LM3876 Sub Amp Guidance - Page 2 - diyAudio
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Chip Amps Amplifiers based on integrated circuits

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Old 14th January 2013, 01:22 AM   #11
Joseph1 is offline Joseph1  Sri Lanka
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Join Date: Dec 2012
Quote:
Originally Posted by DUG View Post
OP2 has a gain of 11 and OP1 has a gain of -10.

To fix this add a 4K7 in series with C10.

The LR in the output path helps isolate capacitive loads from the amp.

"...change R5 to a 100K pot to trim output DC."

Vos on that device can be as much as 15mV. (one each way is 30mV)

If you add to that an imbalance of resistance to the inputs the input current could give you more offset between the two amplifiers.

With the adjustment you could trim that to a very low value.

After you build it (without speaker) adjust the pot and measure the output VDC.

If you don't need it, take it out.

If you don't want to put it in then make it 47K like the other ones.

Totally understood.Thank a lot.

Even with mismatched gains (11 & -10) I can run the system
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Old 14th January 2013, 01:23 AM   #12
Joseph1 is offline Joseph1  Sri Lanka
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Join Date: Dec 2012
Quote:
Originally Posted by volume knob View Post
3886 is a better choice for this application, but you need to reduce your voltage. At +/-30 volts the two 3886's would be able to produce about 150 watts output power into 8 ohms while dissipating 45 peak watts of heat (pdmax) in each 3886, which is above the 40 watt limit National recommends.

At +/- 25 volts would get you about 100 watts into 8 ohms with a peak dissipation of about 30 watts of heat in each chip, which should be o.k as long as your heat sinking is up to the task
Very nice.Thats what I wanted to know

Thanks.
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