Two 75 ohm antenna inputs which can be switched via the front panel, go to the first RF amplifier - a Toshiba 2SK241 FET. The RF front end is tuned by six KV1320 varicap diodes. This arrangement is excellent for image and spurious rejection. The varicap diodes act as a automatic preselector which pass a narrow bandwidth (~ 2MHz) of signals to the first RF amplifier. For this reason the image rejection performance is 100dB.

The FM oscillator is built around a Toshiba 2SK161 FET. The FM mixer consists of a Toshiba 3SK122-K dual gate MOSFET.

Two IF stages are provided for wide and narrow IF bandwidth. Two 180 KHz Murata filters are used for wide if bandwidth. Two 180 KHz and two 150 KHz Murata filters are used for narrow if bandwidth. The IF amps used in the IF stages are Toshiba uPC1163HA ICs.

A quadrature detector precedes the audio frequency amplifier.

Subjective operation

I liked the feel of the main tuning control on the front panel. This is much preferable to push button electronic tuning.

The signal strength can be read from a 2 digit digital display. The threshold level for the digital display is around 1-1.5 uV (17dB). For strong signals, the display reads 70dB+.

The frequency digital display is small, hence difficult to read from a distance.

The ST-SA5ES's selectivity is inferior compared to the Onkyo T-9090 11. The reason for this is clearly apparent when reference is made to the circuit diagram. The Onkyo uses five 150 KHz filters in the narrow IF stage, which provides a selectivity specification of 80dB ( +/- 300 KHz). The Sony ST-SA5ES only uses two 180, and two 150 KHz filters, which provide a selectivity specification of 65dB (+/- 300 KHz narrow).

For about 20 dollars, a few extra 150 KHz filters and uPC1163HA IC IF amplifiers, would have increased the ST-Sa5ES's narrow IF selectivity equal to the Onkyo T-9090 11.

One example of the difference in the selectivity performance, was how the Onkyo T-9090 11 tuner was able to receive 101.5 MHz JJJ Canberra. The Sony was unable to receive JJJ Canberra, which was between 101.7 MHz 2WS Sydney, and 101.3 MHz Gosford.

Otherwise, the selectivity on the Sony tuner was found to be adequate for most DX situations.

It is interesting to note that due to congested FM band conditions in Europe, most European FM DXers replace the ST-SA5ES's IF filters with Murata SFE 10.7 MHY-A 110 KHz filters.

The ST-SA5ES also has RDS (Radio Data System). Unfortunately, very few FM stations in Australia broadcast RDS.

Conclusion

The Sony ST-SA5ES is an excellent tuner for FM-DX. There are only a handful of FM tuners which can either match or exceed its DX performance. Onkyo integra FM tuners generally have superior DX performance, however, they are often hard to find. I consider the Onkyo T-4711 to be a better performer with regards to selectivity and tuning steps, than the Sony ST-SA5ES.

In Australia, good FM tuners for DX are very hard to find new or second hand. The Sony ST-SA5ES retails around $1,000 new and $500 second hand.

Specifications

Tuning range: 87.5 - 108 MHz (50 KHz steps)
Sensitivity - usable 10.3 dBf 0.9 uV (75 ohms), 1.8 uV (300 ohms)
Sensitivity at 50dB 38.5 dBf 23 uV (75 ohms), 46 uV (300 ohms)
Harmonic distortion Wide: 0.004% (mono)
0.0075% (stereo)
Narrow: 0.04% (mono)
0.07% (stereo)
Stereo separation Wide: 70 dB
Narrow: 50 dB
Selectivity Narrow: 65 dB (+/- 300 KHz)
Wide: 70 dB (+/- 400 KHz)
Image rejection ratio 100 dB

Modifications

If you need to remove the muting on the ST-Sa5ES, so you can hear the FM band all the time when tuning up and down, i.e. no silence, simple cut off JW79 on the power supply area on the circuit board.

The following modification has been successfully performed by European FM DXers, and will considerably improve the IF selectivity of the ST-Sa5ES.

Remove the CF203 and CF204 150 KHz filters, and replace with Murata SFE10.7 MHY-A filters. The wide selectivity will now be the same as before, and the narrow selectivity will be superior.

Wide bandwidth = CF201 + CF202. Narrow bandwidth = CF201 + CF202 + CF203 + CF204.

What you should have is:
CF201 + CF202 (150 KHz filters).
CF203 + CF204 (110 KHz filters).