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Topics - blackhole

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Analog Audio Stuff / Let's make some noise!
« on: December 31, 2010, 12:28:21 PM »
All want no noise... let's be different, let's make noise!
White one, for measurements... let's say from 0.1Hz to 25MHz - OK, that's a little but too optimistic.
And it must run on batteries, one or two 9V. I like to use them for low noise PS.
Any ideas?

I think of using zener. Which one? 5.6V, 7.5V? Ordinary or special noise diodes, e.g. NoiseCom NC104 or NC202 - how to get those?!! I have no idea regarding their price.
Simple resistor or CSS to feed the zener to avoid 9V battery voltage drop? I am not sure about this. Moreover, I do not want to sneak to much of resistor/CSS 1/f noise in.
What current though the zener? I say you'll say try and measure :)

Has anyone measured zener noise spectra? Where is typical 1/f region? Noise bandwidth? Any suggestions?

After settling this down there is a need to amplify this noise... I think of:
fixed gain + variable LP RC filter + variable gain. The critical is first stage.
It should not contribute any 1/f. Around G=40dB, I guess. FET gain device (or IC).

All this are just my first ideas.


Swap Meet / InterFET IF9030
« on: December 09, 2010, 02:46:31 PM »
I am looking for this low noise FET. Does anybody have them for sale... or know how to get it?
I've tried to contact InterFET directly, but without success.


Analog Audio Stuff / RC filter and electrolytic capacitor leakage
« on: October 07, 2010, 09:27:06 AM »
Hi, all!

I have one question regarding electrolytic capacitor leakage.
Let's say you have a voltage reference (IC or CCS+LED).
Since they are quite noisy (we want nV) and use RC filter to lower the noise, time constant < 1Hz.
This is then buffered by opamp.
To make such filter I usually use 1k resistor and 1mF capacitor -  electrolytic, of course. However, they
there is a concern regarding capacitor leakage. OK, this means we have some DC error (let's assume we have taken care of opamp DC errors, leakage, etc.).
If we do not care about the absolute value but we care only "medium term" (cca 1Hz and above) stability (usually case in audio),  this is OK. But is this all? Are there any other side effects? Hmm...

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