Want to measure µV on the scope: should I buy a new one or build a low noise preamp? - Page 3 - diyAudio
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Old 27th December 2004, 02:48 PM   #21
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DAC output with less than 1 uV hardly excists. It's above 120 dB S/N

PS under 5-10 uV is also pretty good.

Anyway, good luck with your preamp.
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Old 27th December 2004, 03:04 PM   #22
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2V RMS with 96dB dynamic range is something like 30uV for the LSB
not so far from the uV
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Old 27th December 2004, 03:17 PM   #23
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Quote:
Originally posted by Bricolo
2V RMS with 96dB dynamic range is something like 30uV for the LSB
not so far from the uV

What is so interesting here ?
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Old 27th December 2004, 03:28 PM   #24
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I was just explaining that some uV aren't too precise to measure a dac
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Old 27th December 2004, 04:19 PM   #25
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Quote:
Originally posted by Bricolo
mostly power supplies, and dac outputs
for power supplies you should bandwidth limit the amplifier -- the high pass filter, consisting of the two 1000uF electrolytics and 10K resistor is 100 milliHertz, and the optional high pass filter is 10Hz.

you can make a similar differential or instrumentation amplifier from 3 low-noise opamps -- butyou need to very carefully match the gain setting and feedback resistors. The SSM2019 is about 1/2 the price of an AD797 and is, I believe, primarily aimed at the microphone amplification market.
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Old 27th December 2004, 04:47 PM   #26
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limitting the bandwidth, but how much?
AC coupled, that's clearly not a problem
but how much for the high pass? with a *1000 gain, the opamp will limi t itself the bandwidth (with a 797+cap, max is approx 400khz, without the cap it's 100khz)
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Old 27th December 2004, 08:00 PM   #27
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for testing power supplies -- like the super regs or the Sulzer, etc. it is useful to know the noise in the range of just above DC to 10 Hz -- for the DAC's etc. you obviously don't want to limit the upper range this low (i.e. below audibility.)

a small cookie tin is used by the folks at Linear Tech to shield their low noise power supply testing amplifier.
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Old 27th December 2004, 08:50 PM   #28
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ok

does a cookie tin mean a cookie metal box?
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Old 27th December 2004, 10:05 PM   #29
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Quote:
Originally posted by Bricolo
ok

does a cookie tin mean a cookie metal box?

Yes, the one you keep biscuits in.
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Old 27th December 2004, 10:07 PM   #30
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damn, I'll have to eat a lot of my mum's christmas biscuits to have a spare box
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