Want to measure µV on the scope: should I buy a new one or build a low noise preamp?

Bricolo · 23rd December 2004, 03:30 PM

Hi all,

I'd like to be able so see voltages down to the microvolt on my scope (Tektronix 2232, max sensitivity is 2mV/div), to measure low noise power supplies, DACs etc...

I know some old Tek scopes can measure down to the microvolt level, but that could cost me more than 200€

Is a low noise preamplifier possible? In DIY too?

I'd like to have some advices.

Thank you, and merry christmas to all

Alex

Elso Kwak · 23rd December 2004, 03:49 PM

Hi Bricolo, the latter with a ultra low noise opamp like AD797
:idea

Bricolo · 23rd December 2004, 03:59 PM

That's the solution I'd prefer too, but according to the datasheet:

"110MHz GBW"

So, to visualize µV on my mV scale, I'd need a *1000 Gain. The preamp would be limited to 110kHz bandwidth, can't this be a problem?

Bricolo · 23rd December 2004, 07:21 PM

Is Elso the only one interested?

Elso Kwak · 23rd December 2004, 08:06 PM

Quote:

Originally posted by Bricolo
Is Elso the only one interested?

I vaguely remember John Curl is using this opamp for some measurement instrument.

Bricolo · 23rd December 2004, 08:14 PM

OK

I'll try to contact John Curl, and Scott Wurcer to see what they think.
I was also thinking about the 797, but strangely, in the dhatasheet, they recommand other opamps for sources with high impedance (AFAIK, a probe is >100k)

I think the layout and PS won't be trivial for this

Thanks Elso!

Mike Gergen · 23rd December 2004, 08:31 PM

I would try a INA103 with a diiferential front end. The '103 isn't as quiet as the 797 but the diff input may help. Both options have pluses and minuses.

SY · 23rd December 2004, 10:13 PM

What was the opamp that Wurcer used for the capacitor tests?

Yeah, a gain of 60 dB is going to be a real challenge if you want bandwidth. Are you SURE you need to go better than 100kHz at that level?

moamps · 23rd December 2004, 10:25 PM

Hi Bricolo,

I found a schematic of the AC millivoltmeter in an old Elektor issue that you may use as an instrumentation amp. Its most sensitive range is 200uV, which could be just about enough for your purposes. The design itself is quite simple (FET at the input, discrete opamp). The article and the schematic can also be found in "Electronic Test Instruments" by Elektor Electronics, 1994 (ISBN 0 905705 37 8).

Regards,
Milan

john curl · 23rd December 2004, 10:54 PM

I am currently using one of Scott Wurcer's IN-AMP designs, the AD525. It is not as quiet as the AD797, BUT it has built in gain settings, up to 1000, (I use 100) and it has a true differential input. Run it by Scott. I use 9V batteries to power it.

23rd December 2004, 03:30 PM	#1
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	Want to measure µV on the scope: should I buy a new one or build a low noise preamp? Hi all, I'd like to be able so see voltages down to the microvolt on my scope (Tektronix 2232, max sensitivity is 2mV/div), to measure low noise power supplies, DACs etc... I know some old Tek scopes can measure down to the microvolt level, but that could cost me more than 200€ Is a low noise preamplifier possible? In DIY too? I'd like to have some advices. Thank you, and merry christmas to all Alex __________________ Just remember: in theory there's no difference between theory and practice. But in practice it usually is quite a bit difference... Bob Pease

23rd December 2004, 03:59 PM	#3
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	That's the solution I'd prefer too, but according to the datasheet: "110MHz GBW" So, to visualize µV on my mV scale, I'd need a *1000 Gain. The preamp would be limited to 110kHz bandwidth, can't this be a problem? __________________ Just remember: in theory there's no difference between theory and practice. But in practice it usually is quite a bit difference... Bob Pease

23rd December 2004, 07:21 PM	#4
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	Is Elso the only one interested? __________________ Just remember: in theory there's no difference between theory and practice. But in practice it usually is quite a bit difference... Bob Pease

23rd December 2004, 08:14 PM	#6
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	OK I'll try to contact John Curl, and Scott Wurcer to see what they think. I was also thinking about the 797, but strangely, in the dhatasheet, they recommand other opamps for sources with high impedance (AFAIK, a probe is >100k) I think the layout and PS won't be trivial for this Thanks Elso! __________________ Just remember: in theory there's no difference between theory and practice. But in practice it usually is quite a bit difference... Bob Pease

23rd December 2004, 10:13 PM	#8
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	What was the opamp that Wurcer used for the capacitor tests? Yeah, a gain of 60 dB is going to be a real challenge if you want bandwidth. Are you SURE you need to go better than 100kHz at that level? __________________ If there's a sucker born every minute, where do the rest of them come from?


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

23rd December 2004, 03:49 PM	#2
Elso Kwak Banned Join Date: Dec 2001 Location: Zamboanga, City of Flowers, Mindanao	Hi Bricolo, the latter with a ultra low noise opamp like AD797 :idea

23rd December 2004, 08:31 PM	#7
Mike Gergen diyAudio Member Join Date: Sep 2004 Location: Elk River MN	I would try a INA103 with a diiferential front end. The '103 isn't as quiet as the 797 but the diff input may help. Both options have pluses and minuses.

23rd December 2004, 10:25 PM	#9
moamps diyAudio Member Join Date: Oct 2002 Location: Croatia	Hi Bricolo, I found a schematic of the AC millivoltmeter in an old Elektor issue that you may use as an instrumentation amp. Its most sensitive range is 200uV, which could be just about enough for your purposes. The design itself is quite simple (FET at the input, discrete opamp). The article and the schematic can also be found in "Electronic Test Instruments" by Elektor Electronics, 1994 (ISBN 0 905705 37 8). Regards, Milan

23rd December 2004, 10:54 PM	#10
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	I am currently using one of Scott Wurcer's IN-AMP designs, the AD525. It is not as quiet as the AD797, BUT it has built in gain settings, up to 1000, (I use 100) and it has a true differential input. Run it by Scott. I use 9V batteries to power it.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to measure JLH Class A with a Scope	chris ma	Everything Else	84	28th December 2012 08:13 PM
Can I use a scope to measure powerline noise?	Saurav	Parts	23	11th July 2012 06:37 PM
How do I measure - 140 dB noise levels?	gentlevoice	Solid State	23	23rd October 2008 02:39 PM
Why am I picking up so much noise on my scope?	Bricolo	Everything Else	54	8th June 2004 05:20 AM
Can I look for (or even measure) distorsion on an amp with a dual scope?	Bricolo	Parts	17	17th September 2003 02:06 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read