Maker Pro
Maker Pro

Copying Op Amps to Make Mic Amps

D

D from BC

Jan 1, 1970
0
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
 
J

Joerg

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.


Nah, the cool thing to do is to take a few ECC85 tubes and copy the
opamp with those. Then give the glass of the tubes a spit shine for even
lower noise :)))
 
M

martin griffith

Jan 1, 1970
0
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
yep it's a fun subject
But why copy opamp circuits in the first place, they just seem to have
copied the discrete version

FWIW this is a newish guy on the block
http://www.thatcorp.com/1500desc.html


martin
 
E

Eeyore

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.

So am I actually. I'm stunned that the self-appointed 'experts' on here don't
understand the fundamentals of what makes them good for their intended
application. Even the simple versions, never mind the hot-rod one I've posted in
abse.

I thought it would be a beaten to death topic like audio power
amplifier design.

LOL ! You want me to discuss that too ?

I recall my lecturer at college saying that pole-zero compensation was "too
difficult to analyse". Kinda got my interest that did !

Also, by now shouldn't the ultimate microphone amp be a well known
cookbook circuit?.

You're making the flawed assumption that those who put together 'cookbooks' are
competent in this field.

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?

There's nothing fuzzy about it at all. All that's needed is competent design. A
lack of which is seriously evident even here.

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?

A mic amp is a form of instrumentation amplifier. Op-amp topologies are not
relevant.

I recall somebody posted that it's the IC process that creates noisy
transistors in op amps.

ICs have some difficulty replicating the kind of really low-noise discrete
transistors that are possible. In fact they've never ever been able to
realistically compete.

Graham
 
J

Jim Thompson

Jan 1, 1970
0
Nah, the cool thing to do is to take a few ECC85 tubes and copy the
opamp with those. Then give the glass of the tubes a spit shine for even
lower noise :)))

You forgot to mount it inside a glass case, with a brass name plate
;-)

...Jim Thompson
 
M

martin griffith

Jan 1, 1970
0
Yup, it's an integrated copy of an Australian discrete design IIRC.

Graham
and it took Thatcorp a *very* long time to get it right


martin
 
J

Joerg

Jan 1, 1970
0
Jim said:
You forgot to mount it inside a glass case, with a brass name plate
;-)

Ah, you haven't seen the real audio freaks yet. Glass cases are frowned
upon. It has to be a polished base and the tubes must stick out. Also,
preferably there should be a vintage Gibson casually sitting next to the
amplifier even if you can't play the guitar. A lava lamp can't hurt
either. A 1960's VW bus with a peace sign in the driveway would also be
a nice touch.

Glass is decidedly not cool. Smoked glass would be the worst, as that is
identified with the previous generation. I remember a writing on a wall
in one of those freak homes: "We are the people our parents always
warned us about".
 
D

D from BC

Jan 1, 1970
0
Nah, the cool thing to do is to take a few ECC85 tubes and copy the
opamp with those. Then give the glass of the tubes a spit shine for even
lower noise :)))

lol :)
D from BC
 
D

D from BC

Jan 1, 1970
0
yep it's a fun subject
But why copy opamp circuits in the first place, they just seem to have
copied the discrete version

FWIW this is a newish guy on the block
http://www.thatcorp.com/1500desc.html


martin

Ooooo :)
THAT corp. 1510 @ 1nV/root hz input noise (60dB gain)

I don't need a mic amp but now I feel like making one :)
D from BC
 
R

Rich Grise

Jan 1, 1970
0
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?.

Here's the one I used:
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/npnce.html#c2
with appropriate resistor and cap values, of course. :)

Cheers!
Rich
 
R

Rich Grise

Jan 1, 1970
0
Nah, the cool thing to do is to take a few ECC85 tubes and copy the
opamp with those. Then give the glass of the tubes a spit shine for even
lower noise :)))

Pfeh - ECC85 is a 6AQ8 - RF local osc. and mixer. Use ECC83 == 12AX7,
optimized for low-noise audio. :) (the ECC81 (12AT7) and ECC82 (12AU7)
are optimized for switching and RF, but I can't remember which is which.)

Cheers!
Rich
 
J

Joerg

Jan 1, 1970
0
Rich said:
Pfeh - ECC85 is a 6AQ8 - RF local osc. and mixer. Use ECC83 == 12AX7,
optimized for low-noise audio. :) (the ECC81 (12AT7) and ECC82 (12AU7)
are optimized for switching and RF, but I can't remember which is which.)

Guess you are right about that. I didn't do much audio stuff with tubes
and if so I took what was there for free from old TV sets. My area was
RF and there I used ECC81 and UHF tubes from tuners (EC86?).

Oh, I did one audio project. It later became a big RF amp for ham radio
but first I turned it into a Gorilla of an audio amp. Mostly because of
a bet. Not about money, someone said it would never work and I just
could not let that sit. That thing was awesome. But you could not crank
it up and then play a strong chord on the E-guitar because the mains
breaker would trip. Other than that it really made the rafters shake.
 
T

Tim Wescott

Jan 1, 1970
0
Joerg said:
Nah, the cool thing to do is to take a few ECC85 tubes and copy the
opamp with those. Then give the glass of the tubes a spit shine for even
lower noise :)))
Don't forget to dip them in LN2 -- it "aligns the crystalline structure"
for better sound.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
J

Jim Thompson

Jan 1, 1970
0
Analog ICs typically use lots of transistors and few resistors or
capacitors, the reverse of most discrete design. And they can match
the transistors for offset and beta orders of magnitude better than
you can with discretes. That's why a simple-looking analog integrated
circuit may have hundreds of transistors. So the designs are usually
quite different.

Some analog processes can use transistors as good as anything you can
buy as discretes. Opamps like LT1028 have noise below 1 nv/rt hz.

John

Oh, John! You're giving away my secrets ;-)

...Jim Thompson
 
I

Ian Bell

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?.


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

Ian
 
J

John Larkin

Jan 1, 1970
0
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.

Analog ICs typically use lots of transistors and few resistors or
capacitors, the reverse of most discrete design. And they can match
the transistors for offset and beta orders of magnitude better than
you can with discretes. That's why a simple-looking analog integrated
circuit may have hundreds of transistors. So the designs are usually
quite different.

Some analog processes can use transistors as good as anything you can
buy as discretes. Opamps like LT1028 have noise below 1 nv/rt hz.

John
 
J

John Larkin

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

Graham


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
 
Top