Does anyone know some good small-signal MOSFETs?
« on: December 06, 2018, 12:27:32 PM »
I've looked around for small signal MOSFETs but all I can find is the typical power MOSFET, I would like something in to-92 package or even smd.  A quick search in Mouser revealed the BS170 but seems to be optimized for power rather than audio, Any suggestions?
« Last Edit: December 06, 2018, 12:42:53 PM by Dualflip »


gyraf

..note to self: don't let Harman run your company..

JohnRoberts

Re: Does anyone know some good small-signal MOSFETs?
« Reply #2 on: December 06, 2018, 01:10:52 PM »
AFAIK MOSFETS are generally not considered for very low noise applications. 

I looked at a few data sheets I had around from my outlet tester design (I used SMD MOSFETs for their high input impedance). The two datat sheets I just looked at do not even specify noise or NF.

Using google I found a "low noise" MOSFET specifying a respectable 1 dB Noise Figure but at 400 MHz  :o, somewhat above the audio band.

JR

PS: FWIW the semi industry played around with mosfet op amps back in the 80's but AFAIK these never gained popularity. More recently I've seen some CMOS (low current, low voltage, rail to rail) op amps that presumably are reasonable.   https://www.analog.com/media/en/technical-documentation/data-sheets/6244fb.pdf  This part spec's 8nV/rt Hz which doesn't suck, but is not as good as modern bipolar uber opamps
John Roberts
http://circularscience.com
Tune it, or don't play it...

moamps

Re: Does anyone know some good small-signal MOSFETs?
« Reply #3 on: December 06, 2018, 01:38:19 PM »
BS170/250
ZVP/ZVN2016
ZVN/ZVP2110

benb

Re: Does anyone know some good small-signal MOSFETs?
« Reply #4 on: December 06, 2018, 05:59:13 PM »
I understand (The Art of Electronics, 3rd. Edition) that jfets are less noisy, but for both jfets and (small-signal) MOSfets, there are fewer and fewer parts available. A series of jfet part numbers listed in that book (again, 3rd Edition, 2015, three years ago) are now no longer made.

There's also the Toshiba 2sk170 that appeared to be popular in audio applications but also no longer made, though there's this other company apparently making and selling them at "somewhat" higher prices:
https://www.diyaudio.com/forums/pass-labs/317563-replacement-toshiba-2sk170-2sj74.html

Re: Does anyone know some good small-signal MOSFETs?
« Reply #5 on: December 07, 2018, 06:20:28 PM »
Thanks for all the info, I will check them out, have you guys tried using this parts?


 @benb : diyaudio is selling a pair of matched JFETs for 48 dollars! jeez

JohnRoberts

Re: Does anyone know some good small-signal MOSFETs?
« Reply #6 on: December 07, 2018, 08:25:02 PM »
Thanks for all the info, I will check them out, have you guys tried using this parts?


 @benb : diyaudio is selling a pair of matched JFETs for 48 dollars! jeez
JFETs are different animals from mosfets with many low noise versions.

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...


 

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