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Old 10th December 2005, 03:59 PM   #1
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Default paralleling chips

ok maybe this is a stupid question or maybe not

ive always wondered why each chip has to have its own parts and why you cant just put one chip on top of the other(connect the inverting input to the other chips inverting input etc instead of having to use 2X as many resistors etc. if anybody has an answer to this please let me know as im very curious. i have never tried this before as in i have no speakers i am willing to blow to test this. but if anybody tried it let me know the results.

thanks.
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Old 10th December 2005, 05:18 PM   #2
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Default paralleling chips??

Let me get this straight, you mean paralleling the chips and useing a global feed back loop for all parallel chips, same with input net works and output also???
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Old 10th December 2005, 05:22 PM   #3
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Default parralleing chips

Sorry didnt read the post close enough! these chip are not unity gain stable, boostrapping wont work
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Old 10th December 2005, 06:16 PM   #4
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opa549 is unity gain stable so would it work

and jus to make sure what i mean i mean just connecting all the pins from one chip directly to the other chip and just using one fb, input resistor, etc.
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Old 10th December 2005, 06:39 PM   #5
tool49 is offline tool49  Canada
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Due to difference in chips, doing so would cause imbalance. You would to the very least need to have a current sharing method to insure that they're all working to the same degree.

Hope this helps!
Sébastien
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Old 10th December 2005, 07:30 PM   #6
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ive decided im going to try it with 2 opa549's i will repost later
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Old 10th December 2005, 11:26 PM   #7
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Default paralleling chips

Holy chip, it works! I tried it with two LM3875,S I had laying around. Split the input with 2 1K resistors and 1 22K to ground used a common feed back loop with a 22.1K .1%, 47uf tantalum cap, and a 1k .1% to ground fed the outputs to two .15 ohm 1% soldered directly two the pins and took the feedback of the combination of outputs. Might have to take a closer look at this! I got the least amount of DC offset of any chip amp Ive made!!
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Old 10th December 2005, 11:38 PM   #8
troystg is offline troystg  United States
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Picture please.....
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Old 11th December 2005, 01:20 AM   #9
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i know you can do it with BUF634 for headphone amps etc.


tiltedhalo can you try it without the tantalum cap? lots of GCs dont use a cap in the feedback.
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Old 11th December 2005, 03:44 AM   #10
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Default cap removal

The tantalum should not be removed for DC offset, you also need current resistors, but you can use a common feed back network. I would post pics but my wife is out of town and has the digital camera.
I had this strange idea of potting the hole thing in epoxy and soldering the chip to a piece of copper and basically building a parallel module
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