LM3886 Amplifier Gainclone
 
LM3886 Amplifier Gainclone


 

LM3886 Amplifier Gainclone

 


Several years ago, National Semiconductor came up with some very high performance, easy to use audio power amplifier LM3886 circuits. I needed an extra amp so I can bi-amp some of my homemade electrostatic speakers so I tried the LM3886 chip. LM3886 amplifier was chosen because of ease of use, performance, low distortion and a built-in protection against short circuits and thermal instability. There is not much to remove a power amp, than asking. When driving electrostatic speakers, you can not be much protection. There are people who have “golden ears” and the feeling, provided that no application note scheme is never good enough for it to “Optimize” to “improvements” to make a claim. The problem is that most of them do not engineers and have no idea what the possible consequences of their “improvements” can be. For example, for a few years if these chips were popular with the audiophile crowd, it was all the rage at minimum power filter caps for “Best Sound” to use. We are talking about 500 uF on each power rail for each chip used LM3886 amplifier. This is clearly insufficient and leads to a distortion in the volume low enough that the power supply sags under load. The problem was that some of the golden ears of the large power supply rejection IC spec saw and thought it meant that the chip could tolerate the 10V power supply ripple. The pendulum has swung the other way, and now many music lovers are sufficient amounts of energy storage in the diet.


LM3886 Amplifier Gainclone

LM3886 Gainclone Amplifier Chip Amp Circuit Diagram

Another frequent change was the elimination of “Zobel” network with the output of the LM3886 amplifier, because it “sounded bad.” After a couple of people have burned some expensive speakers, they come to realize that the network is for the dead and the speakers sound much worse than the Zobel networks, so these days most people use the network Zobel. I used my amp to drive electrostatic speakers, a fee is particularly difficult because the capacitive reactance and never had any stability problems to delete.

My amp has been using a pattern from right to NS-sheet, with the additional power supply. Perhaps the mentality is to refine the model by manufacturers just do not understand the actual construction practices. One thing that is important for LM3886 is a good performance of an amplifier to use a proper ground. The ground is usually not represented in a diagram, because it is on the mechanical design of the circuit LM3886 amplifier chassis depends. Construction practices such as keeping high-impedance circuits (such as inputs of the amplifier) ​​and son of components by high currents (transformer, power supply and son traveled LM3886 amplifier output) and a “star” of the earth more high-performance-$ 10 resistance and gold plated connectors help. Click here for a schematic representation of the ground star

Normally, the housing is the most expensive part of the amplifier. It has to dissipate the heat from the amplifier and power supply integrated circuits of the transformer, you have to look acceptable and must be large enough to hold everything. My amp came from the housing, a scrap yard in Dallas, where I was able to buy it for $ 1 per pound or about $ 15. The box was originally a mobile phone antenna diversity housed the amplifier.

The side walls are 1 / 4 “thick aluminum, welded at the corners, making it a heavy box, a lot of heat can be dissipated. The top plate is 1 / 2″ thick and is equipped with fins covered dissipate heat even more. The bottom plate, not shown, is 1 / 8 “thick.

There were a number of ports through holes in the sides of the box. I could not use, but others, they were filled with Bondo putty. First I took a few bits of equipment containing PCBs in the box and then coated with Bondo into the hole from the outside. After curing the Bondo, I sanded the outer surface flush with the rest of aluminum. He has worked well and I recommend this technique for anyone who is recycling surplus assets.

I have a few holes where I needed him, enlarged some existing holes, then applied goal ..

One of my other hobbies is restoring old radios. I have a very special radio in my collection, a 1927 Super Six Neutrowound. The radio must have looked like he had the space back in 1927. At that time, most stations were simple, rectangular wooden boxes. This was a steel box with a very unusual view of the Ni-tube fitted covers that protrude from the top, and the exotic blue cracked painted orange!

I like the finish on the radio a lot, so I try to reproduce it on my LM3886 amp decided. Radio has been painted, but I do not have access to spray equipment, so I had to use brushes that apply to the target. I chose a beautiful blue metallic (not quite the same as the radio) and a bright orange for the base layer. The result was not a very good game for radio, but it was kind of interesting anyway.

The finishing steps were the beginning of the coat of orange acrylic-based, acrylic crackle medium, acrylic, metallic blue, and finally a layer of transparent acrylic protection.

Then came the construction of the LM3886 amplifier. The first channel is wired hay, because so few parts were needed, but I did not like the eyes of many, so that the second channel on perf board was built. The plan was eventually to go to circuit boards (later). All reasons to have a single “star” point was placed on the chassis to minimize the possibility of ground loops and associated hum / noise.

The transformer is a device may, 320VA one bit exaggerated since the amp about 30 watts per channel with the specified supply voltage.

The filter plugs into the socket about 100,000 uF total more than enough, but such a low voltage, capacity, cheap ($ 6 for a total of four choices), so why not?

The volume control is located near the entrance located at the back to keep the son of the Short-and signal from the transformer. The expansion of the tree is a piece of 1 / 4 “diameter brass tubing. Alignment of the tree volume and the hole on the front are not perfect, so I made an elastic coupling a piece of urethane tubing and two cable ties. It works well, when you turn the knob above the stopper into the pot, he slips a little, through an emphasis on the pot.

I finally got around to printed circuit boards and built the two LM3886 amplifier channels. I prefer the PCB since the circuits wired together with hay can cause short circuits if the son should be moved to make repairs.




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