BJFE BBBOD - Weak output signal and tone knob grounding

BuddyPrince · Post by **BuddyPrince** » 17 Dec 2017, 16:29

I've been working on this BJFE Blueberry Bass OD - viewtopic.php?f=7&t=25767.

BJFE Original Schematic.png

I used this layout viewtopic.php?f=7&t=25767#p248977

BJFE BBBOD_zpsjuwjb2fh.png

I've got it mostly working, but have a few questions as I learn more about building and understanding circuits. I should say that my circuit isn't a perfect match. I couldn't get all of the correct resistor values, but used values that were very close e.g. 15K resistor in place of 14.7K. It's also possible that I've got some of my ceramic capacitors switched (I don't have a magnifying glass to read the codes, but I think I've got them right).

1. The layout and schematics say to wire tone lug 2 to ground, but when I did this I wasn't getting any signal coming out of the tone knob (I traced the audio signal with an audio tracing tool). I disconnected the ground from lug 2 and just wired lugs 1 and 3 according to the layout. It seems to work. Why was there no sound when lug 2 was connected to ground? Am I missing something? What problems, if any, might arise if I take out that ground wire?

2. My output signal is really weak. Seems that another user also had some trouble with output. It was recommended by the original designer of the pedal to "connect a 1uF cap in series with 4K7 across 2K6 written as R14 in schematic" to get about 6dB increase in signal. What does "across" mean? Does that mean 1uf and 4K7 in series, wired in parallel with the 2K6? Why would the signal drop so much? Where in the circuit would that happen? Is it related to the output of the op-amp? Maybe not enough voltage coming out of the op-amp? Is that affected by the input bias?

Thanks for helping a relative noob out!

BuddyPrince · Post by **BuddyPrince** » 18 Dec 2017, 01:58

Update:

The signal gets really weak where the 2n2 and 27K at the bottom right of the layout connect to Volume. Everything seems pretty strong and solid up to that point. Any thoughts as to what's going? If the wrong value capacitor is in there, could that be a cause?

deltafred · Post by **deltafred** » 18 Dec 2017, 10:32

It sounds like there is a problem around C11 or the tone pot. You did say when you disconnected the tone pot wiper things improved. Double check all connections for shorts, solder bridges or maybe a whisker of copper remaining where a track should be cut.

BuddyPrince · Post by **BuddyPrince** » 18 Dec 2017, 16:46

Thanks deltafred. I'll give it another close look and see what I can find...

BuddyPrince · Post by **BuddyPrince** » 18 Dec 2017, 23:10

Well, now I'm thinking it's the FET. I realized that the electronics store I bought my supplies from gave me part number NTE312, the equivalent for BF244A. Turns out the pins are different on the NTE312. I wired in some leads to my board that I could connect to the correct pins on the FET to help wth troubleshooting, but I got some weird sounds out of it, and now nothing. I think maybe I fried it somewhere along the way...

I've got some parts coming in from Small Bear later this week, we'll see how it goes...