JFET Audio Switch Circuit - 2n5457

Taking a look at the common JFET circuits used in guitar pedals to switch effects in and out of the audio path.
A test circuit was breadboarded to investigate the 2n5457 N channel JFET.
I also scoped the wet and dry outputs of a TS808 Ibanez Tube screamer to observe the JFET switching.
Note: in my breadboard experiment I was directly switching the gate diode between 9 V and ground when turning the FET on and off, but in a practical circuit there’s an RC Delay between that control signal and the diode cathode to slow down the switching time and help eliminate noise pops.
I also forgot to add a bypass capacitor on the 4.5v rail so I did a follow up video simulating the circuit in SPICE and showing how the bypass capacitor works:
• Bypass Capacitors in A...
Audio and/or Guitar Effect Links:
www.electrosmash.com/tube-scr...
www.diystompboxes.com/smfforu...
sound.whsites.net/articles.htm
www.premierguitar.com/authors...
www.geofex.com/
Transconductance unit converter
www.translatorscafe.com/unit-...
JFET Datasheets
www.mouser.com/ds/2/149/2N545...
datasheet.octopart.com/2SK30A...
Patreon: / gadgetreboot
Pinterest: www.pinterest.ca/GadgetReboot
Twitter: @GadgetReboot / gadgetreboot
Background music from the RUclips music library:
A Rising Wave by Jeremy Blake
Ridge Racer by DivKid
I'm Happy For This Guitar by Freedom Trail Studio

[@pileofstuff]

Thanks for the theory refresher.

[@Hearthglow]

The description of how JFETs work, how they are biased, and how to create the split voltage rails is one of the best presentations I have seen. The audio is clear, the pace is great. I am not interested in the pedal application, but it is worth the wait to get the JFET information. The explanation at the end about how to read JFET data sheets is necessarily a bit fuzzy, but it is our job to learn to read them with the introduction given here. Props to Gadget Reboot, and many thanks for the time spent on this vid.

[@hnatyshyn]

Thanks for the light on the subject. I was working on a pedal design and added a jfet switch circuit (with a 2n5457) without really understand it. But your explanations actually confirmed most of my own analysis (without the measurement details).

[@DrexProjects]

Way back around 1985 I made a guitar FX pedal and didn't use JFETS to switch. I used a regular push on / push off switch. Every time I enabled it there was a loud noise to the amp. Not good. Always had to turn the volume down 1st. It's still in a box in the closet and perhaps I will dig it out and add your switching circuit to it. Thanks for the detailed video.

[@StudioDevil1]

Thank you. Wonderful explanation and demonstration.

[@electronic7979]

Useful video 👍

[@jonasdeoliveira965]

You is a hero man thanks very much information

[@AlexAmayaGuitar]

Thanks for you time!! 🙌🙌

[@Bianchi77]

Creative video, thanks :)

[@HazeAnderson]

Well, glad I got those 2n5457 JEFTs now! I am still trying to understand why a JFET works here but a BJT does not. Someone told me biasing but that just doesn't sound right to me ... I can't help but think it's an impedance thing ...

[@nickpelov]

The bleed through resistors is only possible if you have really bad 4.5V supply. If your 4.5V supply is low impedance (buffered through an opamp for example) the cut off should be a lot better.

[@MCDbits]

I'm using this jfet set up with negative gate voltage provided by the output off a 555 timer (astable set up) via a schottky diode (ensures no positive signal to jfet)... Problem is I get a pretty mighty pop every time it switches... Any ideas?

[@lukegalea6237]

Hi! great video 🙂 Would you mind clarifying the following?

[@henrikjensen3278]

Any power rail is supposed to be ground when talking AC, this is, of course, depend on the decoupling (I did not see any on your breadboard for 4.5V) and it will never be ideal.

[@ekasatriabahari2264]

How Can jfet 2n5457 make output sound dropped too low?