Why the Sony CXA1019S AM-FM-Audio Chip is so great!

 Video posted May 27, 2026 :: https://youtu.be/eyBEh5sqnsQ

An experimeters look deep inside the CXA1019S -- a legendary Sony AM-FM-Audio chip.
Join us as try to better understand the signal path and perform testing with both instruments and ears.

 

Why the Sony CXA1019S AM-FM-Audio Chip is so great blog  support notes

Despite making long-form videos We cut over 13 minutes of video content because our goal is to keep video time between 15-25 minutes . This is all original content -- and it took us many hours to make this video. 

Please support hardworking creators who make their own content -- too many are reposting and/or reacting to the labours of others without putting in the hard work. Then — they have the gall to e-beg for your hard-earned money !?! 

Please consider supporting hard-working, original content creators if you can. If you choose to support So Simple Radio --- please do so by watching our videos.   Thank you!

Above — During the week prior to this 1 (May 24-30), the top 5 countries who visited our video support blog.  Thank you for visiting us -- and many thanks to those who emailed us. We appreciate your feedback. 

Above — A figure showing the main technical differences between AM and FM reception on a CXA1019-based receiver.

We no longer do medium wave DXing  ( with exception of when we travel to Eastern Europe ),  nor do we listen to local AM "talk-radio".  Thus, we didn't cover the AM side of the CXA1019 IC. The signal path is similar except for the ferrite rod antenna, different VFO frequency and IF -- plus detecting audio happens in some form of an envelope detector. No detector details get shown in the datasheet.

Above — Our guess about the schematic of the AF stage within the CXA1019S chip. This guess comes from reviewing datasheets -- and the measures we took of the harvested IC.
The big dilemma is what parts go at the ?   We've tried many times to make a suitable amp, but could not make it work well without driving the final pair with lots of current.

We'll hopefully figure this out one day. Making rail-rail output at low DC voltages seems to be an advanced skillset.

Q ---  What digital radio comes closest to the CXA1019S? 

Above — The Sony ICF-506 contains the Skyworks Si4831/35-B30 , a mechanically tuned 100% CMOS AM/FM/SW radio receiver IC.  This is our radio and we took all the photos of it.

Above  — A glimpse of the main PCB showing the receiver-on-a-chip digital IC (with mechanical tuning). We love this receiver and it's our main AC powered indoor FM receiver. It does take three 1.5 volt batteries for portable use, but battery life expectancy is lower than the CXA1019-based receiver.
The IC may also be used with a digitally tuned oscillator ( so can the CXA1019S), but this adds increased current consumption due to the the synthesiser/ PLL and the digital frequency display.

 

Above  —  The Sony ICF-506 contain a lovely speaker.  A wonderful radio to own.

Q ---  What's the best hand held FM receiver you've ever owned? 

Above  —  The Sony SRF-49 <<Walkman>> Canadian Model is the best FM radio we've owned that cost under $100.00. The heart of this radio = CXA1129N AM-FM stereo IC with 2 local oscillators and a very clever IF filtration system; plus a stereo headphone-audio amp -- the Sanyo LA4537M. 

Around 2002 or so, some mods were available in online forums and such -- we did 2 of these mods and 1 of our own. The 2 mods included increasing the output caps from 47 µF to 220 - 390 µF or so [to get more bass response] ,  plus changing the 2 de-emphasis capacitor values [to get more treble response]. 

We also added an external antenna jack to ours. At the ski hill, you could tune FM broadcast stations up and down the valley. The stereo field sounded massive. All with a single AA battery.  Amazing technology from Sony back in the day.

Further -- we still have the headphones. These are the most sensitive and efficient headphones we've ever used--  and we now use them for our crystal radio set.

They blew away all the other headphones we've tried including some antique Western Electric high Z phones that were coveted & hyped by collectors. 

Sadly, this receiver was loaned to relative who forgot it on the Sky Train and it's long gone. All of this content got stricken from the video. 

 ...more updates later..... 

 -- thanks and Best!
Lid, MJ - Bars and Munchie

Jovian Receiver Schematic from 2016 posted as a resource

My Jovian builder friends wanted our I-Q Jupiter receiver schematic posted for posterity. Done.  

We’ve posted it on its own web page accessed from the side menu
Thank you and best!!!

 

L-C VFO Notes added

 Greetings!

In 2025, a builder emailed to ask if I had leftover LC-VFO notes from a former video we made on this topic. I told him no since we couldn’t find any notes – which seemed strange since we normally do. 

The deleted video had several technical problems including audio in only 1 channel . One day, we hope to remake this video — however, we're uncertain it’s worthwhile in this time of cheap frequency synthesisers + abundant free source code libraries.

In Feb 2026, another separate e-mailer asked whether we had VFO notes available! We searched all our drives and found the main file in a completely random disk directory. Strange indeed!

We’ve posted them on our Resources for our Viewers web page:

Thank you and best!!!

Audio Amp Archive added

Greetings!

By request. We've added an archive of audio power amps to the menu & shall continue to do so over time. I'll cover any newly listed amp stages in future videos.

I'm an older mostly analog bench experimenter who enjoyed/enjoys a wonderful audience in the home built radio and solid-state guitar amp niches.  Thanks for your time and attention in our busy, whirling and often distracting world.

My raison d'être is not nostalgia.  I just want to have fun -- and get better at understanding radio + audio amp design,  plus, I enjoy making signals bigger!  

So Simple Radio covers all modes of radio reception such as FM, SSB and QAM. 
We love to explore all types, shapes & forms of radios.  With joy and curiosité, here we celebrate & make radios for pleasure,  plus to learn and share ideas + knowledge.

In the meantime -- please try to avoid wonky oscillations like those shown below.
Best to you -- and thanks!   Fantastica. Lid 

 

P.S.  I added my Gilbert cell notes under the resources & tools menu item

A last listen to the Canada Weather Radio service for me.

 Video Uploaded:: March 8, 2026

A last listen to Canada Weatheradio service for me. 
Environment Canada is ending its Weatheradio service on March 16, 2026, after 50 years of operation.

In addition, to listening to weather updates --- I used the WeatherRadio service to tune up many narrowband FM radio amps and detectors over 3 decades. I will miss this service.

I made a discrete transistor LM386 !

 Video posted Feb 23, 2026 :: https://youtu.be/F5MqMnCxcHM

 

A deep dive into the LM386 audio power amp IC. I built a discrete version and compare
it to the real thing. Technical, long-form video for those who seek to learn more about
the LM386 audio amp. No AI used at all -- all images, audio and video are homebrew.

 

Linux Laptops & Lectronics

Video posted June 3, 2025 :: https://youtu.be/ldBTBlY-D3M

 

Resources::

 [1]  Source code for the parallel resistor program "par" coded in C

To get GNU compilers in the BASH terminal -->  $ sudo install build-essential

/*
 *  C program to calculate the resistance of 2 - 4 resistors in parallel
 *  Command Line. Runs in a terminal with Linux BASH shell.
 *  Minimal error checking. None on the input -- some on the output to prevent ridiculous answers
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

// copy this text into a text file and call it par.c ( or whatever you like)
// place that file in a directory -- in this case the directory is called /home/Code
//
// path =  /home/Code
// to compile program, type --------------------------> gcc par.c -o par
// to run the executable (ELF) file, type ------------>./par R1 R2 etc.


// Function Definition -- the error message that appears if the user does not put in at least 
// 2 resistor values, or > 4 resistors
// When calling usage(), pass the name of the app via char *argv  "example output: ./appName" 
// type the ./ appname with no arguments for "help"

void usage(char *argv){
      printf("Usage:\n"
      "    %s [#1 resistor value in Ω] [#2 resistor value] [#3 resistor value] [#4 resistor value]\n"
      "    Must enter at least 2 resistor values -- maximum 4 resistor values.\n" 
      "    seperate resistor values with a space.\n"    
      "    Decimals OK. Resistors stored as floating point variables.\n" 
      "\n", argv);
}

int main(int argc, char *argv[]) 
{

  int i; 
  float R1, R2, R3, R4, sum = 0;

    if (argc < 3 || argc > 5) {  // 2-4 resistor values must be entered else you get a usage    
    // message to guide you
    usage(argv[0]);  // error --- pass the app name to usage()
    return 0;  
   }

 
    else  {
        i = argc - 1;
        printf("%d parallel resistors: ", i);  // display how many resistors are in parallel
        for(i=1; i < argc; i++) {
        printf("%s ", argv[i]);  // show each entered resistor's value
      }
    
          switch(argc)   // 3 different computations based on the # of resistors in parallel
      {
        case 3: // 2 resistors in parallel
            R1 = atof(argv[1]);
            R2 = atof(argv[2]);
            R1 = 1.0 / R1; 
            R2 = 1.0 / R2; 
            sum = R1 + R2;
          
            break;

        case 4: // 3 resistors in parallel
            R1 = atof(argv[1]);
            R2 = atof(argv[2]);
            R3 = atof(argv[3]);
            R1 = 1.0 / R1; 
            R2 = 1.0 / R2; 
            R3 = 1.0 / R3;   
            sum = R1 + R2 + R3;
            
            break;

        case 5:  // 4 resistors in parallel
            R1 = atof(argv[1]);
            R2 = atof(argv[2]);
            R3 = atof(argv[3]);
            R4 = atof(argv[4]);
            R1 = 1.0 / R1; 
            R2 = 1.0 / R2; 
            R3 = 1.0 / R3;
            R4 = 1.0 / R4;    
            sum = R1 + R2 + R3 + R4;
           
            break;

        }
   
 }

sum = 1.0 /sum;  // final calculation

/*   Some error checking of sum
     Does not catch some negative resistance value entries - don't do this please!  
*/

if (sum <= 0 ) { // Check if sum <= 0 and this also catches -inf
        printf("* Error * - the calculated result is <= to 0 Ω\n");
        return 0; 
    } 

  // Not a number 
  else if (isnan(sum)) {
        printf("* Error * - the calculated result is NaN\n");
        return 0; 
    }
   
 // infinity     Example: 2 parallel resistors: 1E2 -1E2 
  else if  (isinf (sum)) {
        printf("* Error *- the calculated result is Inf\n");
        return 0; 
    } 
 
 else { // OK to display calculated result in sum with 1 decimal point significance
       printf("\nResult = %.1f Ω\n", sum);
      } 

return 1;
} 

[2]  Probably, an original author of simple or suckless Amateur Radio design programs is Wes, W7ZOI . He wrote a book in the 1980s:

Above — Introduction to Radio Frequency Design (IRFD) was written around the time of Solid State Design for the Radio amateur (SSD) and originally published by Prentice-Hall in 1982. I purchased this book published by the ARRL in 1996. It came with a floppy disk of DOS Command Line programs.

Later when Experimental Methods in Radio Frequency Design [EMRFD] was published, EMRFD contained a CD with Windows GUI programs written by Wes, W7ZOI. These GUI
programs are still available on the W7ZOI Site

Click on Technical Stuff | EMRFD Errata for download

These ladpac programs were GUI ports of the original DOS IRFD programs that first appeared on that floppy disk. These programs serve as inspiration and provide some history of Wes' software. 

The IRFD collection of programs by Wes, W7ZOI

Excerpts from IRFD2MAN.txt ( the manual text file that came on the floppy disk)

1.0  Filter Programs:
       
GPLA...General Purpose Ladder Analysis
G0...A "no graphics" version of GPLA.
G87...A faster version of GPLA that supports a coprocessor.
L...Low Pass and High Pass (Butterworth and Chebyshev) filter designs, along with k and q calculations.
B...Coupled Resonator LC Bandpass filter design.
X...Lower Sideband Ladder Crystal filter designs. 
Meshtune...This is a utility for tuning individual meshes in a 
crystal filter.
STC...Single Tuned (LC) Circuit.
ZMAT...Impedance Matching Networks.
DTC ....Double Tuned Circuit. (The circuit designed uses parallel resonators that are coupled with a small capacitor between the "hot" end of the tuned circuits.  The end 
matching is realized with a tapped capacitor arrangement)

2.0  General Programs: 

NPNBIAS.EXE  (positive voltage)
JFETBIAS.EXE  (positive voltage)
PADCAP.EXE   (deals with tuned circuits with padding 
capacitors.  These might be used in an oscillator.  A combination of 
series and/or parallel capacitors are used with a single inductor and a 
variable capacitor)
RESONANC.EXE
PHASEPI.EXE presents an alternative way to design a pi network.  
PADS.EXE is a program for the design of resistive attenuators.  
PLL.EXE is one of the more extensive programs in the collection, 
requiring a computer with a VGA display.
FBA.EXE
COILS.EXE is a simple program for the design of toroid and single 
layer solenoid inductors.
COLPITTS.EXE is an analysis program that investigates the Colpitts 
oscillator
APSN.EXE examines an Audio Phase Shift Network. 
CASCADE.EXE is a relatively simple program that has proved itself 
to be a real "work horse" in numerous projects, ham and otherwise.  
CASCADE.EXE calculates the gain, noise figure, and third-order 
intermodulation intercepts (input and output) for a chain of up to eight 
stages.
SPURTUNE.EXE is a mixer evaluation program.
SCTU.EXE is a Smith Chart tutorial.

Disk image of files::