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!

 

[redclover7!]

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!

did you figure ou?t i am in process of this build myself i install , wait for more parts to come in , etc. i just burned one of the pads but i think i can jump to next component

 

[redclover7!]

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!

why tape under pots?

 

[redclover7!]

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.

hello, i ordered JFETS from China that's the only place i could find, don't remember if Digi key had, but is China known for having ONLY cheap parts? could i get lucky and receive good parts? thanks

 

[comradehoser]

why tape under pots?

Potentiometers that are situated over top of the board (which in the low tide is all of them) are hovering over the solder points of your components. The backs are made of conductive metal, therefore if they contact the solder points, you're effectively bridging components, which might not be optimal. It's a common point of failure.

Generally, diligent builders will isolate the backs of their pots situated over the board with tape (not ideal because component legs can still poke through) or plastic dust covers. I don't bother doing this with pots whose backs are floating off-board (i.e. at the tops of boards).

 

[comradehoser]

hello, i ordered JFETS from China that's the only place i could find, don't remember if Digi key had, but is China known for having ONLY cheap parts? could i get lucky and receive good parts? thanks

There's no reason why they couldn't be good, but you have to verify. There are unscrupulous sellers that will rebadge common transistors to "desirable" or boutique components just to sell them at a higher price if there's a margin to be made. Through-hole j201s fall into this category since they are out of production aside from interfet, who also sells them at a distinct premium. Same thing with ICs like the LM308. Unfortunately, many of these sellers tend to originate from China.

The issue isn't that the original components have some sort of originality cachet. If the dudes/dudettes would actually make clone transistors and ICs to spec, it wouldn't be an issue, but they often sell components with wildly different parameters and functionality from what they are claiming, and of course, this can affect the outcome of the build, especially in something as finicky as the Low Tide.

I usually find what I need between Mouser and Stomp Box Parts, and Amplified Parts at most, but you have to be ready for sticker shock.

 

[redclover7!]

There's no reason why they couldn't be good, but you have to verify. There are unscrupulous sellers that will rebadge common transistors to "desirable" or boutique components just to sell them at a higher price if there's a margin to be made. Through-hole j201s fall into this category since they are out of production aside from interfet, who also sells them at a distinct premium. Same thing with ICs like the LM308. Unfortunately, many of these sellers tend to originate from China.

The issue isn't that the original components have some sort of originality cachet. If the dudes/dudettes would actually make clone transistors and ICs to spec, it wouldn't be an issue, but they often sell components with wildly different parameters and functionality from what they are claiming, and of course, this can affect the outcome of the build, especially in something as finicky as the Low Tide.

I usually find what I need between Mouser and Stomp Box Parts, and Amplified Parts at most, but you have to be ready for sticker shock.

i have used all the 3 companies you sited, i think i will look again! thx

 

[redclover7!]

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!

i noticed in your pictures of the neurocyton preamp calls for 4 trim pots! i ordered only one i got confused on the parts list, 4 to bias! wow i will cross that bridge when i get ther