SOLVED Vibrobot replacing 2n7000 with a 2n5457, need help

[EricGuitar]

Not satisfied with the switching capacities of the 2n7000 or bs170, therefore I want to replace this with a 2n5457, can someone please help me with this conversion, and make a drawing of how to do this?

 

[Sturdag Lagernathy]

Sorry - There's... a lot to unpack from what you've asked. How about explaining a bit more of the situation.. What's wrong with those poor little mosfets?

 

[Cybercow]

There's a difference between how a JFET and MOSFET operates and in this instance the MOSFET is NOT being employed as a simple switch. Rather, it's set up as more of a variable resistor than a switch.

What about the existing configuration leaves you unsatisfied?

 

[EricGuitar]

The way of switching (or resisting) is not the cleanest way, it distorts a little, more users had this problem, readable in other topics in this forum, suggestions are adjusting and using a bs170. Common solving tips. But I want to adress this problem in a better way by using a jfet, a jfet is better at such a task I read somewhere, but I lack the knowledge to make this technical possible,and I see it as a challenge to make this improvement.
Shouldn't be to hard for someone with technical knowledge I think(hope)

 

[Cybercow]

A BS170 is the same as a 2N7000, a MOSFET but with reversed pinouts. In this application, the MOSFET is not directly in the signal path and should not be injecting any distortion. Here, the MOSFET is acting as a variable resistor to bleed the signal to ground as determined by the waveform generated by the LM741 IC. A MOSFET provides for a larger swing (voltage range) in its transmittance from Drain to Source. A JFET on the other hand has a very narrow swing (voltage range) in its Darin to Source transmittance. So some rather specific changes would need to me made on the LM741 LFO circuit section to address the narrower gate voltage range of a JFET.

Can you better describe the distortion to which you refer?

 

[Nostradoomus]

this video should shed some light on potential problems even though I'm still not sure what your problem is.

 

[EricGuitar]

A BS170 is the same as a 2N7000, a MOSFET but with reversed pinouts. In this application, the MOSFET is not directly in the signal path and should not be injecting any distortion. Here, the MOSFET is acting as a variable resistor to bleed the signal to ground as determined by the waveform generated by the LM741 IC. A MOSFET provides for a larger swing (voltage range) in its transmittance from Drain to Source. A JFET on the other hand has a very narrow swing (voltage range) in its Darin to Source transmittance. So some rather specific changes would need to me made on the LM741 LFO circuit section to address the narrower gate voltage range of a JFET.

Can you better describe the distortion to which you refer?

Good explanation, thanks for the answer, could't dial the distortion out with the 100K trimmer, replaced it with a 200K and now it's much better!

 

[EricGuitar]

this video should shed some light on potential problems even though I'm still not sure what your problem is.

Thanks for your answer, didn't know that there is difference in tolerance in the the chips, built 2 of them one was ok the other I couldn't dial the distortion out, now with a 200k trimmer it is ok, next time I better select the chips