Test bulb is on. Need help with BrianGT's LM3875. - 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 26th September 2007, 12:36 AM   #1
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
Default Test bulb is on. Need help with BrianGT's LM3875.

I just completed the BrianGT's LM3875 Rev C. One PSU board, two channels powered by 42V CT. The PSU board has only 4 diodes and provides sort of correct voltage. I have measured V+ to PG+ and got ~33.5V (I have analog meter that might not be that accurate). Same on V- to PG- (also ~33.5V). Everything looks OK so far.

Now today, I have connected the amp boards using three wires going out from PSU (V+, PG+ and V-). They go to V-, PG+ and V- on amp boards (respectively). When I turn the whole system on thru the 100W test bulb is on (big thanks to AndrewT). I have turned the system immediately off to prevent any damage.

What should I test now? Please mind that I am complete noob so if you compose your reply, please try to stick to the labels from Brian's board as I might not know all the specific terms

My connection layout was posted here:
Connection layout
as part of this thread: Connection thread
The changes I have made to this layout are:
1. G from power socket is connected to the chase next to the socket (not together with CHG from amp board) - as pointed in the other thread
2. Pink wires from PG- on PSU to PG- on amp boards are gone - as suggested in the other thread

Any help is appreciated.
  Reply With Quote
Old 26th September 2007, 01:49 AM   #2
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Quote:
I have connected the amp boards using three wires going out from PSU (V+, PG+ and V-). They go to V-, PG+ and V- on amp boards (respectively)
Izzat a typo?
  Reply With Quote
Old 26th September 2007, 01:57 AM   #3
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
Yes, it is. Should be:
They go to V+, PG+ and V- on amp boards (respectively).
Can't edit my original post.
  Reply With Quote
Old 26th September 2007, 06:33 AM   #4
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Does your transformer have 2 seperate secondaries, or does it just have a split one (likely only 3 wires comming out of it)?
  Reply With Quote
Old 26th September 2007, 12:03 PM   #5
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
My transformer has just three wires 21V-0-21V.
  Reply With Quote
Old 26th September 2007, 06:16 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
nothing to do with this light on problem, but you have three different star grounds in this version of the amplifier.
Star ground as labeled has CHGL +CHGR + Safety Earth connected to it.
PSU PG+ has PG+L & PG+R connected to it.
PSU PG- has PG-L & PG-R connected to it.
Then the signal grounds on the PCBs have pot ground and RCA chained via pot ground to the respective LSG & RSG.
That is a recipe for confusion when you come to debugging your hum problems.
__________________
regards Andrew T.
  Reply With Quote
Old 26th September 2007, 06:19 PM   #7
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
oh of course yes, otherwise he would have bigger problems... its just that 50% of the problems we see is because people don't get the rectifiers right for their transformer setup......
  Reply With Quote
Old 26th September 2007, 06:22 PM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
how long did you leave the amp powered up with the bulb lit?

The bulb should flash very briefly if only the rectifier is connected to the transformer.
The flash should dim progressively, over two or three seconds, to a dimglow or completely off with smoothing connected to the rectifiers.
With one amp connected the delay may take a second or so longer and with both amps another second or so longer.

Disconnect the transformer from all three rectifier connections and tell us what the bulb does at switch on.

I'm away out, back later.
__________________
regards Andrew T.
  Reply With Quote
Old 26th September 2007, 11:06 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
just noticed post 1 notes that didn't sink in first reading.
My post 6: ignore comment about star ground with Safety Earth attached. But are CHG L & CHG R connected to chassis?

Also ignore extra star ground labelled PG-. It has transformer centre tap only feeding via shorting link to PG+
__________________
regards Andrew T.
  Reply With Quote
Old 26th September 2007, 11:42 PM   #10
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
CHG L and CHG R are connected to the chassis.

PG- on the PSU is not connected to the amp boards. This is the wire from my connections diagram that I have never used.

For the first try, I had the amp powered for less than 2 seconds. I tried it now plugged in for about 10 seconds (or more) and the light did not go off. It is bright light (not dimmed) and I am using 100W bulb.

When I disconnect the transformer from the PSU board and turn the amp on, the light stays off. Does not even blink.

Hope I have answered all your questions AndrewT.
  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
FA: BrianGT LM3875 amp in case fireman Swap Meet 1 4th September 2006 05:40 PM
P3A and BrianGT's LM3875 nina Solid State 5 19th March 2006 01:57 PM
LM3875 BrianGT kit not working waltson Chip Amps 9 28th January 2006 08:00 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 02:03 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