Noise even if the signal doesn't pass through a component? - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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 3rd December 2015, 02:08 PM   #1
diyAudio Member
 
Join Date: Sep 2008
Default Noise even if the signal doesn't pass through a component?

Here's a question that I can't wrap my head around.

Even if a signal doesn't pass through a certain component, the signal can still be affected. Are any effects/noise/distortion the same as if the signal passed through the component?

Let me illustrate:
Click the image to open in full size.

The picture to the left is a standard voltage divider.

- Signal comes in
- Signal goes through R1,
- Part of the signal goes to GND through R2
- Resulting signal is available at the output.

The signal at OUTPUT never passed through R2, but it is affected by R2's properties and noise/interference may be introduced.

The picture to the right is an RC filter, which essentially is a frequency dependent voltage divider.

The same thing occurs here. The signal never goes through the capacitor C1, but it is affected by C1's properties.

The question is: Are the effects on the signal from R2/C1 the same as if the signal actually passed through it? Or are the effects different in any way? I am not talking about faulty components here, just if the fully functioning components that "look like" they are outside of the signal path affect the signal in the same way as if they were.

Last edited by skrodahl; 3rd December 2015 at 02:10 PM.
  Reply With Quote
Old 3rd December 2015, 02:17 PM   #2
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
"in the signal path" can be given "too simple" interpretations

the shunt/grounded component in the divider/filter circuits are "signal path" components for an engineer's understanding of the circuits
  Reply With Quote
Old 3rd December 2015, 02:18 PM   #3
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by skrodahl View Post
The signal at OUTPUT never passed through R2, but it is affected by R2's properties and noise/interference may be introduced.
The signal does pass through R2. It is the voltage developed across R2 in response to the current flow through R2 that is the output voltage.

The same happens for the cap. Here, the voltage across the cap and current flowing through the cap are not in phase and this gives rise to the output voltage both varying in amplitude with frequency, and also the phase shift of the output voltage compared to the input voltage.

In both cases, whatever you load the output terminal with has the property of modifying and altering the output voltage still further.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 3rd December 2015, 02:19 PM   #4
diyAudio Member
 
Join Date: Sep 2008
I probably should have left out the signal path part, I just wanted to highlight that it looks like it even though that's not the case.

Is there any difference if the resulting signal physically goes through the component or not, that's what I'm trying to understand.
  Reply With Quote
Old 3rd December 2015, 02:20 PM   #5
diyAudio Member
 
Join Date: Sep 2008
Thanks Mooly, that's where I couldn't connect the dots. Excellent explanation.
  Reply With Quote
Old 3rd December 2015, 02:25 PM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Your welcome.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 3rd December 2015, 02:36 PM   #7
rayma is online now rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Location: Upper midwest
Quote:
Originally Posted by skrodahl View Post
Even if a signal doesn't pass through a certain component, the signal can still be affected.
Are any effects/noise/distortion the same as if the signal passed through the component?
I think that you're confusing current and voltage.
Current "flows" between two circuit nodes of differing potential (voltage),
through the component(s) that are connected between the two nodes.
Voltage is measured at a particular circuit node, relative to another circuit node.

A crude fluid analogy is: voltage => water pressure, and current => water flow.

Last edited by rayma; 3rd December 2015 at 02:41 PM.
  Reply With Quote
Old 3rd December 2015, 02:38 PM   #8
diyAudio Member
 
Join Date: Sep 2008
Perhaps this is a better way to view it?

Click the image to open in full size.

The blue arrow is where I get the signal.
  Reply With Quote
Old 3rd December 2015, 02:46 PM   #9
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Yes.

Look at this which shows the voltage applied in green (1volt peak) and the voltage at Vout2 (in blue) and the current in C1 (in red). Notice the phase shift of the current and voltage.
Attached Images
File Type: jpg P1.JPG (230.2 KB, 101 views)
File Type: jpg P2.JPG (167.9 KB, 99 views)
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 3rd December 2015, 02:47 PM   #10
rayma is online now rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Location: Upper midwest
Quote:
Originally Posted by skrodahl View Post
The blue arrow is where I get the signal.
The output signal (the voltage across C) is caused by the current flow through the R and C,
due to the input voltage between IN and ground. Since there's no load impedance,
there is no load current flow, and all the current goes through R and C

Last edited by rayma; 3rd December 2015 at 02:51 PM.
  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
FS: New TechDIY Pass F5 component kits and Audio Sector boards orthoefer Swap Meet 2 26th July 2013 06:40 PM
component reduction in signal chain chokesrule Tubes / Valves 4 6th February 2013 03:00 PM
Noise when signal is turned off mholst Chip Amps 4 8th February 2012 03:41 PM
Signal tube noise! M Gregg Tubes / Valves 15 16th November 2010 07:18 PM
Questions re: component orientation for lowest noise? jtsaudio Solid State 12 3rd April 2008 02:53 AM


New To Site? Need Help?

All times are GMT. The time now is 02:10 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki