Problems with subwoofer phase control picking up noise - 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 23rd April 2013, 09:14 AM   #1
JanErik is offline JanErik  Finland
diyAudio Member
 
Join Date: Aug 2010
Location: Vasa
Default Problems with subwoofer phase control picking up noise

I have built this circuit: Project 103 - Subwoofer Phase Controller
Now it seems as if the invert switch works as an antenna when it is open and picking up disturbance, atleast with the board still on the desk.
This is a tricky case since the "antenna" is directly on the opamp input and there is 22k+47k to ground. Do you still think it could be better with board+switch mounted in a metal case?
I am using a microphone cable with screen grounded.
  Reply With Quote
Old 23rd April 2013, 11:46 AM   #2
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Are all loops closed up by twisting all wire pairs tightly? You have to keep both wires of each pair together, everywhere, or the the resulting loop will be an antenna.

The switch wiring should be placed very close to R1 and R2 and their connection, all the way from one end to the other. Otherwise you get enclosed loop area, and an antenna.

Last edited by gootee; 23rd April 2013 at 11:51 AM.
  Reply With Quote
Old 23rd April 2013, 12:17 PM   #3
JanErik is offline JanErik  Finland
diyAudio Member
 
Join Date: Aug 2010
Location: Vasa
I cant have it really close since I want the switch on the panel. Will be around 10cm (4") cable.
  Reply With Quote
Old 24th April 2013, 12:27 AM   #4
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Sorry. I did not explain clearly-enough.

Whichever two conductors go to the switch, they should be twisted tightly together, all the way from the board to the switch.

But there is a little more to it. The input and the ground ALREADY need to be twisted together, ALL the way to the top of R1, from which the ground follows the body of R1 to its other end. (Or, maybe you have a ground plane on a PCB from where the twisted input signal and input ground enter the copper, with the ground plane under at least the area where R1 is.) Also, the loop that R2 and R3 are part of will be "collapsed", compared to the way the schematic is drawn, probably with R2 and R3 against each other, and very close to the IC pins and R1.

If there is a ground plane, the ground connection for the switch can originate right next to the other switch connection, near R2. Otherwise, simply run one of the two switch wires from where it connects to the circuit, along the bodies of R2 and R1, to where the other switch wire connects to the circuit, and then twist them together from there to the switch. That way there won't be much "geometric area enclosed by a loop", so your antennas will not be as good, which is what you want.

Of course, you would also break the "ground" conductor shown in the schematic, so that the input ground reference (bottom of R1 and bottom of switch) is NOT connected to the bottom of C3, or anything to its right in the schematic, except at the star ground point, which will probably be just after the last power supply smoothing cap. [The two grounds should each have their own separate conductor that goes back to the star ground. Otherwise, the currents from the decoupling caps and output will induce voltages across the ground-return conductor that will appear at the non-ground end. If those voltages were allowed to be at the bottom of R1, they would be arithmetically summed with the input voltage, which you do not want.]

Also, keep the feedback loops as short as possible. And always connect all components as close as possible to IC pins.

l would also parallel the 0.1 uF X7R ceramic caps at the power supply pins each with a standard 10 uF electrolytic.
  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
HELP: PC (USB) problems with Subwoofer LOUD white noise sunil Digital Source 8 5th July 2011 05:12 AM
Subwoofer phase problems? odysseybmx414 Car Audio 11 31st August 2010 03:59 PM
Subwoofer variable phase control AudioFreak Solid State 23 18th July 2004 03:54 PM
Why am I picking up so much noise on my scope? Bricolo Everything Else 54 8th June 2004 05:20 AM
amp picking up noise Roepke Solid State 10 15th June 2001 02:24 PM


New To Site? Need Help?

All times are GMT. The time now is 12:54 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