Non-Phool jellybean audio-frequency JFET

E

Ecnerwal

Guest
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
 
Ecnerwal wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
Click to expand...
A few BF862s in parallel, for choice. About 0.8 nV 1-Hz noise in the
flatband, 1/f corner around 1 kHz.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
 
On Aug 20, 12:33 pm, Ecnerwal
<MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
Click to expand...
OPA2134? ~$2 at the 100 quant. 8nV/rtHz, (only 8MHz)

George H.
 
George Herold wrote:
On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.
Click to expand...
BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
 
On Aug 20, 12:33 pm, Ecnerwal
<MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
Click to expand...
Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.
 
On 8/22/2012 1:45 PM, Phil Hobbs wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.
Click to expand...

BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs
Click to expand...
Just because I was curious I searched BF862 preamp and found a
high performance phono stage that uses 8 parallel BF862s.

http://www.synaesthesia.ca/LNschematics.html

3/4 downpage

I'm clueless as to whether it is a good circuit.

Mikek
 
amdx wrote:
On 8/22/2012 1:45 PM, Phil Hobbs wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.


BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs


Just because I was curious I searched BF862 preamp and found a
high performance phono stage that uses 8 parallel BF862s.

http://www.synaesthesia.ca/LNschematics.html

3/4 downpage

I'm clueless as to whether it is a good circuit.

Mikek
Click to expand...
BF862s parallel just fine. But for audio, even just one is better than
good enough. There's no need for subnanovolt noise in audio.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
 
On Aug 22, 2:45 pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.

BF862s, really.  They're the cat's pajamas.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -
Click to expand...
Geesh Phil, I don't know. Mostly I can't tell the difference between
a Jfet and a J stroke.

(They've got BF862's at newark for ~$0.30/100)
.... I might have a use for a 0.8nV Fet. Where's the 1/f knee?
At the moment it's a ~10kHz resonace, but I could move that up, some.

George H.
 
On Aug 22, 4:39 pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
amdx wrote:

On 8/22/2012 1:45 PM, Phil Hobbs wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

BF862s, really.  They're the cat's pajamas.

Cheers

Phil Hobbs

   Just because I was curious I searched BF862 preamp and found a
high performance phono stage that uses 8 parallel BF862s.

http://www.synaesthesia.ca/LNschematics.html

3/4 downpage

I'm clueless as to whether it is a good circuit.

           Mikek

BF862s parallel just fine.   But for audio, even just one is better than
good enough.  There's no need for subnanovolt noise in audio.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -
Click to expand...
You 'pay' 10pF of input C for each one.

(According to the 'one' npx spec sheet I looked at.)

George H.
 
George Herold wrote:
On Aug 22, 4:39 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
amdx wrote:

On 8/22/2012 1:45 PM, Phil Hobbs wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs

Just because I was curious I searched BF862 preamp and found a
high performance phono stage that uses 8 parallel BF862s.

http://www.synaesthesia.ca/LNschematics.html

3/4 downpage

I'm clueless as to whether it is a good circuit.

Mikek

BF862s parallel just fine. But for audio, even just one is better than
good enough. There's no need for subnanovolt noise in audio.

You 'pay' 10pF of input C for each one.

(According to the 'one' npx spec sheet I looked at.)

George H.
Click to expand...
Right, but this is audio after all. I use them in boatloads to make
photodiode bootstraps that work up to ~20 MHz. You put a good-quality
current source in the sources, which gets rid of Cgs pretty well, and
then bootstrap the drains to get rid of Cdg and Cds. You still get the
voltage noise differentiated by Cdiode+Cin, but since they're so quiet,
that's still a big win.

I'm experimenting with using BF862/pHEMT combos with diplexers to get
low 1/f noise and extreme bandwidth.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
 
George Herold wrote:
On Aug 22, 2:45 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.

BF862s, really. They're the cat's pajamas.


Geesh Phil, I don't know. Mostly I can't tell the difference between
a Jfet and a J stroke.

(They've got BF862's at newark for ~$0.30/100)
... I might have a use for a 0.8nV Fet. Where's the 1/f knee?
At the moment it's a ~10kHz resonace, but I could move that up, some.

George H.
Click to expand...
It's about 1 kHz. They're firmly in the flatband at 10 kHz.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
 
On 8/22/2012 1:45 PM, Phil Hobbs wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.

BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs
Click to expand...
Hey Phil,
Do you have a compliment to the BF862?
Mikek
 
On 8/23/2012 9:38 AM, amdx wrote:
On 8/22/2012 1:45 PM, Phil Hobbs wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg
cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are
class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still
marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below
100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will
go away.

Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.

BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs


Hey Phil,
Do you have a compliment to the BF862?
Mikek
Click to expand...
Ok, ok, Hello BF862, you've got some really nice parameters there.
Do you have a complement for the BF862?
Mikek
 
On 08/23/2012 10:38 AM, amdx wrote:
On 8/22/2012 1:45 PM, Phil Hobbs wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg
cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are
class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still
marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below
100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will
go away.

Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.

BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs


Hey Phil,
Do you have a compliment to the BF862?
Mikek
Click to expand...
Don't I wish. Try a BF862 in an inverted cascode with some nice quiet
PNP transistor, e.g. a 2N5087 at low frequency or a BFT92 at high frequency.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs


Hey Phil,
Do you have a compliment to the BF862?
Mikek

Don't I wish. Try a BF862 in an inverted cascode with some nice quiet
PNP transistor, e.g. a 2N5087 at low frequency or a BFT92 at high
frequency.

Cheers

Phil Hobbs

Ya, most of this is over my head, I was just thinking about
Click to expand...
replacements for an AM radio antenna preamp circuit I know of.
Is this a physics problem building a P type to match an N type?
Thanks, Mikek
 
They fit the mold of what I was thinking might be the case - an "RF"
part with application elsewhere. I had actually found Phil's earlier
postings praising them (and verified that they were still available)
before I posted, but was not at all clear after looking at a datasheet
that cut off frequency specs at 0.1 Mhz on the low end if they'd work
reasonably for audio, given that they were being touted for RF in car
radios and a lot of what Phil does goes up there a ways.

Quite a price variance between digikey/newark/mouser, with mouser
winning strongly (27 cents for 1, 23.3 for 100.)

Given a lack of directly comparable graphs I have a hard time telling if
the slightly more expensive (43/29.9) and smaller (smaller not being an
advantage for me as a one-off tinkerer) 2SK880 has a _slightly_ lower
corner frequency or not really, but I suspect it's not enough of a
difference to actually matter (not going phoolish), given that I'm
mostly looking for a reasonable part to have on hand and play with in
the same way I have a pile of 3904/6, LM833, etc.

Now to see how I do with Larkin's x-acto/copper foil prototyping
technique, since I can't see getting boards made for every iteration of
goofing around I want to do, and these things are seriously small...

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
 
On 08/23/2012 01:52 PM, Ecnerwal wrote:
They fit the mold of what I was thinking might be the case - an "RF"
part with application elsewhere. I had actually found Phil's earlier
postings praising them (and verified that they were still available)
before I posted, but was not at all clear after looking at a datasheet
that cut off frequency specs at 0.1 Mhz on the low end if they'd work
reasonably for audio, given that they were being touted for RF in car
radios and a lot of what Phil does goes up there a ways.

Quite a price variance between digikey/newark/mouser, with mouser
winning strongly (27 cents for 1, 23.3 for 100.)

Given a lack of directly comparable graphs I have a hard time telling if
the slightly more expensive (43/29.9) and smaller (smaller not being an
advantage for me as a one-off tinkerer) 2SK880 has a _slightly_ lower
corner frequency or not really, but I suspect it's not enough of a
difference to actually matter (not going phoolish), given that I'm
mostly looking for a reasonable part to have on hand and play with in
the same way I have a pile of 3904/6, LM833, etc.

Now to see how I do with Larkin's x-acto/copper foil prototyping
technique, since I can't see getting boards made for every iteration of
goofing around I want to do, and these things are seriously small...
Click to expand...
I bought a reel of BF862s a year or two back for $650, or about 22 cents
each.

Using SOT23s in protos isn't too hard. You can mount them easily on the
pad-per-hole style of perf board, or get some prototyping adapters, e.g.
the Bellin Systems ones.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On 08/23/2012 12:45 PM, amdx wrote:
BF862s, really. They're the cat's pajamas.

Cheers

Phil Hobbs


Hey Phil,
Do you have a compliment to the BF862?
Mikek

Don't I wish. Try a BF862 in an inverted cascode with some nice quiet
PNP transistor, e.g. a 2N5087 at low frequency or a BFT92 at high
frequency.

Cheers

Phil Hobbs

Ya, most of this is over my head, I was just thinking about replacements
for an AM radio antenna preamp circuit I know of.
Is this a physics problem building a P type to match an N type?
Thanks, Mikek
Click to expand...
Yes. The hole mobility in silicon is low, which makes the
transconductance low, which makes P-channel devices noisier.

BJTs don't have the same issue since the base is so narrow and the
transconductance is very high, independent of device polarity. (PNPs
used to be slightly quieter than NPNs, but not any more.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Aug 23, 9:12 am, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
George Herold wrote:

On Aug 22, 2:45 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
George Herold wrote:

On Aug 20, 12:33 pm, Ecnerwal
MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties. No golden-ear BS,
just things that can be measured. Mic preamps, instrument pickup
preamps, a FET to have in the junkbox for unknown things yet to be
cobbled in the small-signal audio range. Cheap is also good. Jeorg cheap
would be even better ;-) Old-fashioned packaging would be nice, but its
unlikely these days, I think.

Mouser has one item that comes up with Audio JFET (that's not a jfet
input something else...) Audio FET gets a few more, but most are class D
power devices.

Toshiba 2SK880 in "irritatingly tiny" package. Par for the course these
days and I have adapted to soldering irritatingly tiny if I have no
other choice in packaging. 43 cents for 1, $29.50 for 100 Looks to be 5
years old judging by the datasheet date.

One that is mentioned in some older web circuits that's still marginally
available (in the 150% larger SOT23 only) is the J201, which seems to
have somewhat worse noise numbers. 23 cents for 1, $21.90 for 100, and
all of its relatives in other packages are already obsolete, so it may
not be long for this world, either?

Digi-key's search is as usual near useless (or it and I search
differently), and Newark comes up with a bunch of class-D power fets
that probably won't like non-switching use (If I have even a vaguely
correct recollection of what "class D audio amp" means. Looks like I do
per 5 seconds of checking my memory)

There are of course lots of RF parts that have no specs below 100Khz, or
1 Mhz, or 1 Ghz, depending on part. Perhaps some of them work fine for
audio. Anyone care to clue me in?

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

Hey, I was leafing through electronic design at lunch, and thought of
you when I saw an add for Jfets from linear systems.
(linearsystems.com)

George H.

BF862s, really.  They're the cat's pajamas.

Geesh Phil, I don't know.  Mostly I can't tell the difference between
a Jfet and a J stroke.

(They've got BF862's at newark for ~$0.30/100)
... I might have a use for a 0.8nV Fet.   Where's the 1/f knee?
At the moment it's a ~10kHz resonace, but I could move that up, some.

George H.

It's about 1 kHz.  They're firmly in the flatband at 10 kHz.
Click to expand...
Great, that's perfect. A colleague was chattering about active
damping (as was used to damp torsional fibers back in the day.) And I
mentioned that we could try active damping to kill some of the johnson
noise in a high Q RCL circuit. A nice low noise jfet might be
perfect. But I need to think about it some more.

George H.
Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -
Click to expand...
 
"Ecnerwal"
Trying to pick a JFET that's still being made with reasonable low noise
characteristics for simple audio preamp type duties.
Click to expand...

** JFETs have many desirable properties and one HUGE drawback.

The sample to sample parameter spread is massive - so much so that it is
normal to select devices for a given circuit so that bias / operating point
conditions will be met.

If you need diff pairs with low input offsets - then be prepared to waste
a lot of FETS.

FET input op-amps and matched FETs on a chip are the way to go.



..... Phil
 
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