LM3875 Layout - 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 6th November 2012, 07:21 AM   #1
diyAudio Member
 
Join Date: Dec 2011
Default LM3875 Layout

I'm relocating my Daniels LM3875 gainclone to its new home in a diyAudio compact chassis with Quasi heat sinks.

I'm no expert, but I figure it's a good idea to keep the AC lines as short as possible. So, it's just a couple of inches from the IEC switch/jack to the transformer, then on the front side of the chassis, just a couple of inches to the rectifier board, which is located right behind the front panel. Obviously, I'm going to trim the AC wires very short.

DC wires will run around along the sides. I'll use a 14ga copper wire for the star ground that will run from the rectifier, around the transformer to each board and tie in with the transformer shield and chassis ground.

Amps themselves will be positioned very close to the rear panel to keep input leads and speaker outputs as short as possible. This is a straight up power amp, so no attenuator.

This layout will allow me to keep the DC wires away from the AC wires. They will never cross. Does this matter, or am I wasting my time worrying about the wiring layout? Would love to hear any ideas you might have.
Attached Images
File Type: jpg PB060013.jpg (238.8 KB, 215 views)

Last edited by autoformer; 6th November 2012 at 07:26 AM.
  Reply With Quote
Old 6th November 2012, 12:51 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I agree with your wiring philosophy.
Keep the transformer rectifier smoothing caps as tight as posible.

Use twisted pairs everywhere, except dual polarity where twisted triplet is the equivalent.

Don't cut your transformer wires just yet.
You may find that hum can be reduced by rotating the transformer around it's fixing bolt.
Find the optimum and then cut the wires to fit.
You may have to replace the solid core transformer wires to flex to allow this to be done. Twisted solid core 1sqmm is very stiff.
Twisted solid core 1.5sqmm is even stiffer.
__________________
regards Andrew T.
  Reply With Quote
Old 6th November 2012, 10:32 PM   #3
diyAudio Member
 
Join Date: Dec 2011
Thank you very much for your post, Andrew. That's exactly the kind of tip I was looking for. I'll try rotating it as you say. The transformer wires are stranded, so no problem there.

Speaking of toroids, do you think higher quality custom-made toroids, such as those available from Canterbury Windings are worth considering for gain clones? The toroid I'm using now is a Chinese-made Antek, and the amp does have the slightest amount of hum, but I thought might have been due primarily to having the rectifier so close (less than 20mm) to the boards. Then again, I didn't try turning the transformer as you suggest.
Canterbury Windings Home
  Reply With Quote
Old 7th November 2012, 09:40 AM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I got a quote from Canterbury after I saw a recommendation here.
I will use Toroidy in future for HQ toroids.
__________________
regards Andrew T.
  Reply With Quote
Old 7th November 2012, 11:56 AM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by AndrewT View Post
I agree with your wiring philosophy.
Keep the transformer rectifier smoothing caps as tight as possible.
longer wires from PSU to circuit are not a problem. I consider longer to be an asset. Longer = more wire to wire capacitance and that capacitance is very high quality, due to plastic film and air for the dielectrics. Longer also increases the r for more HF attenuation. Longer also increases inductance for more 2pole HF attenuation. Thinner also increases r for more attenuation of HF.
__________________
regards Andrew T.
  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
lm3875 single sided pcb layout SolderN Chip Amps 18 12th August 2009 11:11 PM
5 channel lm3875 layout bjefferys Chip Amps 2 23rd March 2005 10:21 PM
LM3875 PCB Layout Sci Chip Amps 28 27th August 2004 05:32 AM
LM3875 Inverted Layout Comments Please ppereira Chip Amps 43 4th November 2003 11:46 PM


New To Site? Need Help?

All times are GMT. The time now is 08:54 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