INA 217 replacement

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Samuel Groner

Well-known member
Joined
Aug 19, 2004
Messages
2,940
Location
Zürich, Switzerland
Hi

I'm looking for an instrumentation amp similar to INA 217, for a simple mic pre; should be DIP-8 and running on +-18 V, +-21 V would be better. INA 217 would be perfect, but I don't get it in Switzerland.

Found AD620, but is a bit noisy for my taste...

Thanks for your help!
Samuel
 
mmm i will build a mic pre with the INA103(dip16) or ssm2019
the INA134 is a diferential amp but without input impedance improbe and a CMRR of 90db instead the 100db of the INA103

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?paramTable=yes&familyId=587&templateId=5275


http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?paramTable=yes&familyId=505&templateId=3

let me know what do you think , maybe I forget something.

I think you can get some samples from texas or analog, I do that and I live in chile.
 
> i will build a mic pre with the INA103... or ssm2019... the INA134 is a diferential amp but...

The INA134 is unity-gain line-level and much higher noise than the mike amps. 103 noise is around 0.2 microvolts, 134 noise around 7 microvolts, a BIG difference. The 134 topology sticks 50K of dead resistance in front of the input, so with a weak 200 ohm source it has self-noise 23 dB higher than the noise of the source. Not a problem at line-level, but mighty hissy to put a microphone right into (even if you boost the gain).

> a CMRR of 90db instead the 100db of the INA10

Don't look too much at CMRR numbers, especially over 40dB. They are just boasting. You can measure that on a test bench, but (on the INA134) if you get 25 ohms unbalance between inputs it falls to 60dB. In real life you are lucky to get 40dB, and usually quite happy if you do.

Any of the chips on the Micke Preamp page will make acceptable mike preamps. The chips on the Differential Amp page mostly won't, or not without a lot of tricks.
 
Can I just jump in here with a very short comment about the time line of this stuff.

I think there may have been a SSM2015 Mic chip long in the past.
... but more recently was the SSM2016 and this was popular in pro units like the Euphonics and AMS Neve etc.

Then came the PRE-trimmed SSM2017 which does have different pin layout to the 16. Very popular with many manufacturers in both pro and semi-pro ... Digi001 and many many other things we all own.
now discontinued

THAT Corp have been promising the THAT1510 chip for just so long ... :roll:
still not a reality.

Then came some equivalent chips like the INA217. same pins

The SSM2017 is now discontinued.

It took a very long time but finally Analog Devices replaced the 2017 with the SSM2019 chip.


Of the samples I have, I still prefer the 2017 and my best 2016 chips but the 2019 is a fine replacement and the INA217 operates well as a drop in
... but
refer to Rogers comments above.
Perhaps I should heed these and do my listening tests again.

thanks Roger

:roll:
carry on
 
103 noise is around 0.2 microvolts, 134 noise around 7 microvolts, a BIG difference
how do you get that ?
I´m a little confused I saw the datasheet of the ina103. and I see the noise voltage v/s frecuency curve the noise with a gain of 100 or more is less than with a gain of 1. I can understand that .
 
>> 103 noise is around 0.2 microvolts, 134 noise around 7 microvolts

> how do you get that?

I am taking the maker's word. And I am foolishly looking at "Typical specs", when I know that only the Guaranteed Maximum Specs are to be trusted (and not too far or too literally).

But I'm also using common sense. The 103 has naked high-current transistor inputs. The 134 is wrapped up in resistors.

INA-103.gif

This is input noise, what we usually look at when dealing with weak sources.

INA-134.gif

This is "output noise", but it is unity-gain so if we refer it to the input we get the same noise.

The "1KHz spot noise" is claimed to be: INA103=1
nvsqrthz.gif
; INA134=52
nvsqrthz.gif


The total noise depends on the bandwidth you care about. In audio this is usually 50Hz-15KHz or 20Hz-20KHz. The bass-end makes little difference if the noise is "flat": 15,000 and 14,950 are "the same". The noise usually is not flat, but then again our ears are very un-flat for low-level bass. Since so many speakers and many listeners are fairly flat to 20KHz, assume 20KHz.

Total noise increases with the square-root of bandwidth. The square-root of 20,000 is 141.

So the total 20KHz noise will be about: INA103= 141*1
nvsqrthz.gif
= 141 nanoVolts (0.141 microVolts); INA134= 141*52
nvsqrthz.gif
= 7332 nanoVolts (7.3 microvolts). The 134 spec actually says 7uV.

Passive 200 ohm microphones will tend to have 100-200uV (0.1-0.2 microVolt) self-noise, so the preamp's noise should be in that area.

"Line level" is usually 20dB-60dB higher than pro-mike level, so 20dB-60dB (10X to 1000X) more noise is tolerable. The INA134's 7uV of noise is not the very best we can do, but really good enough for almost any line-level use.

> I´m a little confused I saw the datasheet of the ina103. and I see the noise voltage v/s frecuency curve the noise with a gain of 100 or more is less than with a gain of 1. I can understand that.

"can" or "can not" understand? Well, I mentioned the concept in another thread but didn't beat it to death yet.

B-B's official explanation is:
INA-4.gif

Since they cite the specs with ZERO source impedance (Rg), they say total input noise is the sum of input-stage noise and the output-stage noise divided by input stage gain. They also say the 103's output stage (which is very similar to a 134) has more noise (it should be less because lower resistances).

I am looking at the gain-set feedback resistor. Its thermal noise sums with the source noise and the transistor noise.
INA-3.gif


The expected source resistance is about 200 ohms. That also seems to be about the optimum source for these transistors.

At gain of 1,000 or 100, the gain-set resistor is 6 or 60 ohms, much less than 200 ohms. It adds nearly no noise.

At gain of 10, the gain-set resistor is 660 ohms, much more than the source resistance. It adds a lot of noise.

At gain of 1, the gain-set resistor is "infinity". Actually the added noise resistor includes the two 3K series resistors, so the noise source is 6K. This is much-much higher than 200 ohms, and should give about 8 times the noise. More because all those 6K resistors in the second stage. Even so the noise is higher than you figure from simple resistor thermal noise... the input transistors are working way off of their optimum (200 ohm) impedance, and shouting-out their current noise. If we only used it at lower gain, we would bias the input transistors to a lower current to reduce their current noise.

Mackie has several papers about low-noise mike amps featuring low-impedance gain-set networks, and several trademark names implying "Very Low Impedance". They are certainly correct: there was a whole generation of transfomerless mike amps with large feedback resistors. When used at high gain, the gain-set resistor is smaller than 200 ohms so the noise is low. But when used at low gain, the gain-set resistor value is high, total noise resistance seen by the input is high which degrades noise, plus at some point the current-noise in this resistance rises directly as gain (instead of square-root of gain). And in some designs the noise got quite high at moderate gains.

As I said, Mackie is on the right track, but implementation of VERY low feedback resistors for all gains is tough. See my "novel preamp" thread. To get really low resistance noise at moderate gains requires resistance values you can not do on an affordable variable resistor, and probably a capacitor too big to fit in a modern channel strip. And more drive current than you can get from affordable chips. Mackie's designers probably sketched-up the "right way", then multiplied by 8, 12, 16, or 24 and esitmated the cost, and went back to the drawing board. Their "Very Low Impedance" mike amps are better than many, and really quite good in many situations, but for practical reasons are not all the way down to the noise floor at all gains.
 
[quote author="Kev"]I think there may have been a SSM2015 Mic chip long in the past.[/quote]
Yes. I built a preamp with two of them a couple of years ago.

Best regards,

Mikkel C. Simonsen
 
[quote author="mcs"][quote author="Kev"]I think there may have been a SSM2015 Mic chip long in the past.[/quote]
Yes. I built a preamp with two of them a couple of years ago.

Best regards,

Mikkel C. Simonsen[/quote]

Yeah that right...I have about uhh..24 #ch from a "old" Amek Classic mixingboard in my basement somewhere..all the micpreamps in that console is build around the SSM2015 chip.

Kind regards

Peter
 
Thanks for all the answers! I'll check the SSMxxxx chips, I'm sure I'll find one that fits. Actually, I wanted to order samples from TI for the INA 217, but I got an error-message from the server. Very strange, have to try again...
Samuel
 
the INA163 is a lower noise version of the INA217.

the gain calculation is a little different, although you should be able to use a similar circuit.

/R
 
i'm only looking for a clean PCB (if exist..., GIF or PDF) of the KDMP, I'll use INA217, or the THAT stuff....

Thanks :thumb:
 
:oops: :oops: :oops:

talk about slack
Kev is useless
and some of those images at rosswood are also useless
... need to do some work but just too lazy

mmm
:roll:
try the Factory

I should do a new board just for the THAT chips
both mic-pre and balanced line driver
... could call it THAT-DMP (THAT Dual Mic-Pre)
:roll:
I should do a lot of things
:sad:


don't forget there is the new chip from Analog Devices SSM2019
... and don't forget Mikkel has some boards / kits

www.diyfactory.com/projects/kdmp/kevsdmp_CP.pdf
www.diyfactory.com/projects/kdmp/kevsdmp_BL.pdf
www.diyfactory.com/projects/kdmp/kevsdmp_TL.pdf
 
Hi all, the use of a input transformer whit 1:1 ratio can improve my performance?
Certainly, it provides a good galvanic isolation, but what happens whit the load impedenceat at input of the Ina 217?
 
Sallivan said:
Hi all, the use of a input transformer whit 1:1 ratio can improve my performance?
No, it will make noise performance slightly worse, because the reflected impedance will be higher (due to leakage and DCR) and the signal level slightly lower (due to losses). But a 1:2 xfmr may bring some marginal improvement. Most of theses mic pre chips are optimised for 800R-1k source Z, because actual mic Z varies from 100R to 1k. Also optimizing for 150-200R source Z requires several milliamps idle current in the input devices; makes the devices less desirable and prone to thermal drift and increased offset.
Ratio of Vn to In defines the optimal source Z.
Example: THAT1570 Vn= 1nV/sqrtHz In= 2pA/sqrtHz => opt source Z = 500R
 

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