lose down this news group.

[terryS]

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

 

[Michael Black]

On Mon, 26 Apr 2010, terryS wrote:

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

There are a few things at play.

First, you post from google, which is where a lot of the spam
is being posted through.

Second, proper newsfeeds often filter the most outrageous spam,
so the rest of us don't always see what the people whining at
google see.

Third, yes, I see a couple of instances of clusters of spam in the
past week or so, but that doesn't represent the ongoing newsgroup,
it sounds like you just pop in every so often, and then all you
see is spam.

Fourth, the newsgroup started "going downhill" years ago. One reason is
that new people stopped coming at the extent that they used to, they don't
know about newsgroups and they go elsewhere. A newsgroup actually needs
a steady stream of newcomers to make it viable. Then ISPs started
dropping Usenet, always claiming that people aren't interested in it,
so access isn't a default like it used to be.

Compounding that decline is that as people came, they saw a less lively
group, and then posted their questions in .design even outright saying "I
know this isn't the place, but it has more traffic". So that lessens
the traffic even more, and is bound to be bad for those posters, since
..design is not the same thing as .basic.

Now, one thing that happens over in .design is that it slowly became
a hangout, people posting about their off-topic junk instead of
finding the appropriate place, and then big arguments over off-topic
things, which makes .design look healthy in terms of traffic, but
actually indicates an equal decline of .design, it's just that they
are constantly yammering so it doesn't look "dead".

So few new posters come, then if they come they decide to post in
the wrong newsgroup. And then, any spam that might appear looks
worse than it did because traffic is so low that a few bits of
spam dwarf the new threads started here.

Michael

 

[Tom Biasi]

"Michael Black" <et472@ncf.ca> wrote in message
newsine.LNX.4.64.1004261515220.30246@darkstar.example.net...

On Mon, 26 Apr 2010, terryS wrote:

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

There are a few things at play.

First, you post from google, which is where a lot of the spam
is being posted through.

Second, proper newsfeeds often filter the most outrageous spam,
so the rest of us don't always see what the people whining at
google see.

Third, yes, I see a couple of instances of clusters of spam in the
past week or so, but that doesn't represent the ongoing newsgroup,
it sounds like you just pop in every so often, and then all you
see is spam.

Fourth, the newsgroup started "going downhill" years ago. One reason is
that new people stopped coming at the extent that they used to, they don't
know about newsgroups and they go elsewhere. A newsgroup actually needs
a steady stream of newcomers to make it viable. Then ISPs started
dropping Usenet, always claiming that people aren't interested in it,
so access isn't a default like it used to be.

Compounding that decline is that as people came, they saw a less lively
group, and then posted their questions in .design even outright saying "I
know this isn't the place, but it has more traffic". So that lessens
the traffic even more, and is bound to be bad for those posters, since
.design is not the same thing as .basic.

Now, one thing that happens over in .design is that it slowly became
a hangout, people posting about their off-topic junk instead of
finding the appropriate place, and then big arguments over off-topic
things, which makes .design look healthy in terms of traffic, but
actually indicates an equal decline of .design, it's just that they
are constantly yammering so it doesn't look "dead".

So few new posters come, then if they come they decide to post in
the wrong newsgroup. And then, any spam that might appear looks
worse than it did because traffic is so low that a few bits of
spam dwarf the new threads started here.

Michael

Well said Michael, of course I didn't see the original post because I filter
Google Groups.
Tom

 

[Baron]

Michael Black Inscribed thus:

On Mon, 26 Apr 2010, terryS wrote:

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

There are a few things at play.

First, you post from google, which is where a lot of the spam
is being posted through.

Second, proper newsfeeds often filter the most outrageous spam,
so the rest of us don't always see what the people whining at
google see.

Third, yes, I see a couple of instances of clusters of spam in the
past week or so, but that doesn't represent the ongoing newsgroup,
it sounds like you just pop in every so often, and then all you
see is spam.

Fourth, the newsgroup started "going downhill" years ago. One reason
is that new people stopped coming at the extent that they used to,
they don't
know about newsgroups and they go elsewhere. A newsgroup actually
needs
a steady stream of newcomers to make it viable. Then ISPs started
dropping Usenet, always claiming that people aren't interested in it,
so access isn't a default like it used to be.

Compounding that decline is that as people came, they saw a less
lively group, and then posted their questions in .design even outright
saying "I
know this isn't the place, but it has more traffic". So that lessens
the traffic even more, and is bound to be bad for those posters, since
.design is not the same thing as .basic.

Now, one thing that happens over in .design is that it slowly became
a hangout, people posting about their off-topic junk instead of
finding the appropriate place, and then big arguments over off-topic
things, which makes .design look healthy in terms of traffic, but
actually indicates an equal decline of .design, it's just that they
are constantly yammering so it doesn't look "dead".

So few new posters come, then if they come they decide to post in
the wrong newsgroup. And then, any spam that might appear looks
worse than it did because traffic is so low that a few bits of
spam dwarf the new threads started here.

Michael

Well said.

--
Best Regards:
Baron.

 

[steamer]

--Killfiles are your friends; get the knack of using them and half
the battle's won. That, and shell: some call it primitive but it solves a
myriad of problems..

--
"Steamboat Ed" Haas : Come see my stuff
Hacking the Trailing Edge! : at Maker Faire!!
www.nmpproducts.com
---Decks a-wash in a sea of words---

 

[John Larkin]

On Mon, 26 Apr 2010 12:08:42 -0700 (PDT), terryS
<tsanford@nf.sympatico.ca> wrote:

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

My usenet provider and spam filters do a pretty good job of keeping
the junk down. That said, there's little actual activity left.

John

 

[Michael Black]

On Mon, 26 Apr 2010, John Larkin wrote:

On Mon, 26 Apr 2010 12:08:42 -0700 (PDT), terryS
tsanford@nf.sympatico.ca> wrote:

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

My usenet provider and spam filters do a pretty good job of keeping
the junk down. That said, there's little actual activity left.

Now I know why the post sounded familiar, it's more than simply because

we see such posts from time to time.

Back on January 8th of this year (2010) the same poster posted about
spam, posting nonsense and even suggesting this newsgroup be "closed
down". That explains the subject header this time around, he isn't
taking nonsene but "close down this news group".

So like I said, he isn't paying attention. Probably this is the
first time since then that he's looked in here.

Michael

 

[John Larkin]

On Mon, 26 Apr 2010 20:19:25 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:
Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!


OK, I still like this group. Here's today's problem. I was measuring
the power supply noise that was feeding my input opamp. And when I
did that the noise went down! opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground. The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

Emitter followers love to oscillate when the base impedance is low.
The fix is a series base resistor, or a ferrite bead if you're afraid
of Johnson noise.

This is an energetic, ballpark 100 MHz oscillator:



+10
|
|
|
c
+5----------------b most any NPN
e
|
+----------out
|
1K
|
|
|
gnd

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

George H.

The OPA is spec'd for 8 nv/rthz typ, so you're about there. Most
opamps have really ratty PSRR at high frequencies, so a clean supply
is mandatory.


John

 

[Paul E. Schoen]

"George Herold" <ggherold@gmail.com> wrote in message
news:8c2d90ba-9e79-42c5-bf7c-db403e62eb85@v18g2000vbc.googlegroups.com...
On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

OK, I still like this group. Here's today's problem. I was measuring
the power supply noise that was feeding my input opamp. And when I
did that the noise went down! opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground. The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

======================================================================

Not big enough to filter spam. I put a couple of 30 uF 660 VAC oil filled
capacitors on my computer screen, and I no longer saw any spam!

I think it may be time to "lose down" and go with a polyester alternative.
PETA agrees.

Seriously, I enjoy selecting and deleting the spam. It's like shooting
ducks, and I imagine my delete key sending shock waves back to the
perpetrators.

Google may be doing a disservice by listing the most popular active
newsgroups. That attracts spammers and their posts add to the activity and
boost the ratings and fuels the spammers' greed. If legitimate posts
dwindle, then the spammers will be trying to sell their crap to each other.

Paul

 

[Sjouke Burry]

George Herold wrote:

On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:
Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!


OK, I still like this group. Here's today's problem. I was measuring
the power supply noise that was feeding my input opamp. And when I
did that the noise went down! opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground. The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

George H.
You might also check for very high frequency oscilation.

Changes occurring when you barely tough a circuit is the first
symptom.

 

[George Herold]

On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:

Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

OK, I still like this group. Here's today's problem. I was measuring
the power supply noise that was feeding my input opamp. And when I
did that the noise went down! opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground. The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

George H.

 

[John Larkin]

On Tue, 27 Apr 2010 00:44:49 -0400, "Paul E. Schoen"
<paul@pstech-inc.com> wrote:

"George Herold" <ggherold@gmail.com> wrote in message
news:8c2d90ba-9e79-42c5-bf7c-db403e62eb85@v18g2000vbc.googlegroups.com...
On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:
Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!


OK, I still like this group. Here's today's problem. I was measuring
the power supply noise that was feeding my input opamp. And when I
did that the noise went down! opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground. The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

======================================================================

Not big enough to filter spam. I put a couple of 30 uF 660 VAC oil filled
capacitors on my computer screen, and I no longer saw any spam!

Wrap your monitor in tinfoil. I've heard that works.

John

 

[John Larkin]

On Tue, 27 Apr 2010 08:10:06 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Apr 27, 9:43 am, George Herold <ggher...@gmail.com> wrote:
On Apr 27, 12:20 am, John Larkin





jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 26 Apr 2010 20:19:25 -0700 (PDT), George Herold

ggher...@gmail.com> wrote:
On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:
Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

OK, I still like this group.  Here's today's problem.  I was measuring
the power supply noise that was feeding my input opamp.  And when I
did that the noise went down!  opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground.  The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

Emitter followers love to oscillate when the base impedance is low.
The fix is a series base resistor, or a ferrite bead if you're afraid
of Johnson noise.

This is an energetic, ballpark 100 MHz oscillator:

Yeah with a 2N3904 the thing would sometimes 'sing' up at
2-300MHz....



                      +15
                       |
                1K-----+
                 |     |
                 |     c
                 +----b     2n3904
                 |     e
                 C     |
                 C     +-------To opamp supply pin.
                 |     |
                GND    C
                       C
                       |
                      GND

Ferrite beads on the base lead helped a bit... a 10ohm resistor worked
better.  But with a 2N4401 I never observed any 'singing'.  So the
beads and R are left in the base and I used the 2N4401's.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

George H.

The OPA is spec'd for 8 nv/rthz typ, so you're about there. Most
opamps have really ratty PSRR at high frequencies, so a clean supply
is mandatory.

John- Hide quoted text -

- Show quoted text -

Yeah the noise is exactly what the spec sheet claims.  I was going to
have the students measure the noise on the power supply.  But I don't
know what to tell them when measuring it makes the amplifier noise
smaller... very confusing.  I sprinkled some film caps on the power
supplies but that didn't change anything.  When I put some load on the
power supply the effect became smaller.  (pulled about 100mA from it.)

I'm going to try and measure the supply noise with an opamp powered
from some other supply.... (Guessing it might be some weird coherence
thing.)

Oh I also tried a BJT opamp (opa228)  Here the effect was much
smaller!  But still at perhaps the 1% level the noise was less when
the opamp was looking at one of it's supply rails that when it was
looking at ground.  (ground either through a cap or a 1 ohm
resistor.)

 George H.- Hide quoted text -

- Show quoted text -

OK for anyone who cares, I was able to measure the ~ 1nV/rtHz of noise
on my power rails when I power up the opamp from a different supply.

My brain starts to hurt when I try to imagine how looking at the power
rail could reduce the meausred noise. So I'm just ovserving it and
moving on....

George H.

Opamp front ends tend to rectify ambient RF noise, like from radio
stations and cell phones. If they do, minor alterations of the
environment, like scope probing or moving cables around or just
touching stuff, can change things a lot. Ditto if some other part on
the board is oscillating. The most fun is a stage that only oscillates
at some operating points, like a class AB power stage. We recently did
a complicated bootstrapped power amp that only oscillated when the
output was in two narrow ranges in the vicinity of +4 and -4 volts,
and the oscillation got into a front-end opamp. Yuk.

Whenever we have an unexpected DC offset or noise level, I do the
laying-on-of-hands thing. Fingers have amazing RF damping properties.
A side benefit is that you can tell if something is running too hot.

It's surprising how many techs and EEs won't touch things because they
are afraid of being shocked, even when they know none of the supplies
exceed 30 volts. I know otherwise sensible people who are afraid of 9
volt batteries. Lots of people are afraid of car batteries.

John

 

[George Herold]

On Apr 27, 12:20 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 26 Apr 2010 20:19:25 -0700 (PDT), George Herold





ggher...@gmail.com> wrote:
On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:
Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

OK, I still like this group.  Here's today's problem.  I was measuring
the power supply noise that was feeding my input opamp.  And when I
did that the noise went down!  opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground.  The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

Emitter followers love to oscillate when the base impedance is low.
The fix is a series base resistor, or a ferrite bead if you're afraid
of Johnson noise.

This is an energetic, ballpark 100 MHz oscillator:

Yeah with a 2N3904 the thing would sometimes 'sing' up at
2-300MHz....

                      +15
                       |
                1K-----+
                 |    |
                 |    c
    +----b     2n3904
                 |     e
                 C     |
                 C     +-------To opamp supply pin.
                 |    |
                GND    C
C
|
GND

Ferrite beads on the base lead helped a bit... a 10ohm resistor worked
better. But with a 2N4401 I never observed any 'singing'. So the
beads and R are left in the base and I used the 2N4401's.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

George H.

The OPA is spec'd for 8 nv/rthz typ, so you're about there. Most
opamps have really ratty PSRR at high frequencies, so a clean supply
is mandatory.

John- Hide quoted text -

- Show quoted text -

Yeah the noise is exactly what the spec sheet claims. I was going to
have the students measure the noise on the power supply. But I don't
know what to tell them when measuring it makes the amplifier noise
smaller... very confusing. I sprinkled some film caps on the power
supplies but that didn't change anything. When I put some load on the
power supply the effect became smaller. (pulled about 100mA from it.)

I'm going to try and measure the supply noise with an opamp powered
from some other supply.... (Guessing it might be some weird coherence
thing.)

Oh I also tried a BJT opamp (opa228) Here the effect was much
smaller! But still at perhaps the 1% level the noise was less when
the opamp was looking at one of it's supply rails that when it was
looking at ground. (ground either through a cap or a 1 ohm
resistor.)

George H.

 

[John Fields]

On Tue, 27 Apr 2010 07:05:10 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 27 Apr 2010 00:44:49 -0400, "Paul E. Schoen"
paul@pstech-inc.com> wrote:


"George Herold" <ggherold@gmail.com> wrote in message
news:8c2d90ba-9e79-42c5-bf7c-db403e62eb85@v18g2000vbc.googlegroups.com...
On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:
Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!


OK, I still like this group. Here's today's problem. I was measuring
the power supply noise that was feeding my input opamp. And when I
did that the noise went down! opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground. The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

======================================================================

Not big enough to filter spam. I put a couple of 30 uF 660 VAC oil filled
capacitors on my computer screen, and I no longer saw any spam!

Wrap your monitor in tinfoil. I've heard that works.

---
A little pricey, though...

http://www.alfa.com/en/gp140w.pgm

JF

 

[George Herold]

On Apr 27, 9:43 am, George Herold <ggher...@gmail.com> wrote:

On Apr 27, 12:20 am, John Larkin





jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 26 Apr 2010 20:19:25 -0700 (PDT), George Herold

ggher...@gmail.com> wrote:
On Apr 26, 3:08 pm, terryS <tsanf...@nf.sympatico.ca> wrote:
Looks like this news group has gone the way of some others.

It's inundated with advertising; for Gucci and Rolex cheap copies,
imitation or over-stock Nike shoes etc. doubtful services or site
references and so on.

So it's now virtually useless for it's original purpose. i.e.
discussion of basic electronics and allied matters.

Personally make a point of NEVER contacting or buying anything from
any one of these advertising interlopers to what once was a useful
discussion group.

Anyone agree? Bye the bye ...................... goodbye!

OK, I still like this group.  Here's today's problem.  I was measuring
the power supply noise that was feeding my input opamp.  And when I
did that the noise went down!  opamp was opa134 with 1uF film cap to
the power supply rail and 10k ohm to ground.  The power supply came
from a switcher ~100kHz, I have a ~30kHz LC filter in front of
it(100uH torroids and ??? tantalum caps.), followed by a two pole
capacitor multiplier. (2N4401/3..2N3904/6's oscillated too much.) 1
kohm, and 100uf Al electro. in parallel with 0.1 uF ceramic.

Emitter followers love to oscillate when the base impedance is low.
The fix is a series base resistor, or a ferrite bead if you're afraid
of Johnson noise.

This is an energetic, ballpark 100 MHz oscillator:

Yeah with a 2N3904 the thing would sometimes 'sing' up at
2-300MHz....



                      +15
                       |
                1K-----+
                 |     |
                 |     c
                 +----b     2n3904
                 |     e
                 C     |
                 C     +-------To opamp supply pin.
                 |     |
                GND    C
                       C
                       |
                      GND

Ferrite beads on the base lead helped a bit... a 10ohm resistor worked
better.  But with a 2N4401 I never observed any 'singing'.  So the
beads and R are left in the base and I used the 2N4401's.

The noise went down from ~8 nV/rtHZ when the 1uF cap was connected to
ground to about 5% lower... 7.7 nV/ ... Maybe I should start hanging
1uF metal films everywhere?

George H.

The OPA is spec'd for 8 nv/rthz typ, so you're about there. Most
opamps have really ratty PSRR at high frequencies, so a clean supply
is mandatory.

John- Hide quoted text -

- Show quoted text -

Yeah the noise is exactly what the spec sheet claims.  I was going to
have the students measure the noise on the power supply.  But I don't
know what to tell them when measuring it makes the amplifier noise
smaller... very confusing.  I sprinkled some film caps on the power
supplies but that didn't change anything.  When I put some load on the
power supply the effect became smaller.  (pulled about 100mA from it.)

I'm going to try and measure the supply noise with an opamp powered
from some other supply.... (Guessing it might be some weird coherence
thing.)

Oh I also tried a BJT opamp (opa228)  Here the effect was much
smaller!  But still at perhaps the 1% level the noise was less when
the opamp was looking at one of it's supply rails that when it was
looking at ground.  (ground either through a cap or a 1 ohm
resistor.)

 George H.- Hide quoted text -

- Show quoted text -

OK for anyone who cares, I was able to measure the ~ 1nV/rtHz of noise
on my power rails when I power up the opamp from a different supply.

My brain starts to hurt when I try to imagine how looking at the power
rail could reduce the meausred noise. So I'm just ovserving it and
moving on....

George H.

 

[Michael A. Terrell]

John Larkin wrote:

Lots of people are afraid of car batteries.

Have you ever had one explode in your vehicle?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

http://www.flickr.com/photos/materrell/

 

[John Larkin]

On Tue, 27 Apr 2010 18:47:08 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

John Larkin wrote:

Lots of people are afraid of car batteries.


Have you ever had one explode in your vehicle?

No. I've heard of it happening but it's very improbable. But it won't
shock you.

John

 

[krw@att.bizzzzzzzzzzzz]

On Tue, 27 Apr 2010 16:02:35 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 27 Apr 2010 18:47:08 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

John Larkin wrote:

Lots of people are afraid of car batteries.


Have you ever had one explode in your vehicle?

No. I've heard of it happening but it's very improbable. But it won't
shock you.

You'd be at least surprised, if it exploded in your face!

;-)

 

[baron]

krw@att.bizzzzzzzzzzzz Inscribed thus:

On Tue, 27 Apr 2010 16:02:35 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 27 Apr 2010 18:47:08 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

John Larkin wrote:

Lots of people are afraid of car batteries.


Have you ever had one explode in your vehicle?

No. I've heard of it happening but it's very improbable. But it won't
shock you.

You'd be at least surprised, if it exploded in your face!

;-)

Saw a mechanic once that took a battery terminal off whilst the engine
was running. It didn't explode the battery but some of the fill plugs
certainly shot out...

--
Best Regards:
Baron.