Discrete Opamp Open Design - Page 108 - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, 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 20th September 2012, 10:55 AM   #1071
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Quote:
Originally Posted by RNMarsh View Post
The harmonics of a single tone produces some 'grass' on the FFT plot. Say .01% thd worth; Can't be heard. More simultanious tones, more grass growning and IM grass, too. After 20,000 tones have been applied, that .01% THD of each of thousands of tones adds up to enough to reach audible levels. The audible effect is an equivalent increase in the background noise level. Which is described as masking details or changing character of the sound depending on music freq content played. This might be why we need Really low thd numbers on a single tone test.... to prevent the accumulated harmonics of many simultaneous tones from reaching an audible threshold. -Thx RNM
Okay, let's go back to the original premise: "accumulated harmonics of many simultaneous tones from reaching an audible threshold". Let's try for infinity (and beyond!): what happens when the number of tones increases a magnitude, for each trial: by Richard's assertion, at each tenfold increase in number of tones the overall level of distortion will increase by at least some amount. So the limit as the number of tones approaches infinity is that the signal becomes completely distortion, nothing but. So an input signal that is composed of a number of tones approaching infinity is also output totally as distortion. Hmmm, where's the hole here ... ?

Frank

Last edited by fas42; 20th September 2012 at 10:58 AM.
  Reply With Quote
Old 20th September 2012, 11:08 AM   #1072
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by bcarso View Post

One thing I noticed about Bob's non-global-feedback MM preamp: it assumes the cartridge is connected differentially. This I suspect in large part accounts for the reasonable distortion numbers, as even harmonics will nearly cancel.
This is a blunder, I've had common mode effects on the brain lately; MM single-sided operation will be fine, especially given the cascoding, as long as the other side is grounded through a lot less than 100k. Thanks SG for pointing this out.
  Reply With Quote
Old 20th September 2012, 11:59 AM   #1073
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Quote:
Originally Posted by janneman View Post
Let me try:

You have 20k amplifiers each having a transfer characteristic 'A', each being fed a signal S1....S20k. Each amp output is thus A*S1....A*S20k. After the perfect summer you have A*(S1+S2+...S20k).

Now take a single 'A' amp and feed it (S1+S2...S20k). Output will be A*(S1+S2...S20k).

Looks like a match to me. Of course, we could have skipped all of this by just invoking the superposition principle

jan
There's a simple counter example to this scenario: take an amplifier with extreme even harmonic distortion, positive excursions severely differ from negative excursions in wave shape. Take 2 perfect sine waves of matching frequency and amplitude, but opposite phase as input: output from summing device is the difference between the positive and negative wave shapes; but that from the combined signals fed into single amplifier will be a null.

Frank

Last edited by fas42; 20th September 2012 at 12:02 PM.
  Reply With Quote
Old 20th September 2012, 12:53 PM   #1074
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally Posted by fas42 View Post
There's a simple counter example to this scenario: take an amplifier with extreme even harmonic distortion, positive excursions severely differ from negative excursions in wave shape. Take 2 perfect sine waves of matching frequency and amplitude, but opposite phase as input: output from summing device is the difference between the positive and negative wave shapes; but that from the combined signals fed into single amplifier will be a null.

Frank
Yes if you sum two perfect sinewaves that are 180 degr out of phase you get zero. Send that through an amp and the output is still zero.
Not sure what that proves?

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 20th September 2012, 12:58 PM   #1075
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
In the other case, say your amp has a transfer function of 1*Vi + 0.5*Vi^2 (lots of 2nd harmonics as you postulated).
The 'pos' sine wave V gets an output of 1*V + 0.5*V^2.
The other is 180 degr out of phase so that amp gets an input of -V and the output is 1*-V + 0.5*-V^2. Add that after the two amps and again you get zero.
You'll have a hard time to prove the superposition principle wrong.

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 20th September 2012, 01:41 PM   #1076
fas42 is offline fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Quote:
Originally Posted by janneman View Post
The 'pos' sine wave V gets an output of 1*V + 0.5*V^2.
The other is 180 degr out of phase so that amp gets an input of -V and the output is 1*-V + 0.5*-V^2. Add that after the two amps and again you get zero.
Or is that, 1*-V + 0.5*(-V)^2? That does not sum to zero ...

Frank
  Reply With Quote
Old 20th September 2012, 01:50 PM   #1077
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally Posted by fas42 View Post
Or is that, 1*-V + 0.5*(-V)^2? That does not sum to zero ...

Frank
Hmmm...
__________________
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 20th September 2012, 02:33 PM   #1078
Waly is offline Waly  United Kingdom
diyAudio Member
 
Waly's Avatar
 
Join Date: Jan 2011
Location: London
Quote:
Originally Posted by janneman View Post
Hmmm...
The superposition principle (it is actually a theorem) holds for linear systems only.
  Reply With Quote
Old 20th September 2012, 02:49 PM   #1079
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Yes I just found that out too. I thought it was valid for continuous systems as opposed to discrete time systems.
Another learning moment! Life is good

Edit: another give-away that I was wrong was, that if I was right, we wouldn't have the cancellation of harmonics in push-pull systems. Silly me.

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 20th September 2012, 05:09 PM   #1080
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 fas42 View Post
Okay, let's go back to the original premise: "accumulated harmonics of many simultaneous tones from reaching an audible threshold".
Frank
I'm unconvinced that amp distortion level remain at same low level.... more tones begets more harmonics from amp nonlinearities. But, an interesting thought.
  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
Discrete OPAMP audio-gd Vendor's Bazaar 27 20th September 2012 04:02 PM
discrete opamp help blackpowderaudio Parts 0 16th December 2009 03:46 PM
THAT transistor headphone amp (250ma discrete opamp) design sanity check. Russ White Headphone Systems 19 13th December 2007 12:52 PM


New To Site? Need Help?

All times are GMT. The time now is 12:20 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