Generic snubber values: fixed-/variable-voltage regs - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 7th February 2008, 04:05 PM   #21
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
Hi, i mean just use two green LEDs to ground in place of R2. Each contributes about 1.9v, so the output sits at 1.9+1.9+1.25v = 5.00 near as dammit.

Each green led represents about 10-20ohm impedance (depending on how much current you pour through via R1) so the result is really rather 'low noise' - note LEDS are forward-biased PN junctions, not a breakdown mechanism like zener/avalanche diodes.
  Reply With Quote
Old 7th February 2008, 05:22 PM   #22
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Quote:
Originally posted by martin clark
Hi, i mean just use two green LEDs to ground in place of R2. Each contributes about 1.9v, so the output sits at 1.9+1.9+1.25v = 5.00 near as dammit.

Each green led represents about 10-20ohm impedance (depending on how much current you pour through via R1) so the result is really rather 'low noise' - note LEDS are forward-biased PN junctions, not a breakdown mechanism like zener/avalanche diodes.
Okay, gottcha.

About LEDs...lots of DIYers use them in various ckts and recommend them generically -- "green LED", "red LED" -- but not specifically in terms of type/brand/etc. I've found that type/brand/etc. can sometimes make a difference. To that end, do you recommend any specific type/brand/etc "green LED"?

Thx
-hm
  Reply With Quote
Old 7th February 2008, 05:59 PM   #23
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
Yes - cheap ones!

  Reply With Quote
Old 7th February 2008, 06:19 PM   #24
diyAudio Member
 
Eric Juaneda's Avatar
 
Join Date: Dec 2006
Location: Avignon, France
There is an interesting thread about LED and Zener's noise.

Some noise measurements for LEDs and zener diodes

Green LED lower noise is not so clear.

Eric
  Reply With Quote
Old 7th February 2008, 07:07 PM   #25
diyAudio Member
 
Join Date: Jul 2003
Location: Bath, UK
No, that's true enough, but here they produce a convenient forward voltage and have very low dynamic impedance (10-20ohms I find, vs. 10-20x that for a true zener at reasonable bias currents). Those ar the reasons I use them.

Anytime you want a low (even lower)-noise reference, it's usually trivial to add some RC filtering.
  Reply With Quote
Old 7th February 2008, 08:48 PM   #26
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Default Super Ultra-Bright LED Lamp

Quote:
Originally posted by Eric Juaneda
Green LED lower noise is not so clear.

Here's what I use.
I used this same LED for a Flea clock regulator; it seems to work just fine.

Click the image to open in full size.
  Reply With Quote
Old 7th February 2008, 09:03 PM   #27
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Default Re: Listening LM317 filtering

Quote:
Originally posted by Eric Juaneda
I wrote an article on relation between LM317 decoupling and sound rendering.

LM317, understanding and listening
The info on this page, to me anyway, is somewhat confusing...

The "First listening test" seems to indicate (AFAICS) that having no Cout and no Cadj is best for subjective sound. This despite the o'scope noise you noted on this page.

Fast-forwarding to the end of the article the following note and schematic comes out of nowhere (i.e., no description, analysis, raison d'etre, etc.) ...

"Here is an example of good subjective sounding solution."

Click the image to open in full size.
The use of Zeners in the R2 position is similar to Martin's suggestion, so I'm assuming you used the same reasoning. Are subjective tests to follow for this ckt?
  Reply With Quote
Old 7th February 2008, 09:51 PM   #28
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
I don't recall any of the tests having a high-ESR or electrolytic output capacitor, either, which seems questionable, to me.
__________________
The electrolytic capacitors ARE the signal path: http://www.fullnet.com/~tomg/zoom3a_33kuF.jpg
  Reply With Quote
Old 8th February 2008, 02:22 AM   #29
Khron is offline Khron  Romania
diyAudio Member
 
Join Date: Jul 2005
Location: Finland
Send a message via AIM to Khron Send a message via MSN to Khron Send a message via Yahoo to Khron
I quote from the site:

"With regulator, we think at first noise rejection. The LM317 datasheets from National semiconductor gives decoupling solution. What about sound and musicality?"

Thus, the point wasn't "finding the best combination of caps, out of ANY combination"... But let's look on the "bright side": at least no "fantabulous" / overhyped caps were tested (ie. BlackGates and other marketing-spawned stuff)
  Reply With Quote
Old 8th February 2008, 06:49 PM   #30
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally posted by Khron
I quote from the site:

"With regulator, we think at first noise rejection. The LM317 datasheets from National semiconductor gives decoupling solution. What about sound and musicality?"

Thus, the point wasn't "finding the best combination of caps, out of ANY combination"... But let's look on the "bright side": at least no "fantabulous" / overhyped caps were tested (ie. BlackGates and other marketing-spawned stuff)
OK. That's a 'plus', at least. ;-)

But I was mainly trying to make the point that since it's typically not a good idea to use low-ESR capacitors at the output of a three-terminal regulator, it seems like a 'listening comparison test' should at least include what might be the 'best case' scenario, at least if the main objective of the test is to find something that 'sounds better'. Or, maybe I misunderstood the objective. At any rate, I would like to have seen the results of a comparison between doing it 'the right way' and what I felt obligated to point out were probably all sub-optimal cases (about which I could be wrong, of course).

Ironically, maybe, If one reads the stuff at the other link, that was in a message nearby, i.e. at http://www.acoustica.org.uk/t/3pin_reg_notes1.html , and one then also follows the link, there, to http://www.tnt-audio.com/clinica/reg...edance1_e.html , one can see an explanation of
why a low-ESR capacitor at the output of a typical three-terminal regulator is (typically, at least) 'a bad thing'. (I could be wrong, but that seems to me to have been corroborated by many other sources, including the regulator manufacturers, themselves.)

Eric (and all): I am sorry if it seemed like I was 'piling on', in a negative or inappropriate way. I do admit that I am biased, in the sense that I am less comfortable with subjective 'testing' than I am with engineering methods and measurements, which, I also admit, sometimes does cause me to have a 'less positive' attitude toward some of the information and ideas that I perceive to have come from the 'subjectivist' camp. (However, FWIW, I do actually believe that 'listener impressions' testing can, ideally at least, provide extremely-important and useful data. This is "audio", after all.)

(Not to put too fine a point on it, but) I probably should have crafted my message so that it would have been perceived more as an attempt to try to provide helpful or educational information, rather than as mere criticism. As an engineer, I usually welcome and appreciate blunt technical criticism, but very often forget that most other types of people might not be accustomed to that style of communication.
__________________
The electrolytic capacitors ARE the signal path: http://www.fullnet.com/~tomg/zoom3a_33kuF.jpg
  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
Snubber network and the values okina Power Supplies 9 22nd September 2009 11:12 PM
calulating snubber values Ted205 Chip Amps 2 11th September 2008 06:10 PM
fixed regs pete.a Everything Else 0 31st January 2004 11:58 AM
Source for HQ fixed 15V regs anyone? Lenin Solid State 9 16th March 2003 06:31 PM
Help calculating RC values for rectifier snubber Eric Pass Labs 2 31st January 2003 06:57 PM


New To Site? Need Help?

All times are GMT. The time now is 04:25 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