[volt-nuts] Best reference after LTZ1000

[Charles P. Steinmetz]

Marvin wrote:

>At least empirically, Geller's reference has been around since 2004, 
>he now has longevity statistics on his side that his board is a 
>capable of at least a 1 month transfer of 10. 000 00 Vdc reference 
>from his lab to you, if so inclined.

>Its interesting this has come up for his services several times, the 
>issue of sales.  But I think differently.

Geller has a patent covering a method of improving the temperature 
coefficient of an AD58x or similar monolithic reference using an 
LM399 or other ovenized reference 
(http://www.pat2pdf.org/patents/pat7382179.pdf).  A friend has a 
little reference box he bought from Geller that claimed to use a 
circuit based on the patent.  However, according to the patent, 
Geller didn't use opposite tempcos to offset each other, he 
essentially just swamped the internal reference and used the AD58x as 
an output scaling amplifier for the ovenized reference.  So why use 
an AD58x in the first place?  You could do significantly better with 
a precision op amp and the ovenized reference, with a little 
attention to details.  So, the patent appears to be what we used to 
call a puff patent.

I notice that his current offering is just a PCB with an AD587 and a 
voltage trimmer 
(http://gellerlabs.com/SVR%20schematic.pdf).  Apparently, he 
concluded that his patented circuit didn't improve things over the 
current AD parts enough to be worthwhile.

This is not to say that his references aren't any good, or don't do 
what he says, or aren't good value.  They are certainly reasonably 
priced, and he is very clear about what they are and are not 
(http://gellerlabs.com/SVR%20M.html).

Best regards,

Charles