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This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor. The 10k potentiometer will give the amplifier a variable gain from zero up to the maximum.

This project shows how to build an Audio amplifier based on LM386 IC. The circuit is very simple and construction is easy on a breadboard. The LM386 IC is unique in that the gain can be modified by changing Resistor R2 and Capacitor C2. This configuration will give us a gain of 20. By removing R2 and connecting C2 across pins 1 and 8, we can increase the gain to 200. It is important to understand that increasing the gain does not increase the output power. The increased gain is only used when a very low input signal is to be amplified. In a previous article I discussed building audio amplifiers using discrete transistors. While it is possible to build good audio amplifiers from discrete transistors, they are no match for the many audio amp IC's available to us. IC's offer many advantages including high efficiency, high gain, low standby current, low component count, small size and ,of course, low cost. It is little wonder that audio amp IC's have replaced discrete transistors in most consumer electronic devices. While many experimenters have stayed away from these little black mysteries, I am going to uncover some of their secrets and demonstrate how easy they are to use.

It's always handy to have a little amp kicking around to trace audio signals, test mics, CD tape and TV audio outputs. You know, something that doesn't weigh a lot and isn't clumsy. There are tons of uses for this little circuit. There are a couple of versions of this amplifier chip. Both are 8 pin DIP packages and the difference between the two are apparent by their part numbers. Either are suited for this circuit provided the supply voltage does not exceed the recommended 5 to 12 volt DC range. Power output can range from about 325 mW to about 750 mW within this supply range when using an 8 ohm speaker. Power it with batteries or a small DC supply...why not solar cells or a little windmill generator?

Gainclone is a single integrated circuit based on an operational amplifier (op amp) on a single substrate of silicon. The LM3875 is the "weapon of choice". This great chip, is a little larger than the size of a thumbnail and can deliver up to 56W RMS continuous with 100W peaks and it can do this at 0.05% distortion! Because they are DC amplifiers (DC coupling right through the amp) they can go all the way to 400kHz! The first chipamp I built was a pair of monoblocks. Though these are a little industrial looking, they deliver big time.

You read where the subjective reviewer tells of the equipment vanishing and revealing the music unfettered. Well for the first time with any of mine or anyone else's gear that this is what I hear. There are no speakers there is just the music. A soundstage projecting from the wall behind and from the sides fills the room (7 x 8 x 2.5 m) with clear detail and multilayer texture and complex timbres. The setup consists of a NAD C542 CD Player, DIY Cotton ConneX interconnects (similar to the DIY Silver Interconnect Cables but with cotton insulation), the Synergy LM3875 amp and small two-way bookshelf speakers. Speaker cables are twin runs of oxygen free copper cable. I expect the amp to improve over the next weeks but for now I am stunned!

Gainclone amplifiers have VERY few components and this one is based on the National Semiconductor LM3875 IC. The PCBs and components are very simple and quick to make, only took about 20 mins to assemble both amps and rectifier board. DC offset was about 80mV on one channel and about 40mV on the other. I used the optional Ci capacitor in the national datasheet for the IC which reduced it to between 0-4mV: This is the capacitor I chose, its an Elna Starget (expensive). The case was MUCH more time consuming and difficult to make though. I bought all the aluminium from a scrap metal yard including the heatsink. I got my aluminium panels cut at a sheet metal shop as I cant make straight cuts with a hack saw.

This is a basic design with a single LM3875TF chip per side, and one shared toroidal transformer. I will be making two of these amplifiers simultaneously but with a few critical component differences. One is based on standard components, and one on premium components. There was a lot of deliberation on the type of transformer to get, particularly the secondary voltages. The concern here is the target load as, generally speaking, the higher the voltage, the less suited it is to drive low impedance loads (4ohms). I settled on 20 volt secondaries which I think is a good compromise, feeling that 18v is perhaps a little too low and 22v a little too high to get the max with a 4 ohm load whilst minimising output loss if using 8 ohms. The ability to run stable at 4 ohms is paramount to me to keep it open to different applications, and output wattage is relatively unimportant for this design.

The amp described on this page, is a very simple poweramp based on the National Semiconductor chip LM3875. According to National it's a chip meant for TVs, compact stereos etc. But many people claim that these chips are great high-end amps... So I decided to try building one. The "design" work was quickly done, as I just used the guidelines and sample circuit of the datasheet. I designed a small PCB for the amp (I'm lazy), and I made it double sided to make it easier to keep all the ground lines separate, as recommended by National. The prototype board can be seen below with a 100VA toroid I used for testing.

The amp is based on the Project 19 PCB, so uses a pair of LM3876 (or LM3886) power opamps, run from a ±35V supply. I used a cut-down P88 preamp PCB because I only wanted one preamplifier stage, but the entire board can also be used. Alternatively, the P19 amp can be run at higher gain than normal, alleviating the need for a preamp at all. The down side of this is that the noise level will be higher, and background noise may be audible with efficient speakers and/ or very quiet surroundings.

When I fired it up for the first time, I was immediately surprised with how much power was available, the level of detail and the nice bass response. It sounded much better than I was expecting and much better than it should considering the simplicity and low cost. Initially, I thought it sounded a little bright, but after about 12 hours the sound became more relaxed.