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Old 22nd April 2012, 11:18 PM   #22631
bcarso is offline bcarso  United States
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Quote:
Originally Posted by vacuphile View Post
That's indeed the practical way to do it, Wheatstone, sorry I forgot about you. Actually, don't need a battery; my prototype supply is by now quiet enough as it is for that kind of thing, and even faster and quieter parts will be coming in next week. The apparent paradox is that to create perfect DC, you need unlimited bandwith.

vac
There is a very interesting article about regulators in the April 2012 issue of Power Electronics Technology, "An Unconditionally Stable Linear Voltage Regulator", by Sandler and Hymowitz of Picotest. Although they give some performance results and claim an approximate regulator bandwidth of 300MHz, they don't show a schematic. However the circuit is apparently on their Picotest Voltage Regulator Test Standard kit.

The article appears to be available here:

An Unconditionally Stable Linear Voltage Regulator
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Old 23rd April 2012, 12:51 AM   #22632
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Originally Posted by ThorstenL View Post
BTW, in a certain specific part of an MC input stage the difference in noise between a "generic film resistor" and my "magic resistor" came up to around 10dB at LF, starting below 1KHz. The resistor formed the tail of a folded cascode BTW, with a 1:1000 ratio between cascode impedance and resistor value...

Ciao T

This is a concrete spec that can be tested, the scientific community knows of numerous brands of resistors with very low excess noise. In fact there are folded cacode input op-amps with corner frequencies below 3Hz using (yuch!) 400 atom thick thin film resistors.

BTW by bad do mean to say everyone here using "ordinary" MF resistors is just going from bad to worse with their designs.
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Old 23rd April 2012, 12:55 AM   #22633
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Quote:
Originally Posted by vacuphile View Post
But, if some resistors exhibit excess noise, this might introduce a systematic error in the way I now tend to calibrate my measurements, giving me a false sense of accomplishment.

Is there a ball park figure for the deviations you or others have measured in metal film resistors from different makes?


vac
In the absense of DC current there is no excess noise as long as some care is taken to keep the two ends of the resistor at the same temperature (not that hard actually).
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Old 23rd April 2012, 01:35 AM   #22634
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I repeat this exhaustive survey of excess noise, plenty of choices (if you can sort out the colors ).

https://dcc.ligo.org/public/0002/T09...rent_noise.pdf
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Old 23rd April 2012, 01:43 AM   #22635
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You mean Isabellenhütte PBH, Vishay S102K, and Welwyn RC55Y are not on the bottom ?
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Old 23rd April 2012, 02:30 AM   #22636
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Originally Posted by jacco vermeulen View Post
You mean Isabellenhütte PBH, Vishay S102K, and Welwyn RC55Y are not on the bottom ?
They might be but there are too many similar colors for me to sort by eye, heaven forbid you're color blind (this is a government program they probably violate some rule ).

EDIT - IIRC the Vishay S102K are the crappers for sound.
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Old 23rd April 2012, 05:45 AM   #22637
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Having trouble seeing differences in some colors, I use a small utility called WhatColor.
(It doesn't indicate at the top, but there is a Win7 download further down the page.)


The Susumu thin films look like they measure well.

.
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Last edited by johnferrier; 23rd April 2012 at 06:12 AM.
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Old 23rd April 2012, 06:22 AM   #22638
PMA is offline PMA  Europe
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Quote:
Originally Posted by scott wurcer View Post
I repeat this exhaustive survey of excess noise, plenty of choices (if you can sort out the colors ).

https://dcc.ligo.org/public/0002/T09...rent_noise.pdf
Very nice link.

So a new pseudo-theory explaining "resistor sound" should be created?
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Old 23rd April 2012, 06:23 AM   #22639
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I happened to measure hundreds and hundreds of the Susumu resistors (0.1%, 25PPM tempco) to hand select parts out of two resistor kits for very precise pair of stepped attenuators. It surprised me to find the part to part variation so tight. Many of the values would have met tighter accuracy tolerances (0.01%). Not knowing how to listen to resistors myself, I go with larger wattage and lower tempco when available.


.
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Last edited by johnferrier; 23rd April 2012 at 06:26 AM.
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Old 23rd April 2012, 06:29 AM   #22640
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by scott wurcer View Post
I repeat this exhaustive survey of excess noise, plenty of choices (if you can sort out the colors ).

https://dcc.ligo.org/public/0002/T09...rent_noise.pdf
Wow - very nice paper.

What is striking is the difference in noise peformance - orders of magnitude between resistors of the same value but from different manufacturers

Would be interesting to have a similar set of results for uV/V linearity and inductance.
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