strange feedback - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

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 21st February 2008, 02:54 AM   #1
Clipped is offline Clipped  Thailand
diyAudio Member
 
Join Date: Mar 2005
Location: home
Send a message via MSN to Clipped
Default strange feedback

i was testing an amp i just got , when testing it i used 'kicker' twisted pair speaker wires , hooked up to a 6x9...

the amp did not have terminals , but wires...when i hooked the amp up to the twisted pair wires, i slit the twisted pair wire and pulled the insulation out about 1 centimeter, not off....and wrapped the amps wires around in a perpendicular fashion.

when i did this the amp made a humming noise, if i just wrapped it around loosely the noise would be weak, but if i actually squeeze on the wire tight the humming would become louder,

tightly wound the humming would stay and be very loud.

then i pulled the insulation completely off, and just twisted them together regularly....and there was no humming noise.

my question is...wtf? ... ive never had this happen
  Reply With Quote
Old 21st February 2008, 06:52 AM   #2
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Was it close to the case of the amp? Or, it might have been 'defeating' the benefits of twisting the wires, maybe aligning one of the wires with the changing electromagnetic field from the other, at the worst angle and in just the wrong place.

EDIT: You weren't touching a wire with your fingers the whole time it was humming, were you?
__________________
The electrolytic capacitors ARE the signal path: http://www.fullnet.com/~tomg/zoom3a_33kuF.jpg
  Reply With Quote
Old 21st February 2008, 03:49 PM   #3
Clipped is offline Clipped  Thailand
diyAudio Member
 
Join Date: Mar 2005
Location: home
Send a message via MSN to Clipped
it made the noise whether i touched it or not... this is really weird.

the wires were close to the amp but, wired regularly it didnt make the noise, so i dont think this would effect it.
  Reply With Quote
Old 21st February 2008, 08:59 PM   #4
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally posted by Clipped
it made the noise whether i touched it or not... this is really weird.

the wires were close to the amp but, wired regularly it didnt make the noise, so i dont think this would effect it.
I'm not saying that I am sure that I know exactly what happened, there. But I AM sure that the wire's location and orientation versus the amp actually 'COULD' affect it (and definitely would, to some degree, even if that wasn't the dominant cause of the effect you noted, in this case), since both a conductor's orientation and location within a changing electromagnetic field do affect (and actually 'effect it', i.e. 'cause it', in this case) the current that is induced in the conductor by the field. (Check out some of the ramifications of 'Faraday's Law', and 'Maxwell's Equations'.)

This is also the reason why so many manufacturers' application notes say to keep wires perpendicular to a circuit board for a distance of at least a couple of inches, whenever a wire must enter or leave a board. It's the same reason why they also say that two wires that must cross each other should do so at a right angle to each other. It's to minimize cross-coupling (by not having the electromagnetic field from each wire induce current in the other wire, or at least induce as little as possible by not aligning the EM field with the other wire). Alignment/orientation definitely matters, for conductors in changing electromagnetic fields, as does distance/location from the field's source.

I guess you could just try repositioning and reshaping the wires, to see if you can make it happen again, to find out. I'm guessing that there's more chance of it happening close to the amp than farther away (i.e. It's less likely with the wires bent at a right angle but not near the amp). I'm guessing that when the wire was perpendicular to the other wire, it was in parallel with some EM field source within the amp (or maybe even on the chassis itself), such that a much larger current was induced in the wire than when it was not oriented like that.

Is the amp's chassis steel or aluminum (or something else)? I think that steel might be worse, for this effect, since it is a ferrous metal. Or I could be wrong and it's the opposite way. But neither steel nor aluminum is a very good shield for magnetic fields, even though they can both be pretty-good shields for electric fields. And a changing magnetic field induces currents in conductors. (The 'enclosed loop area' of the wires matters, too, but is not the whole story.)

Sorry to have blathered-on for so long, about all of that.
__________________
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
strange feedback issue ( wiring ) east electronics Solid State 3 3rd February 2009 11:03 AM
Strange circuit - heater hum opt feedback? m6tt Tubes / Valves 3 23rd April 2008 06:13 PM
Strange feedback method hotbottle Tubes / Valves 4 12th April 2008 09:38 PM
current feedback strange behaviour?? aaronboumans Pass Labs 5 27th October 2004 11:52 AM
Brazil, and some strange laws, not too much strange! destroyer X Everything Else 0 11th September 2004 12:38 PM


New To Site? Need Help?

All times are GMT. The time now is 06:07 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