[[email protected]]

If you have a choice of using either 1 good op amp that meets specs, or 2 poorer
op amps in series to do the same thing, would the 2 choice be guaranteed to have
more noise? I assume there would be more 'devices' in 2 amps then in 1 therefore
more sources of noise? Also I assume a poorer gain/bandwidth amp would also be
noisier...

[Phil Allison]

If you have a choice of using either 1 good op amp that meets specs, or 2
poorer
op amps in series to do the same thing, would the 2 choice be guaranteed
to have
more noise?


** Noise originates at the input of the first amplifier in a chain - then
it gets amplified.

So, a low noise op-amp will always produce less noise than multiple
inferiors - however wired.


I assume there would be more 'devices' in 2 amps then in 1 therefore
more sources of noise? Also I assume a poorer gain/bandwidth amp would
also be
noisier...


** Read the specs.

Input noise figures are GBW are not related.



......... Phil

[Patrick Turner]

wrote:

If you have a choice of using either 1 good op amp that meets specs, or 2 poorer
op amps in series to do the same thing, would the 2 choice be guaranteed to have
more noise? I assume there would be more 'devices' in 2 amps then in 1 therefore
more sources of noise? Also I assume a poorer gain/bandwidth amp would also be
noisier...

The input noise of a device with NFB cannot be reduced by the NFB.
The noise is ahead and not included in the NFB loop, so cannot be
reduced.

Using a second amp produces noise, but it will be at
such a low level compared to that made by the first amp
you can neglect it..

Try building a two stage amp with total gain = 1,000.

Measure the performance accurately. Then you will
fully answer your own question, and will have learnt something useful.

Patrick Turner.

[[email protected]]

On Sat, 28 Apr 2007 03:48:50 GMT, Patrick Turner
wrote:



wrote:

If you have a choice of using either 1 good op amp that meets specs, or 2 poorer
op amps in series to do the same thing, would the 2 choice be guaranteed to have
more noise? I assume there would be more 'devices' in 2 amps then in 1 therefore
more sources of noise? Also I assume a poorer gain/bandwidth amp would also be
noisier...

The input noise of a device with NFB cannot be reduced by the NFB.
The noise is ahead and not included in the NFB loop, so cannot be
reduced.

Using a second amp produces noise, but it will be at
such a low level compared to that made by the first amp
you can neglect it..

Try building a two stage amp with total gain = 1,000.

Measure the performance accurately. Then you will
fully answer your own question, and will have learnt something useful.

Patrick Turner.

If I were to build a 2 or 3 transistor preamp, I should only concern myself with
the noise of the input transistor, then? (and the input resistor...) That way a
noisy 741 could be boosted to a gain of 1000?

[Phil Allison]

If I were to build a 2 or 3 transistor preamp, I should only concern
myself with
the noise of the input transistor, then? (and the input resistor...) That
way a
noisy 741 could be boosted to a gain of 1000?


** Was common in the past to see 741s with a differential pair of
transistors up front.

For Phono and tape head pres.

You know SFA about op-amps, the 741 or any other.

Quit the stupid trolling.




........ Phil

[Patrick Turner]

wrote:

On Sat, 28 Apr 2007 03:48:50 GMT, Patrick Turner
wrote:



wrote:

If you have a choice of using either 1 good op amp that meets specs, or 2 poorer
op amps in series to do the same thing, would the 2 choice be guaranteed to have
more noise? I assume there would be more 'devices' in 2 amps then in 1 therefore
more sources of noise? Also I assume a poorer gain/bandwidth amp would also be
noisier...

The input noise of a device with NFB cannot be reduced by the NFB.
The noise is ahead and not included in the NFB loop, so cannot be
reduced.

Using a second amp produces noise, but it will be at
such a low level compared to that made by the first amp
you can neglect it..

Try building a two stage amp with total gain = 1,000.

Measure the performance accurately. Then you will
fully answer your own question, and will have learnt something useful.

Patrick Turner.

If I were to build a 2 or 3 transistor preamp, I should only concern myself with
the noise of the input transistor, then? (and the input resistor...) That way a
noisy 741 could be boosted to a gain of 1000?

Some ppl used a relatively quiet discrete pair of transistors or j-fets
as a differential input pair then followed up with a 741, which wasn't
any noisier than a
12AX7 and so there was no need for the 741 to be silent just like there
isn't any need for the 12AX7 to be silent
either, if used as a following amplifier to bring total gain to 1,000.

Its done in phono amps routinely.

Build some amps and learn something!!!!

Patrick Turner.

[Eeyore]

wrote:

If I were to build a 2 or 3 transistor preamp, I should only concern myself with
the noise of the input transistor, then? (and the input resistor...)

The input device is *normally* of most concern but one should be aware of 'noise
buildup' in any signal path from various sources.


That way a noisy 741 could be boosted to a gain of 1000?

It would still have the input noise of the 741. Several 741s with a combined gain of
1000 won't be any quieter than a single one. In fact they'll be noisier.

I suggest you drop the idea of using 741s and move on to something that at least
originated in the 80s !

Graham

[Arny Krueger]

wrote in message


If you have a choice of using either 1 good op amp that
meets specs, or 2 poorer op amps in series to do the same
thing, would the 2 choice be guaranteed to have more
noise?

The problem is stated so vaguely that no firm conclusions can be reached.

I assume there would be more 'devices' in 2 amps
then in 1 therefore more sources of noise?

An over-simplification.

If you want to achieve low noise with cheap devices, you connect them in
parallel, and mix the outputs together. Their noise will be uncorrelated,
and when summed dynamic range will improve about 3 dB for every doubling of
device count.

Also I assume
a poorer gain/bandwidth amp would also be noisier...

Another over-simplification.

It's not unusual for the parameter choices that result in broad bandwidth to
also increase noise. Also, noise sources geneate noise at the rate of so
much for a band of a certain width. Increase the bandwidth of the noise
measurement, and the noise measurement will increase.

[[email protected]]

On Sun, 29 Apr 2007 03:45:06 +0100, Eeyore
wrote:



wrote:

If I were to build a 2 or 3 transistor preamp, I should only concern myself with
the noise of the input transistor, then? (and the input resistor...)

The input device is *normally* of most concern but one should be aware of 'noise
buildup' in any signal path from various sources.


That way a noisy 741 could be boosted to a gain of 1000?

It would still have the input noise of the 741. Several 741s with a combined gain of
1000 won't be any quieter than a single one. In fact they'll be noisier.

I suggest you drop the idea of using 741s and move on to something that at least
originated in the 80s !

Hey it isn't me wanting to use 741s!!!

Graham

[[email protected]]

On Sun, 29 Apr 2007 11:20:00 +1000, "Phil Allison"
wrote:





If I were to build a 2 or 3 transistor preamp, I should only concern
myself with
the noise of the input transistor, then? (and the input resistor...) That
way a
noisy 741 could be boosted to a gain of 1000?


** Was common in the past to see 741s with a differential pair of
transistors up front.

For Phono and tape head pres.

You know SFA about op-amps, the 741 or any other.

Really? How would you know that?

What would you like to know that I know? Just off the top of my head...


OP amps have 2 inputs and 1 output, as well as power supply leads. (They may
also have frequency/gain compensation inputs, not required for a theory
discussion.)

1 input is marked + and the other is marked -.

The + input is usually called the follower input, and can have a high input
impedance.

The - input is the opposite differential pair, and is a virtual ground. Signal
cannot be measured here.

The output of the amp is usually connected to the - input in some way, for
normal amplifier applications.

If the connection is direct, the amp will have a gain of 1, and the + input is
used for input. This is used as a buffer since it may have current gain.

If a resistance is used, another resistor has to be connected to ground, and the
gain of the amp will be (Rf/Rg)+1 (Note the gain can't be less than 1)

The - input can also be used as an input. In this case the required series input
resistor is the former ground connect resistor. Note the input must have a path
to ground through the source. The + input in this case is usually conned to
ground through a resistor, but can be shorted.

The gain when using the - input is roughly equal to (Rf/Ri). The gain can be
zero!

Connecting a capacitor from output to - input gives us an integrator, where the
gain of the amp is maximum until a signal arrives, whereupon the charging
current gives us the feedback signal delayed by the capacitor. Connecting a
diode gives us a rectifier that works below the .2v or .5v diode threshold since
the gain is also maximum until the output voltage rises enough to overcome the
diode barrier.

Well that's enough for now... I'm tired of typing...


Quit the stupid trolling.

Ok - if you say so...


....... Phil

[Eeyore]

wrote:

The + input is usually called the follower input,

No it isn't. It's called the non-inverting input.


and can have a high input impedance.

It *does* have a high input impedance.


The - input is the opposite differential pair,

The inverting input.


and is a virtual ground.

No it isn't. It's also high impedance. See a schematic of the internal circuitry if
you doubt me.


Signal cannot be measured here.

It damn well can ! Even when it's a virtual earth. Note *virtual*. I've seen up to
75mV here.


The output of the amp is usually connected to the - input in some way, for
normal amplifier applications.

The expression you're looking for is negative feedback.

You need to learn more.

Graham

[Chris Hornbeck]

On Sun, 29 Apr 2007 21:31:25 -0400, wrote:

The + input is usually called the follower input, and can have a high input
impedance.

The - input is the opposite differential pair, and is a virtual ground. Signal
cannot be measured here.

Incorrect.

The output of the amp is usually connected to the - input in some way, for
normal amplifier applications.

Usually incorrect.

If the connection is direct, the amp will have a gain of 1, and the + input is
used for input.

Incorrect.

If a resistance is used, another resistor has to be connected to ground, and the
gain of the amp will be (Rf/Rg)+1 (Note the gain can't be less than 1)

() Incorrect at all frequencies.

The gain when using the - input is roughly equal to (Rf/Ri). The gain can be
zero!

The latter is incorrect.

All good fortune,

Chris Hornbeck
"But of course, when you need it, it ain't headroom any more."
- Don Pearce

[robert casey]

The - input can also be used as an input. In this case the required series input
resistor is the former ground connect resistor. Note the input must have a path
to ground through the source. The + input in this case is usually conned to
ground through a resistor, but can be shorted.

The gain when using the - input is roughly equal to (Rf/Ri). The gain can be
zero!

More precisely, it's a negative gain. To express the fact that the
output signal is inverted.

[[email protected]]

On Mon, 30 Apr 2007 03:42:56 +0100, Eeyore
wrote:



wrote:

The + input is usually called the follower input,

No it isn't. It's called the non-inverting input.

It can be called either since it follows the input like an emitter follower.

and can have a high input impedance.

It *does* have a high input impedance.

"CAN" have a high Z since high or low is relative. A 741 input is low compared
to a TL071.


The - input is the opposite differential pair,

The inverting input.

That's what I said.


and is a virtual ground.

No it isn't. It's also high impedance. See a schematic of the internal circuitry if
you doubt me.

Yes it is. Read a book by Jung if you doubt me.


Signal cannot be measured here.

It damn well can ! Even when it's a virtual earth. Note *virtual*. I've seen up to
75mV here.

Maybe you have poor equipment. Last time I looked I saw nothing with my scope at
full gain.


The output of the amp is usually connected to the - input in some way, for
normal amplifier applications.

The expression you're looking for is negative feedback.

I'm not looking for any expression...

You need to learn more.

You too.

Graham

[[email protected]]

On Mon, 30 Apr 2007 02:45:20 GMT, Chris Hornbeck
wrote:

On Sun, 29 Apr 2007 21:31:25 -0400, wrote:

The + input is usually called the follower input, and can have a high input
impedance.

The - input is the opposite differential pair, and is a virtual ground. Signal
cannot be measured here.

Incorrect.

Guess you never tried...

The output of the amp is usually connected to the - input in some way, for
normal amplifier applications.

Usually incorrect.

You're saying that connecting an op amp with negative feedback is not
normal?????

If the connection is direct, the amp will have a gain of 1, and the + input is
used for input.

Incorrect.

Do you know what an inverter or buffer is?

If a resistance is used, another resistor has to be connected to ground, and the
gain of the amp will be (Rf/Rg)+1 (Note the gain can't be less than 1)

() Incorrect at all frequencies.

That's a dumb statement...

The gain when using the - input is roughly equal to (Rf/Ri). The gain can be
zero!

The latter is incorrect.

Really? So with a feedback resistor of 0 ohms and a series source resistor of
10m what is the gain?

All good fortune,

Chris Hornbeck
"But of course, when you need it, it ain't headroom any more."
- Don Pearce

[Eeyore]

wrote:

Eeyore wrote:
wrote:

The + input is usually called the follower input,

No it isn't. It's called the non-inverting input.

It can be called either

No it can't.


since it follows the input like an emitter follower.

No it absolutely does NOT !


and can have a high input impedance.

It *does* have a high input impedance.

"CAN" have a high Z since high or low is relative. A 741 input is low compared
to a TL071.

Regardless, typically greater than1 Megohm. Even with bipolar ICs.


The - input is the opposite differential pair,

The inverting input.

That's what I said.

No it isn't.


and is a virtual ground.

No it isn't. It's also high impedance. See a schematic of the internal circuitry if
you doubt me.

Yes it is. Read a book by Jung if you doubt me.

It is *NOT* a virtual ground unless the op-amp is wired as an inverting amplifier in
which case the virtual ground is the result of feedback, and is unrelated to the
characteristics of the IC itself.

You can also make a valve grid a virtual ground for example. The key is the word
*virtual* !


Signal cannot be measured here.

It damn well can ! Even when it's a virtual earth. Note *virtual*. I've seen up to
75mV here.

Maybe you have poor equipment. Last time I looked I saw nothing with my scope at
full gain.

That's because you're clueless.

Taking the typical TL071 family with a gain bandwidth product of 3MHz, the gain of the
op-amp at 10kHz is 3M/10k = 300.

For an output voltage of 10V rms the voltage on the - input ( in an inverting
configuration ) will be 10/300V = 33 mV @ 10kHz. That's readily measureable.


The output of the amp is usually connected to the - input in some way, for
normal amplifier applications.

The expression you're looking for is negative feedback.

I'm not looking for any expression...

You'd have trouble finding your arse with both hands.


You need to learn more.

You too.

I'm an expert you utter ****wit. I've spent most of my life designing pro-audio kit.

Graham

[Eeyore]

wrote:

Do you know what an inverter or buffer is?

Do you know where the door is ?

You're welcome to leave and take your total and complete ignorance with you.

Graham

[robert casey]

The gain when using the - input is roughly equal to (Rf/Ri). The gain can be
zero!


Should be -(Rf/Ri). Think about it. Suppose I feed into this opamp
circuit 1V DC. The + input is tied to ground. The op-amp is going to
work hard to get the "virtual ground" on the - input very close to
ground voltage, and the only way it can do that is to suck enough
current thru Rf to make that point near ground. The - input is very
high impedance, so the only place that current can really come from is
the input, thru Ri. Thus, the input signal (the 1VDC) sees what looks
like a resistor of Ri ohms to ground. This also means that the op-amp
output has to go to some negative voltage to keep drawing that current
past the virtual ground.

Other issues like "slew rate" can also come into play if the high
frequencies in the input become too big, or you try to squeeze too much
gain. Also, when the opamp can't slew fast enough, the feedback loop
stops working right. Which can lead to smaller higher frequencies
getting lost momentarily. Which could make for bad sound.

Ever wonder why there are a shjtload of different opamps in the data
book? No one opamp can do it all. Need low noise? There's ones for
that, but low power or wide frequency response may take a hit. Fast
slew rate? may be a power hog. But you weren't thinking of portable
battery operated equipment here, no... You may need to use the low
noise opamp at low gain up front, and follow it up with a higher slew
rate but noisier opamp to get the gain up to what you need, at noise you
can live with. A little like tubes, where you wouldn't use a 6BQ5 in
the front end of an FM tuner...

And the input impedance is equal to Ri. This would matter if the source
is high impedance.

[robert casey]

and is a virtual ground.

Only if you design the circuit to have it be that.

It is possible, and commonly done, to design an op-amp

circuit to accept a differential input signal from, say a microphone.
To cancel or reduce hum. You could see the "virtual ground" on that
op-amp having the hum signal, but not the desired signal.

[Eeyore]

robert casey wrote:

Other issues like "slew rate" can also come into play if the high
frequencies in the input become too big

Not in the audio band they don't (barely just with a 741 actually). Do the maths.

The slew rate required for any sinewave (see Fourier theory) of frequency f and
amplitude Vpk is 2.pi.f.Vpk

Graham

[Phil Allison]

"robert casey"


Other issues like "slew rate" can also come into play if the high
frequencies in the input become too big


** Slew rate is an output level issue - got SFA to do with input.


or you try to squeeze too much gain.


** Slew rate is not related to gain, only output level and frequency.


Also, when the opamp can't slew fast enough, the feedback loop stops
working right.


** Just like it does when the output peaks are clipped.


Which can lead to smaller higher frequencies getting lost momentarily.


** TIM and SID have gone out to lunch

- wish you would join them .




........ Phil

[Chris Hornbeck]

On Tue, 1 May 2007 12:15:52 +1000, "Phil Allison"
wrote:

** Slew rate is not related to gain, only output level and frequency.

The *limit* of slew rate is expressed as the time
rate of change of output voltage, but the mechanism
that causes the limit is (in conventional single
dominant pole op-amp design) determined by the
input differential stage's ability to charge and
discharge a capacitor.

Robert is quite correct to point out that this
is a potential stability issue in a feedback amplifier.
Bode plots apply only for small signals.

All good fortune,

Chris Hornbeck

[Phil Allison]

"Chris Hornbeck ****ing Mental Defective "


** Slew rate is not related to gain, only output level and frequency.


The *limit* of slew rate is expressed as the time
rate of change of output voltage, but the mechanism
that causes the limit is (in conventional single
dominant pole op-amp design) determined by the
input differential stage's ability to charge and
discharge a capacitor.


** So not related to gain or input level.

The slew rate of an op-amp is an internally fixed parameter.


Robert is quite correct to point out that this
is a potential stability issue in a feedback amplifier.


** Which he simply did not do.

**** OFF YOU RETARDED FREAK !!




......... Phil

[Chris Hornbeck]

On Tue, 1 May 2007 12:50:22 +1000, "Phil Allison"
wrote:


"Chris Hornbeck ****ing Mental Defective "


** Slew rate is not related to gain, only output level and frequency.


The *limit* of slew rate is expressed as the time
rate of change of output voltage, but the mechanism
that causes the limit is (in conventional single
dominant pole op-amp design) determined by the
input differential stage's ability to charge and
discharge a capacitor.


** So not related to gain

Not per se, but related indirectly by choice of compensation
capacitor. And *lower* closed-loop gains require larger
capacitors, of course.

or input level.

This is incorrect. The slew limit is most completely
defined (if using only a single number) by the current
rate of change available from the input differential
pair. Knowing only the transconductance of the input
diff pair, this is directly translatable to time
rate of change of input voltage.

The slew rate of an op-amp is an internally fixed parameter.


Robert is quite correct to point out that this
is a potential stability issue in a feedback amplifier.


** Which he simply did not do.

You do have to actually read the post first.

**** OFF YOU RETARDED FREAK !!

You and BobF have a nice thread. You'll get along well,

Chris Hornbeck

[[email protected]]

On Mon, 30 Apr 2007 23:54:38 +0100, Eeyore
wrote:



wrote:

Eeyore wrote:
wrote:

The + input is usually called the follower input,

No it isn't. It's called the non-inverting input.

It can be called either

No it can't.

If it's set up as a unity gain buffer it can be...


since it follows the input like an emitter follower.

No it absolutely does NOT !

I wouldn't say absolutely... the output follows the + input in polarity, and
sometimes in amplitude. (buffer connection)


and can have a high input impedance.

It *does* have a high input impedance.

"CAN" have a high Z since high or low is relative. A 741 input is low compared
to a TL071.

Regardless, typically greater than1 Megohm. Even with bipolar ICs.


The - input is the opposite differential pair,

The inverting input.

That's what I said.

No it isn't.

OK - The - input is the opposite INPUT OF THE differential pair... I guess I
have to spell things out here...


and is a virtual ground.

No it isn't. It's also high impedance. See a schematic of the internal circuitry if
you doubt me.

Yes it is. Read a book by Jung if you doubt me.

It is *NOT* a virtual ground unless the op-amp is wired as an inverting amplifier in
which case the virtual ground is the result of feedback, and is unrelated to the
characteristics of the IC itself.

You can also make a valve grid a virtual ground for example. The key is the word
*virtual* !

OK I was thinking only of the inverter mode of connection, you are right.


Signal cannot be measured here.

It damn well can ! Even when it's a virtual earth. Note *virtual*. I've seen up to
75mV here.

Maybe you have poor equipment. Last time I looked I saw nothing with my scope at
full gain.

That's because you're clueless.

Now now - you'll never be another Phil...

Taking the typical TL071 family with a gain bandwidth product of 3MHz, the gain of the
op-amp at 10kHz is 3M/10k = 300.

For an output voltage of 10V rms the voltage on the - input ( in an inverting
configuration ) will be 10/300V = 33 mV @ 10kHz. That's readily measureable.


The output of the amp is usually connected to the - input in some way, for
normal amplifier applications.

The expression you're looking for is negative feedback.

I'm not looking for any expression...

You'd have trouble finding your arse with both hands.

Now now, I told you, you aren't Phil... but you do have his anal fixation...


You need to learn more.

You too.

I'm an expert you utter ****wit. I've spent most of my life designing pro-audio kit.

Graham

Really? That's nice... how much you make last year?

[[email protected]]

On Mon, 30 Apr 2007 23:55:44 +0100, Eeyore
wrote:



wrote:

Do you know what an inverter or buffer is?

Do you know where the door is ?

You're welcome to leave and take your total and complete ignorance with you.

Graham

Hey, if you don't know what an inverter is, or what a buffer is, you don't have
to get angry...

An inverter is an op amp where the negative input is used as the signal input,
and a feedback resistor equal to the series input resistor is used, to give a
gain of 1.

A buffer is an op amp with a zero ohm feedback resistor and usually no
connection from - in to ground, and the + input is used as signal input, and the
output voltage matches the input but with a lower Z.

BTW... there are no "doors" on the Internet... you're so funny!

[[email protected]]

On Tue, 01 May 2007 01:23:24 GMT, robert casey wrote:



and is a virtual ground.

Only if you design the circuit to have it be that.

It is possible, and commonly done, to design an op-amp

circuit to accept a differential input signal from, say a microphone.
To cancel or reduce hum. You could see the "virtual ground" on that
op-amp having the hum signal, but not the desired signal.

You're right - I was thinking only of the inverter connection mode at the
time...

People here are so full of hostility!

Thank you for answering in a civilized way!

[Eeyore]

wrote:

Eeyore wrote:
wrote:

Do you know what an inverter or buffer is?

Do you know where the door is ?

You're welcome to leave and take your total and complete ignorance with you.


Hey, if you don't know what an inverter is, or what a buffer is, you don't have
to get angry...

DON'T KNOW ?

Don't be so bloody ridiculous.


An inverter is an op amp where the negative input is used as the signal input,

No it isn't. The signal input absolutely DOES NOT connect to the inverting input of
the op-amp. It's not called a 'negative input' either.


and a feedback resistor equal to the series input resistor is used, to give a
gain of 1.

A buffer is an op amp with a zero ohm feedback resistor and usually no
connection from - in to ground, and the + input is used as signal input, and the
output voltage matches the input but with a lower Z.

That's a voltage follower. 'Buffers' are far more generalised than that. You can
indeed have an inverting buffer.


BTW... there are no "doors" on the Internet... you're so funny!

And you're an UTTER CRETIN. Jeeezzzz... it be the full moon or something bringing
them out !

This group is about thermionic valves btw - not ICs.

Graham

[Patrick Turner]

Eeyore wrote:

wrote:

Eeyore wrote:
wrote:

Do you know what an inverter or buffer is?

Do you know where the door is ?

You're welcome to leave and take your total and complete ignorance with you.


Hey, if you don't know what an inverter is, or what a buffer is, you don't have
to get angry...

DON'T KNOW ?

Don't be so bloody ridiculous.

An inverter is an op amp where the negative input is used as the signal input,

No it isn't. The signal input absolutely DOES NOT connect to the inverting input of
the op-amp. It's not called a 'negative input' either.

and a feedback resistor equal to the series input resistor is used, to give a
gain of 1.

A buffer is an op amp with a zero ohm feedback resistor and usually no
connection from - in to ground, and the + input is used as signal input, and the
output voltage matches the input but with a lower Z.

That's a voltage follower. 'Buffers' are far more generalised than that. You can
indeed have an inverting buffer.

BTW... there are no "doors" on the Internet... you're so funny!

And you're an UTTER CRETIN. Jeeezzzz... it be the full moon or something bringing
them out !

This group is about thermionic valves btw - not ICs.

Graham

But you can have a tubed opamp, and in fact they were used,
and mounted on a socket or card edge plug/socket strip
so they could be unplugged, taken away to be repaired after a
replacement amp
was plugged in.

The operating principles were exactly the same,
and you had a low Rout output assumeed to be positive
and two high Z inputs which required a positive V and negative V
applied to produce the positive V output.
The terms inverting, non-inverting, virtual earth, feedback, ß,
open loop gain, closed loop gain, bandwidth product,
slew rates and all the other CONVENTIONAL terms applied
to modern chip amps are applicable to old fashioned tube amps,
and should be, so that once the terms are agreed upon,
then people can talk about them more easily.

The sooner the unknowing folk here addopt the conventions, the better,
lest they clutter the discussion with bull****
because they don't like conformity, and don't understand
the reasons behind the conventions.

For discussions to happen amicably, we need to
have similar vocabularies and alphabets.

The basics about opamps are now covered in many websites,
and before the Web the many books written about
their use post 1970 also cover the subject.

I couldn't care less if ppl here bull**** about
opamps until they are red in the face.
The real guts about opamp use is clearly established elsewhere than
r.a.t,
and remains quite unforgotten in most clear minded
engineer's minds.
Intelligent ppl will naturally be rational enough to see through BS,
and find the truth and adopt the conventions, and
understand because

THEY DO NOT RELY ON NEWS GROUPS FOR THE TRUTH AND NOTHING BUT THE WHOLE
TRUTH.

News groups sometimes do provide a truth or two, or three,
but always somone disputes it, or offers only opinion,
and so what you get is continuing discourse, but
it ain't no BIBLE that we are creating as we produce
this somewhat stormy sea of words. I don't expect
us to write a BIBLE. And I know men are only men,
and they spend half their life arguing.

So when I see BS, sometimes it just doesn't matter,
because anyone with a reasonable mind will see the BS for what it is,
BS,
and trying to undo each turd of BS soon after it drops is utterly
pointless
and obsessional. One would like a bull****ter subject to
having the BS forced back from whence it came, but its work
I don't enjoy, and the pay's lousy, and I know how to avoid the pong,
and I'm too busy to be the Town BS Cleaner Upperer.

Meanwhile, I have used opamps in much of my own test gear I have built.
Great little critters they are, and so much easier to use than a
bunch of discrete transistors.

They are a bit too small though, i'd like then to have 6mm between pins.
Alas the latest ones are so small you need tweezers to pick them up,
and building anything at home with them is so tedious I'd much rather
use a triode.

Patrick Turner.

[[email protected]]

On Wed, 02 May 2007 02:05:08 +0100, Eeyore
wrote:




An inverter is an op amp where the negative input is used as the signal input,

No it isn't. The signal input absolutely DOES NOT connect to the inverting input of
the op-amp. It's not called a 'negative input' either.

There you go again... applying your twisting propaganda... I didn't say "direct
connection" now did I?? Did you read the NEXT SENTANCE?? About the series input
resistor??


and a feedback resistor equal to the series input resistor is used, to give a
gain of 1.


See? Your methods are well known...

A buffer is an op amp with a zero ohm feedback resistor and usually no
connection from - in to ground, and the + input is used as signal input, and the
output voltage matches the input but with a lower Z.

That's a voltage follower. 'Buffers' are far more generalised than that. You can
indeed have an inverting buffer.

Are you the guy who said that there were no follower op amp circuits? I get you
psychos confused, really I do... there are so many of you here ruining this
group.


BTW... there are no "doors" on the Internet... you're so funny!

And you're an UTTER CRETIN. Jeeezzzz... it be the full moon or something bringing
them out !

Speak for yourself...

This group is about thermionic valves btw - not ICs.

I didn't start this topic... neither did I start a post to you - you butted in
as mister know it all hero trying to discredit everything I said to Phil.

Phil never said anything to me about what I posted, but you decided to attack -
but you are quite ****ed up. If you think I listen to anything you say, you are
delusional.

Now if Phil had critiqued my post I would listen to him, he is quite expert on
theory, even if he is quite obnoxious at times.

All you people suffer from the same problem - delusions of grandeur!

If you were so ****ing great I would have heard of you - but you are all
nobody's.

Get used to it.

bye