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.
> 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.
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
<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.
OPA2134? ~$2 at the 100 quant. 8nV/rtHz, (only 8MHz)
<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)
> 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
>> 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.
> 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.
<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
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.
> > 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.
> > 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
> 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.
> > > 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.
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
> 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.
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
>> 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
> 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
Ok, ok, Hello BF862, you've got some really nice parameters there.
Do you have a complement for the BF862?
Mikek
> 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
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
>> 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
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.
> 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...
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
>>> 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
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
<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.
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.
> Trying to pick a JFET that's still being made with reasonable low noise
> characteristics for simple audio preamp type duties.
** 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.
> > Trying to pick a JFET that's still being made with reasonable low noise
> > characteristics for simple audio preamp type duties.
> ** 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
That's all too true of every JFET that I know about except one: the
BF862. Have a look at the datasheet--they're magic. I'd never use a
JFET in anything if it weren't for these ones. Their transconductance
is very high, so the action is all over in about 400 mV. They're very
predictable for a JFET, comparable to a pHEMT, and almost as good as a
BJT. You just parallel them up and away you go.
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
> > > Trying to pick a JFET that's still being made with reasonable low noise
> > > characteristics for simple audio preamp type duties.
> > ** 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
> That's all too true of every JFET that I know about except one: the
> BF862. Have a look at the datasheet--they're magic. I'd never use a
> JFET in anything if it weren't for these ones. Their transconductance
> is very high, so the action is all over in about 400 mV. They're very
> predictable for a JFET, comparable to a pHEMT, and almost as good as a
> BJT. You just parallel them up and away you go.
One other thing: Since they're so quiet, and not _that_ well matched, I
very often use a BF862 follower driving the inverting input of a very
low noise bipolar op amp such as an ADA4898. Use an adjustable current
sink to bias the FET's source, and use a FET op amp in a very slow
feedback loop, holding V_GS at zero. (This is often called "snooping
the summing junction". Do it via a 10k-1M resistor to keep from loading
the SJ, and keep the snooper's loop bandwidth low enough that you don't
care about the big resistor's noise.)
That gets you an excellent FET input amp for inverting applications: <
100 pA input current, ~1.2 nV/sqrt(Hz) noise, ~100 MHz GBW. With a few
AC fiddles, e.g. bootstrapping various things, this makes a really
brilliant TIA among other things.
You can do the same sort of thing for noninverting use, but you have to
be a bit careful about the large signal performance of the current sink
and the snooper.
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
<pcdhSpamMeSensel...@electrooptical.net> wrote:
> Phil Hobbs wrote:
> > Phil Allison wrote:
> > > "Ecnerwal"
> > > > Trying to pick a JFET that's still being made with reasonable low noise
> > > > characteristics for simple audio preamp type duties.
> > > ** 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
> > That's all too true of every JFET that I know about except one: the
> > BF862. Have a look at the datasheet--they're magic. I'd never use a
> > JFET in anything if it weren't for these ones. Their transconductance
> > is very high, so the action is all over in about 400 mV. They're very
> > predictable for a JFET, comparable to a pHEMT, and almost as good as a
> > BJT. You just parallel them up and away you go.
> One other thing: Since they're so quiet, and not _that_ well matched, I
> very often use a BF862 follower driving the inverting input of a very
> low noise bipolar op amp such as an ADA4898. Use an adjustable current
> sink to bias the FET's source, and use a FET op amp in a very slow
> feedback loop, holding V_GS at zero. (This is often called "snooping
> the summing junction". Do it via a 10k-1M resistor to keep from loading
> the SJ, and keep the snooper's loop bandwidth low enough that you don't
> care about the big resistor's noise.)
> That gets you an excellent FET input amp for inverting applications: <
> 100 pA input current, ~1.2 nV/sqrt(Hz) noise, ~100 MHz GBW. With a few
> AC fiddles, e.g. bootstrapping various things, this makes a really
> brilliant TIA among other things.
> You can do the same sort of thing for noninverting use, but you have to
> be a bit careful about the large signal performance of the current sink
> and the snooper.
> 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
Very cool thanks Phil.
I think I followed about 1/2 of that. (You make me feel like a cave
man rubbing two resistors together at times.)
I was thinking about using the jfets as a differential pair in front
of a 'nice' opamp. (a B. Pease circuit fragment.)
For a simple resistor only circuit, I've recently been turned on to
this artifical resistor circuit by R.L. Forward.
(US patent 4176331, or J. Appl. Phys. (53) 3365, 1982
Three resistors and an opamp. Just my speed! (I'm still working on
the noise analysis.)
("Dragons Egg" (sci fi.) by R.L. Forward is a fun read.)
> On Aug 24, 9:42 am, Phil Hobbs
> <pcdhSpamMeSensel...@electrooptical.net> wrote:
> > Phil Hobbs wrote:
> > > Phil Allison wrote:
> > > > "Ecnerwal"
> > > > > Trying to pick a JFET that's still being made with reasonable low noise
> > > > > characteristics for simple audio preamp type duties.
> > > > ** 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
> > > That's all too true of every JFET that I know about except one: the
> > > BF862. Have a look at the datasheet--they're magic. I'd never use a
> > > JFET in anything if it weren't for these ones. Their transconductance
> > > is very high, so the action is all over in about 400 mV. They're very
> > > predictable for a JFET, comparable to a pHEMT, and almost as good as a
> > > BJT. You just parallel them up and away you go.
> > One other thing: Since they're so quiet, and not _that_ well matched, I
> > very often use a BF862 follower driving the inverting input of a very
> > low noise bipolar op amp such as an ADA4898. Use an adjustable current
> > sink to bias the FET's source, and use a FET op amp in a very slow
> > feedback loop, holding V_GS at zero. (This is often called "snooping
> > the summing junction". Do it via a 10k-1M resistor to keep from loading
> > the SJ, and keep the snooper's loop bandwidth low enough that you don't
> > care about the big resistor's noise.)
> > That gets you an excellent FET input amp for inverting applications: <
> > 100 pA input current, ~1.2 nV/sqrt(Hz) noise, ~100 MHz GBW. With a few
> > AC fiddles, e.g. bootstrapping various things, this makes a really
> > brilliant TIA among other things.
> > You can do the same sort of thing for noninverting use, but you have to
> > be a bit careful about the large signal performance of the current sink
> > and the snooper.
> > 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
> Very cool thanks Phil.
> I think I followed about 1/2 of that. (You make me feel like a cave
> man rubbing two resistors together at times.)
Didn't mean to be mysterious about it. The main op amp runs with its
noninverting input grounded, so its feedback will hold the BF862's
source at ground. The remaining problem is to make sure that the gate
of the BF862 is also at ground, for which you need a current sink in its
source that's adjusted to exactly I_DSS.
The current sink should be a BJT with a couple of volts drop across its
emitter resistor (which gets rid of its shot noise pretty well). The
snooper op amp is connected as a slow integrator, with its inverting
input connected to the gate of the BF862 through a sufficiently large
resistor, and its noninverting input grounded. Its output controls the
current source. (Make sure you can get any current from about 8 to 25
mA, and watch out that you don't crank up the current high enough to
forward-bias the GS junction.)
The bad news is that you get the Johnson noise of the big resistor, but
it goes away for frequencies more than ~10 times the loop BW. Another
RC bypassing the base of the BJT to the negative supply helps with high
frequency noise and PSRR.
That way the BF862 always runs at exactly I_DSS, and you avoid the
offset, drift, and extra noise caused by using a BF862 diff pair.
> I was thinking about using the jfets as a differential pair in front
> of a 'nice' opamp. (a B. Pease circuit fragment.)
The main problem with that, as with all composite amps, is frequency
compensating it without getting all sorts of whoop-de-doos at late times
in the step response. (Putting a pole-zero pair inside a feedback loop
doesn't get rid of it entirely--it replaces it with two closely spaced
pairs, and the error shows up as ~1%-ish ripples in the step response.)
> For a simple resistor only circuit, I've recently been turned on to
> this artifical resistor circuit by R.L. Forward.
> (US patent 4176331, or J. Appl. Phys. (53) 3365, 1982
> Three resistors and an opamp. Just my speed! (I'm still working on
> the noise analysis.)
> ("Dragons Egg" (sci fi.) by R.L. Forward is a fun read.)
Thanks. I'm an old Forward fan, ever since coming across some of his
science writing when I was about 12. I've read Dragonfly, Rocheworld,
and a few others. Good medicine. He also wrote a really great paper
about using interferometers to detect gravity waves in about 1972.
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
