Help needed to sort noise issue with amp build - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 1st December 2008, 09:37 PM   #11
diyAudio Member
 
Nico Ras's Avatar
 
Join Date: Nov 2005
Location: East Coast of South Africa
Also consider the placement of the transformers. Try wiring them opposite so the stray magnetic fields cancel.

Toroidals are prone to hum and especially on on top of another wired in the same direction. Try putting one up-side-down.
  Reply With Quote
Old 1st December 2008, 09:52 PM   #12
diyAudio Member
 
ShinOBIWAN's Avatar
 
Join Date: Feb 2004
Location: UK
Quote:
Originally posted by Nico Ras
Also consider the placement of the transformers. Try wiring them opposite so the stray magnetic fields cancel.

Toroidals are prone to hum and especially on on top of another wired in the same direction. Try putting one up-side-down.
Hi Nico

I already have one upside against the other. Will wiring the opposite direction still make any difference here?

When you say wiring the opposite do you mean just the primary on one toroid?
  Reply With Quote
Old 1st December 2008, 09:56 PM   #13
diyAudio Member
 
ShinOBIWAN's Avatar
 
Join Date: Feb 2004
Location: UK
I played around with mains wiring as the noise I'm hearing appears to hum related.

Here's what I tried and discovered:

- With mains wiring in the case but with only one toroid, PSU3 and two modules running(the best noise performance one and the worst) I noted identical performance compared to all electronics running. This includes performance with or without input - no change for either.

- With exactly the same conditions as above but with the mains harness(from IEC mounted on rear panel to primary winding) lengthened so that it didn't pass directly through the case from front to rear. No change again.

- The next experiment was as shown in the photo below. I bypassed that rear IEC and simply wired directly to the mains. This meant the mains input came in through the front of the case instead of rear. I also omitted chassis ground as I was getting desperate, this is only a temporary measure. I noted that noise on the worse effected module was significantly reduced. Instead of being able to hear the hum from at the listening position you needed to get around a foot from the driver.

Any thoughts?

Click the image to open in full size.
  Reply With Quote
Old 1st December 2008, 10:48 PM   #14
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
Hi Ant,
It can be really tricky to eliminate all sources of noise/hum, but you should be ahead of the game with balanced inputs. Even so, your internal wiring may pick up some garbage, therefore it's always a good idea to plan ahead of time to try and minimize some of the potential problems.
I found out the hard way on my first multichannel build that it's pays to lay everything out so as to avoid trouble. I took that further with this new one, where I have been conscious from the beginning about what needs to be done.
See in the pic the amps are shielded from the centre (where the toriod and power supplies are) with the solid sheet of aluminum. This joins with the shelf where the modules are attached to shield the bottom also. Notice the aluminum wire chase around the heatsink that carries the shielded input leads to each amp module. The power leads are twisted and neatly attached to the shield.

Click the image to open in full size.

The RCA inputs will be shielded also with a wrap around cover. As it sits, there is complete silence - no hum, no noise (other than a faint "tick tick" from the DCX2496).
This may seem extreme, but it is worth the effort IMO.
  Reply With Quote
Old 2nd December 2008, 04:12 AM   #15
cbdb is offline cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
Your shields in a ballanced line should be connected to ground at one end only to prevent ground loops. The XLR pins are +,- (hot, cold) and ground and theres usually a ground lug thats not used (usually the same as the pin ground) If your hum is there with the inputs shorted (+, -) the hum is generated internally.
  Reply With Quote
Old 2nd December 2008, 04:30 AM   #16
cbdb is offline cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
Are the amp input ccts. actually balanced or are you jus tusing XLRs ?
  Reply With Quote
Old 2nd December 2008, 04:45 AM   #17
cbdb is offline cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
your module 4 is sitting alot closer to the transformer than the others, can you move the transformer a few inches for a test?
  Reply With Quote
Old 2nd December 2008, 04:46 AM   #18
diyAudio Member
 
ShinOBIWAN's Avatar
 
Join Date: Feb 2004
Location: UK
Quote:
Originally posted by cbdb
Your shields in a ballanced line should be connected to ground at one end only to prevent ground loops. The XLR pins are +,- (hot, cold) and ground and theres usually a ground lug thats not used (usually the same as the pin ground) If your hum is there with the inputs shorted (+, -) the hum is generated internally.
Hi cbdb

Would running a link, at the chassis connector, from shield to ground achieve anything? Since they're mounted on perspex plastic with no direct connection to the chassis then I think the shield isn't needed.

Happy to proved wrong since it will be something else for me try.

Quote:
Originally posted by cbdb
Are the amp input ccts. actually balanced or are you jus tusing XLRs ?
The modules are Aussieamps NXLSP400se which allow for a native balanced input.
  Reply With Quote
Old 2nd December 2008, 04:51 AM   #19
cbdb is offline cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
and test for output noise with the inputs shorted, or the noise might be preamp noise
  Reply With Quote
Old 2nd December 2008, 04:52 AM   #20
diyAudio Member
 
ShinOBIWAN's Avatar
 
Join Date: Feb 2004
Location: UK
Quote:
Originally posted by cbdb
your module 4 is sitting alot closer to the transformer than the others, can you move the transformer a few inches for a test?
Its bolted down good but could try moving since its only bolted down.

Me and the amp designer, Anthony Holton have been talking in emails and we've discovered the source of most of the noise.

The large input film capacitors. These seem to suck up AC like crazy and then feed into the amps. If you notice there's four of these for two modules close to the IEC inlet. I moved my wiring out the way and the amps got a lot quieter regarding hum.

I cut the caps out the signal chain for one module and then shorted signal + and -. The result was complete silence and this is the module closest to the toroids.

I'm now in the process of rewiring the amp almost completely.
  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
Deluxe Reverb Re-Issue High Frequency Noise. jordankersten Tubes / Valves 1 22nd December 2008 09:20 AM
LM3886 noise issue zeus_threat Chip Amps 25 15th August 2008 09:26 AM
Help Needed!! Tubescreamer build; Pot noise problems eviljoe Instruments and Amps 5 10th February 2008 08:43 PM
DCX2496 ch6 noise issue akunec Digital Line Level 5 30th March 2006 10:10 PM
I have an odd transformer issue (want to build the gainclone) Jerry Parker Chip Amps 9 22nd October 2003 12:37 AM


New To Site? Need Help?

All times are GMT. The time now is 11:26 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