SOLVED Neurocyton preamp help!

[innerlight]

Hi again all!
Just finished building the Neurocyton. It’s currently passing signal, however it’s a considerable volume drop from bypass when engaged. I attempted to bias the trimmers for the JFETs, these were my measurements.
1) 4.05
2) 8.6 (this was at the lowest setting on the trimmer)
3) 8.7 (this was also at the lowest setting)
4) 4.05.

I think all are meant to be set to 4v right? Would JFET 2 and 3 being too high indicate a wrong part in there somewhere?
Not sure where to begin here, photos attached for your perusal.
Thanks so much in advance all!

 

[innerlight]

Hi all! Checking back in from purgatory here.
I have now re-wired the foot-switch, Ive re-flowed all solder points (they all seemed fine), and checked all caps, pentameters, diodes and resistors against the BOM, all seem correct.
Ive also checked voltages on the JFETs,
Q1: 8.8 (at lowest possible adjustment)
Q2: 4.04
Q3: 8.6 (at lowest possible adjustment)
Q4: 4.05

Can someone possibly weigh in here? I am completely stuck. No idea what my next step should be.
Pedal is currently un-housed, passing signal in bypass, and I'm able to hear some noise when adjusting pots with the pedal engaged. LED is working.
I realize there's a little flux left on the PCB, ill give it a good clean now.
Photos in current state attached.
PLEASE HELP!
MANY MANY THANKS!

 

[innerlight]

@Chuck D. Bones any ideas about this one Mr Wizard?

 

[spi]

Did you happen to measure the Vp and Iss of your jfets before they were in circuit?
It could be you have out-of-spec or fake jfets, which is not uncommon these days.

 

[innerlight]

Did you happen to measure the Vp and Iss of your jfets before they were in circuit?
It could be you have out-of-spec or fake jfets, which is not uncommon these days.

I didn't no!
I got them from Mouser though, so they should be ok right?

 

[fig]

I’d audio probe the input pad of the pcb and determine if signal is making it to the board. From there, I’d probe pin 3 (gate) of each transistor for audio.

[corrected]

 

[innerlight]

I’d audio probe the input pad of the pcb and determine if signal is making it to the board. From there, I’d probe pin 1 of each transistor for output.

Also, there are 4-bias adjustments (kinda like a Boogie Monster maybe?). Have you taken any voltage measurements from the drains (pin 3)?

I’ll try the probe tonight and I’ll report back! Thank you @fig.
Voltage measurements are above, seems like Q2 and 3 and getting too much voltage! If anyone has any ideas of how to address that please let me know.

 

[fig]

I would think the control settings have an effect on biasing…

 

[innerlight]

I would think the control settings have an effect on biasing…

I had all controls maxed.

 

[innerlight]

This build is especially bizarre because it’s one of the simpler builds I’ve ever done! Please help me people, I need closure! So very stumped.

 

[almondcity]

do the voltages go higher when you adjust the trimpots on Q1 and Q3 or do they do nothing?

 

[innerlight]

do the voltages go higher when you adjust the trimpots on Q1 and Q3 or do they do nothing?

The trimpots adjust all voltages on all JFETS. I actually just double checked and in the process the LED stopped working. Perhaps I shorted something?

 

[innerlight]

I replaced the LED and now it is still not illuminating, or passing any signal.

 

[fig]

Let’s back up. Were you able to audio probe as described? Is any signal reaching the input pad of the pcb?

 

[innerlight]

Let’s back up. Were you able to audio probe as described? Is any signal reaching the input pad of the pcb?

Just replaced the LED, that’s functional again. Just probed for continuity, signal passes to the input on the PCB.

 

[fig]

Great! You may want to try probing pin one of each transistor…this may reveal what section the issue is in.

 

[Robert]

These are the bias voltages for all four transistors measured from the original.

Q1 - 4.45V
Q2 - 4.3V
Q3 - 4.46V
Q4 - 4.75V

 

[innerlight]

Great! You may want to try probing pin one of each transistor…this may reveal what section the issue is in.

How would you recommend going about this? Sorry I am a newbie! I appreciate the response!!

 

[fig]

You’ll want to rig an audio probe. What it does is create a bridge between the contact point and the output jack, or a cable to your amp.

A 12” length of wire
Alligator or grabber clip
10nF cap
paperclip
Solder one pin of the cap to the alligator clip and the other to the wire. solder the other end of the wire to the paperclip. Attach the alligator clip to the output jack (tip) of the pedal. Engage & power the effect, then run an audio signal through it. Carefully contact the mentioned points and you should hear audio. The cap is there to filter a bit of DC current, but I try to stay away from the power rails.
First, touch the input pad of the pcb, and let us know if you get audio.

 

[innerlight]

You’ll want to rig an audio probe. What it does is create a bridge between the contact point and the output jack, or a cable to your amp.

A 12” length of wire
Alligator or grabber clip
10nF cap
paperclip
Solder one pin of the cap to the alligator clip and the other to the wire. solder the other end of the wire to the paperclip. Attach the alligator clip to the output jack (tip) of the pedal. Engage & power the effect, then run an audio signal through it. Carefully contact the mentioned points and you should hear audio. The cap is there to filter a bit of DC current, but I try to stay away from the power rails.
First, touch the input pad of the pcb, and let us know if you get audio.

OK, thanks @fig! I'm learning a lot over here.
Im going to build this probe in the coming days and report back.