Power supply problem (or something) - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 23rd August 2003, 07:55 AM   #1
ir is offline ir  New Zealand
diyAudio Member
Join Date: Aug 2003
Location: WGTN, NZ
Send a message via ICQ to ir
Default Power supply problem (or something)


i r a total noob at building amps that aren't in kitset form (hell, anyone can build a kitset) and i've whacked together a 20W stereo amp using an LM1876TF stereo 20W IC

see pics here. also it's worth noting if you see a flaw in any of the pics, the amp has changed since they were taken and is now "complete"

the design is almost exactly based on the "Auxillary Amplifier" schematic contained within the
datasheet from National, the only difference being larger caps

it sounds beautiful - while it works, nice bass response, VERY good volume (especially considering the size of the thing). after about a minute however it shuts down. i initially thought it might be overheating but in theory the temperature protection should shut it down then turn it back on again once the chip cools. besides that, the chip isn't even remotely hot. the shutdown time is always the same regardless of volume, somewhere between 60 and 70 seconds.

anyways, after puzzling over it for quite some time and searching these forums as well as the web for an anwser, i thought to check the PSU voltages while the amp is running and noticed that the +VE rail was slowly increasing while the -VE rail was decreasing. once it gets below -10V the amp shuts down due to it's power supply rejection system as it would be expected really. the +VE rail eventually reaches the PSU total of ~44V (relative to ground) while the -VE rail sits at around zero (to ground). at startup the supply is +/-22V

i tried swapping my big caps on the amplifier (5600uF) with the 1000uF the design calls for the amp does the same only shuts down much sooner (makes sense really)

has anyone else had this problem? or failing that, does anyone know a: what would cause this problem, and more importantly b: how to fix it

  Reply With Quote
Old 23rd August 2003, 08:07 AM   #2
diyAudio Member
analog_sa's Avatar
Join Date: Aug 2002
Location: Cascais
Defective/undersized/thermally- protected transformer?
  Reply With Quote
Old 23rd August 2003, 08:07 AM   #3
moamps is offline moamps  Croatia
diyAudio Member
Join Date: Oct 2002
Location: Croatia

Maybe your ground is floating. Is your transformer secondary centre taped? I don't see on your PS board ground (middle) point from transformer.

  Reply With Quote
Old 23rd August 2003, 08:30 AM   #4
ir is offline ir  New Zealand
diyAudio Member
Join Date: Aug 2003
Location: WGTN, NZ
Send a message via ICQ to ir
nope. no center tap. it's not ideal at all really. should it matter tho?. the whole set up had cost me absolutely nothing tho.

the tranny is not thermally protected as far as i know. also i'd expect the fuse to blow before any thermal protection kicks in considering how little power the amp actually draws.

i just tested the suppy minus the amp, it still does drift but very slowly. so now i'm happy, the amp works fine and damn well too
just need to find some cash for a "real" transformer i guess. ah well, if' i'm gonna do that it might as well swap the dual20W chip out for the dual50W that turned up today

then i'll switch to the BIG supply on my PSU board. (you'll see in the power supply pics, i'm using the bridge on the right with the appallingly small 470uF 50V caps)
  Reply With Quote
Old 23rd August 2003, 08:44 AM   #5
ir is offline ir  New Zealand
diyAudio Member
Join Date: Aug 2003
Location: WGTN, NZ
Send a message via ICQ to ir
also, although the tranny has two secondaries they asre different voltages so i can't make a center tap by twisting some wires

ah well, i'll have a hunt for a better tranny then
  Reply With Quote


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
Power supply problem Niila Tubes / Valves 6 12th April 2008 01:39 AM
Power Supply problem Landoctor Chip Amps 3 8th September 2007 07:50 PM
Power supply problem krzanik Tubes / Valves 19 1st May 2007 03:56 PM
problem with LM's and power supply KostasTheGreat Chip Amps 14 10th March 2005 02:13 PM
Power supply problem PassFan Tubes / Valves 6 24th October 2003 10:03 PM

New To Site? Need Help?

All times are GMT. The time now is 11:31 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2