Want to measure V on the scope: should I buy a new one or build a low noise preamp? - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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
Reply
 
Thread Tools Search this Thread
Old 23rd December 2004, 03:30 PM   #1
Bricolo is offline Bricolo  France
diyAudio Member
 
Bricolo's Avatar
 
Join Date: Nov 2002
Location: Grenoble, FR
Question Want to measure V 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
  Reply With Quote
Old 23rd December 2004, 03:49 PM   #2
Banned
 
Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Send a message via Yahoo to Elso Kwak
Hi Bricolo, the latter with a ultra low noise opamp like AD797
:idea
  Reply With Quote
Old 23rd December 2004, 03:59 PM   #3
Bricolo is offline Bricolo  France
diyAudio Member
 
Bricolo's Avatar
 
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 V 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
  Reply With Quote
Old 23rd December 2004, 07:21 PM   #4
Bricolo is offline Bricolo  France
diyAudio Member
 
Bricolo's Avatar
 
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
  Reply With Quote
Old 23rd December 2004, 08:06 PM   #5
Banned
 
Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Send a message via Yahoo to Elso Kwak
Lightbulb AS797

Quote:
Originally posted by Bricolo
Is Elso the only one interested?
I vaguely remember John Curl is using this opamp for some measurement instrument.
  Reply With Quote
Old 23rd December 2004, 08:14 PM   #6
Bricolo is offline Bricolo  France
diyAudio Member
 
Bricolo's Avatar
 
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
  Reply With Quote
Old 23rd December 2004, 08:31 PM   #7
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.
  Reply With Quote
Old 23rd December 2004, 10:13 PM   #8
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
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?
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 23rd December 2004, 10:25 PM   #9
moamps is offline moamps  Croatia
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
  Reply With Quote
Old 23rd December 2004, 10:54 PM   #10
diyAudio Member
 
john curl's Avatar
 
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.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


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?

All times are GMT. The time now is 12:45 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2