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!

 

[fig]

It is a handy rig to have.

A nice alternate to the alligator clip is a jack....this allows you to add a GND clip and removes the OUTPUT jack of the pedal from the test circuit.

 

[spi]

I was going to suggest swapping positions of the transistors and see if the biases moved with the transistor. But I see you didn't socket them. My advice for future builds is always socket transistors, especially jfets or mosfets.

 

[innerlight]

I was going to suggest swapping positions of the transistors and see if the biases moved with the transistor. But I see you didn't socket them. My advice for future builds is always socket transistors, especially jfets or mosfets.

Will do! Did not realize

 

[innerlight]

Ok all! Built the audio probe.
It was fun!
So here is my update.
Audio is present on the input pad.
Audio is present on gate of Q1. On Q2 there is no audio present on the gate pin, there is on the drain though.
Q3 has audio on the gate. Q4 has no audio at all.
Hope this helps!!
C

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.

 

[dylanadd]

I’m having the exact same problem. No audio signal getting through the first transistor. And no continuity through any of the others.

 

[innerlight]

Welcome to my journey! Let us find salvation together

 

[fig]

I’d reflow R9-R11 and the Q2/Q3 trimpots.

 

[innerlight]

Ill get on that now and report back! Thanks @fig

 

[innerlight]

I’d reflow R9-R11 and the Q2/Q3 trimpots.

Tried that, to no avail! joints are all looking good visually

 

[fig]

Are you pretty confident in your J201 source?

 

[innerlight]

Are you pretty confident in your J201 source?

Got them from Mouser, should I order and try different ones?

 

[fig]

I wouldn’t think so.

 

[innerlight]

I wouldn’t think so.

I’m officially stuck! I feel that this one may be bound for the shelf of despair

 

[fig]

I wouldn’t want to wager a guess at this point. I have a Boogie Monster that runs a hot bias on two transistors but sounds fine (which is not your experience here). I built it prior to measuring all transistors and figured they were out of the trimmer’s range of effect.

Does the GAIN control effect the bias voltages at all?

 

[almondcity]

I'm building another one of these soon I'll see if mine makes it. Have you checked the trim pot values are correct? I think they were 100k

 

[dylanadd]

So in my case, I had fake j201 transistors. I replaced those, and finally started getting sound out of it, but the sound is very quiet and broken up. Could this be a bias issue? It’s almost like it’s acting like an extreme compressor and I only get any kind of volume it I pluck a string really hard. Anyone have any ideas what might be going on?

 

[innerlight]

I'm building another one of these soon I'll see if mine makes it. Have you checked the trim pot values are correct? I think they were 100k

Yes sure did!

 

[dylanadd]

So in my case, I had fake j201 transistors. I replaced those, and finally started getting sound out of it, but the sound is very quiet and broken up. Could this be a bias issue? It’s almost like it’s acting like an extreme compressor and I only get any kind of volume it I pluck a string really hard. Anyone have any ideas what might be going on?

Update: after replacing the fake JFETs, the issue was the bias. I adjusted to taste and it works fantastic!

 

[STEVE]

i just finished building one of these and i have zero signal when turned on but audio travels through when
off, any ideas what the problem could be? all contacts are solder well and clean

 

[Drayve85]

I don’t believe this one is solved yet for the OP.