SOLVED Parentheses noise with no input

[Phasma888]

Good day!

Please help me understand what the problem is.

I did not find any physical damage on pcb, short circuits, etc. I put 2n5458 instead of pf5102 and a 33pf capacitor instead of 30pf. The incoming signal overlaps pcb’s own noise.



It doesn't matter if there is an input connection – always just the same noise.



I hope everything I wrote is clear - using translator.)

https://disk.yandex.ru/i/5udOiqeL_UzRxw

 

[Cybercow]

The PF5102 and 2N5458 JFETs have vastly different pinch-off voltage (Vgs[Off]) specifications. I suspect the JFET substitution is problematic.

 

[Phasma888]

The PF5102 and 2N5458 JFETs have vastly different pinch-off voltage (Vgs[Off]) specifications. I suspect the JFET substitution is problematic.

Thanks, but how it may work here in this case?
https://forum.pedalpcb.com/threads/parentheses-w-demo-vid.5117/

 

[Cybercow]

Thanks, but how it may work here in this case?
https://forum.pedalpcb.com/threads/parentheses-w-demo-vid.5117/

Because the 2N5457 has lower range of Vgs(Off) than the 2N5458. The Vgs(Off) range of the 2N5457 is from -0.5v to -6v. and matches can be found for the PF5102 which has a Vgs(Off) range of -0.7v to -1.6v. The 2N5458 Vgs(Off) range is from -1v to -7v and the ones you have may not fall into that lower range offered by the PF5102. Swapping out JFETs can be a PITA to find the correct Vgs(Off) - even with correctly selected parts. Of course, this is just speculation based on the datasheets for the parts in question.

 

[Phasma888]

Because the 2N5457 has lower range of Vgs(Off) than the 2N5458. The Vgs(Off) range of the 2N5457 is from -0.5v to -6v. and matches can be found for the PF5102 which has a Vgs(Off) range of -0.7v to -1.6v. The 2N5458 Vgs(Off) range is from -1v to -7v and the ones you have may not fall into that lower range offered by the PF5102. Swapping out JFETs can be a PITA to find the correct Vgs(Off) - even with correctly selected parts. Of course, this is just speculation based on the datasheets for the parts in question.

Thanks again for the explanation!
Many sources write that almost any N-channel JFET will work since they are used as buffers, so I'm confused.
Will install IC socket and try 5457 tomorrow.)

 

[Phasma888]

Because the 2N5457 has lower range of Vgs(Off) than the 2N5458. The Vgs(Off) range of the 2N5457 is from -0.5v to -6v. and matches can be found for the PF5102 which has a Vgs(Off) range of -0.7v to -1.6v. The 2N5458 Vgs(Off) range is from -1v to -7v and the ones you have may not fall into that lower range offered by the PF5102. Swapping out JFETs can be a PITA to find the correct Vgs(Off) - even with correctly selected parts. Of course, this is just speculation based on the datasheets for the parts in question.

It works now with 5457! It remains to paint the box and pack it all inside.
Thanks for patronage in transistor’s alternative(that's what PITA means, right?)

 

[Cybercow]

It works now with 5457! It remains to paint the box and pack it all inside.
Thanks for patronage in transistor’s alternative(that's what PITA means, right?)

Glad to hear the good news. And actually, "PITA" means "pain in the ass".