John Curl's Blowtorch preamplifier part II - Page 2053 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

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 9th February 2012, 01:25 PM   #20521
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
Interestingly I was with a customer today talking about oscillators. High volume SOTA oscillators for clocks are at about 0.3ps phase noise with better models offering 0.1ps phase noise. Design of the PLL and associated circuitry is important to get these levels. On board LDO's do the donkey work.
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 9th February 2012, 01:27 PM   #20522
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
Anyone want to hazard a guess at what these cell for in volume?

:-)
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 9th February 2012, 02:13 PM   #20523
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by janneman View Post
Demian,

If you have some Zout on the supply, wouldn't the oscillator's high speed switching cause appreciable noise on the supply line?
That isn't addressed at all by the Finesse.

jan
The supply only feeds the oscillator!
  Reply With Quote
Old 9th February 2012, 02:20 PM   #20524
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
For clarification, on more closely reading the power supply noise reduction papers linked here, I realize that my superficially similar SHUNT REGULATOR operates on the more primitive principle as a shunt regulator and not by Finessing. The parts count and position are similar, but the two are different in operation. Still, I think that this problem of noise with the LM317 has now been well covered by outside sources and proves that the problem exists outside my imagination. (thank goodness) '-)
  Reply With Quote
Old 9th February 2012, 02:55 PM   #20525
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
Quote:
Originally Posted by janneman View Post
Demian,

If you have some Zout on the supply, wouldn't the oscillator's high speed switching cause appreciable noise on the supply line?
That isn't addressed at all by the Finesse.

jan
If your oscillator is switching then your phase noise will go through the roof. A good oscillator is in its linear region always. All of the current demand will be at the oscillator frequency. A cap can do a really good job of supporting that. Getting low Z from an amplifier at 10 MHz or higher doesn't really work.

Jitter specs for Sonet have little to do with audio. The usual jitter spec on a crystal oscillator is for 12 KHz to 20 MHz phase noise. All of the jitter that matters for audio is below 100 KHz and stretches to 100 Hz (AES) or 10Hz or lower (Audiophilia Nervosa). The low frequency phase noise is hard to get low.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 9th February 2012, 03:04 PM   #20526
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally Posted by 1audio View Post
If your oscillator is switching then your phase noise will go through the roof. A good oscillator is in its linear region always. All of the current demand will be at the oscillator frequency. A cap can do a really good job of supporting that. Getting low Z from an amplifier at 10 MHz or higher doesn't really work.

Jitter specs for Sonet have little to do with audio. The usual jitter spec on a crystal oscillator is for 12 KHz to 20 MHz phase noise. All of the jitter that matters for audio is below 100 KHz and stretches to 100 Hz (AES) or 10Hz or lower (Audiophilia Nervosa). The low frequency phase noise is hard to get low.
OK, I get that. But at a certain point you've got to shape up the oscillator output to a good square wave with very fast risetimes, right?
How do you then supply THAT circuitry to avoid phase noise?

jan
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W. S. Maugham
Check out Linear Audio!
  Reply With Quote
Old 9th February 2012, 03:27 PM   #20527
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Jan,

Quote:
Originally Posted by janneman View Post
OK, I get that. But at a certain point you've got to shape up the oscillator output to a good square wave with very fast risetimes, right? How do you then supply THAT circuitry to avoid phase noise?
Hopefully the Cap Demian mentioned will also do a good job at the harmonics of the oscillator frequency.

I now use mainly SMD oscillators and usually put 10nF 0402 directly at the power connections and 1uF 0603 nearby and some 10uF 1206 close by, but I will use 10uF 0612 in future designs...

The big "canned" oscillators actually have on board decoupling and noise improvements, at least the ones we use.

Ciao T
  Reply With Quote
Old 9th February 2012, 04:49 PM   #20528
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Default Ballast resistors (or matching) for paralleling JFETís = A humbug

The calculations are easy to do. Take 2 2SK170ís and parallel them and run them at 10mA total. A matched pair runs at 5mA each for about a total gm of 52.9mS. Now take the two most mismatched possible 2SK170BLís (6mA Idss and 12mA Idss), the current splits 2.8mA and 7.2mA BUT the net gm is 51.8mS only 2% degradation and only a 1% increase in noise. ANY useful ballasting will degrade the noise much more.
__________________
"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 9th February 2012, 05:31 PM   #20529
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
Quote:
Originally Posted by ThorstenL View Post
Jan,

... but I will use 10uF 0612 in future designs...

Ciao T
horribly piezo - the only way to cram that much C into so little ceramic

large V and T coeffs too

I use the somewhat less bad dielectric 1uF in a ring around my 100 MHz uC - but I have no mechanical vibration to jitter spec to meet

Last edited by jcx; 9th February 2012 at 05:34 PM.
  Reply With Quote
Old 9th February 2012, 06:08 PM   #20530
diyAudio Member
 
Chris Hornbeck's Avatar
 
Join Date: May 2011
Location: Little Rock
Quote:
Originally Posted by scott wurcer View Post
The calculations are easy to do. Take 2 2SK170ís and parallel them and run them at 10mA total. A matched pair runs at 5mA each for about a total gm of 52.9mS. Now take the two most mismatched possible 2SK170BLís (6mA Idss and 12mA Idss), the current splits 2.8mA and 7.2mA BUT the net gm is 51.8mS only 2% degradation and only a 1% increase in noise. ANY useful ballasting will degrade the noise much more.
Very cool. I'd never even thought to ask. Since gm curvature with Id is so similar among devices of the same type (2SK170, for example) this implies that linearity is also averaged.

Much thanks,
Chris
  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



New To Site? Need Help?

All times are GMT. The time now is 04:48 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