LM3875 kit Horrible hum.... in all 4 monoblocks... - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 May 2009, 04:59 PM   #1
diyAudio Member
 
speakrsrfun's Avatar
 
Join Date: May 2005
Location: Toronto
Default LM3875 kit Horrible hum.... in all 4 monoblocks...

OK so these sound great I build 4 monoblocks and couln't be happier with the way they perform but when introduced to my main system they hum like mad. I isolated the majority of the noise to when the television is on and it dies to almost a dead silence when it isn't on. I have a satalite reciver within 6 feet and also several other pieces of kit, all plugged into a monster stage 2 power conditioner. So before I go and add a few 220uF caps accross the inputs I'd like to hear what others think, plugged into any other socket with an Ipod or another media source they are quite dead silent, odd but I'm thinking of resoldering the grounds with solid core wire grounding to the post in my 1/8" aluminum chassis.

Any suggestions, RF, ground loop, heck anybody it's driving me nuts.... Peace.
__________________
What was that?... I can't hear you I have a line array filling my ears.
  Reply With Quote
Old 21st May 2009, 08:01 PM   #2
diyAudio Member
 
Join Date: May 2008
You could try one of these
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 21st May 2009, 09:34 PM   #3
diyAudio Member
 
speakrsrfun's Avatar
 
Join Date: May 2005
Location: Toronto
Forgott to mention that they are currently running in a Bi-amp system with a Fostex FE126E and four Siver flute 5.5" so even with the silence I can still hear some hum due to the efficiency of the system, this I'm not worried about, more the hum I get when other electronics specifically the television are turned on, because a horrible and very audible hum isn't going to fly with me.... Grounds seem good so I'm thinking RF or something to do with a signal they are sensitive to being transmittted by the TV. You'd think with so much metal around them they wouldn't be so sensitive, kind of a faraday cage type deal.... Oh well.....

So back to the drawing board, Peace.
__________________
What was that?... I can't hear you I have a line array filling my ears.
  Reply With Quote
Old 21st May 2009, 10:10 PM   #4
enzoR is offline enzoR  Netherlands
diyAudio Member
 
Join Date: Mar 2008
i suppose you use RCA interconnects? The problem coule be that that the outer ring is grounded on both connections: ground loop.
  Reply With Quote
Old 22nd May 2009, 07:04 AM   #5
diyAudio Member
 
Join Date: May 2008
Default Re: LM3875 kit Horrible hum.... in all 4 monoblocks...

Quote:
Originally posted by speakrsrfun
I isolated the majority of the noise to when the television is on and it dies to almost a dead silence when it isn't on.
Try one of these
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 22nd May 2009, 04:27 PM   #6
diyAudio Member
 
speakrsrfun's Avatar
 
Join Date: May 2005
Location: Toronto
Thanks for the suggestion Pacificblue (for the second time LOL), I'll take a look at our local Ratshack and tell you if it made any difference. I know it's not a construction issue as I made sure to take things slow and ensure proper build so my other guess like you say is a ground loop. I'll try this and maybe get some 220nF caps while I'm out also.... Peace and thanks to all who helped.

__________________
What was that?... I can't hear you I have a line array filling my ears.
  Reply With Quote
Old 23rd May 2009, 12:17 AM   #7
wwenze is offline wwenze  Singapore
diyAudio Member
 
Join Date: Mar 2008
You can try this:

Click the image to open in full size.
(Credits to various owners of schematics found on diyaudio)

Easy to implement and doesn't hurt the signal a bit.
  Reply With Quote
Old 23rd May 2009, 12:52 AM   #8
diyAudio Member
 
speakrsrfun's Avatar
 
Join Date: May 2005
Location: Toronto
Umm I'm a tad lost as to what that is, looks like a loop of diodes to me...... care to explain what this is to a reletively unexperienced fellah and where I'd impliment, I'm assuming on the RCA input end of thing yes?
__________________
What was that?... I can't hear you I have a line array filling my ears.
  Reply With Quote
Old 23rd May 2009, 02:21 AM   #9
wwenze is offline wwenze  Singapore
diyAudio Member
 
Join Date: Mar 2008
The arrow pointing up is to be connected to the chassis ground, so instead of connecting the chassis ground directly to the ground or earth wire you connect it through this.

What the diodes do, is they have a voltage drop of 0.7V across each of them, so any ground loop signal through the earth wire will be blocked. But in the case of an earth leakage, the diodes will allow 110V to pass through for the circuit breaker to trip.

Reason for the loop, it's diodes pointing opposite directions in parallel actually, is because AC supply keeps switching between positive and negative.

By the way is the amp connected to the TV either directly or indirectly?
  Reply With Quote
Old 23rd May 2009, 03:33 AM   #10
diyAudio Member
 
speakrsrfun's Avatar
 
Join Date: May 2005
Location: Toronto
The amps are not connected to the Television whatsoever other than being plugged into the same Clean power unit. The only RF signal would be my in from the satellite, everything else runs RCA, DVI or HDMI to the TV from there. I don't get it.

Odd part is I can hear the transformer power up on the Television and can also hear the degaussing circuit on the TV charge thru the amps when the TV is turned on, then the steady hum once it runs it's course. I can't reproduce this in any other room with a satellite and TV although the other TV's are actually LCD's. Accept for a very very small hum when my ear is close the other rooms don't have the same artifacts. Could I be picking up interference from the TV itself, this is a 34" 16:9 Toshiba tube unit.

The diode loop(?) I may try if I can't isolate the issue and fix it, as this seems like a good alternative, any suggestion on what diode types?. Everything would then ground to the arrow pointing down from my star ground point correct? If I can't get rid of the issue I'm looking at 4 monoblocks that will have to move to another system because the hum is vexing to say the least....
__________________
What was that?... I can't hear you I have a line array filling my ears.
  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
Speaks build.... a few P.Daniel LM3875 monoblocks.... speakrsrfun Chip Amps 5 13th March 2009 01:44 AM
Transformers for LM3875 Monoblocks Chip-Audiophile Chip Amps 27 13th June 2008 12:01 PM
Horrible hearing shock! bigwill Everything Else 30 23rd August 2006 08:33 AM


New To Site? Need Help?

All times are GMT. The time now is 03:16 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