3875 PCB: Suggestion please? - 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 25th October 2006, 02:02 PM   #1
diyAudio Member
 
Join Date: May 2005
Location: Jakarta
Default 3875 PCB: Suggestion please?

Hi there,
I've been here quite long but passive as readers only. I see so many diyers here and want to ask some recommendation.

I have played a lot with gainclone (1875/3875). So far I didnt use and PCB and p2p wiring. On my last 3875 project, I used 4 trafo (around 2,5A each) around 18V AC. Quality is quite impressed for such simple design. I add 6dj8 tube buffer single stage and got better result.

Few days ago, I decided to make it better look by making the PCB. So, here's my first PCB in my life (my 2nd actually, the 1st was at my junior high school on electrical class). I need input/recommendation/critics or whatsoever to improve my PCB (or how to design a good PCB in general). I dont know a lot about good ground plane etc. So this is an hour job with Sprint Layout.

Few notes to add:
- I prepare a space for Choke. Yes I use and believe choke in power supply (though in my last 3875 I didnt use it). If you don't need it, just plug a jumper (or I will add extra route so I could use shorter jumper).
- Two filter caps use (C-L-C design). The first near the bridge, the the last near the chips. Two separated with Choke. I also add extra space for third capacitor (smaller, polypropelene or HQ non-polar is recommended). Don't know whether this will give some improvement, but if they dont, just remove them or add few jumper.
- I use 3 ground. The GND_S is for signal and negative input. The GND_C is for capacitor and speaker negative out. The last is GND_CT from transformer. All of them should be bolted together to your case. I recommend using big cables and bolt together to one of your screw case.
- This design use 4 diodes only for one channel. I will add for 8 diodes later. But that's not my main concern right now.

That's it. Any critics/suggestion/etc please post it here.
Attached Images
File Type: gif jim.gif (21.6 KB, 621 views)
  Reply With Quote
Old 25th October 2006, 05:04 PM   #2
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
I would move the two caps at the bottom, a little north, so you could change them with bigger ones if the need arises...
  Reply With Quote
Old 26th October 2006, 01:18 AM   #3
diyAudio Member
 
Join Date: May 2005
Location: Jakarta
The one after the bridge?

Suggestion accepted. Thanks.

Anyone else?
  Reply With Quote
Old 26th October 2006, 08:14 AM   #4
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Yes.
Where would yuor input caps go, good ones tend to be quite big...
  Reply With Quote
Old 26th October 2006, 08:28 AM   #5
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Thicker tracks. You have plenty of space, use it!

Oh, and chokes in the PSU are only a good thing for constant current supplies, such as preamps and Class A power amps. For AB they are not a good idea at all...
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 26th October 2006, 08:38 AM   #6
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
I agree on th tracks, especialy the power and ground rail traces..
  Reply With Quote
Old 27th October 2006, 12:37 AM   #7
diyAudio Member
 
Join Date: May 2005
Location: Jakarta
@pinkmouse:

Thanks for the suggestion.

For chokes, I prepare the space so I could do A-B test easily with and without chokes...
  Reply With Quote
Old 27th October 2006, 08:06 AM   #8
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Quote:
Originally posted by xneakers
For chokes, I prepare the space so I could do A-B test easily with and without chokes...
Fair enough, I won't argue with your attempt to check things for yourself. However, a simplified concept of what chokes do might help you understand why it is a bad idea.

A choke or inductor basically is a reactive device that attempts to keep the power flowing though it the same. This is a good thing for pre amps and class A stages that constantly draw the same current, as it smooths out any ripples or noise that the supply puts into the rails. However, the nature of a class B/AB load is that is contantly drawing the current it needs for the current load from the supply, and this changes with the music signal. The choke acts to try and keep this current constant, exactly the opposite of what is required.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 27th October 2006, 09:06 AM   #9
diyAudio Member
 
Join Date: May 2005
Location: Jakarta
Quote:
Originally posted by pinkmouse


Fair enough, I won't argue with your attempt to check things for yourself. However, a simplified concept of what chokes do might help you understand why it is a bad idea.

A choke or inductor basically is a reactive device that attempts to keep the power flowing though it the same. This is a good thing for pre amps and class A stages that constantly draw the same current, as it smooths out any ripples or noise that the supply puts into the rails. However, the nature of a class B/AB load is that is contantly drawing the current it needs for the current load from the supply, and this changes with the music signal. The choke acts to try and keep this current constant, exactly the opposite of what is required.
I prefer a regulator for Class A and no regulator for Class AB (so regulator somehow could kill the dynamics in class AB), but I dont know if chokes could affect the AB too. I dont play a lot with chokes, until I play with tube later this years and use big chokes (from 2 H to over 100H).

I will try on this and will discuss it later. Thanks for your input.

The bad things is imo, it's very difficult to get a good choke. Without a good choke, you better dont use it imo. Good choke will cost you a lot... so I think that's why people prefer R than L (though R has problem with it's bigger resistance and voltage drop).

Btw, about the tracks... do you think 4 mm is sufficient? You ask me to wider the tracks... but how wide? Sorry dont have enough experience designing a PCB

Thanks.
  Reply With Quote
Old 27th October 2006, 09:33 AM   #10
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
4mm should be fine, but if you can make them wider, go for it.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  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
Need help with 3875 kit and DC Johnny693 Chip Amps 29 2nd March 2009 12:11 PM
Need suggestion for the improvement of Petter gainclone 3875 kit huy5005 Chip Amps 6 20th January 2008 01:49 AM
3875 GC Hum Crash&Burn Chip Amps 5 7th September 2005 10:12 PM
New Amp: Hex-Fet or LM 3875 Higo Solid State 8 2nd July 2003 09:36 PM


New To Site? Need Help?

All times are GMT. The time now is 07:17 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