Should I Stock Linear Systems FETS?

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SSLtech

Well-known member
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Jun 3, 2004
Messages
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Location
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Well, since you stock Gigohm resistors, I think that the 170 is a natural companion, for FET-mic projects.

I'll buy mine from you along with the GΩ R's... that's for sure!!!

Keith
 
Are these much better than original Toshiba's or are those now gone?

The dual matched is OK but 20 mV these days seems like a lot...

My recollection is highest I dss is supposed to correlate with lower noise (voltage), but I defer to Brad on that factoid.

I used the 2SK170 back in the '80s and liked them...

JR
 
Toshiba 389s are gone but there was some fair amount of NOS last time I inquired. Erno B. said others are scheduled for deletion but didn't give details, so I am really greatful to LIS for developing their own subs.

Higher Idss does correlate with lower e sub n, but the effect is not terribly strong. And the part tends to run warmer of course. One reason for getting the high bracket Idss parts (at least when they were Toshiba parts) is that they tend to be close to zero tempco Vgs at Idss.
 
[quote author="okgb"]Ptown may need some of the duals for a second round of
G.R. preamps[/quote]

Nope, going with the originals for the next round...and (no offense to wayne, i really do enjoy him being around) if i need linear systems parts, i'll buy them from linear systems.
 
Ordering quantities >$50 from Linear Systems distributors is fine.
If you want small quantities, you are out of luck unless you have an arrangement such as Wayne has proposed.
I'm interested.

ZAP
 
AmpsLab, if you don't mind getting 20 at a time.

http://ampslab.com/trans_2sk170bl.htm

Wayne offering small quantities would be great for the DIY'ers that just want a few to experiment. Thanks to Wayne for all the great components and projects he's brought our way. :thumb:
 
[quote author="RogerFoote"]Wayne

Isn't that what is called for in the THAT app note with the current mirror AR circuit?

Roger[/quote]

Hi Roger,

from memory I believe it is. That very circuit is what delayed me from finishing the pico you sent me. I got bogged down waiting for parts and making switchable options. I should've just built it as you designed it - in fact that's what I've decided to do. I'll pick up the new stereo board and do some attack and release experiments with that.

As I mentioned to Wayne in a recent post I really really appreciated your generosity during a very difficult time - it really picked up my spirits. Everything is starting to work out now - my health is improving all of time and I decided to get a job to help straighten out my finances (after 8 years fully self employed).

Talk to you soon,
Ruairi
 
A lot of china built microphones schoeps and transformer I have looked at use a 170 FET. I wonder were they get them?
 
[quote author="mediatechnology"]

* Then of course there's NSC doing the opposite putting modern op amps in TO packages which has me really stumped.[/quote]

My guess is that they got audiophile feedback about how much people like to see metal cases. I remember when such folk would pop the hood on a preamp from somebody with high-end pretensions and see those NSC dual FETs in DIP-8, and sneer that they were using evil dirty opamps :razz: When it's a metal case it seems to be less objectionable.

Funny thing is I believe, and I seem to recall Bob Pease said, that the plastic is often lower leakage and loss than the borosilicate kovar sealing glass, the latter being a significant noise contribution for charge amplifiers. When TI still was in the discrete biz their 2N4416s were the best---not just because they were very good chips, but because the construction of the package had the minimal volume of glass surrounding the gate lead.

This could actually have bearing on condenser mic pres, if it weren't for the likelihood that the capsule is a far more important dielectric loss source. And of course probably many other noise sources dominate that, including thermo-mechanical noise in the diaphragm and almost always ambient acoustical noise.

At one point Siliconix had some little ceramic packaged JFETs that I hoped would have low packaging loss. But alas, they weren't very good chips, and also possibly the cement they used to seal the package was lossy.
 
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