I attempted a Son of Ben preamp and read most of the existing threads concerning JFET biasing during the build. I'm getting power to the LED, but no sound when the pedal is engaged. When the pedal is off, I'm getting sound to the amp. If anyone has any insight, I'd really appreciate it. Here's a little background:
Any insight would be very much appreciated! Thank you!
- I'm using InterFET J201s purchased at Mouser. Unfortunately, I didn't test the transistors prior to installation, and I didn't use sockets. According to the Mouser data sheet (as referenced in another thread), the pin outs are different than standard J201 pin outs, so I installed them in a flipped orientation.
- I was able to adjust Q1 to 2K using Trim Pot 1, but I'm only seeing 1.40V at the Q1 drain.
- I'm seeing a range of ~ 0.8V to 1.51V measured at the Q2 and Q3 drain when adjusting the trim pots from fully CCW to fully CW, respectively. I'm not able to reach the ~4V at Q2 and Q3.
- I've measured the following voltages when the pedal is powered on:
- R5 - 1.4V (top side); 7.68V (bottom side)
- R9 - 1.5V (top side); 9.00V (bottom side)
- R100 - 6.55V (top side); 0V (bottom side)
- R12 - 1.51V (top side); 9.00V (bottom side)
- I also probed throughout for continuity using the schematic, and I also didn't find any evidence of unintentional grounding.
- I powered off and tested each resistor in the circuit (by attaching DMM probes to either side of each resistor), and all tested well, except for R3, R1, R8, and R10. I tested those resistors before installing them in the circuit, and they were all very close to stated values (within tolerance). However, I couldn't remember if those resistors (each with one lead going to ground), would read normally on a DMM once installed in the circuit.
Any insight would be very much appreciated! Thank you!