In response to various posts please find attached a mic amp which has seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?


--
Thanks,
- Win

"Winfield Hill" wrote in message
...
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?


--
Thanks,
- Win

Now theres no resistors, the diff voltage input to the op amp is always
zero,
so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

Colin =^.^=

Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?



The opamp has not enough distorsion to his taste maybe.


--
Thanks,
Fred.

Winfield Hill wrote:

Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

It doesn't. The + and - op-amp input nodes see almost no differential ac signal
voltage due to feedback action.

Hence no-need for active loading either. The 680Rs simply set the DC condition.

Graham

colin wrote:

"Winfield Hill" wrote in message
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

Now theres no resistors, the diff voltage input to the op amp is always
zero,

Damn small at least !

so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

You got it.

Graham

Fred Bartoli wrote:

Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

The opamp has not enough distorsion to his taste maybe.

IDIOT.

Graham

Eeyore a écrit :

Fred Bartoli wrote:

Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
The opamp has not enough distorsion to his taste maybe.

IDIOT.


Wasn't expecting anything else than that splendid remark.


--
Thanks,
Fred.

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote:
Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
The opamp has not enough distorsion to his taste maybe.

IDIOT.

Wasn't expecting anything else than that splendid remark.

If you will insist on saying silly things !

Graham

Eeyore a écrit :

Winfield Hill wrote:

Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

It doesn't. The + and - op-amp input nodes see almost no differential ac signal
voltage due to feedback action.

Hence no-need for active loading either. The 680Rs simply set the DC condition.


Win wasn't speaking about this. Well, you've splendidly succeeded in
reducing the loop gain by a 1:11 factor.

You don't even understand the simplest implications of what you... hem,
well... design, even when someone point his finger at it, and then call
others name?

Who's the idiot? (I was about to put a smiley there, but finally I won't)


--
Thanks,
Fred.

Eeyore a écrit :

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote:
Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
The opamp has not enough distorsion to his taste maybe.
IDIOT.
Wasn't expecting anything else than that splendid remark.

If you will insist on saying silly things !


It wasn't silly at all. See my other response below.


--
Thanks,
Fred.

Eeyore wrote:

In response to various posts please find attached a mic amp which has seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

The user manual for the product it's used in can be found here btw with some basic
performance specs.
http://www.studiomaster.com/userg/c1u.pdf

The likes of Fred Bloggs can buy one here to test so he can discover how wrong he is
about the performance.
http://cgi.ebay.co.uk/STUDIOMASTER-C...QQcmdZViewItem

Graham

Fred Bartoli wrote:

Eeyore a écrit :
Winfield Hill wrote:

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

It doesn't. The + and - op-amp input nodes see almost no differential ac signal
voltage due to feedback action.

Hence no-need for active loading either. The 680Rs simply set the DC condition.

Win wasn't speaking about this. Well, you've splendidly succeeded in
reducing the loop gain by a 1:11 factor.

Come on then. Let's see your explanation.

Graham

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote:
Eeyore a écrit :
Fred Bartoli wrote:
Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
The opamp has not enough distorsion to his taste maybe.
IDIOT.
Wasn't expecting anything else than that splendid remark.

If you will insist on saying silly things !

It wasn't silly at all. See my other response below.

Like the other Fred you're all hot air and no substance.

If you want to criticise it you'll need to offer your analysis.

Graham

Eeyore a écrit :

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote:
Eeyore a écrit :
Fred Bartoli wrote:
Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
The opamp has not enough distorsion to his taste maybe.
IDIOT.
Wasn't expecting anything else than that splendid remark.
If you will insist on saying silly things !
It wasn't silly at all. See my other response below.

Like the other Fred you're all hot air and no substance.

If you want to criticise it you'll need to offer your analysis.


I wasn't criticizing. I certainly wouldn't for people of so much
substance and so dense.

BTW, such an 'analysis' requires at least, maybe half a second,
including time to look at the schematics.

What's amazing is that it wasn't blindingly obvious to You, not even
counting that you still don't understand it.

You might try some appnote at TI. They do have some tutorials about
opamps and feedback and such advanced concepts.


--
Thanks,
Fred.

Eeyore a écrit :

Fred Bartoli wrote:

Eeyore a écrit :
Winfield Hill wrote:

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
It doesn't. The + and - op-amp input nodes see almost no differential ac signal
voltage due to feedback action.

Hence no-need for active loading either. The 680Rs simply set the DC condition.
Win wasn't speaking about this. Well, you've splendidly succeeded in
reducing the loop gain by a 1:11 factor.

Come on then. Let's see your explanation.


And you need more explanation than what Win and I said for such an
elementary matter?
ROFL!

Ok, if we really have to spell it.
What's the opamp feedback loop made with?


--
Thanks,
Fred.

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote:
Eeyore a écrit :
Fred Bartoli wrote:
Eeyore a écrit :
Fred Bartoli wrote:
Winfield Hill a écrit :
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
The opamp has not enough distorsion to his taste maybe.
IDIOT.
Wasn't expecting anything else than that splendid remark.
If you will insist on saying silly things !
It wasn't silly at all. See my other response below.

Like the other Fred you're all hot air and no substance.

If you want to criticise it you'll need to offer your analysis.

I wasn't criticizing. I certainly wouldn't for people of so much
substance and so dense.

BTW, such an 'analysis' requires at least, maybe half a second,
including time to look at the schematics.

What's amazing is that it wasn't blindingly obvious to You, not even
counting that you still don't understand it.

You might try some appnote at TI. They do have some tutorials about
opamps and feedback and such advanced concepts.

I'm still waiting for your answer.

I read what TI and National had to say on these matters around 30 years ago btw.

So, are you going to elaborate or just continue to post a bunch of whiny crap ?

Graham

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote
Eeyore a écrit :
Winfield Hill wrote:

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
It doesn't. The + and - op-amp input nodes see almost no differential ac signal
voltage due to feedback action.

Hence no-need for active loading either. The 680Rs simply set the DC condition.
Win wasn't speaking about this. Well, you've splendidly succeeded in
reducing the loop gain by a 1:11 factor.

Come on then. Let's see your explanation.


And you need more explanation than what Win and I said for such an
elementary matter?
ROFL!

Ok, if we really have to spell it.
What's the opamp feedback loop made with?

I'm not playing any silly guessing game with you.

Explain yourself or shut up.

Graham

On 14 Mar 2007 04:34:10 -0700, Winfield Hill
wrote:

Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

That troubled me on the original version which throws away 90% of the
signal CURRENT.

With my misunderstood gain of 15dB, that loss is an additional NF
booster.

With the capacitively coupled version, trying to raise that ratio
moves a high frequency pole inward, rolling off the high end.

Direct coupled, I'd replace the 680's with current sources.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

On Wed, 14 Mar 2007 11:53:54 GMT, "colin"
wrote:

"Winfield Hill" wrote in message
...
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?


--
Thanks,
- Win

Now theres no resistors, the diff voltage input to the op amp is always
zero,
so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

Colin =^.^=


Sno-o-o-orkle! Does not!

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

Eeyore a écrit :

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote
Eeyore a écrit :
Winfield Hill wrote:

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
It doesn't. The + and - op-amp input nodes see almost no differential ac signal
voltage due to feedback action.

Hence no-need for active loading either. The 680Rs simply set the DC condition.
Win wasn't speaking about this. Well, you've splendidly succeeded in
reducing the loop gain by a 1:11 factor.
Come on then. Let's see your explanation.

And you need more explanation than what Win and I said for such an
elementary matter?
ROFL!

Ok, if we really have to spell it.
What's the opamp feedback loop made with?

I'm not playing any silly guessing game with you.

Explain yourself or shut up.


There's no guessing at all there and that you still don't see it is
quite eloquent about your abilities.

I just can hear what 'the other Fred' would have to say about this :-)


--
Thanks,
Fred.

Jim Thompson wrote:

wrote:
"Winfield Hill" wrote in message
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

Now theres no resistors, the diff voltage input to the op amp is always
zero, so theres no diff voltage accross the 680r so they dont have an effect
on
diff voltage.

Sno-o-o-orkle! Does not!

...Jim Thompson

Do you have some bizarre new theory of op-amp operation ?

For a TL07x family device Avol @ 1 kHz for example is 4000.

For a 1 volt rms output the differential input voltage at the op-amp inputs will
be 1/4000 volts = 250uV. That means 250uV/2x680R of signal current is 'wasted'
= 184nA.

Graham

Fred Bartoli wrote:

Eeyore a écrit :
Fred Bartoli wrote:
Eeyore a écrit :
Fred Bartoli wrote
Eeyore a écrit :
Winfield Hill wrote:

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
It doesn't. The + and - op-amp input nodes see almost no differential ac signal
voltage due to feedback action.

Hence no-need for active loading either. The 680Rs simply set the DC condition.
Win wasn't speaking about this. Well, you've splendidly succeeded in
reducing the loop gain by a 1:11 factor.
Come on then. Let's see your explanation.

And you need more explanation than what Win and I said for such an
elementary matter?
ROFL!

Ok, if we really have to spell it.
What's the opamp feedback loop made with?

I'm not playing any silly guessing game with you.

Explain yourself or shut up.

There's no guessing at all there and that you still don't see it is
quite eloquent about your abilities.

I just can hear what 'the other Fred' would have to say about this :-)

Your posturing is getting boring. If you haven't got anything to offer just shut up.

Graham

On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 11:53:54 GMT, "colin"
wrote:

"Winfield Hill" wrote in message
...
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?


--
Thanks,
- Win

Now theres no resistors, the diff voltage input to the op amp is always
zero,
so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

Colin =^.^=


Sno-o-o-orkle! Does not!

...Jim Thompson

Not clear speech... Does not have any effect.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

On Wed, 14 Mar 2007 08:12:04 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 11:53:54 GMT, "colin"
wrote:

"Winfield Hill" wrote in message
...
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?


--
Thanks,
- Win

Now theres no resistors, the diff voltage input to the op amp is always
zero,
so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

Colin =^.^=


Sno-o-o-orkle! Does not!

...Jim Thompson

Not clear speech... Does not have any effect.

...Jim Thompson

Damn. I still can't say it right.

The 680 ohm resistors don't affect gain to the output (from the
input), but they do affect the OpAmp loop-gain operating point.

I wonder what stability, and possibly distortion effects, result?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

On Wed, 14 Mar 2007 08:16:48 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 08:12:04 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 11:53:54 GMT, "colin"
wrote:

"Winfield Hill" wrote in message
...
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?


--
Thanks,
- Win

Now theres no resistors, the diff voltage input to the op amp is always
zero,
so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

Colin =^.^=


Sno-o-o-orkle! Does not!

...Jim Thompson

Not clear speech... Does not have any effect.

...Jim Thompson

Damn. I still can't say it right.

The 680 ohm resistors don't affect gain to the output (from the
input), but they do affect the OpAmp loop-gain operating point.

I wonder what stability, and possibly distortion effects, result?

...Jim Thompson

One more comment. Noise gain?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

Eeyore a écrit :

Jim Thompson wrote:

wrote:
"Winfield Hill" wrote in message
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?
Now theres no resistors, the diff voltage input to the op amp is always
zero, so theres no diff voltage accross the 680r so they dont have an effect
on
diff voltage.
Sno-o-o-orkle! Does not!

...Jim Thompson

Do you have some bizarre new theory of op-amp operation ?


Your feedback theory is bizarre.

For a TL07x family device Avol @ 1 kHz for example is 4000.

Yep.

For a 1 volt rms output the differential input voltage at the op-amp inputs will
be 1/4000 volts = 250uV.

Yes, and don't forget that this make your output error 250uV*11=2.75mV,
which is 11 times worse than necessary and that you'll obtain with a
current source load.
I said you that was simple. But you'll probably find this difficult as well.

Oh yes, I know. Just posturing.

Maybe you should reread about loop gain, and the difference between CFB
and VFB.


That means 250uV/2x680R of signal current is 'wasted'
= 184nA.

Graham



--
Thanks,
Fred.

Jim Thompson a écrit :
On Wed, 14 Mar 2007 08:16:48 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 08:12:04 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 07:30:52 -0700, Jim Thompson
wrote:

On Wed, 14 Mar 2007 11:53:54 GMT, "colin"
wrote:

"Winfield Hill" wrote in message
...
Eeyore wrote...
In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Content-Type: image/jpeg; "mic amp.jpg"
It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?


--
Thanks,
- Win
Now theres no resistors, the diff voltage input to the op amp is always
zero,
so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

Colin =^.^=

Sno-o-o-orkle! Does not!

...Jim Thompson
Not clear speech... Does not have any effect.

...Jim Thompson
Damn. I still can't say it right.

The 680 ohm resistors don't affect gain to the output (from the
input), but they do affect the OpAmp loop-gain operating point.

I wonder what stability, and possibly distortion effects, result?

...Jim Thompson

One more comment. Noise gain?


Let Eeyore explain you that this has no impact, and on distortion too.


--
Thanks,
Fred.

Jim Thompson wrote:

Jim Thompson wrote:
Jim Thompson wrote:
"colin" wrote:
"Winfield Hill" wrote
Eeyore wrote...

In response to various posts please find attached a mic amp
which has seen volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

It's nice to see the diff-pair currents going directly to
the output opamp, with it's 6.8k resistors. But why'd ya
steal away loop gain so aggressively by choosing 680-ohms?

Now theres no resistors, the diff voltage input to the op amp is always
zero,
so theres no diff voltage accross the 680r so they dont have an effect on
diff voltage.

Sno-o-o-orkle! Does not!

...Jim Thompson

Not clear speech... Does not have any effect.

...Jim Thompson

Damn. I still can't say it right.

The 680 ohm resistors don't affect gain to the output (from the
input), but they do affect the OpAmp loop-gain operating point.

How ?


I wonder what stability, and possibly distortion effects, result?

...Jim Thompson

None.

Graham

Jim Thompson wrote:

One more comment. Noise gain?

Uh ? Would you care to elaborate ?

Graham

Fred Bartoli wrote:

Eeyore a écrit :

Do you have some bizarre new theory of op-amp operation ?

Your feedback theory is bizarre.

It's entirely conventional.


For a TL07x family device Avol @ 1 kHz for example is 4000.

Yep.

For a 1 volt rms output the differential input voltage at the op-amp inputs will
be 1/4000 volts = 250uV.

Yes, and don't forget that this make your output error 250uV*11=2.75mV,

What 'output error' ?

Graham

On Wed, 14 Mar 2007 10:38:22 +0000, Eeyore
wrote:

In response to various posts please find attached a mic amp which has seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham

Operating within 0.7V of the common-mode voltage spec troubles me.

I'd bump up those 680 ohm resistors to say 2.2K, making the
common-mode operating point approximately -7V.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

Jim Thompson wrote:

Eeyore wrote:

In response to various posts please find attached a mic amp which has seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Operating within 0.7V of the common-mode voltage spec troubles me.

0.7V ? That's loads ! It was thoroughly chjecked.


I'd bump up those 680 ohm resistors to say 2.2K, making the
common-mode operating point approximately -7V.

The 680R is to be honest a carry over from the previous style of design. With
that 2k2 you'd get close to cutting off the input devices with a very large
input signal.

Graham

"Eeyore" wrote in message
...
In response to various posts please find attached a mic amp which has seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham


Here you go...... Listening to the criticism that others are giving you I'd
do something like this. As to wether I've got it right is another matter.

I'd also claim that U1 and U2 also cascode the input stage improving
bandwidth.

DNA

On Wed, 14 Mar 2007 17:38:02 GMT, "Genome"
wrote:


"Eeyore" wrote in message
...
In response to various posts please find attached a mic amp which has seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham


Here you go...... Listening to the criticism that others are giving you I'd
do something like this. As to wether I've got it right is another matter.

I'd also claim that U1 and U2 also cascode the input stage improving
bandwidth.

DNA


Oooooey, patoooey! What's the gain ?:-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

Genome wrote:

"Eeyore" wrote
.
In response to various posts please find attached a mic amp which has seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.


Here you go...... Listening to the criticism that others are giving you I'd
do something like this. As to wether I've got it right is another matter.

I'd also claim that U1 and U2 also cascode the input stage improving
bandwidth.

That's an interesting design.

The constant current source in the 'tail' I've seen before. ISTR one guy I know
who did that found it increased the noise unfortunately. You're missing the
variable gain bit though. You need 2 current sources in place of Q5 with the
gain setting bits connected between Q1 and Q2 emitters.

The 'collector loads' are cute too. I'm tempted to try it btw but I'm just about
to post another one that's a bit more up to date. Check that one out.

Graham

"Jim Thompson" wrote in
message ...
On Wed, 14 Mar 2007 17:38:02 GMT, "Genome"
wrote:


"Eeyore" wrote in message
...
In response to various posts please find attached a mic amp which has
seen
volume production in commercial equipment.

Feel free to ask any questions / criticise whatever.

Graham


Here you go...... Listening to the criticism that others are giving you
I'd
do something like this. As to wether I've got it right is another matter.

I'd also claim that U1 and U2 also cascode the input stage improving
bandwidth.

DNA


Oooooey, patoooey! What's the gain ?:-)

...Jim Thompson

Sigh, bearing in mind that I am not Gods gift to my own arsehole, before I
waste my head figuring out the wrong answer....... was I close about the
reduction in re (hre?) by the compound connection of the transistors? Am I
even close about gm being 1/re.

You did have a larf at my analysis in the other place didn't you.

I could get worried about coming up with a 'complicated' equation like Fred.

I don't know (remember/didn't pay attention to) this stuff so I've got to do
it from my own concept of first principles and it'll still end up half
arsed.

DNA

On Wed, 14 Mar 2007 18:37:35 GMT, "Genome"
wrote:


"Jim Thompson" wrote in
message ...
[snip]

Oooooey, patoooey! What's the gain ?:-)

...Jim Thompson

Sigh, bearing in mind that I am not Gods gift to my own arsehole, before I
waste my head figuring out the wrong answer....... was I close about the
reduction in re (hre?) by the compound connection of the transistors? Am I
even close about gm being 1/re.

You did have a larf at my analysis in the other place didn't you.

I could get worried about coming up with a 'complicated' equation like Fred.

I don't know (remember/didn't pay attention to) this stuff so I've got to do
it from my own concept of first principles and it'll still end up half
arsed.

DNA


The compound device, as you've applied it, has an _effective_ re of
approximately....

re(NPN)/beta(PNP)

So you need to stick some real R in there.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

"Jim Thompson" wrote in
message ...
On Wed, 14 Mar 2007 18:37:35 GMT, "Genome"
wrote:


"Jim Thompson" wrote in
message ...
[snip]

Oooooey, patoooey! What's the gain ?:-)

...Jim Thompson

Sigh, bearing in mind that I am not Gods gift to my own arsehole, before I
waste my head figuring out the wrong answer....... was I close about the
reduction in re (hre?) by the compound connection of the transistors? Am I
even close about gm being 1/re.

You did have a larf at my analysis in the other place didn't you.

I could get worried about coming up with a 'complicated' equation like
Fred.

I don't know (remember/didn't pay attention to) this stuff so I've got to
do
it from my own concept of first principles and it'll still end up half
arsed.

DNA


The compound device, as you've applied it, has an _effective_ re of
approximately....

re(NPN)/beta(PNP)

So you need to stick some real R in there.

...Jim Thompson

That looks upside down to me.

What I said... in the other place, was........

quote

Best, at the moment that I can guess.....

Short circuit the gain setting pot/capacitor and throw away the NPN
transistors. It's a differential pair. The gain is gmRC. gm is set by the
'tail' resistor which is R2||R6.

Put the NPNs back in again. It's still a differential amplifier but the NPNs
'pin' the PNP currents at Vbe/Rbe which makes gm some different value......,
gm' less than before.

However the NPNs 'boost' that value by approximately their Beta....Bnpn [1]
So

Av = BnpnRCgm' = BnpnRCIcpnp/25E-3 = BnpnRCVbe/25E-3Rbe

That might be a factor of two out because it's a diferential amplifier.

Open circuit the gain setting network and it's just a pair of 'thingy'
amplifiers with

Av = RC/RE

In between........ I couldn't be bothered.

/quote

DNA

On Wed, 14 Mar 2007 18:59:59 GMT, "Genome"
wrote:

Genome, Your differential gain is....

10K/re(equivalent)

Or...

10K/re(NPN)*BETA(PNP)

Take re(NPN) = 26

Take BETA(PNP) = 150

Your gain is 57.69K or 95dB

That gain also multiplies any offset mismatches :-(

You dig ?:-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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