Using Low Noise, High Freq, RF amp, mixer, switch Jfet for stompbox?

[Thecomedian]

http://html.alldatasheet.com/html-pdf/75131/MICRO-ELECTRONICS/2N3823/1445/1/2N3823.html


Is it possible to use this thing, or would a general purpose low freq amp be better to use? I have these things for free, so I figured I might as well.

[amptramp]

It is useable, but look at the spread of transconductance and Vp values - you would have to design for a subset of these values and select transistors for your design.  OK if you are building one for your own use, not so good if you are going into production.  You may need a 15 VDC supply rail just to get some of the transistors to wake up.  You can build the JFET matcher in www.geofex.com and the characterizer circuit (unfortunately, geofex will not allow you to go to a subpage), so search JFET and you will get fetmatch.htm and "foolin' with FETs"  A breadboard may be a good investment.

[Thecomedian]

k, got it to work in LTspice as a simple booster circuit from 5mv to 80mv. I've had a breadboard for a while. As long as it functions, is there anything else to be concerned about, such as maybe it sounds like crap, or is the activating part the only hurdle?

[amptramp]

As long as you get the bias right, it should sound good.  The 8 nV/Hz^(1/2) noise is better than the typical op amp, so this should not be a problem.  The distortion from  JFET is mainly second harmonic which is very musical, even if it is a departure from the original signal.  Getting the bias right may mean running off more than 9 volts.

[duck_arse]

from the spec sheets I looked at, it seems vaugely similar to a bf245b, or a j210, or 2n5486, or everyone's favourite mpf102. the high Idss means low channel resistance, so you can throw it at some vcr circuits and see how they go.

and the metal can is a better look than to92 anytime.

[WaveshapeIllusions]

I've used some JFETs like those. They work pretty well. All you have to worry about is proper bias.