INA103 differential stage

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"Ben Bradley"

> You absolutely need the differential-conversion stage (with
> highly=precise, matched resistors to get good CMRR) for a mic preamp,


** Bullshit - the input stage rejects common mode by the same factor as
it has gain.


> as the mic signal could be a few millivolts and the common-mode signal
> can be several volts.


** What planet are you living on ??????????

Don't just make things up - dickhead.



> To turn the situation around so that the mic
> signal is much larger instead, you need to cancel the common signal
> with a very high precision.

** There is virtually ZERO common mode signal with a microphone &cable in
normal circumstaces.


>The instrumentation amplifier configuration helps by giving (up to
> about) 1,000 times gain for differential signals, and only a gain of 1
> for common-mode signals, but you still need the differential stage to
> cancel out the common-mode signals.


** Like a record stuck in a groove - isn't he ??






............... Phil

 

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Mike Rivers schrieb:

> This is why the single-ended so-called "impedance balanced" output
> configuration is so popular. It doesn't matter if you short the
> non-driven side to ground because there's no signal on it. Much
> cheaper than a transformer, simpler than a cross-coupled see-saw
> output stage, and good enough for even some of the finest microphones.

That would get me going with just one op for the differencial stage and
two matched series resistors. But the way I understand it, this setup
will result in half the output amplitude if fed into a symmetrical
input. Is that correct?

Rob

 

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"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:43030A15.E99D08CC@hotmail.com...
>
> Paul Stamler wrote:
>
> > "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
> > news:4302B5E7.BE5703E0@hotmail.com...
> >
> > > For a while I followed the 'inverting is best' suggestion but
eventually
> > > abandoned it since it generally leads to increased noise. I see no
sign of
> > this
> > > issue with modern op-amps.
> >
> > It's there, although more with FET-input op-amps than bipolars like the
> > 5532. Try high-frequency IM tests on an OPA-604 or 2604 (same design,
dual
> > package) in non-inverting mode, first with a low-impedance source, then
with
> > something like 25k source impedance. More distortion.
>
> More THD with the high Z source ?

More THD, especially at high frequencies and low gain, so the input sees a
high-level signal, and more high-frequency IMD.

> Ah well, I keep signal impedances low too ! ;-)

But sometimes you can't, at which point some interesting juggling becomes
necessary.

Peace,
Paul

 

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Robert Angst <robert.angst@tu-berlin.de> wrote:
>
>My idea is to use a INA103 but without the second differential stage as
>a mic-pre. One possibility would be of course to replace the
>differential stage it with another OP or a discrete setup but my
>question goes in another direction:

This works very well, and it reduces the total distortion considerably.
Most of the actual distortion of the INA103 comes from the output stage.

But if you're going to do this, you might as well just skip the INA103
altogether and just go with a discrete transistor array for the front
end.

>Since I want the output to be symmetrical anyway wouldn't it be possible
>to amplify each phase separately with a single OP and use that as a
>symmetrical output? Sounds a little to simple, I know. Am I missing
>something here?

Yes, but you don't have an instrumentation amp any more. Do you care
about CMRR? If you don't really care about CMRR, using a single op-amp
is just fine.

If you do care about CMRR, the guys at THAT have just produced a
chip that is a pin-compatible replacement for the SSM2017. Samples are
just now coming out. I can't tell you if it performs as well as the
data sheet yet, but once I get back from Colorado and get another dozen
higher priority (ie. better-paying) projects out of the way I hope to
give the things a try.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

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Graham Stevenon - Net Stalker


** You will STOP posting your mindless garbage under every post I put up.

That is criminal behaviour.



> I suggest you go look up the meaning of criminal.

** I suggest you go straight into hell.



> If I wanted to netstalk you, trust me you'd know about it.


** You are net stalking me and I do know about it.

Stop or will contact your employers.

I promise that will not be the slightest bit funny.





............ Phil

 

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In article <ddvc12$i5$1@mamenchi.zrz.TU-Berlin.DE> robert.angst@tu-berlin.de writes:

> > This is why the single-ended so-called "impedance balanced" output

> That would get me going with just one op for the differencial stage and
> two matched series resistors. But the way I understand it, this setup
> will result in half the output amplitude if fed into a symmetrical
> input. Is that correct?

It's a matter of interpretation. With a symmetrical balanced output
stage, one side goes to -5V with reference to 0V when the other side
goes to +5V. To a differential input, that's a voltage difference of
10V.

With an impedance balanced, single ended output, one side of the
differential input always sees 0V since there's no
"opposite-but-equal" leg of the output. So when the hot side goes to
+5V, the differential input sees 5V.

So, yes, you can get twice the output from a symmetrical output stage
into a differential input because you're essentially connecting the
two outputs in series. You can't do that if you have only one ouptut,
of course, but all of that output voltage does indeed get to the
differential input.


--
I'm really Mike Rivers - (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

 

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On Tue, 16 Aug 2005 14:26:00 +0200, Robert Angst
<robert.angst@tu-berlin.de> wrote:

>My idea is to use a INA103 but without the second differential stage as
>a mic-pre. One possibility would be of course to replace the
>differential stage it with another OP or a discrete setup but my
>question goes in another direction:
>
>Since I want the output to be symmetrical anyway wouldn't it be possible
>to amplify each phase separately with a single OP and use that as a
>symmetrical output? Sounds a little to simple, I know. Am I missing
>something here?

You really, really want to get your common-mode rejection
up-front and believable, preferably before any electronics
(but that costs money), and trusting to your electronics
to linearly handle the potentially large common mode
signal is foolish, not to put too fine a point on it.

In too many real-world situations *huge* common-mode
signals can bite one's butt. Don't trust your reputation
to wishful thinking and Internet wanking. Wanna be
professional? Think tough; think military; think medical.

And don't put too much confidence in certain... well....

Good fortune,

Chris Hornbeck

 

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Scott Dorsey schrieb:

<snip>

> But if you're going to do this, you might as well just skip the INA103
> altogether and just go with a discrete transistor array for the front
> end.

I read your postings about this approach but I guess I don't have
experience and time to design something like this from scratch. Now that
my SX202 is done I get into mic-tinkering again as well (neg. supply for
fig.8)

<snip>

> If you do care about CMRR, the guys at THAT have just produced a
> chip that is a pin-compatible replacement for the SSM2017. Samples are
> just now coming out. I can't tell you if it performs as well as the
> data sheet yet, but once I get back from Colorado and get another dozen
> higher priority (ie. better-paying) projects out of the way I hope to
> give the things a try.
> --scott
>

Actually the 103 was intendet to be my workaround for that. I am trying
to replace an SSM2017 and I was quite pleased with what I read in the
datasheet of the new THAT1512. Even lower noise than the THAT1510.
Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
just two. I haven't found a single comment on its performance yet, but I
would realy like to try it. I'll look around a little more..
Rob

 

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In article <de1in2$avk$1@mamenchi.zrz.TU-Berlin.DE> robert.angst@tu-berlin.de writes:

> I was quite pleased with what I read in the
> datasheet of the new THAT1512. Even lower noise than the THAT1510.
> Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
> just two. I haven't found a single comment on its performance yet, but I
> would realy like to try it. I'll look around a little more..

It's brand new, so you probably won't see any in products for a while
yet. Why not contact THAT and ask for a couple of samples? They're
still a small company and you can actually reach real people there.


--
I'm really Mike Rivers - (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

 

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Robert Angst wrote:

> Scott Dorsey schrieb:
>
> <snip>
>
> > But if you're going to do this, you might as well just skip the INA103
> > altogether and just go with a discrete transistor array for the front
> > end.
>
> I read your postings about this approach but I guess I don't have
> experience and time to design something like this from scratch. Now that
> my SX202 is done I get into mic-tinkering again as well (neg. supply for
> fig.8)
>
> <snip>
>
> > If you do care about CMRR, the guys at THAT have just produced a
> > chip that is a pin-compatible replacement for the SSM2017. Samples are
> > just now coming out. I can't tell you if it performs as well as the
> > data sheet yet, but once I get back from Colorado and get another dozen
> > higher priority (ie. better-paying) projects out of the way I hope to
> > give the things a try.
> > --scott
>
> Actually the 103 was intendet to be my workaround for that. I am trying
> to replace an SSM2017 and I was quite pleased with what I read in the
> datasheet of the new THAT1512. Even lower noise than the THAT1510.
> Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
> just two. I haven't found a single comment on its performance yet, but I
> would realy like to try it. I'll look around a little more..

You're really not being very sensible. You're virtually using only the input
differential pair on the INA103 - kind of a waste ot time.

A pair of 10 cent 2SA1084s is probably quieter.

Graham

 

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Phil Allison wrote:

> Graham Stevenon - Net Stalker

< snip >


> > If I wanted to netstalk you, trust me you'd know about it.
>
> ** You are net stalking me and I do know about it.
>
> Stop or will contact your employers.

Oh please do. They're not strictly my employers btw. They're a client.

> I promise that will not be the slightest bit funny.

I expect that the Studiomaster guys will find it very funny indeed actually.
They could do with a laugh. I've already apprised them of your 'bohemian'
behaviour way back btw.

Now stop making hollow threats.

Graham

 

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Robert Angst <robert.angst@tu-berlin.de> wrote:
>Scott Dorsey schrieb:
>
>> But if you're going to do this, you might as well just skip the INA103
>> altogether and just go with a discrete transistor array for the front
>> end.
>
>I read your postings about this approach but I guess I don't have
>experience and time to design something like this from scratch. Now that
>my SX202 is done I get into mic-tinkering again as well (neg. supply for
> fig.8)

If you want a little bit of gain, and you want differential input and
differential output, you probably want just a simple differential amplifier
stage with two transistors.

Get the service manual for the Mackie 1202VLZ Pro and look at the front
end of the mike section. Steal the design. It's a really good one.

The RCA Radiotron Handbook has the best description of how the circuit
works, too. It's old and it uses tubes in the example, but the same
long-tailed-pair differential amp stage is still one of the most popular
circuit designs today.

>datasheet of the new THAT1512. Even lower noise than the THAT1510.
>Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
>just two. I haven't found a single comment on its performance yet, but I
>would realy like to try it. I'll look around a little more..

I don't think more than a handful of people have actually tried them
yet. Don't know about European distribution but shoot them a letter. They
have talked about getting small quantity distribution through Mouser.
You might want to ask them if they can sign Buerklin up as well.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

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In article <znr1124363024k@trad>, Mike Rivers <mrivers@d-and-d.com> wrote:
>In article <de1in2$avk$1@mamenchi.zrz.TU-Berlin.DE> robert.angst@tu-berlin.de writes:
>
>> I was quite pleased with what I read in the
>> datasheet of the new THAT1512. Even lower noise than the THAT1510.
>> Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
>> just two. I haven't found a single comment on its performance yet, but I
>> would realy like to try it. I'll look around a little more..
>
>It's brand new, so you probably won't see any in products for a while
>yet. Why not contact THAT and ask for a couple of samples? They're
>still a small company and you can actually reach real people there.

They are right now being completely overwhelemed with sample requests.
This thing has been in the works for six years now and we keep hearing
about it, and it's finally out. So everyone and his brother is trying
to get samples out of THAT right now after years of hearing about it.

Preliminary tests look pretty damn good.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

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Graham Stevenon - Net Stalker


> Oh please do. They're not strictly my employers btw. They're a client.


** As I suspected - you an posturing, unemployed fake.



>> I promise that will not be the slightest bit funny.
>
> I expect that the Studiomaster guys will find it very funny indeed
> actually.


** Then you have no idea what I intend.


> Now stop making hollow threats.


** Fair warning is no threat.

Go find out the law - you pig ignorant ass.




.............. Phil

 

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Phil Allison wrote:

> Graham Stevenon - Net Stalker
>
> > Oh please do. They're not strictly my employers btw. They're a client.
>
> ** As I suspected - you an posturing, unemployed fake.
>
> >> I promise that will not be the slightest bit funny.
> >
> > I expect that the Studiomaster guys will find it very funny indeed
> > actually.
>
> ** Then you have no idea what I intend.
>
> > Now stop making hollow threats.
>
> ** Fair warning is no threat.
>
> Go find out the law - you pig ignorant ass.

The law would say you're threatening me. It's such a lame threat I don't
concern myself about it.

You really are piece of astonishingly mentally defective detritus.

Graham

 

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Mike Rivers schrieb:

> It's brand new, so you probably won't see any in products for a while
> yet. Why not contact THAT and ask for a couple of samples? They're
> still a small company and you can actually reach real people there.

Looks like that was a good hint. One of the distributors in Germany
promised to send some.. *when* they get some.

Obviously you guys in the states are asking more samples than THAT can
produce ;-)

I'll report my findings when I have them plugged in and compared.

Rob