LM3886 pathology, TDA7293 better?

mobyd · 7th September 2005, 10:42 AM

I fix pro audio gear for a crust, and one of the brands I fix is JBL.
JBL make a powered speaker called an EON, which uses an LM3886 to drive the compression driver tweeter. Occasionally these things go bang and almost invariably take the diaphragm out as collateral damage ($$$$) (dias don't like -38 volts DC).
I use the 3886 myself by the bucket in installation amps (museums etc) and find them pretty trouble free unless I run them close to the max voltage limit (like JBL does). Would I be safe in assuming that it is overvoltage that shags them or is there something else (like parisitic oscillation) that lays them low.
Recently had one of the latest eons in for repair and noticed that JBL had switched over to TDA7293s for the tweet - ahh good, I thought- higher voltage rating, less bang potential - but alas no, the TDA had blown to bits (literally) and taken out the dia, just like old times. Interestingly, I've never seen a single catastrophic failure in the LF amps, which are discrete design.
M

mwmkravchenko · 7th September 2005, 12:21 PM

I always thought that the chip would go into protection mode. I have learned something new here. Definitly sounds like a over voltage failure.

Mark

Russ White · 7th September 2005, 02:35 PM

Actually the problem described sounds much more like a faulty circuit implementation than any problem with the chip itself. But there is no way to know without a schematic and other details.

Tarzan · 2nd November 2005, 07:49 AM

Have a look here for the schematic.
The tweeter not allways go's, only two of the tree times.

http://www.jblproservice.com/navigat...%20Series.html

Cheers, Zilog

sagarverma · 2nd November 2005, 08:08 AM

tda7293 is delicate one.(its the only chip that smoked out in a ckt made by me).its failure is not a surprising for me ,its great one(better sound and clarity than lm) but it needs extreme care too.

i wonder how lm 3886 goes wrong.its a very tough one.one i built an year ago still workin inspite of abusive use.must be bec(surely) of high voltage.. + - 35v is at the edge of safety envelope for it. + -38v is way too high.mine operates at conservative + - 30 v

lets see what comes out of this thread

7th September 2005, 10:42 AM	#1
mobyd diyAudio Member Join Date: Sep 2004 Location: Auckland	LM3886 pathology, TDA7293 better? I fix pro audio gear for a crust, and one of the brands I fix is JBL. JBL make a powered speaker called an EON, which uses an LM3886 to drive the compression driver tweeter. Occasionally these things go bang and almost invariably take the diaphragm out as collateral damage ($$$$) (dias don't like -38 volts DC). I use the 3886 myself by the bucket in installation amps (museums etc) and find them pretty trouble free unless I run them close to the max voltage limit (like JBL does). Would I be safe in assuming that it is overvoltage that shags them or is there something else (like parisitic oscillation) that lays them low. Recently had one of the latest eons in for repair and noticed that JBL had switched over to TDA7293s for the tweet - ahh good, I thought- higher voltage rating, less bang potential - but alas no, the TDA had blown to bits (literally) and taken out the dia, just like old times. Interestingly, I've never seen a single catastrophic failure in the LF amps, which are discrete design. M

7th September 2005, 12:21 PM	#2
mwmkravchenko diyAudio Member Join Date: Jan 2002 Location: Perth Canada	The chip is pretty tough I always thought that the chip would go into protection mode. I have learned something new here. Definitly sounds like a over voltage failure. Mark __________________ Mark

7th September 2005, 02:35 PM	#3
Russ White diyAudio Member Join Date: Jan 2005 Location: Nashville, TN, USA	Actually the problem described sounds much more like a faulty circuit implementation than any problem with the chip itself. But there is no way to know without a schematic and other details. __________________ Less pulp more juice Twisted Pear Audio.

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2nd November 2005, 07:49 AM	#4
Tarzan diyAudio Member Join Date: May 2004 Location: Genk	Have a look here for the schematic. The tweeter not allways go's, only two of the tree times. http://www.jblproservice.com/navigat...%20Series.html Cheers, Zilog

2nd November 2005, 08:08 AM	#5
sagarverma diyAudio Member Join Date: Feb 2005 Location: NEW DELHI	tda7293 is delicate one.(its the only chip that smoked out in a ckt made by me).its failure is not a surprising for me ,its great one(better sound and clarity than lm) but it needs extreme care too. i wonder how lm 3886 goes wrong.its a very tough one.one i built an year ago still workin inspite of abusive use.must be bec(surely) of high voltage.. + - 35v is at the edge of safety envelope for it. + -38v is way too high.mine operates at conservative + - 30 v lets see what comes out of this thread

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