John Curl's Blowtorch preamplifier part II

[Magura]

Any suggestions?
I was under the impression that the 2sk369 was about the best I could get for the purpose.


Magura

[auplater]

Originally Posted by Key

Sorry to mess up the thread. You do realize though that the constant quoting of me and asking me question in a tone that is far from civil is much more disruptive to the thread than anything I posted? I'll say it again if it's off topic or I offend any of you that much by my opinion than why don't you just ignore it? It's really that simple.

Looks like the real problem here is, this thread seems to be one of the "not so DIY Audio" pointers thread, where those with commercial interests and products can probe each others IP, sort of like writing a patent such that the examiner will approve it as having legs, but witholding enough info to truly protect the trade secret that makes it unique (and hopefully profitable).

All those DIY'ers not in the industry posting her, raise your hands...

[syn08]

Originally Posted by auplater

All those DIY'ers not in the industry posting her, raise your hands...

Me

[AndrewT]

Any suggestions?
I was under the impression that the 2sk369 was about the best I could get for the purpose.

out of specification LSK170c with Idss >20mA!!!

I have a few that go to 29mA Idss. As best as I can measure with my methods.

[Magura]

Originally Posted by syn08

Me

You don't count! As you give useful advice, that actually has value to those of us less experienced

The same goes for Scott, he also can't claim any status in that clan.

Magura

[john curl]

Well, has everyone had their say? I will now ask a couple of experts, the people who actually design fets, and see what they say.

[syn08]

Originally Posted by AndrewT

out of specification LSK170c with Idss >20mA!!!

I have a few that go to 29mA Idss.

Unlikely.

They typically have double the 2SK170 transconductance and this can't be only a gaussian tail. Most likely, a larger area chip of the same cell layout.

[Magura]

Originally Posted by AndrewT

out of specification LSK170c with Idss >20mA!!!

I have a few that go to 29mA Idss. As best as I can measure with my methods.

That's would be real close to a 2sk269, but I bet that the capacitances also is higher than for an average LSK170c?


Magura

[AndrewT]

does that rule out lsk170c (in spec) and lsk170c+ (higher than spec Idss) from some or all circuit uses? the c+ is roughly equivalent to 2sk369v.

Which uses would not suit a higher die area, if that is what linear are producing?

[scott wurcer]

Originally Posted by Magura

Any suggestions?
I was under the impression that the 2sk369 was about the best I could get for the purpose.


Magura

Unfortunately some of these might be equally obsolete, I was thinking of things like the old E410 series from Siliconix which might be available from Linear Systems. The noise gets down to 3nV or so and the C's are only 1-3pF. By linearity I mean gos. The input Vgs-Id transfer function is the same square law for all FET's.

EDIT- Hand matched 2SK222's would give you a good go too. 10mS at 1mA and only 8-10pF.