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Old 2nd March 2009, 01:05 AM   #1
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Default Problem with Lm3886 output voltage

Hi,
My output voltage is about 20% higher out of the right terminals. I haven't hooked up any speakers yet but measurements with my meter shows more output gain on one side.
A little info: BrianGT's Stereo kit with Antek 300v 22v rails.
Measured the secondary voltage and everything was perfect: around 32v dc each. Hooked up the chips and now have what seems to me more gain on the right. Only thing that's different to me is the length of cable is longer to the left. Could this be it.
Don't want to hook up speakers to it yet so any help would greatly be appreciated... Thanks JohnnyP.
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Old 2nd March 2009, 07:43 AM   #2
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What do you call output voltage and what exactly do you measure?
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Old 2nd March 2009, 07:50 AM   #3
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Quote:
Only thing that's different to me is the length of cable is longer to the left. Could this be it.
No way
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Old 2nd March 2009, 09:46 AM   #4
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How well matched are your NFB resistors?
Have you used a 10k by mistake?
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Old 2nd March 2009, 01:33 PM   #5
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Gain or OFFSET ?
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Old 2nd March 2009, 08:47 PM   #6
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I followed the instructions as per BrianGt's kit.

He states "measure the output DC voltage between the + and - output terminals to verify that a low DC offset is obtained."
I did that and also measured the ohms just to see if there was a difference.

I used the kit so unless I screwed up a resistor, didn't really check the tolerances too closely. I'm going to comb through it again... Thanks for your help... JohnnyP.
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Old 2nd March 2009, 08:53 PM   #7
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But what did you measure? If you measured mV's of offset and had say 32mV on one channel and 75mV on the other, that is 'normal' and is down to the variations in the chips.
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Old 2nd March 2009, 08:59 PM   #8
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I'm a noobie when it comes to measuring DC so this could be wrong. I got 104 for the left and 92 mV for the right.
using the ohm setting I got 222 and 196. Which from what I understand doesn't mean anything but shouldn't they be closer in tolerances... JohnnyP.
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Old 2nd March 2009, 09:03 PM   #9
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92mV and 104mV are OKish.

If you are a newbie then may I suggest that you go here and do some homework!
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Old 2nd March 2009, 09:13 PM   #10
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I didn't install the dc offset cap(Ci). I'm thinking that's maybe why my DC offset is high. From what I understand it should be safe to wire speakers, I hope!!!

At this point is there anything I could do without replacing resistors to make them more identical...

Thanks for the info and all of your help... JohnnyP.
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