LM3886 Amp components


2002-04-21 4:49 pm
I'm building a simple LM3886 amp, pretty much like the typical application on the data sheet from national. I was wondering what ratings(power for resistors, voltage for caps) should be safe for the external components such as the resistor in parallel with the coil on the output, and the feedback components. Any info on this would be very helpful.

I have recently built a subwoofer amp for my car. Apart from the switching power supply, the power stage is built from 4 LM3886's in bridge-parallel configuration.
The conecpt is similar to National's app. note, but without the servo circuits and only non-inverting amplifiers.

You only have to build 4 non-inverting stages, like the one in the data-sheet, but selecting resistor values (mainly for the ones that fix the gain) almost identical (within 1%) is critical.
Connect two stages in parallel, directly excited from the source (or better with a buffer).
You also need a inverting amplifier, made from an op-amp, to feed the other pair of stages. You have to connect the outputs together but with a 0.1Ohm/3W resistor in series.
Then connect the speaker bridged (min 4 Ohms and supply power no more than +/-27V ) You should get about 250W rms if everything goes OK.

I don't know if it is clear for you, if it is not, don't hesitate to e-mail me ([email protected]).

Sound of 3886

Hi folks,

I've been at the DIY amp chips site. There is a lot of discusions about the different sound of the 3886, the 1875 and the 3875.
Then I downloaded the PDF information from the National site, and the chips appear to be very similar, mainly the 3886 and the 3875/76.
Have any of you had a chance to listen to those differences?
I have a 3886 amp that I built for test and it sounds very nice, as long as you do not push the chip into the spike protection mode.

Also there are many discussions about an amplifier named "gaincard". What is that?