BSIAB problem question

[caspercody]

I made the BSIAB II using the GGG PCB layout, and I do get sound out of it. But it sounds like it is fizzy out. Sounds like a bad fuzz pedal. I checked the voltages on all the Jfets, and they match up with the GGG voltages. I am planning on using a audio probe tonight, but wanted to see if there is anything I should look at first?

Like I said I get sound, but it sounds like it is shorting out. No good strong sound.

Thanks
Rob

[Ice-9]

It sounds like a bias problem, have you set the trim to give about 1/2 supply. Or even just adjust it till you get a good sound.

[caspercody]

I actually tried a fixed 15k in the trim pot spot. The voltage is around 5v. I will replace this with a 100k trim first tonight, and see what happens.

Thanks!!

[Ice-9]

Yeah definitely stick in a 100k trim and just adjust it till it sounds good, there will be a huge difference in volume when you near the sweet spot. After that measure what voltage you have. you could also measure the resistance the pot is set at and replace it with a resistor of the closest value.

[caspercody]

Replaced with trim pot, no difference. All voltage readings are what they are suppose to be, according to the GGG readings. Checked wiring, and traces on board nothing looks like it is shorting out. Up to C6 (150p) it sounds alittle distorted. The other side of C6 gets quieter, same level into gate on Q3. Q3 source out is bad sounding. Tried to replace Q3, no difference.

[Ice-9]

You should have plenty volume and dirt on either side of C6, Try removing your Q3 and take the output jack straight from the centre of the gain pot and C6 junction. This should sound loud, and adjusting the gain pot will increase /decrease volume.

If this works ok you can then go onto test the rest of the circuit. I beleive the most likely problem lies in and around Q3. Also the voltage on the trim doesn't always bias out at 1/2 v , i have a BSIAB that is running really nice nearer 7.5v.

Also check that your voltage divider resistors are the correct value and check/ replace C7 .
Let us know how you get on

[caspercody]

I actually took my original BSIAB pedal and did the mods to this one. I could not figure out what was wrong with the one I was just trying to build. I swapped the J201s, and nod parts from my new board to my existing BSIAB. It (my existing BSIAB) now works with the new mods I did. Still not sure what part is bad on my new board, maybe some day I will work on it again. I had this down to the board with only the gain, and tone knob. Funny how it could be (1) part making it so it does not work right.

My new BSIAB (Pinnacle clone) works great, but I do have some noise, especially when the tone is turned all the way to the treble side. Need to look into this?

Thanks