DIY LM3886 Chip Amplifier (Gainclone) Kit

DIY LM3886 Chip Amplifier (Gainclone) Kit

So what the heck is a Gainclone? Originally, the term Gainclone meant a clone of the 47 Laboratory Gaincard. The 47 Laboratory Model 4706 Gaincard is understood to have the following general features:

• 9 parts per channel based around the National Semiconductor LM3875
• A very short signal pass and NFB loop
• PSU filter with 1000µF to 2200µF capacitors
• Voltage regulation with a 170 VA cut-core transformer

However, a Gainclone is now generally understood to mean: any low component chip amp intended for high quality sound.
Photograph 1 below shows a 47 Laboratory Model 4706 Gaincard which retails for about $3300US. Despite the high retail cost of the Gaincard, you should easily be able to build a great sounding gainclone for less than $200US.

Photograph 1: 47 Laboratory Model 4706 Gaincard and Power Humpty

OK, so now you are interested in a Chip Amplifier and you are wondering where the heck should you start? A good starting point would be chipamp.com. At Chipamp.com, you can buy kits or PCBs to build your own chip amp. A search of "LM3886 chip amp" will net you more information than you can likely digest.
For more information about this kit, see the Users Guide for the Non-Inverted LM3886 Chipamp Kit - (PDF 280KB). The amplifier circuit of the LM3886 chipamp is shown below in Figure 1.

Figure 1: LM3886 Chipamp Schematic

The power supply circuit for the kit is shown in Figure 2 below.

Figure 2: LM3886 Chipamp Power Supply Schematic

DIY TDA2050 IC Hi-Fi Chip Amplifier

DIY TDA2050 IC Hi-Fi Chip Amplifier

This project which I call a "Mini Gainclone" is a stereo amplifier with an added headphone output. The amplifier is built around a single integrated circuit (IC), the TDA2050V which is produced by STMicroelectronics. From the data sheet, the TDA2050V is intended for use as a Class-AB hi-fi audio amplifier. The chip will operate within a supply voltage range of +/-4.5V to +/-25V. At about 25W of power output the efficiency is about 65%. One thing to note is that the gain of the circuit needs to be at least 24dB to maintain stability.
The amplifier was built to drive a pair of my friends Klipsch RB-51 Bookshelf speakers. The speakers are 8 ohms and have a sensitivity of 92dB @ 2.83V / 1m, so it does not take much power to get high SPL which makes the TDA2050 a nice match. The amplifier can be driven by most line-level sources such as an mp3 player, cd player, tuner and so on. The small TDA2050V chip can sound very well, similar to the popular ICs from National Semiconductor.

Construction - DIY TDA2050 Amplifier

Before we get started, I suggest you take a look at the TDA2050 Data sheet - (PDF 2.25MB), particularly if you want to make some changes to match your stereo setup. Figure 1 below is from the data sheet and shows the typical application using a split supply.

Figure 1: TDA2050 Typical Hi-Fi Amplifier Schematic

The data sheet also includes a PCB design (shown in Figure 2) that one can use. I used a protoboard for my amplifier (details below). 

Figure 2: TDA2050 Hi-Fi Amplifier PCB Design

A schematic of the amplifier I built is shown below (Figure 3). Only one channel is shown. A double pole, double throw (DPDT) switch is shared between both channels and this allows switching the output between speakers output or headphone output. If you do not need a headphone output, you can eliminate the DPDT switch and the resistors after the switch. The headphone adapter is from the Rod Elliott (ESP) site which you can reference for more details.
The gain of the circuit is 33 (30 dB) which should work well for most line level sources. You can adjust the gain, but note that note that the minimum gain for stability is 16 (24dB)

DIY Chip Amplifier Power Supply

Before I describe the power supply, I want to say a few things about safety. This project requires a mains wiring connection (120 or 220V) which you do not want to get in between. Faulty or incorrect mains wiring can result in death or serious injury! Please refer to your local electrical code for the mains connection requirements. Use appropriate fuses and connect the chassis to the mains "earth".
The power supply generally follows the "snubberized" Gainclone PSU design Carlos Filipe (CarlosFM). A torroidal transformer with dual 18 Volt secondaries and rated at 120VA (3.3A per secondary) is used. For the rectifiers I used 35A rectifier bridges (15-25A bridges should also work). In the original PS schematic by Carlos Filipe ultra-fast MUR860 diodes are used. Discrete ultra-fast rectifiers can also be used at an increased cost. I found no need to use them. Each power supply rail has a 10,000uF capacitor which is shared between the channels. The supply has only very slight hum which can only be heard with my AKG headphones when I turn the volume to max and no signal connected.