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Old 13th February 2004, 10:34 AM   #1
Phear is offline Phear  Sweden
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Default Problem with high DC on speaker terminals

HI!
I finished my CG with LM3886 late last night. Joy!? Well, no. I went on measuring DC on the speaker terminals. Eek! 33V. Obviuosly I have done something wrong. I was to tired to start checking for errors last night so that became today's problem. I thought maybe you guys can give me some hints about what errors to look for...

The chipamp i've built is the one found at Linkwitzlab.com
Click the image to open in full size.

cheers/Per
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Old 13th February 2004, 10:47 AM   #2
Mad_K is offline Mad_K  Norway
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Is it dc on either +/- input?
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Old 13th February 2004, 10:51 AM   #3
SY is offline SY  United States
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Do a quick voltage map- start by measuring DC voltage on each pin. 9 times out of 10, that will quickly lead you to where the error is.
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Old 13th February 2004, 12:31 PM   #4
Nuuk is offline Nuuk  United Kingdom
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Sounds like one rail is down, or not connected to the chip.
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Old 13th February 2004, 01:37 PM   #5
GregGC is offline GregGC  Canada
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Default Re: Problem with high DC on speaker terminals

Quote:
Originally posted by Phear
HI!
I finished my CG with LM3886 late last night. Joy!? Well, no. I went on measuring DC on the speaker terminals. Eek! 33V. Obviuosly I have done something wrong. I was to tired to start checking for errors last night so that became today's problem. I thought maybe you guys can give me some hints about what errors to look for...

The chipamp i've built is the one found at Linkwitzlab.com
Click the image to open in full size.

cheers/Per

The speacker is connected to 0V rail and the rest of the GNDs are connected to GND simbol. The speacker should be connected also to the GND symbol and the GND symbol should be connected to 0V reail directly. The 2Ohm res is between GND/0V and Chassie.
The way you have it your decapling caps have 2 ohms res in ser with the speaker. Not good IMHO
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Old 13th February 2004, 02:18 PM   #6
Phear is offline Phear  Sweden
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I forgot to mention that i don't use Ro & Ci

I found out what was wrong! It aparently slipped my mind to connect the signal ground to the powerground.

thanks anyways guys!

I haven't listened to it yet so ti remains to see if if I have to re-wire the whole damn thing due to the sweet sound of motorboats.
Here's a pic of my amp:
Click the image to open in full size.
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