Low-distortion Audio-range Oscillator - Page 166 - 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 31st January 2013, 12:12 AM   #1651
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by richiem View Post
My experience with the active twin-t is that 40dB of fundamental attenuation is enough, but I like to use 60dB to be sure. I'm at the point where I don't know if it's the active filter or the oscillators I have that are my limiting factors for spur amplitudes. I really want to know, but I need a 1kHz oscillator that I know has all spurs at least -150dBV in order to verify. If anyone can assure me that Victor's oscillator will do that, then I'm all over it.
Hi Dick,

I don't know about -150dB but they are stunningly quiet.

Still waiting on some decal material to label the case for the TT. Once I have that the TT should be assembled and I'll send you some measurements.
__________________
David.
  Reply With Quote
Old 31st January 2013, 12:32 AM   #1652
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
John Curl suggested using a shunt cap to add an extra -6 dB/octave reduction in the harmonics of the source. I can't say that would be enough to address these issues or would even work at this level.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 31st January 2013, 12:34 AM   #1653
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by 1audio View Post
John Curl suggested using a shunt cap to add an extra -6 dB/octave reduction in the harmonics of the source. I can't say that would be enough to address these issues or would even work at this level.
As a passive LP?
__________________
David.
  Reply With Quote
Old 31st January 2013, 12:47 AM   #1654
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
Sorry for not being clearer, yes.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 31st January 2013, 01:44 AM   #1655
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by 1audio View Post
Sorry for not being clearer, yes.

Hi Demian,

You can try this. It does work but with a variable tuned oscillator it means one more circuit stage to tune.
__________________
David.
  Reply With Quote
Old 31st January 2013, 05:57 AM   #1656
diyAudio Member
 
Join Date: Jun 2005
Location: Zürich
Quote:
With the two trim technique I seem to be able to walk to a >70 dB null even with just 2 single and one 2-parallel caps. I think the pots can be made a small enough portion of the resistor to not be an issue.
It all depends on what trim range, operating level and distortion contribution we're looking for. I'm just saying that the wiper contact resistance can be really, really bad (that applies even for the bulk metal trimmers--the $$$ I've spent for those were a complete waste), depends on the position, varies a lot from specimen to specimen and may go bad over time. So for stuff approaching -140 dB I'm inclined to prefer selected parallel resistors to trim the center frequency to its nominal value. If trimmers are included, it might be helpful to arrange them such that one end is at (virtual) ground if possible--so one could measure their distortion contribution in isolation.

Quote:
Maybe you can shed some light on how Weiss would verify the distortion numbers quoted for this amp module: http://www.weiss-highend.ch/op-amp/d...bipolar_r1.pdf . They seem too good to be true. For $130 ea. they could be a great value. That's close to the internal cost for the modules I designed for Nuforce.
The quoted figure is the input referred harmonic distortion voltage. This is quite easily measured by running the amp at high noise gain, and subtracting the noise gain from the measurement. Same trick as I've used for the opamp measurement series (although I did not subtract the noise gain there), and what TI uses for their IC opamps.

Samuel

Last edited by Samuel Groner; 31st January 2013 at 06:01 AM.
  Reply With Quote
Old 31st January 2013, 07:21 AM   #1657
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
Quote:
Originally Posted by Samuel Groner View Post
I'm just saying that the wiper contact resistance can be really, really bad (that applies even for the bulk metal trimmers--the $$$ I've spent for those were a complete waste), depends on the position, varies a lot from specimen to specimen and may go bad over time. Samuel
Which version of the trimmer? My experience has been much better but none of mine are less than 10 years old.


Quote:
Originally Posted by Samuel Groner View Post
The quoted figure is the input referred harmonic distortion voltage. This is quite easily measured by running the amp at high noise gain, and subtracting the noise gain from the measurement. Same trick as I've used for the opamp measurement series (although I did not subtract the noise gain there), and what TI uses for their IC opamps.

Samuel
I see, that is measured in the way TI, Burr Brown, AD and National do it. Probably the only way to measure such low levels of distortion.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 31st January 2013, 07:32 AM   #1658
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 RNMarsh View Post
Awhile back i suggested taking oscillator distortion and inverting it and adding it back to cancel distortion. No takers. One way is as a unbal to bal converter using a bridge configuration to cancel thd... see below;

And the other is an iteritive circuit (using unbal/unbal). This can be used as the basis to make an oscillator of zero distortion. trim the values to null output thd. see below;

Pre-amplifier and power amp circuits can be made this way as well - using the error take-off point to cancel thd. It overcomes the basic limitation of neg fb which is - increasingly limited open loop gain with increasing freq. [Very low thd at very high freq can be accomplished this way]

[invented by A.M.Sandman] Thx RNMarsh
Bridge amp.jpg

Error take-off.jpg

Last edited by RNMarsh; 31st January 2013 at 07:43 AM. Reason: low thd without gnfb -
  Reply With Quote
Old 31st January 2013, 07:44 AM   #1659
diyAudio Member
 
Join Date: Jun 2005
Location: Zürich
Quote:
This is much smaller.
I use those for some simple circuits like R-R attenuators, RC filters or diode clamps. I agree with Demian that these are pretty tight for a notch filter, but it might work out with some care.

Quote:
Which version of the trimmer?
1248W--larger versions probably have lower wiper contact resistance.

Samuel
  Reply With Quote
Old 31st January 2013, 07:49 AM   #1660
diyAudio Member
 
Join Date: Jun 2005
Location: Zürich
Quote:
This can be used as the basis to make an oscillator of zero distortion.
It might theoretically reduce amplifier distortion contribution towards arbitrary low levels, but it does nothing whatsoever about passives, layout effects, contribution from multiplier and level detector ripple... These are the real challenges.

Samuel
  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 10:46 AM
ultra-low distortion audio oscillator geekysuavo Analog Line Level 16 26th March 2013 03:04 PM
Low distortion oscillator? rjm Equipment & Tools 30 4th May 2011 10:45 PM
Can we improve this low distortion sine oscillator ? gaetan8888 Solid State 22 29th March 2009 12:30 PM
Simple, low distortion 1kHz oscillator jackinnj Solid State 4 6th October 2003 03:58 AM


New To Site? Need Help?

All times are GMT. The time now is 06:32 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