preference. I hope swapping those resistors doe the trick for you. ;)

The output difference (notwithstanding the counter-effects of R8) of R10 between 1k and 1m in the voltage divider is .9µV vs 818mv @ 100%. R8 is part of the LPF.
 
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Swapped resistors, no sound now. Something's probably shorting out somewhere or I fried something. Or the circuit board is cursed. The investigation continues!
 
I rarely find that I've fried something. It is almost always a short, and usually because I eyeballed the drilling of the in and out jacks and some part is touching the enclosure.
 
I rarely find that I've fried something. It is almost always a short, and usually because I eyeballed the drilling of the in and out jacks and some part is touching the enclosure.
I probably shorted something out on the back side of the PCB, there's no other reason I can think of why swapping two resistors would kill the sound, especially since it let sound through when the resistors were wrong...
 
A suggestion (for anyone who doesn't already do this)... when polulating a PCB or vero, orient all resistors left>right, or top>down. What I mean by that is for resistor bands, it's good form to have the color bands read from left-to-right, or from the top to the bottom (if oriented vertically) for easy identification. This will greatly help you (the builder) and us (the troubleshooters) when looking at a build and checking component values used. Same goes for for cap markings (except, of course, for electrolytics, which should be oriented based on required polarity.)

Please feel free to ignore. ;)
 
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