Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

Briangt rev 2 LM3875 build advice
Briangt rev 2 LM3875 build advice
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 19th March 2020, 02:56 AM   #1
ultrachrome is offline ultrachrome  United States
diyAudio Member
 
Join Date: Jan 2002
Location: Puget Sound
Default Briangt rev 2 LM3875 build advice

I built two rev 1 LM3875 amps back in the day and was gifted a pair of rev 2 boards that I never built. I have most of the parts necessary to build these save for the transformer and I need an extra amp so I'm looking at building these.

Looking at chipamp.com on the Wayback Machine I came across the rev 3 / carlosfm unregulated PSU. I've come across a few variations of the schematic. Is this rev 3 PSU still the way to go?

My rev 1 builds are using 330VA 25+25V transformers. I don't currently have particularly difficult speakers to drive but would it make sense to use a lower voltage transformer for this build? With Avel Lindberg through parts-express, it seems my only other option would be 250VA 18+18V. Searching Digikey gives basically the same result.

Thanks.
  Reply With Quote
Old 19th March 2020, 07:22 AM   #2
chermann is offline chermann  Austria
diyAudio Member
 
Join Date: Jan 2017
Location: Vienna
Hi ultrachrome



You wrote that you have no "difficult" speakers. If you look at the Figure 27 in the datasheet you get an overview which maximum operating supply is recommended to use different speakers impedance.


so for 8R speakers its fine to use the maximum operating voltage (all diagrams are done at +/-35V into 8R)...dont use the maximum ratings!


for 4R speakers i would recommend to use your planed 18-0-18VAC transformer
to avoid the chip getting too hot and starts the current limiter....etc..


chris
Attached Images
File Type: jpg Supply voltages vs speakers impedance.JPG (33.0 KB, 138 views)
  Reply With Quote
Old 20th March 2020, 02:28 AM   #3
rabbitz is offline rabbitz  Australia
diyAudio Member
 
rabbitz's Avatar
 
Join Date: Jul 2003
Location: Newcastle, Australia
I've always used a 18-0-18 transformer on these as I never know what speaker will be used. The lower voltage also reduces heatsink size and current requirements.

Looking at the Overture Design guide (used default standard component values):
35V rails 57W into 8R, 50W into 4R (IC current limited and required heatsink too large... see attached)
25V rails 29W into 8R, 47W into 4R

I've attached Rev 3 details but I've used my own power supply on the last build.
Attached Images
File Type: jpg LM3875_4R_ODG.jpg (107.2 KB, 128 views)
Attached Files
File Type: pdf lm3875rev3.pdf (255.1 KB, 28 views)
__________________
If there are no dogs in Heaven, then when I die I want to go where they went - Will Rogers
  Reply With Quote
Old 20th March 2020, 05:02 AM   #4
ultrachrome is offline ultrachrome  United States
diyAudio Member
 
Join Date: Jan 2002
Location: Puget Sound
Thanks. I forgot about that spreadsheet.

I also just found the carlosfm regulated supply so now I'm considering whether to do that instead. Approaching analysis paralysis.
  Reply With Quote
Old 20th March 2020, 05:57 AM   #5
chermann is offline chermann  Austria
diyAudio Member
 
Join Date: Jan 2017
Location: Vienna
Thank you Rabbitz


Where you get this excel sheet? i am searching around but without success


thx
chris
  Reply With Quote
Old 20th March 2020, 10:16 PM   #6
ultrachrome is offline ultrachrome  United States
diyAudio Member
 
Join Date: Jan 2002
Location: Puget Sound
This site apparently has a version.

A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics
  Reply With Quote
Old 22nd March 2020, 07:18 AM   #7
rabbitz is offline rabbitz  Australia
diyAudio Member
 
rabbitz's Avatar
 
Join Date: Jul 2003
Location: Newcastle, Australia
Overture Design Guide attached zip file.
Attached Files
File Type: zip Overture_Design_Guide15.zip (64.8 KB, 18 views)
__________________
If there are no dogs in Heaven, then when I die I want to go where they went - Will Rogers
  Reply With Quote
Old 22nd March 2020, 03:08 PM   #8
chermann is offline chermann  Austria
diyAudio Member
 
Join Date: Jan 2017
Location: Vienna
Quote:
Originally Posted by rabbitz View Post
Overture Design Guide attached zip file.



thanks rabbitz- you are my hero
  Reply With Quote

Reply


Briangt rev 2 LM3875 build adviceHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
LM3875 Build Advice DreadPirate Chip Amps 2 21st January 2011 01:45 AM
BrianGT LM3875 and power LED - how to? maurycy Chip Amps 9 3rd February 2010 04:06 PM
P3A and BrianGT's LM3875 nina Solid State 5 19th March 2006 01:57 PM
WTB: BrianGT LM3875 boards guzzler Swap Meet 1 10th December 2004 10:34 PM
NIB BrianGT LM3875 Premium GC kit. Tony D. Swap Meet 9 1st September 2004 03:43 PM


New To Site? Need Help?

All times are GMT. The time now is 09:52 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki