View LM #3) BPA – W Bridged/Parallel AB Amp reference design. Specifications, support documents, and additional tools available at Digi-Key. Your load looks mostly resistive, not capacitive. I think most design include a large capacitor between the speaker and the driver to block DC. W-power-amplifier-with-bridge-parallel-configuration The project is based on six LM to produce a well designed audio.
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With the right layout and component selection, you can build an excellent sounding Hi-Fi audio amplifier that will rival high-end amps retailing for several thousand dollars or more. I highly recommend reading the datasheet before building your amplifier. Application note AN has additional information that fills in gaps left out of the datasheet.
Overture Application Note AN This is an Excel spreadsheet that calculates output power, heat sink size, gain, and other useful parameters:. You can also check out this video to see a quick overview of the design process.
At the end I wire up the amp so you can hear what it sounds like:. The formula to use is:. Sound quality is severely compromised when the SPiKe circuitry is enabled, so to prevent this we need a heat sink with a thermal resistance low enough to dissipate the maximum power dissipated by the LM The thermal resistance of the gap between the chip case and the heat sink. The thermal resistance from the heat sink to the ambient air. The minimum gain setting of your amplifier will depend on your input voltage, speaker impedance, and output power according to the formula:.
Setting it too low might make your amplifier too quiet. To convert voltage gain to decibels db gain, use this formula:. I decided on a gain of around 27 db Which is close enough to 27 db, and above the If these resistors vary much between the two channels, the gains will be different and one channel will be louder than the other. Metal film resistors with a tolerance of 0.
After setting the gain, the next step is to balance the input bias currents by choosing values for R in and R b:. If the currents at the ml3886 input pin 9 and the inverting input pin 10 are different, a voltage will develop between them.
Lower than 2 to 4 Hz is ideal. I started with 1. Electrolytics, ceramics, and tantalum capacitors should be avoided. A good quality polypropylene metal film, or even better a polypropylene metal film in oil capacitor will sound best here. We can use the F c equation with R i and C i:. Broadcast radio frequencies in the USA are:.
PA – 3x LM PCB assembly guide
With a pF capacitor, the F c becomes:. The best way to determine values for R f2 and C f is with circuit simulation software such as LTSpice. At high frequencies, the impedance of C sn is very low, so high frequency current is shorted to ground.
The datasheet gives a value of 2. In order to bring this down to a more reasonable level, I decided on using 4. Inductors have a low impedance to low frequency current and a high impedance to high frequency current. Audio signals are relatively low lm388, so they will flow through the inductor uninhibited. High frequency oscillation current will be impeded by the inductor and be forced to flow through the resistor, which will dampen it.
Since the brldge will be carrying the full output current of the amplifier, the wire should be heavy gauge. The LM has one negative power supply pin pin 4 and two positive power supply pins pins 1 and 5. Larger values will improve the bass response. That bdidge be found with this formula:. Click on the image to edit the schematic or change component values. Low current grounds are the ground feeds to the input circuitry and feedback loop. High current grounds are the ground feeds to the power supply decoupling capacitors, the Zobel network, and the speakers.
These grounds should connect only once at a set of terminals called the main system ground. The main system ground is located as close as possible the reservoir capacitors on the power supply. PCB design also has a major influence on lj3886 performance of your amplifier. The components on the PCB layout match the schematic above. The finished boards look great. The power ground and signal ground are the only ground networks on the PCB. Each one has its own electrically isolated ground plane on the bottom layer.
The feedback loop should be kept as short as possible to reduce the loop area. L3m886 wiring layout is just as important as the PCB layout and grounding layout. Use the diagram below as a guide for wiring the various parts together:.
Vridge used solid core 22 AWG, which works well because it can be twisted into bfidge tight coil. Audio input cables running from the source to the amplifier chassis bridve pick up interference. The main system ground connects to the ground protection circuit discussed belowwhich then connects to the chassis. The two Thiele networks are located close to the speaker output bridfe. In this arrangement, the heat sinks provide some shielding from the Thiele networks and the AC wires leading to the transformer:.
A Complete Guide to Design and Build a Hi-Fi LM Amplifier – Circuit Basics
Under normal operating conditions, low voltage ground loop currents flow through the resistor R1 to earth the chassis. The resistor reduces this current and breaks the ground loop.
If a high current fault occurs, the fault current can flow through the diode bridge to earth. The capacitor is there to filter any radio frequencies picked up by the chassis.
The amplifier I built sounds incredibly good. You can really feel it. The highs are clear, but not harsh at all. I can hear details in songs that I never knew were there.
The video at the beginning of the post will give you an idea of what it sounds like. Due to the length of this post, I decided not to cover the power supply in detail, but I may do so in the future.
And be sure to like, share, and subscribe if you found this helpful! Talk to you next time…. I use the LM on my biamped mains. A single chip for each tweeter and a parallel pair for the woofers. This setup drives them quite well. I am interested in buying two ,m3886 plates and one power supply. I am asking for information by email desoto wp. Great post and well explained.
Great detail and explanations of the individual aspects of the circuit. I also really like how you supplied the calculations for determining the size of the components. If not a full post cover it, could you at a minimum post a link to the pcb? Great project; thank you for sharing.
A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier
Thank you for sharing this. I was wondering the same thing. I think this is an omission in bdidge article. Depending on the rectifier and diodes used, this should be anywhere from 1. Thank you for this really great article.
Do you think you could post the exhaustive list, brandd and referenced of the components? I wish I had had this guide years ago when I first tried building an LM amp. A complete schematic, as well as components values for the power supply will be greatly appreciated, Thank you so much in advance. Thanks for the ln3886. Could you also consider doing a solid state discrete power amp with dual dc power supply. A very nice explanation. A lot of effort obviously went into this. Many hridge too for the fantastic links.
You seem to know what you are doing as well as having a lot of experience. Thus, I was wondering if you bridgge state the specifications of your amp, distortion and noise characteristics so it can be compared to other LM designs, so see if one needs to improve anything. Lmm3886, I would try to slide the capacitors away from the heatsink more on the PCB design so that the modules would have a longer life in many years time before breakdowns.
Thanks a lot for sharing this wonderful job. I will definetly try a build on my brdige. Awesome writeup, many thanks! Should I still include a ground loop protection circuit or is it not needed for this approach?
The two silver mica capacitors 47pF and pF appear to be reversed in your pictures.