EEVblog #529 – HP 35660A DSA Upgrade InvestigationPosted on September 30th, 2013 6 comments
A teardown of the front end PCB in the HP 35660A Dynamic Signal Analyser.
Dave does some preliminary investigation to see what opamps and FET’s are unsed in the analog front end to see if they can be upgraded for better performance.
This is more for Dave’s record than interesting info.
Previous video: http://www.youtube.com/watch?v=Y0jkPLuFdnM
Is it worth taking TP1 & TP2 to 0v to see what happens to the noise floor. Then TP3 and finally TP4? As far as I can tell from my limited knowledge no harm would be caused and at least you’d gain some insight as to what degree of improvement might be possible.
Thanks for the interesting series of videos on the 35660A.
The large value resistors R9, R10, and R20 in series with the inputs contribute a significant portion of the total noise. The thermal noise from these resistors alone is about 14 nV/rtHz. The FET and op amp buffer stage is unity gain, so in addition to contributing its own noise it offers no noise immunity from the following stages which have 2k ohm series resistors.
Check out the new LSK489 dual low noise JFET by Linear Integrated Systems…
here is a hint!
If the JEDEC part number is not listed in the products part list description, use a HP Xref to convert HP part numbers to JEDEC (www.jedec.org) part numbers.
For your Part, 26-0715 (18 is dropped).
Therefore, the HP part number for the Op-Amp is 1826-0715.
Using one of the HP Xref’s, this equates to a LM725H and not a NE5534!
It seems you have another part in one of the locations or possibly an equialent.
Changes like this is usually documented in the manual for your serial number range.
The Original HP cross reference was posted in HP bench briefs regularly so there are quite a few different scanned copies around.
I also triple check part numbers before ordering/replacement, just to be sure!
This is my main Xref – http://www.vk2hmc.net/blog/?wpfb_dl=7 (!warning 21Mb)
Be aware here are a number of different cross reference lists present in the file.
If the part is not in the 1st list, be persistant and keep searching.
Also, I find that this searchable excel spreadsheet is pretty quick, accurate and fairly complete – http://www.vk2hmc.net/blog/?wpfb_dl=6
Actually, once you get used to the HP part system, it is quite easy to both remember and find the JEDEC part number if you have to.
Sorry Dave, for some reason I got the part number in my head as 1816-0711 (LM725H) and not 1816-0715 (NE55340) bloody HP part numbers strikes again?!
You are correct the part is NE5534.
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