Tweaks of the high fidelity tuner Sony ST-S555ES

All electrolytic capacitors within the signal path will be either replaced by MKT foil capacitors (where possible) or smaller MKT foil capacitors will be connected in parallel to improve the high frequency behaviour. The operational amplifiers within the AF signal path will be replaced by better ones. The voltage/current converter in the output stage will be removed as it makes the sound worse compared to a direct output. An additional advantage in doing this is that the power supply branches of the removed amplifier can be added to the remaining amplifier stages leading to decreased influences of the AF signal on the power supply lines.

After these modifications have been done no further readjustments are necessary. All component names refer to the schematics and are also printed on the pcb.

All modifications are done on your own risk and lead to the cancellation of any warranty.

See also the comments from people who did some of the modifications.

The modifications in detail:

Open the case:
1. remove the 4 screws on the side walls.
2. remove the lid.
3. remove both nuts from the antenna connectors.
4. unscrew the earth connection from the input pcb to the main pcb at the side wall and lay the input pcb onto the main pcb.
5. unscrew the earth connection from the tuner module to the side wall.
6. unscrew the output socket.
7. unsolder the earth connection at the output socket.
8. remove the 6 screws which hold the main pcb in place.
9. remove the 2 screws which hold the mains transformer.
10. lift the mains transformer together with the main pcb and let the main pcb rest in vertical position leaning against the front wall. Keep the transformer in this position, preferably using a vice.
Carry out the modifications:
- Replace the 10 µF electrolytic capacitors C221, C271 and C143 by 10 µF MKT foil capacitors.
  The MKT foil capacitors are quite big and must be mounted in vertical position. The upper contact then has to be connected to the main pcb using a short isolated cable. It's not easy but possible.
  When later moving the case you must be careful because these capacitors are mounted with only one fix contact.
- Connect 100 nF MKT foil capacitors parallel to each of the electrolytic capacitors C154, C155, C218, C219, C201 and C202.
- unsolder IC103 (TL071, composite signal amplifier) and solder in a socket. Plug in a OPA134 or OPA604 (both made by Burr-Brown).
  In principle you can choose any single fet input operational amplifier which is compensated for amplification of 1 and has better performance than TL071 regarding slew rate, band width, noise and distortion.
- unsolder IC203 (TL072, AF output stage) and solder in a socket. Plug in a OPA2134 or OPA2604 (both made by Burr-Brown).
  In principle you can choose any dual fet input operational amplifier which has better performance than TL072 regarding slew rate, band width, noise and distortion.
- remove IC204 (TL082 or NE5532, voltage/current converter).
- cut the connections to R216 and R266.
- connect R224 and R226 in parallel.
- connect R225 and R227 in parallel.
- unsolder the connection cables to the proprietary output socket and solder a solder base point at the earth contact of the main pcb.
- mount two (preferably gold plated) cinch sockets at the rear wall (there is enough place). Be careful while drilling the holes and prevent metal remains falling onto the PCB. Vaccuum clean afterwards!
- connect the earth pins of both cinch sockets to the solder base point at the main pcb (where before the output socket was connected).
- connect the life pin of the cinch socket for the right channel with pin 7 of IC203 via a 51 Ohm resistor.
- connect the life pin of the cinch socket for the left channel with pin 1 of IC203 via a 51 Ohm resistor.
remount the case:
1. put the mains transformer and the main pcb back into the horizontal position.
2. remount the transformer with both screws.
3. remount the main pcb with the 6 screws.
4. solder the earth connection from the bottom of the case to the solder base point at the main pcb.
5. remount the old output socket (without any internal connection) on the rear wall.
6. remount the earth connection from the tuner module to the side wall.
7. remount the earth connection from the input pcb to the side wall.
8. remount the input pcb with the two nuts at the rear wall.
9. put on the lid and screw in the 4 screws at both side walls.

Have fun listening to your new tuner. The gain in sound quality is quite unbelievable, especially when listening to stations which deliver uncompressed music. Stereo imaging and high frequency reproduction are comparable to CD reproduction.

Appendix

The schematics are available for a price of DM 22.- (as from 8/97) at:

Schaltungsdienst Hientzsch

Kantstr. 6

D 21629 Neuwulmstorf

Germany

Tel: +49 (40) 7008696
You can download extracts from the service manual which should be sufficent to do the modifications:

an extract from the schematics as GIF image(90 kB) or PDF document (109 kB)
an extract from the PCB layout as GIF image(184 kB) or PDF document (261 kB)

MKT foil capacitors are available e.g. from Wima.

Read comments from people who did some of the modifications:

Mantis Cheng writes:

Well, I have done a few more mods according to your instructions. I replaced all op-amps with OPA134 and OPA2134, including the TL082 voltage/current converter. I didn't remove the V/I converter. But, I added a .1uF bypass cap across the electrolytic coupling caps in the magic box, which I believe convert the current back to voltage.

The sound is even better. The highs (e.g., cymbals and violins) are crisp and have the "right" amount of decay. For the first time, I can hear the ambience (the room) in the radio announcer's studio. I can hear a buzz on some stations' transmitter. I am very happy with my mods. The tuner does sound closer to CD now.

I taped some FM Jazz music before I made last few mods. Now, when I compared the old tapes before the mods to the new ones, I really noticed an improvement in the highs and in the ambience. The soundstage is deeper with the increase in ambience. The clarity also improves the layering in the soundstage. The instruments don't run into each other; each seems to have its own space.

URL: http://www.huennebeck-online.de/mod/ST-S555ES-english.html
Last change: $Date: 2003/05/01 21:49:33 $

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