P3A Problems please help!! - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 29th January 2003, 02:29 AM   #1
diyAudio Member
 
Join Date: Oct 2002
Location: Drayton Valley, AB
Angry P3A Problems please help!!

Hi all I am having some trouble with a p3a. I am not sure what is causing it. I have a series of pictures from my scope I was hoping you could help me with.

First of all let me tell you about my amp. It is a 4 channel amp. 2 p3a boards with 2 channels on the left and right side of the amp. It is powered by a plitron 750VA transformer 25 volt secondaries (more like 28) with +-38 or so going to the amp. I have 30000 uF of capacitance per rail. Each amp has it's own bridge rectifier. I have look at the DC going to each amp both underload as well as unloaded. There is no difference on any channels an it is clean.

Now on to my problem

First the signal from the offending amp with no load. The division on my scope is .01v on DC.

Click the image to open in full size.

Not a huge bump but I can hear it.

With a signal line plugged in .. device on but no real load.


Click the image to open in full size.

This one is much more audible. I am not sure if it gets higher with a real signal on. I do hear it though.

For comparison here is the signal on my right side with the same 2 pictures.


No signal at all

Click the image to open in full size.

Nice and clean

Signal line plugged in

Click the image to open in full size.

Getting a bump. I can hear it but not much.


Here is my wiring. I know it is not the prettiest but I was planning on cleaning it up before using the amp. I have played with the wires while watching the scope and no difference.

Left
Click the image to open in full size.

Right
Click the image to open in full size.

The ground
Click the image to open in full size.

As I said I know this is not the best wiring. I have a much better case on the way so this is my prototype. As well I have better heat sinks.

I am just trying to get it working right now so when I get the rest of my stuff in it is a easy transfer.


I am not even sure what I am seeing. I would have thought I have all but eliminated the chances of the groung loop. I do not even think it is a ground look I am looking at.

Thanks for all your help

Ted
  Reply With Quote
Old 29th January 2003, 07:57 PM   #2
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Most likely there is a problem of ground (0V) wiring. Is not there any ground loop? May any ground loop be closed through signal wires (shields)? It would be helpful if you could attach ground wiring diagram with all 0V wires shown (also for preamp stages).
  Reply With Quote
Old 29th January 2003, 09:36 PM   #3
diyAudio Member
 
Join Date: Oct 2002
Location: Drayton Valley, AB
So you do figure it is a ground loop? My ground as it sits. All 0 v grounds go back to a single point lifted from the chasis. It is a single point floating ground. The pic of the ground is were they all meet.

This is my first amp and it is sure taking longer than expected. I am just not sure what else I can do with it. Nothing I do will remove that signal. It is not present on the right side and the ground is exacally the same over there.

Thanks

Ted
  Reply With Quote
Old 29th January 2003, 10:12 PM   #4
diyAudio Member
 
Join Date: Mar 2001
Location: Brazil
Quote:
Originally posted by TedPolzin
So you do figure it is a ground loop? My ground as it sits. All 0 v grounds go back to a single point lifted from the chasis. It is a single point floating ground. The pic of the ground is were they all meet.

This is my first amp and it is sure taking longer than expected. I am just not sure what else I can do with it. Nothing I do will remove that signal. It is not present on the right side and the ground is exacally the same over there.
Ted,


Don't give up yet. You picked an ambitious project to be your first amp, so don't complain too much.

My first guess is there might be a loop somewhere too.

First of all let's try to be a bit methodic about this. Can you take each amp out of the case and test them individually?

Second: try sending separate wires for each ground block in the pcb to the star point. Maybe you already did that. If you did, maybe there's something wrong in the ground arrangement in the pcb. There should be at least three different and separate grounding points on the pcb.

Try that and let's see what you get.


Carlos
  Reply With Quote
Old 29th January 2003, 10:40 PM   #5
diyAudio Member
 
Join Date: Oct 2002
Location: Drayton Valley, AB
Quote:
There should be at least three different and separate grounding points on the pcb.
Hmm I only have one. The main power one. I brought back the grounds for the input and output directly to the star ground. I have separated the ground between the amps on the individual boards though, so I guess I have 2 different and separate grounds per pcb.

I think I will test each amp out tonight. I'll just disconnect the fuses on the amps I do not wish to test. I am just do not understand why it would affect one side of the case and not the other.

At least you are confirming it is a ground problem and not something else. I was not sure exactly what I was looking at.

Thanks a lot!!

Ted
  Reply With Quote
Old 30th January 2003, 07:11 PM   #6
diyAudio Member
 
Join Date: Oct 2002
Location: Drayton Valley, AB
Ok then where should I start. I removed the fuses from the other amps and the loop, extra signal was about 1/4 of it's previous strength with a signal on it.

Where should I go from here? I was hoping removing the other amps from the equation would have eliminated it.

Thanks

Ted
  Reply With Quote
Old 4th February 2003, 07:15 PM   #7
diyAudio Member
 
Join Date: Oct 2002
Location: Drayton Valley, AB
Any ideas where I should start. Here is what I have found out and done.

I split the ground between the two boards and that helps quite a bit so there are now 2 seperate grounds one to each board. If I combine them the loop increases a lot !! like 5 fold.

If I turn off the power it dissapears totally. I am still drawing from the caps.

Please let me know where I should proceed from here.

Thanks

Ted
  Reply With Quote
Old 5th February 2003, 07:18 PM   #8
diyAudio Member
 
Join Date: Oct 2002
Location: Drayton Valley, AB
Ok here is what I have done

Each ground comes off it's direct source, EG input, output, amp and capacator grounds directly meet. This is rather than input -> pcb -> out.

Each amp is diretly connected to it's own ground points .... which connects to a star point which connects to the transformer ground.

EG. Amp 1 input, output, amp and cap ground collect which then collect with all the other amp grounds and connect to the transformer.

What I get .. a soft ground signal when I have signal going to more than 2 or more amps. If they are on the same physical board it is a little softer than if it going to a diffrent physical board.

If the signal is going to only one board it is virtually with out ground noise.

Please can someone give me some direction as to what to do. I really need the help!!!!! I am lost as where to go next!!! Please!!

Thanks

Ted
  Reply With Quote
Old 7th February 2003, 10:54 PM   #9
diyAudio Member
 
dwjj's Avatar
 
Join Date: May 2002
Location: Round Rock, TX
Default Probe the power rails?

What do the power rails look like (at the output transistors)? Are they the right voltage? Without noise?

Probe the base on the output transistors.
__________________
It's cheaper than a movie, and there's free coffee.
  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
GFA-565 problems ben62670 Solid State 5 14th August 2008 06:36 AM
HK AVR 335 Problems utjay2008 Solid State 0 21st October 2007 02:26 AM
Sub Amp Problems Thanks! crippledchicken Solid State 2 10th January 2007 06:17 PM
JLH problems serosmaness Solid State 11 2nd November 2004 06:17 PM
RFI problems laz Solid State 3 21st February 2004 07:06 AM


New To Site? Need Help?

All times are GMT. The time now is 07:02 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