Can a LM386 used with differential inputs? - diyAudio
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Old 28th April 2010, 12:17 PM   #1
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Default Can a LM386 used with differential inputs?

In short can it be done?

All the circuits I see are with the LM386's negative input tied to ground - but if the signal source is balanced....can such 180 degrees out of phase symetrical inputs feed into the +ve & -ve inputs of the LM386 ok?

If so, are there any specific things I should put in place?
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Old 28th April 2010, 01:09 PM   #2
AndrewT is offline AndrewT  Scotland
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the feedback to the inverting pin usually determines the input impedance of the inverting pin, whereas the non-inverting pin impedance is determined by the filter components attached to the non-inverting input. These +IN and -IN impedances are usually very different.

You will find that a balanced drive is no longer balanced, if the receiver input impedances are not accurately matched at all frequencies in the passband.
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Old 28th April 2010, 01:16 PM   #3
boholm is offline boholm  Denmark
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Yes, you can do it but . . .

The LM386 has an internal amplification set at 20. That means that your differential input will be amplified by 20. So your signal swing has to be below 0,5 volts between the two balanced signals.

So . . . how big a signal are you going to feed the inputs with?

Data sheet: http://www.national.com/ds/LM/LM386.pdf
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Old 28th April 2010, 02:32 PM   #4
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Yes it can be done, but keep in mind the chip is not the same as an op-amp. It has internal 50k ohm resistors to ground on the (+) and (-) inputs. The DC bias for both inputs needs to be a few volts below Vcc, closer to gnd. Not sure if you are using a single power supply or dual.

This chip is not very stable and loves to oscillate or pick up RF (AM radio). You might need a small cap 22-100pF across the two inputs, and use the RC output filter too.
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