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Old 3rd December 2007, 01:05 PM   #1
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Join Date: Mar 2005
Location: Portugal
Default AMP6 Voltage problem (TA2020chip)


At first I have to say that despite he other thread I started earlyer yesterday,this problem has nothing to do with it.Haven't done any fidling to adjust the output bias what so ever

I have used the amp with SMPS.The power regulator,resistors and rectifier etc. haven't been soldered until now.

So finally did solder them and connected the amp to a new transformer,everything measured fine.Tested the amp with an old speakers,took the amp to another room and connected it to main speakers.Everything was nice for the fist minute,then speakers muted with a "thumb" noise.I imediatelly pulled off the power and possibly the red led was lid,not sure because all I was thinking was to protect the main speakers.
Then connected the power again (speakers removed) ,with power connected plugged in the test speakers wires,plenty of sparks and cone pumping........DC

Later in another room the problem with DC didn't appear anymore,not with the test speakers or with resistors as a testload.

When measuring there was few ohms from the regulator chip to the heatsink,some aluminium dust originated from the heatsink was mixed with the heat transfer compound.The same heatsink is used for TA2020 and rectifier.

So here are finally the questions:

-Could the "shorted to ground " regulator cause relatively big amount of DC at output ?

-Is the TA2020 still OK,anyway to test it ?

I'm really afraid to connect the speakers to this amp again,untill made sure there will not be more DC at output.
xxx I should correct my spelling xxx
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Old 3rd December 2007, 06:03 PM   #2
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Join Date: Mar 2005
Location: Portugal
OK problem hopefully fixed.

Shorting the back of the voltage regulator to heatsink, does actually make the DC jump up quite high at the speaker outputs.Not the smartest thing to do ( actually stupid) ,but I shorted the regulator with jumper wire just to test it was this that caused the problem.This time with only a resistors at output.

The amplifier sounds alright and the speakers also,hopefully nothing serious happened.
I'm happy the speakers aren't fried...
xxx I should correct my spelling xxx
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Old 3rd December 2007, 07:02 PM   #3
Pano is offline Pano  United States
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Pikku - yes, the regulator back needs to be isolated! That's why the kit comes with the insulator pad.

The TA2020 chip itself can be tied to ground - but never the regulator.

Hope your speakers are OK. They probably are.
Take the Speaker Voltage Test!
planet10 needs your help: Let's help Ruth and Dave
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Old 3rd December 2007, 08:02 PM   #4
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Join Date: Mar 2005
Location: Portugal
I'm a bit angry for myself for being so careless with the isolation.Used the insulator pad and the O-ring supplyed with the kit.
But then somehow managed to get there some cutting dust mixed with the heat conducting grease, from drilling the hole to the heatsink.Or maybe the hole was too tight for the fixing bolt.I even measured the resistance between the two peaces at assembly accident was waiting to happen.
xxx I should correct my spelling xxx
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