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LM3886 three in parallel board

Posted 12th August 2011 at 08:14 AM by panson_hk
Updated 12th August 2011 at 08:28 AM by panson_hk

Here is assembled LM3886 x 3 (inverting) board. I think you may see similar/identical board before. Who is the original? Copycats are everywhere. The kit comes with a Solen like film cap. Most likely a fake one. The measured data is not too bad though. The three LM3886 are samples from NS. Original!

The kit provides 0.2R 5% instead of 1% for paralleling the three 3886. Gain setting is by 200k and 10 k 1% metal film. Three 50 k trim pot are provided for DC offset adjustment. I do not solder the three 0.2R first in order to see the gain of the three 3886s.

One of the 3886 DC offset can't be adjusted to 0.0 mV. It has ~25 mV. The other two can be turned to 0.0 mV. This may cause a problem among them. Let see.
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  1. Old Comment
    abraxalito's Avatar
    Hi Panson - I'm always interested in paralleled amps

    0.2R does not need to be 1% type - when I did the math I found 5% was quite good enough. However with just 1% types for gain setting, the mismatch can be appreciable - assuming 30V peak swing this can be 29.4V worst case and 30.6V if the tolerance is the opposite direction worst case. 1.2V across 0.4R is 3A whereas the current into 8R would be 3.75A. So worst case the impedance is close to halved - fortunately the typical case is probably around 1/4 of the worst case. I'd be inclined to specify 0.5% as a minimum tolerance for the gain resistors.
    Posted 15th August 2011 at 02:34 PM by abraxalito abraxalito is offline

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