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Copying Op Amps to Make Mic Amps

E

ehsjr

Jan 1, 1970
0
D said:
Wow ...3 threads at same time for mic amps.
"Improved mic amp posted on Rapidshare"
"A Better Microphone Amplifier Yet"
"Is S.E.D. actually sci.electronics.dummies"

I'm surprised mic amps are a lively topic on here.
I thought it would be a beaten to death topic like audio power
amplifier design.
Also, by now shouldn't the ultimate microphone amp be a well known
cookbook circuit?.
Ever since "Mary had a little lamb" (history) there's been plenty of
time to master mic amps.
Is mic amp design still in fuzzy land?

Copying Op Amps to Make Mic Amps
I'm sure the best op amp topologies have been thought out by
designers.
How about just (partially) copying a very good op amp internal design
with discrete low noise transistors for the front end mic circuit?
I recall somebody posted that it's the IC process that creates noisy
transistors in op amps.
D from BC

It is interesting, but why it's called it "mic" amps
is confusing. It seemes to be about comparing the size
of organs. :)

Ed
 
E

Eeyore

Jan 1, 1970
0
John said:
The other problem with audio has to do with business culture. In every
industry, there are superstars and roadies. Doctors and nurses,
researchers and assistants, athletes and trainers. In big-science type
businesses, like scientific instruments and national labs, or pharma,
the PhD scientists are the stars and the engineers are the roadies. In
the recording biz, the stars are the performers and the producers, and
the audio people mostly get noticed when there's hum on the mikes. I
prefer to work in a business where the tekkies are the stars.

Nice work if you can find it.

Graham
 
J

John Larkin

Jan 1, 1970
0
Oh there's plenty of money in it at some levels but the commodity 'prosumer' gear
isn't it.

Graham

The other problem with audio has to do with business culture. In every
industry, there are superstars and roadies. Doctors and nurses,
researchers and assistants, athletes and trainers. In big-science type
businesses, like scientific instruments and national labs, or pharma,
the PhD scientists are the stars and the engineers are the roadies. In
the recording biz, the stars are the performers and the producers, and
the audio people mostly get noticed when there's hum on the mikes. I
prefer to work in a business where the tekkies are the stars.

John
 
P

Phil Allison

Jan 1, 1970
0
"tempus fugit"
"Phil Allison"
I'm using 2 actually. Why, does that make a difference for noise level in
the way it interacts with the preamp?


** Have I got news for YOU !!!!

Condenser mics have * pre-amps* inside them !!!!!!!!!

Almost always, the noise level coming OUT of these internal per-amps is way
MORE than the input noise level of typical mic-pres in mixing consoles and
elsewhere.

There is no noise benefit in using a low noise pre-amp UNLESS it is being
used with a dynamic mic.

This is what the EIN figures always refer to a 150 ohm or 200 ohm source
impedance - ie a DYNAMIC mic !!

It all goes RIGHT OUT THE WINDOW when a condenser mic is used.




........ Phil
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore"
He's alluding to the fact that condenser mics have higher outputs than
dynamics


** No I was not.

and as a result, input noise is less of a problem with them.


** The damn mic generates its own background noise, way about that suggested
by its impedance.




....... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore"
Well no.

The most recent design I posted is a significant improvement over typical
previous examples in every respect.


** But these alleged "improvements" are not of the audible kind.



....... Phil
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin"
I prefer to work in a business where the tekkies are the stars.


** I only know one business like that.




........ Phil
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin"
Please clarify one point. Your mic amp applies phantom power to the
microphone, so isn't the real amplifier out there?


** The mic-pre is a multi purpose circuit

Works with all dynamic mics, all condenser mics ( FET, tube, true condenser
or electret ) plus gadgets called "active DIs".

Most accept balanced audio lines too.

Very versatile.



........ Phil
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"Eeysore"


** No I was not.


** The damn mic generates its own background noise, way about that suggested
by its impedance.

Being active of course it would do.

Graham
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"Eeysore"

** But these alleged "improvements" are not of the audible kind.

Since when isn't noise audible ?

Graham
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore"
Since when isn't noise audible ?


** Usual lack of sane answer noted.

Just another one of Stevenson's idiotic straw men instead.




........ Phil
 
P

Phil Allison

Jan 1, 1970
0
"John Fields"


** Oh - that is a cruel pun.




....... Phil
 
C

cledus

Jan 1, 1970
0
Fred said:
Eeyore a écrit :

The LT1028/1128 has 850pV/rtHz for a diff pair. That's 600pV/rtHz per
transistor. Pretty close.

The 1/f corner is at 3.5Hz typ 100% tested and current noise is 1pA/rtHz.

Offset is 20uV typ, 120uV max over temp with 0.2uV/°C typ. and you have
bias cancellation (Ib=+/-25nA typ, 90max, and +/-40nA typ over temp) for
the same price.

Ok, not all that is relevent to audio, but now try to beat that in
discrete designs *for the same price*.


Why is distortion not specified on the data sheet? Is the distortion
good for this part? Or has a tradeoff been made?

-c
 
J

Jim Thompson

Jan 1, 1970
0
Where's your 500pV/sqrt Hz input device ?

Graham

In a multi-channel sonar chip I designed...

Process = PolarFAB BiCMOS... high beta and high fT NPN's AND PNP's
plus 0.8um feature-size CMOS

...Jim Thompson
 
E

Eeyore

Jan 1, 1970
0
Jim said:
In a multi-channel sonar chip I designed...

Process = PolarFAB BiCMOS... high beta and high fT NPN's AND PNP's
plus 0.8um feature-size CMOS

How much do they effectively cost ?

Graham
 
P

Phil Allison

Jan 1, 1970
0
"cledus"
Why is distortion not specified on the data sheet? Is the distortion
good for this part? Or has a tradeoff been made?



** THD is rarely specified in op-amp data.

There are too many variables affecting THD to make one figure meaningful or
even one graph.

These include frequency, stage gain, output level, output load condition and
topology ( inverting or non inverting).

See this site for a more info on the topic.

http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm


........ Phil
 
E

Eeyore

Jan 1, 1970
0
Phil said:
"cledus"

** THD is rarely specified in op-amp data.

There are too many variables affecting THD to make one figure meaningful or
even one graph.

These include frequency, stage gain, output level, output load condition and
topology ( inverting or non inverting).

That does make it more difficult but it's not unknown to see it specified e.g.
NJM2068

Total Harmonic Distortion THD AV=20dB,VO=5V,RL=2kohms, f=1kHz 0.001%

Graham
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin"
"Phil Allison"
"cledus"

With a typical voltage gain of 30 million and a typical gbw of 75 MHz,
the LT1028 should be pretty good. The datasheet does have thd curves,
hitting numbers like 1 ppm at 1 khz, g=-20, 20 v p-p out. Not bad!


** Shame how that figure is not typical.

For the non inverting mode, with 600 ohms load, gain of 1000 ( as used in a
mic pre-amp ), frequency 20 kHz - the THD figure rises by 1000 times to
a mediocre 0.1%.



....... Phil
 
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