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Old 23rd October 2009, 02:08 AM   #1
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Default An even lower noise measurement technique

Came packaged with the press email on Linear Tech's LTC6655 Reference "775nV Noise Measurement for a Low Noise Voltage Reference" by Jim Williams. Application Note 124 -- published in July, but first I have seen it was this evening:

http://cds.linear.com/docs/Applicati...ote/an124f.pdf

Does not specify whether Danish Butter Cookie Tin or Oreos Tin was used for isolation.
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Old 23rd October 2009, 02:52 AM   #2
iko is offline iko  Canada
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Good one Jack, thanks! I just got an hp3581a but still have no hope of measuring nanovolts at home.
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Old 23rd October 2009, 03:02 AM   #3
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Quote:
Originally Posted by ikoflexer View Post
Good one Jack, thanks! I just got an hp3581a but still have no hope of measuring nanovolts at home.
Look at Figure 3 -- uses an LSK389, but you can use a matched pair of 2sk170s -- the '3581 has a great RMS converter.
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Old 23rd October 2009, 03:28 AM   #4
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Got a whole pile of 2sk170s, not a problem there.

Makes me wonder how Jim Williams gets away with 10,000x amplification of such low noise with the ubiquitous cookie can, thin walled and all, when John Curl was talking with other guys about his need for a thick aluminum case, to keep the noise down to acceptable levels in his Blowtorch preamp.

"Capacitor Dielectric Absorption Requires 24 Hour Charge Time to Insure Meaningful
Measurement. Highest Grade Wet Slug Tantalum Capacitors are Required to Pass This Test"

Now there's something that doesn't cross my mind every day.

Last edited by iko; 23rd October 2009 at 03:36 AM.
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Old 23rd October 2009, 05:21 AM   #5
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I have a gain of approximately 100,000 in the Blowtorch with a phono stage at 50Hz. If you want to reduce the MAGNETIC component (transformers) of the EM interference, you need depth in the shielding. If you don't care, then you can use aluminum foil pasted on a cigar box.
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Old 23rd October 2009, 01:07 PM   #6
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Quote:
Originally Posted by john curl View Post
I have a gain of approximately 100,000 in the Blowtorch with a phono stage at 50Hz. If you want to reduce the MAGNETIC component (transformers) of the EM interference, you need depth in the shielding. If you don't care, then you can use aluminum foil pasted on a cigar box.
Further to your point, the folks from mU Metal suggest that folks who encounter interference problems first try to attack the problem with aluminum foil rather than spending hundreds of bucks on their product. any time you bend or cut muMetal you risk destroying the magnetic properties.

The cookie tin is steel, by the way. I use one for the Uber Oscillator.

I am going to test 6x 220/35V Elna Silk's. I also have some very high quality Spragues and TRW's. No PCB -- but manhattan style construction with Teflon leads.

Last edited by jackinnj; 23rd October 2009 at 01:10 PM.
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Old 23rd October 2009, 01:18 PM   #7
iko is offline iko  Canada
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Quote:
Originally Posted by john curl View Post
I have a gain of approximately 100,000 in the Blowtorch with a phono stage at 50Hz. If you want to reduce the MAGNETIC component (transformers) of the EM interference, you need depth in the shielding. If you don't care, then you can use aluminum foil pasted on a cigar box.
Fair enough. Horses for courses.
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Old 23rd October 2009, 01:23 PM   #8
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Originally Posted by jackinnj View Post
Further to your point, the folks from mU Metal suggest that folks who encounter interference problems first try to attack the problem with aluminum foil rather than spending hundreds of bucks on their product. any time you bend or cut muMetal you risk destroying the magnetic properties.

The cookie tin is steel, by the way. I use one for the Uber Oscillator.

I am going to test 6x 220/35V Elna Silk's. I also have some very high quality Spragues and TRW's. No PCB -- but manhattan style construction with Teflon leads.
Yep, very familiar with the cookie steel box, as I've been using it too for my low-noise amp experiments. In fact my wife gives me strange looks when I reach for the cookie can in the store, as I couldn't care less for sweets or cookies of any kind
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Old 27th October 2009, 11:45 AM   #9
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Quote:
aluminum foil
Now that escapes me completely. Aluminum is not ferromagnetic at all, so how is it supposed to aid in shielding magnetic fields? Mu-metal is a soft ferromagnet, so copper or transformer iron is for sure closer to its properties than alu.

As copper and transformer iron are hard ferromagnets, their shielding properties for 50Hz magnetic fields are anyway only marginal.

Maybe somebody could point out what I'm missing?

Have fun, Hannes
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Old 27th October 2009, 01:15 PM   #10
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Aluminum will shield for RFI and EMI...an aluminum foil hat shields best of all.
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