Non-Phool jellybean audio-frequency JFET

[Phil Hobbs]

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.

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

 

[Phil Hobbs]

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

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

George Herold wrote:

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

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

- Show quoted text -

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

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

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

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

- Show quoted text -

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.)

George H.

 

[Phil Hobbs]

On 08/20/2012 12:33 PM, 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?

BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

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

 

[Phil Hobbs]

On 1/13/2015 12:36 PM, Phil Hobbs wrote:

On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

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

 

[Jim Thompson]

On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

Cheers

Phil Hobbs

You just don't appreciate the finer things in life >:-}

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[John Larkin]

On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

Cheers

Phil Hobbs

What do you have against bread pudding recipes?


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Jim Thompson]

On Tue, 13 Jan 2015 11:32:09 -0800, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

Cheers

Phil Hobbs

What do you have against bread pudding recipes?

Hobbs probably doesn't like grits either ;-)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Phil Hobbs]

On 01/13/2015 02:32 PM, John Larkin wrote:

On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

What do you have against bread pudding recipes?


Bread pudding is a crime against humanity.

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

 

[Phil Hobbs]

On 01/13/2015 03:10 PM, Jim Thompson wrote:

On Tue, 13 Jan 2015 11:32:09 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

Cheers

Phil Hobbs

What do you have against bread pudding recipes?

Hobbs probably doesn't like grits either ;-)

Well, on my current ketogenic diet, it's in the same category as cotton
candy.

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

 

[Jim Thompson]

On Tue, 13 Jan 2015 19:29:17 -0800, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Tue, 13 Jan 2015 15:13:57 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 01/13/2015 02:32 PM, John Larkin wrote:
On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

What do you have against bread pudding recipes?


Bread pudding is a crime against humanity.


I suppose I could work up a version that has a lot of meat in it.

That would ruin it. Ignore those people who don't relish a good bread
pudding.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[John Larkin]

On Tue, 13 Jan 2015 15:13:57 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 01/13/2015 02:32 PM, John Larkin wrote:
On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

What do you have against bread pudding recipes?


Bread pudding is a crime against humanity.

I suppose I could work up a version that has a lot of meat in it.


--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Hobbs]

On 1/13/2015 10:29 PM, John Larkin wrote:

On Tue, 13 Jan 2015 15:13:57 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 01/13/2015 02:32 PM, John Larkin wrote:
On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

What do you have against bread pudding recipes?


Bread pudding is a crime against humanity.


I suppose I could work up a version that has a lot of meat in it.

Or just save the bread, eggs, and sugar for something more like this:

http://tinyurl.com/q8bo96z

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

 

[John Larkin]

On Tue, 13 Jan 2015 20:46:58 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Tue, 13 Jan 2015 19:29:17 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Tue, 13 Jan 2015 15:13:57 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 01/13/2015 02:32 PM, John Larkin wrote:
On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

What do you have against bread pudding recipes?


Bread pudding is a crime against humanity.


I suppose I could work up a version that has a lot of meat in it.

That would ruin it. Ignore those people who don't relish a good bread
pudding.

...Jim Thompson

This is my Custard Bread Pudding. Custard on the bottom, bread and
fruit on top.

https://dl.dropboxusercontent.com/u/53724080/Food/CBP.JPG

Phil doesn't like this sort of thing. Maybe I could make the top layer
bacon. Or just take him to The House Of Prime Rib.

Last night I invented Shrimp and Bacon over fettucine, with a light
garlic cream sauce. Sort of a Shrimp Carbonara. Got good reviews.

I have a really interesting oscillator phaselock problem with wild
numerical things going on, vaguely like the old Tektronix "Random
Sampling" thing, but I can't discuss it in public. Pity.


--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Jim Thompson]

On Wed, 14 Jan 2015 08:25:16 -0800, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Tue, 13 Jan 2015 20:46:58 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Tue, 13 Jan 2015 19:29:17 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Tue, 13 Jan 2015 15:13:57 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 01/13/2015 02:32 PM, John Larkin wrote:
On Tue, 13 Jan 2015 12:42:22 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 1/13/2015 12:36 PM, Phil Hobbs wrote:
On 08/20/2012 12:33 PM, 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?


BF862. About 0.8 nV noise, 1/f corner about 1 kHz. They parallel very
nicely (we had a thread on that a couple of months back). When
parallelled directly, you want to run them at I_DSS, so an op amp servo
to force V_GS to be zero. If you're just using one, run it at about 12 mA.

Cheers

Phil Hobbs

Weird. This showed up on ES as a new post with no replies, and then
suddenly all this discussion from 2012 appeared.

Ah well, even antique circuit discussion is better than zillions of
posts about graduated cylinders and email clients, which in turn is
better than some of the other stuff we get stuck in sometimes. New
circuits discussion is better still of course.

What do you have against bread pudding recipes?


Bread pudding is a crime against humanity.


I suppose I could work up a version that has a lot of meat in it.

That would ruin it. Ignore those people who don't relish a good bread
pudding.

...Jim Thompson

This is my Custard Bread Pudding. Custard on the bottom, bread and
fruit on top.

https://dl.dropboxusercontent.com/u/53724080/Food/CBP.JPG

Looks good!

Phil doesn't like this sort of thing. Maybe I could make the top layer
bacon. Or just take him to The House Of Prime Rib.

Last night I invented Shrimp and Bacon over fettucine, with a light
garlic cream sauce. Sort of a Shrimp Carbonara. Got good reviews.

I regularly grill shrimp (and scallops) wrapped in bacon.

I have a really interesting oscillator phaselock problem with wild
numerical things going on, vaguely like the old Tektronix "Random
Sampling" thing, but I can't discuss it in public. Pity.

Most everything I do I can't talk about, until it's antiquated :-(

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[John Fields]

On Wed, 14 Jan 2015 08:25:16 -0800, John Larkin
<jlarkin@highlandtechnology.com> wrote:

..
..
..

I have a really interesting oscillator phaselock problem with wild
numerical things going on, vaguely like the old Tektronix "Random
Sampling" thing, but I can't discuss it in public. Pity.

---
If you can't discuss it, why on Earth would you even allude to it?

I think we both know the answer to that one...

https://www.youtube.com/watch?v=mQZmCJUSC6g