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 13th September 2010, 01:43 PM   #1
Leo IT is offline Leo IT  Italy
diyAudio Member
 
Join Date: Jun 2010
Location: Italy
Default Problem:the amplifier oscillate with the preamplifier only on subwoofer applications

Hi!..First excuse my English, i'm Italian..I have a problem with my homemade car power amplifier. I have made this amplifier:7100-FT15M.pdf , i supply it with this SMPS p89-f9.gif and protect the speaker whit this speaker protectionp1000232.jpg. I connect this power amplifier into the car but without the preamp volume was too low. So I did a preamplifier like this AMPOP.GIF without other capacitors.
Then i riconnected the amplifier with the preamplifier on the subwoofer RCA out of my car radio but at low volume the subwoofer works and when i increase it the subwoofer oscillate. With an mp3 connected to the preamplifier the amplifier work very well but with car sub out no.
Are there any problems in coupling between amplifier and preamp? Thanks leo
  Reply With Quote
Old 13th September 2010, 08:58 PM   #2
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Your diagrams are very blurred so its hard to see what is going on.

Have you got a coupling capacitor between preamd and amp ?
You need to block DC.
__________________
http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.
  Reply With Quote
Old 14th September 2010, 02:14 PM   #3
Leo IT is offline Leo IT  Italy
diyAudio Member
 
Join Date: Jun 2010
Location: Italy
I'm sorry you're right. I am attaching a PDF with the pattern of all the configurations I tested. If necessary I can show the video of the problem. Thank you!

problem.pdf
  Reply With Quote
Old 14th September 2010, 06:49 PM   #4
Leo IT is offline Leo IT  Italy
diyAudio Member
 
Join Date: Jun 2010
Location: Italy
Update!When I supply the amplifier with an external source (battery or another power supply) works very well but when I connect it at the battery of the car the subwoofer oscillate. Then i think that is the SMPS the problem. I think there is a problem with ground loops, right?..The ground of my smps is the same for the 12 and +/-50V. may be going into conflict with the ground of the RCA and create problems, although I have a differential amplifier input?...Using another type of SMPS with a opsoisolator in the feedback to isolate the ground could be a solution? Thanks!

My SMPS
Click the image to open in full size.
  Reply With Quote
Old 14th September 2010, 07:34 PM   #5
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
From what you have posted so far you don't have a differential (balanced) input. Try the unit with no source connected and see if the problem is still there.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 15th September 2010, 03:29 PM   #6
Leo IT is offline Leo IT  Italy
diyAudio Member
 
Join Date: Jun 2010
Location: Italy
I just did more testing. Then whith no source connected it don't oscillate. If I connect the sub out to the gain variable preamplifier (formed by a differential amplifier and a noninverting amplifier with gain variable) with a gain approximately equal to 1 does not oscillate and the music is heard but a very low volume. While only increasing the gain begins to oscillate. It works only with an external source (not with the car battery) or with the car battery but with a car speaker outputs or an MP3....
  Reply With Quote
Old 15th September 2010, 06:53 PM   #7
diyAudio Member
 
coolet's Avatar
 
Join Date: Jun 2010
Location: Sibale Island
can you show us how you connect the grounding?
  Reply With Quote
Old 15th September 2010, 10:15 PM   #8
Leo IT is offline Leo IT  Italy
diyAudio Member
 
Join Date: Jun 2010
Location: Italy
Sure! This is the complete schematic (I tried to put together on a single sheet) is a little messed up I hope you understand. The ground is the same for 12V and +/-Vcc (it is not opsoisolate)
schematic.pdf

many thanks to all!!
  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
Neo Versus Ceramic In Subwoofer Applications CarlosT Subwoofers 9 27th August 2009 11:37 PM
Improve EMC In Class D Amplifier Applications gmphadte Class D 4 1st March 2006 07:43 PM
Phase-Gain plot, will this oscillate? azira Solid State 105 12th May 2005 07:45 PM
Why does my gainlcone oscillate? gmarsh Chip Amps 6 13th December 2004 08:51 PM
ECL oscillator just won't oscillate capslock Digital Source 45 18th May 2004 11:02 AM


New To Site? Need Help?

All times are GMT. The time now is 07:48 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