Buffered wah debug

[bleubleu]

Hi there!

I just build and wired the tonepad "buffered wah" and I am upgrading my Vox V847. I built is with both input + output buffers and the volume toggle. I wired the "Q control" to a pot and added a 1P4T switch to switch to select between 4 different capacitors (sweep range). It is probable an overkill, but what the hell!





Symptoms : There is no sound coming out of it, the true bypass works great.

Link to the schematics : http://www.tonepad.com/getFile.asp?id=59

Voltage readings:

Q3 (Input buffer) :
  - G: 3.3mV
  - S: 1.28V
  - D: 4.29V

Q1 (Wah #1) :
  - C: 4.33V
  - B: 0.6V
  - E: 6.21V

Q2 (Wah #2) :
  - C: 6.21V
  - B: 3.87V
  - E: 3.34V

Q4 (Output buffer) :
  - G: 6.55V
  - S: 5.8V
  - D: 5.8V

The unit drains only 3 or 4 mA so there is no major shorts. I started to debug it with the audio probe but i am getting nowhere. Here is the path I traced:



After the 68K I am getting nothing. If I am getting something, it is very weak.

Any idea ?

Mat

[bleubleu]

Bump!

[bleubleu]

Wow, I just woke up this morning and re-looked at the pictures & schematics. Q4 (output buffer JFET) is the wrong way around!! Grrrrr, rookie mistake. I will flip it around and post an update.

Mat

[bleubleu]

Ok, I flipped the JFET around and it works now!

The Volume pedal modification (Jen Wah-Volume) was not working very well, so I took it off. The volume was changing, but never turning off completely. The range of the pot for the wah and the volume does not seem to be matching very well. Maybe because I have a 100K pot in my Vox. I dont know.

If anyone is interested in the final voltages, let me know. I can measure them.

Mat