Amp dies off after some time of operation - 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
Reply
 
Thread Tools Search this Thread
Old 13th January 2016, 01:24 PM   #1
diyAudio Member
 
Join Date: Jan 2016
Default Amp dies off after some time of operation

Hello experts.

I have a Warwick BC80 Bass Amp. It has a inbuilt function for compression.
The amplifier works properly when it turns on.

The power stage is built around a TDA7294. There are 2 symmetrical 130 Ohm/2 Watt resistors on the circuit which seem like some kind of bias resistors. One of them operates normally, but the other one heats tremendously.

As the amplifier turns on it operates properly, it's heating starts and over a span of around 2-3 minutes the compression function starts kicking in slowly and the amplifier is muted at the end.

But I also observed that the resistor heating continues even after it is muted. And the amplifier will only function after it is turned off and after the resistor cools down.

How should I solve this problem? I am unable to find any schematics online either.

Awaiting your replies.

Thank you!
  Reply With Quote
Old 13th January 2016, 03:36 PM   #2
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Send a message via Skype™ to JonSnell Electronic
Check Q201/202. Those resistors, R201/204 feed the + - supply to the pre amp and effects. Maybe a leaky decoupling cap?
__________________
Support for Flying Mole Class D, Allen & Heath, Valve amps, older designs & 2CVs. www.jonsnell.co.uk
  Reply With Quote
Old 13th January 2016, 03:52 PM   #3
johnr66 is offline johnr66  United States
diyAudio Member
 
Join Date: Mar 2009
Large resistors such as these are sometimes used in the supply rails for a voltage drop for some other part of the circuit. After looking at the datasheet of the TDA7294, I don't see where they would be needed for its function. Does the IC get very hot when the problem occurs? Comparing the signal entering and exiting the IC could prove it guilty or innocent of the problem. This would require some gear to test with, such as an oscilloscope.

A clear picture of the circuit board, both sides if possible, might help us.

EDIT: well never mind. It looks like someone with a schematic has chimed in.

Last edited by johnr66; 13th January 2016 at 03:54 PM.
  Reply With Quote
Old 13th January 2016, 04:05 PM   #4
diyAudio Member
 
Join Date: Jan 2016
Quote:
Originally Posted by JonSnell Electronic View Post
Check Q201/202. Those resistors, R201/204 feed the + - supply to the pre amp and effects. Maybe a leaky decoupling cap?
Can you post the schematic please? Would be easier for me to debug.

Quote:
Originally Posted by johnr66 View Post
Does the IC get very hot when the problem occurs? Comparing the signal entering and exiting the IC could prove it guilty or innocent of the problem. This would require some gear to test with, such as an oscilloscope.

A clear picture of the circuit board, both sides if possible, might help us.

EDIT: well never mind. It looks like someone with a schematic has chimed in.
The IC was not getting hot. I will recheck again. What should I look for while comparing I/O waveforms of the IC?
I have access to a signal generator and a scope.
  Reply With Quote
Old 14th January 2016, 02:06 PM   #5
johnr66 is offline johnr66  United States
diyAudio Member
 
Join Date: Mar 2009
Quote:
Originally Posted by bellpepper View Post
The IC was not getting hot. I will recheck again. What should I look for while comparing I/O waveforms of the IC?
I have access to a signal generator and a scope.
I suspect the IC is not the culprit in this case. I guess the issues are in the circuits prior to the power amp IC as JonSnell alluded to. Hopefully he or someone with better knowledge of this amp can help you.
  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
Explaining the operation of a VAS in this amp guitar_joe Solid State 9 20th September 2007 11:49 PM
Buffalo Ironworker punches & dies mobyd Parts 0 10th May 2006 12:25 PM
Diac & Triac relay operation? AndrewT Solid State 2 16th February 2006 01:35 PM
TOPWARD MODEL 605 operation manual & Schematic ku5355 Tubes / Valves 0 16th December 2005 10:40 AM
Amp crackles and dies DD_Davo Chip Amps 32 22nd March 2005 09:22 AM


New To Site? Need Help?

All times are GMT. The time now is 11:23 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki