tempus fugit wrote:

Eeyore wrote :

The IC mic amps that are around are internally quite like their discrete
counterparts but just not quite as good and vastly more expensive.

They're a boon for 'designers' who can't actually really design though.


Guys like me.....

lol

Actually Graham that does bring up an interesting question though. The
SSM2019 is only a couple bucks apiece in for 100 or more. I'm sure you must
have close to that in parts in your design.

Nowhere near that much. Both need the pot, so lets take that out of the
equation.

My discrete design needs 2 or 4 transistors ( 2 of them very low noise) and 1 or
2 halves of a dual op-amp plus a few passives.

Total cost in manufacturing quantities is under 50 cents.


There seems to be a preference for discrete designs - what makes them better
than something like the 2019? Or are they actually better?

They actually can outperform a 2019. The later version I posted with overall
differential feedback most certainly so.

Graham

Genome wrote...

Have you tried out my IGBT thing yet?

Could you remind me what you're referring to?


--
Thanks,
- Win

Eeyore wrote...

is left for the preamp to use, as the 3MHz TL072 bandwidth
is reduced to 300kHz. Sheesh!

I know what you're saying but it works out in practice rather
better than the numbers alone might suggest.

I should add I'm thinking of the upper end of the spectrum
where the loop gain is low, for example 5kHz where it'll be
300kHz/5kHz = 60. That can be further reduced as the opamp
drives various loads. I suppose you'll say low distortion
isn't so important at these frequencies. Did you measure
and plot it?


--
Thanks,
- Win

Jim Thompson wrote...

Bang-for-the-buck, the composite PNP/NPN has a nice
noise floor... ~1nV/rt-Hz!

Now you're becoming a fan?


--
Thanks,
- Win

Winfield Hill wrote:

Eeyore wrote...

is left for the preamp to use, as the 3MHz TL072 bandwidth
is reduced to 300kHz. Sheesh!

I know what you're saying but it works out in practice rather
better than the numbers alone might suggest.

I should add I'm thinking of the upper end of the spectrum
where the loop gain is low, for example 5kHz where it'll be
300kHz/5kHz = 60. That can be further reduced as the opamp
drives various loads.

In this situation the mic stage is relatively rarely driving any externals loads
and those that it may do will be quite benign as a rule.


I suppose you'll say low distortion isn't so important at these frequencies.
Did you measure and plot it?

Actually plot it ? I don't recall doing that. I tend to make 'spot measurements'
and I don't recall any problems. You're seriously testing my memory now ! I
certainly don't recall any alarming rise in THD. It's no worse than a normal
20dB gain stage after all. It seems that at all settings THD is dominated by the
compound pair btw.

Graham

Winfield Hill a écrit :
Jim Thompson wrote...
Bang-for-the-buck, the composite PNP/NPN has a nice
noise floor... ~1nV/rt-Hz!

Now you're becoming a fan?



A fan revolves at 3600rpm :-)

--
Thanks,
Fred.

Fred Bartoli wrote:

Winfield Hill a écrit :
Jim Thompson wrote...
Bang-for-the-buck, the composite PNP/NPN has a nice
noise floor... ~1nV/rt-Hz!

Now you're becoming a fan?



A fan revolves at 3600rpm :-)


None of mine do.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Winfield Hill" wrote in message
...
Genome wrote...

Have you tried out my IGBT thing yet?

Could you remind me what you're referring to?


--
Thanks,
- Win

Basic Idea

http://www.genomerics.org/patent/patent.html

Used in a PFC circuit

http://www.genomerics.org/patent/newpfc.html

Used in a Class D amplifier

http://www.genomerics.org/patent/spice.rar

Probably best to ignore me :-)

DNA

On 20 Mar 2007 05:18:56 -0700, Winfield Hill
wrote:

Eeyore wrote...

is left for the preamp to use, as the 3MHz TL072 bandwidth
is reduced to 300kHz. Sheesh!

I know what you're saying but it works out in practice rather
better than the numbers alone might suggest.

I should add I'm thinking of the upper end of the spectrum
where the loop gain is low, for example 5kHz where it'll be
300kHz/5kHz = 60. That can be further reduced as the opamp
drives various loads. I suppose you'll say low distortion
isn't so important at these frequencies. Did you measure
and plot it?

---
Of course not.

He's an audio freak with a rampant ego, and he thinks that what he
thinks sounds good should be good enough for everyone else.


--
JF