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Simple LM386 Audio Amplifier For Radio Projects
Make a simple LM386 audio amplifier that you can use with most radio related projects. I use it as a replacement for the high impedance headphones.
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I always had issue finding high impedance headphones for the simple radio receivers I experimented with. Initially I wanted to build an audio amplifier based on transistors only. But a circuit using the LM386 IC is so simple, that I decided to use this one instead. Is great for crystal radios and similar simple schematics. Right now I am also using it together with the (tr)uSDX Transceiver and also the Pititico CW Transceiver.
Off the topic note, sending a big thanks to Anuj from Feedspot for placing DX Explorer in his Best 30 Ham Radio Websites blog article. It means a lot to me as I spend quite a lot of time making the videos and writing the blog articles. It feels that all the work is appreciated.
THE SCHEMATIC
The schematic of the LM386 audio amplifier is pretty standard. There are just minor changes to make it more useful for the use in radio projects. It has a simple switch that will switch in or out the 10uF capacitor between pins 1 and 8 of the LM386 IC. This way you have the option to have a hi gain or low gain setting. I also placed a very simple audio low pass filter on the input that can be switched in or out depending on your needs. Keep in mind is just a basic low pass filter so it won’t make miracles.
It does make the CW signals sound a little better ( but is not a CW filter ). The low pass filter will basically attenuate any audio signal higher than 720Hz. At least that is what the online filter calculators told me. You can always feel free to play with the value of the R1 resistor and the C2 capacitor to see if you can get it to sound better to your ears. If you use a really tiny speaker, you can also replace the value of C5 to 100uF only.
LM386 AUDIO AMPLIFIER SCHEMATIC
THE PCB DESIGN
The idea was to make it as small as possible easy to carry it around when doing portable work. I did my best to design the PCB board as tight and compact as possible. Remember though, I am not a professional in PCB design. In case you do like it, on the bottom of the article you can download the folder containing the PDF files both of the schematic and the PCB design. With the toner transfer method it should be really easy to make a few LM386 audio amplifier PCB boards in no time. I made a handful of them to use them in the future.
BUILDING THE AUDIO AMPLIFIER
The best tip I can offer, is to build the LM386 audio amplifier in an aluminum enclosure. You will get rid of many possible interferences. Most of the capacitors are electrolytic capacitors. C6 placed on pin 6 of the LM386 IC can be a simple ceramic capacitor. For C2 and C4 is important to use mylar capacitors. They seem to work so much better than any other capacitors in audio circuits. Even if they have the same value as a simple ceramic capacitor, the way they react in the circuit seems to be a little different. The audio amplifier sounds way better with these. You can even use one for C6 if you like, it would not hurt at all.
Paul ( M0BSW ) just reminded me in the comments on the YouTube video about the LM386-4. This one has a 1W output power at 12v. So if you want a little more juice out of the LM386 audio amplifier, you may want to use that one. Here in Romania I had no luck, as all we seem to have in the stores are the LM386 N or M.
I built mine in a temporary PVC case covered on the inside with aluminum foil. But I will build a proper aluminum enclosure soon. Another idea would be to build the amplifier in the same box with a speaker. This way you will have a tiny powered speaker that you could use in many of your future radio builds. For me is a simple way of simplifying a circuit, not having to build the audio amplifier part over and over in each circuit. Is a nice way to save parts, using the same audio amplifier for all the circuits you build.
73 DE YO6DXE
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I would like to see more schematics for crystal radios.
Sorry for the late reply Christopher. I will soon start to update the blog and crystal radios will be one of the topics as well. 73, YO6DXE.
Hello,
I have made a copy of your “Simple LM386 Audio Amplifier For Radio Projects”. It works perfectly, and I particularly like the simple filter on the audio input. I have drawn a copy with Sprint-Layout, and JLCPCB has made the PCBs for me. If you want a PCB, I can send you one for free to Romania 🙂
Glad to hear that you like it. I also like mine a lot and used it often. Ohhh that is nice of you. Thank you so much. Don’t worry… you can make a nice present to some friend that needs it more. I am working with PCBWay lately and will also order some at some point ). I am working now on redesigning all the PCB boards from the articles so I can also share the project on the PCBWay website.
73, YO6DXE
I just finished building this amplifier this evening. I hooked it up to my Sawdust regen receiver kit. It works very well and the simple input filter is great. I think I will be incorporating that input filter into other projects eventually. I found a website that has a design calculator for R/C low pass and high pass filters.
Thanks for a great project. Next is the Sputnik !
73
Rick KA2PBO
Glad to hear that Rick. I also want to build the Sawdust receiver. I don’t have the kit so I will build it from scratch. I just want to replace the audio side with a simple preamp with one transistor, then the LM386 without the 10uF capacitor between pins 1 and 8. The filter is really simple indeed. In the past I used a 100mH inductor and instead I was switching a capacitor in and out. Sounds a little better than the RC filter. I used that in the older Sputnik receiver and it sounds nice. The downside is that for many people is hard to get the inductor, that is why I change it to RC. I think today if I have the time I will also post the schematic with the LC filtering for the Sputnik… so people get to pick what they want to use. Let me know how the Sputnik goes. I don’t think is so sensitive on RX as the Sawdust. Is still close to my heart because it was the first receiver I built for the ham radio bands hehe.
73, YO6DXE
I will let you know . I would have started it already but I wasn’t happy with the way my PC board turned out so I am making another. As far as the coil for the L/C filter goes; since it is only audio and not high current power, you could use small through -hole molded chokes. Here in the states, you can get 100mh molded chokes that are good up to 100ma for less than $2 US ( 8.98 Leu ) from places like Digi-Key and Mouser.
73 KA2PBO
Thank you Rick. I will search Mouser or Digi-Key as they also ship to Europe ( I believe they have warehouses here as well ). I could not find at all 100mH inductors in Romania. Of course the tiny ones are perfect.
73 YO6DXE
Very nice project. You can add a simple pair of transistors to board and s few parts and have a 1 or 2 watt output. Do you have customs problem with parts? Mail me a board for the regen and i will send you a nice selection of transistors and various opamps. Wa2kbz@gmail. 73 Karl
Btw met Romanians here often in orthodox churches. There are some Romanian but usually they go to Greek ones which are 50/50 english theses days. I have seen videos of your beautiful country. Look for me on 20m cw one day.
Hi Karl… I don’t have any boards at the moment, but I want to make a few as I need one for a video… and I also promised one to one of my friends in Canada. So when I will mail him the board, I will mail you one as well. I’m ok with the parts at the moment, the free time seems to be a problem lately haha. And yes you are right about adding a little more to the amp for some more output. I didn’t just because for the little projects I was building so far, it seem to be enough as it was. We keep in touch on the board. I lived in Miami for about five years, but I didn’t go much to the church… I was living aboard my sailboat in South beach. I got to meet a lot of Romanians as they sometimes asked me to film events at the Romanian church there. It felt strange to realize how many of them are over there haha.
73, YO6DXE
It looks very interesting. Thanks for sharing.
Always a pleasure. Yes you should try it is really nice, but remember is also simple so it doesn’t do magic things hehehe. I hope you will be happy about it though.