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Copying Op Amps to Make Mic Amps

D

D from BC

Jan 1, 1970
0
Mic pre design is a complex trade off. There is no perfect design, that's
why there are so many.

Ian

Trade offs....
I'm aware of:
noise
gain
PSRR
CMRR
distortion
dynamic range
stability (DC bias and feedback)
power efficiency
PCB size
cost

How much more can there be?
D from BC
 
P

Phil Allison

Jan 1, 1970
0
Ian Bell said:
Mic pre design is a complex trade off. There is no perfect design, that's
why there are so many.


** This is an unsupported opinion typical of a " sound engineer ".

Mostly, these dudes live a fantasy world of their own invention.

It sure as hell ain't the real world.

And they do not deal in fact.




........ Phil
 
D

D from BC

Jan 1, 1970
0
Transistors are all made out of the same silicon, integrated or
discrete, so the physics is the same. The transistors in the front end
of an LT1028 or INA103 are about that noise level. There will always
be niches where you can squeeze a little more performance out of a
discrete, but with the exception of really big jfets, any advantage is
usually small. The IC boys can just throw so much more resources at a
design... gain-bandwidth, matching, tempco, bias current cancellation,
current sources galore, superbeta, and enough sales volume to pay for
a *lot* of engineering.

As the old stuff gets integrated, the only thing to do is move up the
abstraction stack. As a longtime circuit designer, I sort of regret
that, but that's life. You can't keep designing the same circuit all
your life.


John

Transistors are like atoms and IC's are like molecules.
D from BC
 
P

Phil Allison

Jan 1, 1970
0
"tempus fugit"
I'm a musician myself, and what I
record is largely classical guitar, which requires a very low noise
micpre,
which the SSM2017 is able to deliver.



** You're not using a condenser mic - then?




....... Phil
 
T

tempus fugit

Jan 1, 1970
0
D from BC said:
Trade offs....
I'm aware of:
noise
gain
PSRR
CMRR
distortion
dynamic range
stability (DC bias and feedback)
power efficiency
PCB size
cost

How much more can there be?
D from BC

I think this is a point that Graham has been trying to make. For a musician
or sound engineer, there is a certain sound to micpres, etc., and maybe
that's why his design was successful. In technical terms, I suppose it's
probably some lack of quality (I'm not saying this about Graham's design
BTW) in the design that imparts a difference in tone to whatever's being
recorded. This explains why you see Neve channel strips going for a couple
grand on eBay, even though Rupert himself admits that today's designs are
far better. This may also help explain why the high end boutique micpres can
fetch a similar price, even though there couldn't possibly be enough spent
on actual components or R+D or whatever to justify the cost. Maybe Phil's
right and the engineer types are deluded, but they seem convinced that there
is a difference, and maybe there is - this mysterious tonal quality that
certain designs impart. Whether it is better for the sound or not is a
matter of opinion and personal taste. I'm a musician myself, and what I
record is largely classical guitar, which requires a very low noise micpre,
which the SSM2017 is able to deliver. The noise contributed by the micpre
itself, with whatever resistors or other noisy passives I have in there is
miniscule, and for all intents inaudible, so this one works great for me.
I've not had the fortune to A/B it with a Focusrite to see if the latter has
a better 'sound', although a local studio owner has invited me to bring my
micpre and go head-to-head with his Focusrite. Maybe I'll take him up on it
some day, but I figure that my playing itself needs more work than my
recorded sound anyway. ....
 
D

D from BC

Jan 1, 1970
0
I think this is a point that Graham has been trying to make. For a musician
or sound engineer, there is a certain sound to micpres, etc., and maybe
that's why his design was successful. In technical terms, I suppose it's
probably some lack of quality (I'm not saying this about Graham's design
BTW) in the design that imparts a difference in tone to whatever's being
recorded. This explains why you see Neve channel strips going for a couple
grand on eBay, even though Rupert himself admits that today's designs are
far better. This may also help explain why the high end boutique micpres can
fetch a similar price, even though there couldn't possibly be enough spent
on actual components or R+D or whatever to justify the cost. Maybe Phil's
right and the engineer types are deluded, but they seem convinced that there
is a difference, and maybe there is - this mysterious tonal quality that
certain designs impart. Whether it is better for the sound or not is a
matter of opinion and personal taste. I'm a musician myself, and what I
record is largely classical guitar, which requires a very low noise micpre,
which the SSM2017 is able to deliver. The noise contributed by the micpre
itself, with whatever resistors or other noisy passives I have in there is
miniscule, and for all intents inaudible, so this one works great for me.
I've not had the fortune to A/B it with a Focusrite to see if the latter has
a better 'sound', although a local studio owner has invited me to bring my
micpre and go head-to-head with his Focusrite. Maybe I'll take him up on it
some day, but I figure that my playing itself needs more work than my
recorded sound anyway. ....

Welll...I have some audiophoolery for yah... :)
The mic amp difference is... the distortion.
(Here comes the tomatoes... :) )
Some distortion sounds nice.
But it's gotta be the right flavour of distortion..
Something to do with even harmonic content sounding better than odd
harmonic content..
(A gross example is the Tony Iommi (Black Sabbath) guitar sound. But
much more subtle in a mic amp.)

I keep showering but the audiophoolery doesn't wash off.... :)

More scientifically I'd get an Audio Analyzer from:
http://ap.com/
And test the mic amps for a difference.
It's rentable....
D from BC
 
F

Fred Bartoli

Jan 1, 1970
0
Eeyore a écrit :
Where's your 500pV/sqrt Hz input deice ?

Graham

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*.
 
E

Eeyore

Jan 1, 1970
0
John said:
Transistors are all made out of the same silicon, integrated or
discrete, so the physics is the same. The transistors in the front end
of an LT1028 or INA103 are about that noise level. There will always
be niches where you can squeeze a little more performance out of a
discrete, but with the exception of really big jfets, any advantage is
usually small. The IC boys can just throw so much more resources at a
design... gain-bandwidth, matching, tempco, bias current cancellation,
current sources galore, superbeta, and enough sales volume to pay for
a *lot* of engineering.

As the old stuff gets integrated, the only thing to do is move up the
abstraction stack. As a longtime circuit designer, I sort of regret
that, but that's life. You can't keep designing the same circuit all
your life.

But it's *not* the same circuit. As has been shown, you can do it with one
op-amp or two. The one op-amp solution is attractive where price is the main
driver.

When that mic amp IC gets to 50 cents I'll be interested.

Graham
 
E

Eeyore

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*.

How do you make a true differential amplifier with one LT1028 ? The classic
instrumentation amp configuration will imtroduce the noise of 2 of them so
you're already up to 1.2nV/sqrt Hz.

Never mind the damn *expense* !

Graham
 
K

krw

Jan 1, 1970
0
That's one of the many problems with audio: there's not much money in
it.

Have you ever priced Monster Cables? Oxygen-free connectors?

....or oxygen free gunpowder? ;-)))
 
K

Kevin Aylward

Jan 1, 1970
0
Phil said:
** This is an unsupported opinion typical of a " sound engineer ".

Mostly, these dudes live a fantasy world of their own invention.

It sure as hell ain't the real world.

And they do not deal in fact.

Indeed. Some rare sense from Phil here.

My take, the proliferation of designs is simple a meme replication and
variation for its own replication advantage, like as in religion. There is
no basis in ether as to any superiority, they just multiply as as does any
other virus bcause thats what they do.
 
E

Eeyore

Jan 1, 1970
0
Kevin said:
Indeed. Some rare sense from Phil here.

My take, the proliferation of designs is simple a meme replication and
variation for its own replication advantage, like as in religion. There is
no basis in ether as to any superiority, they just multiply as as does any
other virus bcause thats what they do.

Well no.

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

Graham
 
E

Eeyore

Jan 1, 1970
0
John said:
That's one of the many problems with audio: there's not much money in
it.

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

Graham
 
E

Eeyore

Jan 1, 1970
0
John said:
Please clarify one point. Your mic amp applies phantom power to the
microphone

Condenser microphones. Not dynamics (the majority).
, so isn't the real amplifier out there?

Only in part and you still want the hum rejection of the differential input.

Graham
 
E

Eeyore

Jan 1, 1970
0
John said:
For your application, an INA103 would work.

It still has inferior performance and costs more. Plus you're tied to a single
source.

Graham
 
E

Eeyore

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

He's alluding to the fact that condenser mics have higher outputs than dynamics
and as a result, input noise is less of a problem with them.

Graham
 
J

John Larkin

Jan 1, 1970
0
But it's *not* the same circuit. As has been shown, you can do it with one
op-amp or two. The one op-amp solution is attractive where price is the main
driver.

When that mic amp IC gets to 50 cents I'll be interested.

Graham

That's one of the many problems with audio: there's not much money in
it.

John
 
J

John Larkin

Jan 1, 1970
0
How do you make a true differential amplifier with one LT1028 ? The classic
instrumentation amp configuration will imtroduce the noise of 2 of them so
you're already up to 1.2nV/sqrt Hz.

Never mind the damn *expense* !

Graham

Please clarify one point. Your mic amp applies phantom power to the
microphone, so isn't the real amplifier out there?

John
 
J

John Larkin

Jan 1, 1970
0
How do you make a true differential amplifier with one LT1028 ? The classic
instrumentation amp configuration will imtroduce the noise of 2 of them so
you're already up to 1.2nV/sqrt Hz.

Never mind the damn *expense* !

For your application, an INA103 would work.

John
 
T

tempus fugit

Jan 1, 1970
0
Phil Allison said:
"tempus fugit"




** You're not using a condenser mic - then?




...... Phil
I'm using 2 actually. Why, does that make a difference for noise level in
the way it interacts with the preamp?
 
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