[time-nuts] Hp10811 parts ref

[Charles Steinmetz]

You are very welcome, Gilles.  One point of clarification, and one 
additional note:

I mentioned the LT1012 and OP97 together, then said I've settled on the 
OP97 without further comment.  My choice had nothing to do with 
differences between these two parts.  As far as I can tell from using 
them extensively, there are no differences -- for all I know, they could 
be made using identical masks.  I chose the OP97 for supply-chain 
reasons that won't be relevant to anyone else.

Looking at the 10811A/B schematic, the bridge sampling resistors (R22, 
R23) are 1Mohm.  This is what accounts for choosing U3 with extremely 
low input bias current.  Note that the LT1012/OP97 are roughly 1000 
times better than the LMx08 in this respect (pA for the LT1012/OP97, nA 
for the LMx08) as well as input input offset voltage (mV for the LMx08, 
uV for the LT1012/OP97).

One thing to note when replacing an LMx08 with an LT1012/OP97:  Notice 
C19 (0.01uF from Pin 8 to Ground).  This is an *overcompensation* 
capacitor, used to slow U3 down for lower noise and better transient 
response of the oven control loop.  The LT1012/OP97 use *Pin 5* for 
overcompensation instead of Pin 8, so C19 should be connected from Pin 5 
to Ground.

Best regards,

Charles


On 9/13/2019 11:17 AM, Club-Internet Clemgill wrote:
> Charles,
> Thank you for this very useful information !
> My plan is to « clone » as close as possible the initial 10811 design, as it is well proven.
> Except changing the crystal and possibly use modern components if they bring any improvement, and adapting the « mass » to the crystal format and manufacturing it through 3D printing.
> Did anybody tried something similar ?
> Best,
> Gilles.
>
>
>
>> Le 11 sept. 2019 à 22:05, Charles Steinmetz <csteinmetz at yandex.com> a écrit :
>>
>> Didier wrote:
>>
>>> The LM208 is a single op-amp with low offset (<3mV) and low bias current.
>>
>> Even 3mV offset is verging on horrible for a "precision" opamp these days -- it's hard to find any respectable opamp that doesn't do lots better.
>>
>> The secret sauce of the LMx08 series is the super-beta input pair, which matches FET opamps for input current but also holds that low (room-temp) input current over the full temperature range (the input current of FET opamps generally rises by at least 10x to more than 1000x at warmer to hot temperatures).
>>
>> There is no need for extraordinary measures -- there are a number of more modern opamps specifically designed to upgrade LMx08 sockets.  The OP77 is one:
>>
>> <http://pdf.datasheetcatalog.com/datasheet/analogdevices/206654345OP77_c.pdf>
>>
>> The LT1012 and OP97 are two more.  I've used both extensively, and finally settled on the OP97 for this sort of application:
>>
>> <http://pdf.datasheetcatalog.com/datasheet/analogdevices/140679914OP97_d.pdf>
>>
>> Best regards,
>>
>> Charles
>>
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>