Low-distortion Audio-range Oscillator - Page 271 - diyAudio
Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

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 15th May 2013, 06:51 PM   #2701
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by Samuel Groner View Post
I was more about to say that there is no input level at which an ordinary ADC can estimate the harmonic distortion of the oscillators we're converned with here with reasonably uncertainity, but indeed at zero input the measurement should be pretty good, usually!

Samuel

Yes I know. I was being silly. The emoticons are not working for me. Never have.

Cheers,
__________________
David.
  Reply With Quote
Old 15th May 2013, 07:55 PM   #2702
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
Lowering the noise-
This can be a clear manageable task. The first step would be to figure out where the noise is circuit limited. Usually that issue would be at the first stage but it may be further down the chain. In the distortion analyzer there is an input amp (discrete in the Panasonic and ShibaSoku). It would be worth figuring its noise floor in nV/rtHz since you will not get below that threshold. Looking at Pchi's reverse engineered schematics of the 725C ShibaSoku Automatic Distortion Analyzer most of the circuit is high impedance so a noise floor of 5 nV/rtHz won't limit the performance. Something like an LT1468 would be a fine option if the rest of the circuit is compatible. However it may show no real noise improvement. A TL072 is 18 nV/rtHz or equivalent to a 22K Ohm resistor. Some stages are lower Z than that so it could make a difference. However the input bias current could be a problem. An OPA(n)134 could be an alternative with 8 nV/rtHz.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 16th May 2013, 06:51 PM   #2703
diyAudio Member
 
myhrrhleine's Avatar
 
Join Date: Jan 2006
Location: Avalon Island
Hi all,

The OPA827 might be worth looking at with a noise voltage of 4nv
Noise current is nonexistent
__________________
Just because you can't hear it doesn't mean no one can.
  Reply With Quote
Old 17th May 2013, 06:15 PM   #2704
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by 1audio View Post
Lowering the noise-
. Looking at Pchi's reverse engineered schematics of the 725C ShibaSoku Automatic Distortion Analyzer most of the circuit is high impedance so a noise floor of 5 nV/rtHz won't limit the performance. .
This is true of every osc/analyzer circuit I have. Thus, the opamp replacements in key places with the most modern, SOTA, low noise, low distortion opamps have been so beneficial in upgrading them.

Thx-Richard
  Reply With Quote
Old 17th May 2013, 06:29 PM   #2705
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
This is true of every osc/analyzer circuit I have. Thus, the opamp replacements in key places with the most modern, SOTA, low noise, low distortion opamps have been so beneficial in upgrading them.

Thx-Richard
I hope you realize that you are saying exactly the opposite thing. My experience is the same as Demian's, it is VERY difficult (maybe impossible) to maintain and equivalent noise of even 1K Ohm through an entire oscillator signal chain. The simulation/calculation with perfect noiseless amps is easy enough to do.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  Reply With Quote
Old 17th May 2013, 07:02 PM   #2706
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
I am not disagreeing with Demian nor you. I believe you guys. But the proof is in the results. using other opamps to replace the ones originally used has had a benficial affect in both noise and harmonic distortion levels. IMO Demian just says he finds it fruitless to try to go lower than a certain level. I have not said I wanted noise lower than a 1K resistor. Just lower the noise that is contributable by the opamp used in that particular environment. THAT has been accomplished already -- past tense.

Thx-RNMarsh
  Reply With Quote
Old 17th May 2013, 09:02 PM   #2707
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
I am not disagreeing with Demian nor you. I believe you guys. But the proof is in the results. using other opamps to replace the ones originally used has had a benficial affect in both noise and harmonic distortion levels. IMO Demian just says he finds it fruitless to try to go lower than a certain level. I have not said I wanted noise lower than a 1K resistor. Just lower the noise that is contributable by the opamp used in that particular environment. THAT has been accomplished already -- past tense.

Thx-RNMarsh
I'm saying from the schematics the noise floor is totally dominated by the passives with fairly mundane op-amps, Demian suggests LT1458 the use of expensive 4-5 nV FET amps will not further reduce the noise. The ultra-low noise bi-polar amps are likely to make it worse due to current noise.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  Reply With Quote
Old 18th May 2013, 04:04 AM   #2708
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Does that apply to the HP-339A also?
I havent made any changes yet to the AD725D.

-RNM

Last edited by RNMarsh; 18th May 2013 at 04:08 AM. Reason: OK
  Reply With Quote
Old 18th May 2013, 04:08 AM   #2709
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by RNMarsh View Post
Does that apply to the HP-339A also? I havent made any changes yet to the AD725D.

-RNM
Yes it applies to the 339a too. I couldn't get the noise down past the the stated residual and that's because of the passives.
__________________
David.
  Reply With Quote
Old 18th May 2013, 05:19 AM   #2710
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Ok lets fine tune the subject again --> There is an oscillator and there is an analyzer. The 339a has both. The 725 does not have an oscillator.

I have two 339a here... one is stock and one is modified. I can do real time comparisons. I get a 2-3dB improvement in rms broad band noise levels just with opamp changes. But a much greater reduction in THD.... which was/is the primary goal.

I think the comments of noise in passives compared to the older opamps may not be including the low freq noise levels which are a lot higher in the older opamps than the mid freq levels. Since both the 339a and the 725d have meter displays, you can also see the effect of quieter oscillator circuit at low freq by a steadier meter needle..... its doesnt vibrate and kick around as much with the newer opamps. (nice when tuning for nulls).

Now then, the analyzer side is where i got the most noise reduction.... and the better performance as an analyzer. That is the part, as I have said before, that i want to look at reducing the noise in the other analyzers.... the 7722 and the 725. I have already showed the levels of noise via the analyzer monitor ports... that might also be improved and results in more harmonics being seen with the spectrum analyzer. Without affecting the notch filters, that leaves the output from the notch on towards the monitor port as the only areas to look at.

Thx-RNMarsh

Last edited by RNMarsh; 18th May 2013 at 05:45 AM.
  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
Radford Low Distortion Oscillator Series 2 audiomik Equipment & Tools 21 19th February 2014 11:46 AM
ultra-low distortion audio oscillator geekysuavo Analog Line Level 16 26th March 2013 04:04 PM
Low distortion oscillator? rjm Equipment & Tools 30 4th May 2011 11:45 PM
Can we improve this low distortion sine oscillator ? gaetan8888 Solid State 22 29th March 2009 01:30 PM
Simple, low distortion 1kHz oscillator jackinnj Solid State 4 6th October 2003 04:58 AM


New To Site? Need Help?

All times are GMT. The time now is 06:44 AM.


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