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Chip Amps Amplifiers based on integrated circuits

Input to LM3886.
Input to LM3886.
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Old 10th December 2019, 11:08 PM   #1
edbarx is offline edbarx  Malta
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Default Input to LM3886.

I would like to ask how I should connect the input electrolytic capacitor to LM3886 IC. Searching online did not result in any finds whatsoever. Only one schematic had a properly marked input capacitor. Since an electrolytic capacitor is polarised, I would like to know how this should be connected to the input. The IC's non-inverting input is connected to a resistor chain of two series resistors. The resistor that directly connects to the chip is 1k and the other , 22k, connects to ground. Signals will be fed at the point between these resistors. Which capacitor's electrode should be connected to this point? The input signal will be applied between the capacitor's other terminal and ground.
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Old 10th December 2019, 11:38 PM   #2
Mark Johnson is offline Mark Johnson  United States
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Input to LM3886.
Electrolytic capacitors are also built and sold, in "non polar" (sometimes called "bi polar") configurations. These capacitors are not polarized; their leads are not marked "+" and "-"; you can connect them either way and they'll still work. Here is how to find them on mouser.com (attached image). For your chipamp, you might want to consider the Nichicon "Bi Polar" capacitor series called UES. To name one example, the Nichicon UES 22uF, 50 volt capacitor is Mouser part number 647-UES1H220MPM and its price is less than one dollar.

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Old 10th December 2019, 11:52 PM   #3
rayma is online now rayma  United States
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If you are using a single supply circuit, a polarized input capacitor can be used, with the positive terminal
connected to the amplifier input. With a bipolar supply, I'd use a non-polar capacitor.
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Old 10th December 2019, 11:54 PM   #4
steveu is offline steveu  United States
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Check the LM3886 pdf data sheet equivalent circuit and you will see that the input transistors are NPN. This means that they draw current towards the negative rail so the + and - inputs have a slight negative DC voltage wrt ground. So you need to wire the caps with the negative side towards the chip, assuming you are building a dual voltage supply. If you are building a single supply amp then the inputs are biased at half the supply voltage and positive assuming the negative rail is ground. That includes both the input coupling caps and the feedback de-coupling caps. When you have it up and running, you can verify this by measuring the small voltage on these pins.

Last edited by steveu; Yesterday at 12:00 AM.
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Old Yesterday, 12:14 AM   #5
PRR is offline PRR  United States
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Quote:
Originally Posted by edbarx View Post
I would like to ask...
Why do you ask a question in one thread then start another thread to ask the same question?
What to do about mismatched IC footprints?
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Old Yesterday, 12:50 PM   #6
edbarx is offline edbarx  Malta
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Quote:
Originally Posted by steveu View Post
Check the LM3886 pdf data sheet equivalent circuit and you will see that the input transistors are NPN. This means that they draw current towards the negative rail so the + and - inputs have a slight negative DC voltage wrt ground. So you need to wire the caps with the negative side towards the chip, assuming you are building a dual voltage supply. If you are building a single supply amp then the inputs are biased at half the supply voltage and positive assuming the negative rail is ground. That includes both the input coupling caps and the feedback de-coupling caps. When you have it up and running, you can verify this by measuring the small voltage on these pins.
Thanks, you corroborate my observations.

Regarding using a non-polarized electrolytic capacitor at the input, I think, this is usually not done. I only encountered such capacitors as speaker filters where they are a necessity. At an amplifier input, the voltage variation on an electrolytic capacitor should be very very small. This means, there is no restricting necessity to use bi-polar capacitors.

P.S.
I have two ~2cm ferrite toroids that I am thinking about using as output filter inductors. I will wind a few turns until the inductance is 0.7uH. A few turns will mean the core will never saturate.
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Last edited by edbarx; Yesterday at 12:58 PM.
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Old Today, 02:42 PM   #7
asuslover is offline asuslover  Romania
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Input to LM3886.
The previous posters suggested you to use a non polar cap because in this situations is ok to replace an polarized electrolytic cap with a non/bi polar electrolytic , such as Nichicon ES which is designed for audio path and has very low distortions .
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Old Today, 06:19 PM   #8
edbarx is offline edbarx  Malta
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Quote:
Originally Posted by Mark Johnson
To name one example, the Nichicon UES 22uF, 50 volt capacitor is Mouser part number 647-UES1H220MPM and its price is less than one dollar.
The problem with Mouser is I found it has a prohibitively expensive mail. There are other mail options available to the default option, but, the cost is not given during the order, and one has to pay on arrival of items. The default mail option was about €20 for just a few grams of mail!

I wish I am doing something wrong in my orders, but till now, I am always getting very expensive costings which discourage me from placing orders.
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