SOLVED Son of Ben Preamp Issues

[utmigs]

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:

1. 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.
2. I was able to adjust Q1 to 2K using Trim Pot 1, but I'm only seeing 1.40V at the Q1 drain.
3. 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.
4. 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)
5. I also probed throughout for continuity using the schematic, and I also didn't find any evidence of unintentional grounding.
6. 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.

I've also attached a couple of photos below. I apologize for using all red wire, despite knowing better. It was all I had at the moment. After reading a number of other threads, I went ahead and ordered some pre-soldered J201s from PedalPCB. However, I thought it wouldn't hurt to see if anything stood out before trying to unsolder the current J201s.

Any insight would be very much appreciated! Thank you!

 

[Dan0h]

Transistors are in backwards.

 

[Dan0h]

I also used mouser j201s and put them in opposite of you and they rock! Looks like you’ll need to pull them and flip them, if they are the same as the ones I used. They were like $3something each.

 

[utmigs]

Thanks Dan0h! I'll try that then.

 

[Mcknib]

From the Interfet J201 datasheet looks like you'd need to bend the Source and Drain pin around each other, top is how Q1 should sit on the pcb Drain, Source, Gate bottom is how you have your Interfet transistors soldered in with their pinout Source, Drain, Gate so you were correct about a different pinout but would also need to bend the S and D pins around

https://www.mouser.co.uk/datasheet/2/676/jfet-j201-j202-interfet.r00-1649170.pdf

 

[Dan0h]

Here is the Mouser part number I used.
Mouser #:
106-J201
They are InterFET.

I put them in per the PCB, and they sound amazing.

 

[utmigs]

I just swapped them around, and everything works now. Thanks again for all of your help, guys!

 

[Mcknib]

Here is the Mouser part number I used.
Mouser #:
106-J201
They are InterFET.

I put them in per the PCB, and they sound amazing.

Defo the same part number

Strange datasheet pinout with drain in the middle not used many of those, typo maybe?

But DanOhs used them I haven't

 

[Dan0h]

Defo the same part number

Strange datasheet pinout with drain in the middle not used many of those, typo maybe?

But DanOhs used them I haven't

It has got to be a typo right, if it was correct they wouldn't work?

 

[music6000]

I questioned this about the Mouser Interfet J201 to a supplier in Australia about the Pinout.
He was dumbfounded by my concern & I believe the PDF is wrong as others have used them as NOS J201's replacements & they work!
Others will say S & G are interchangeble & they will still work as is?

 

[Chuck D. Bones]

S & G are definitely NOT interchangeable. S & D are, at least at audio frequencies. I'm seeing the same thing Music6000 is seeing. Note that InterFET shows the top view, Fairchild (now ON Semiconductor) shows the bottom view. I also want to draw your attention to the note in the bottom right corner of the Fairchild datasheet exerpt.