Simple Sony SRF-A100 mod for reduced distotion on C-Quam signals

When Sony designed the SRF-A100 radio, they were supporting the Magnavox AM Stereo system, but equipped it to receive all four AM Stereo systems in use at the time. However with my Panasonic VP-8253P multi-system AM Stereo signal generator, I noticed that the SRF-A100 sounds the best with the Magnavox system, and all three other systems (Motorola C-Quam, Kahn, and Harris) sound quite distorted during heavy single-channel modulation, such as often occurs during 1960s Oldies music.

Luckily there is an internal adjustment to reduce the amount of distortion when receiving AM Stereo signals, RV1. It does require disassembling the radio to get to it, but the process is not too difficult if you follow the instructions in the service manual:

http://www.steampoweredradio.com/pdf/sony/manuals/Sony%20SRF-A100%20AM%20Stereo-FM%20Stereo%20Receiver%20Service%20Manual.pdf

The service manual instructs you to use an AM Stereo signal generator and adjust RV1 for minimum distortion, or if you don't have a stereo signal generator, to simply adjust it to the middle of its rotation angle. With my AM Stereo signal generator I discovered that the middle position is a compromise between what sounds best with the Magnavox system and all the other systems.

Adjusting RV1 fully clockwise gives the cleanest sound with a Magnavox signal, while adjusting it fully counter-clockwise gives the cleanest sound with a C-Quam, Kahn, or Harris signal. 

Unfortunately since there were only ever a handful of stations transmitting Magnavox's AM Stereo system, Sony's factory default compromise adjustment ended up making the SRF-A100 sound more distorted with all three of the far more widely used AM Stereo systems, including C-Quam which eventually became the worldwide standard for AM Stereo.

So anyone using an SRF-A100 these days should open it up and with a small flat-blade screwdriver adjust RV1 fully counter-clockwise. The service manual linked above shows you its location.

All of Sony's other multi-system AM Stereo receivers (and some of Sansui's as well) have a similar distortion adjustment inside them, however I cannot guarantee that the same adjustment positions apply to them as well. It is also quite possible that in later years when it became clear that the Magnavox system wasn't going anywhere and C-Quam was becoming the most popular system, Sony began adjusting their receivers at the factory to the position optimized for C-Quam.

Also note that the SRF-42 Walkman does not have this internal adjustment and with my multi-system signal generator I have confirmed it is already optimized for the best sound with the C-Quam system (even though it actually still uses a multi-system decoder chip and can receive Harris and Magnavox signals as well, just with increased distortion, and Kahn signals without proper stereo imaging due to its lack of a selector switch and the associated phase shift circuitry).