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Realistic STA-20

Solid State AM/FM Stereo Receiver (1975-76)

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Realistic STA-20


Tuning range: FM, MW

Power output: 7 watts per channel into 8Ω (stereo)

Frequency response: 20Hz to 20kHz

Total harmonic distortion: 1%

Input sensitivity: 3mV (MM), 150mV (line)

Signal to noise ratio: 60dB (MM), 60dB (line)

Dimensions: 16.25 x 5.25 x 12 inches

Finish: walnut grain case

Year: 1975

Price: USD $159.95 (1975)



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Reviewed Sep 16th, 2017 by Virginia

This Realistic AM-FM Stereo Receiver is a rare and excellent machine. I have used it as my primary amplifier for a number of years. At some point Radio Shack brought out the Olympus STA-20 AM-FM Stereo Receiver which is a very different machine in form. I like its looks and features which are typical of the Realistic stereo receiver-amplifiers of the time. It was a mid-range price device in a field of quality like amplifiers that Radio Shack was building.



re: STA-20

If anyone`s looking for a service manual for STA-20, the SM for STA-21 is the next best option. Schematics and board layouts for preamp and amp are identical save a few details, alignment procedures apply, voltages on schematics are close enough or identical. Tuner section is a bit different electrically and the board is different, but service and alignment is also doable using the SM for the STA-21, if you have a bit of practice.
1) The preamp is a weird design integrated with RIAA section, that caused some problems with excessive noise in my unit.
2) Some signal cables are unshielded and introduce noise to the preamp, need replacing.
3) Power switch on the volume knob collides with preamp board layout, some components are placed on the solder side of the board.
4) Replacing noisy transistors, especially in differential amps (amp board), is a good idea, so is full recap.
5) Preamp board is very unpleasant to work on while in the unit, lots of those pesky silver coated poles with wires wound on them, tuner dial gets in the way plus mains voltage near the volume potentiometer. Beware.

re: STA-20

No, it isn't an amp or preamp problem, it's the MPX and also the FM tuner seems a little weak IMO, don't know how to describe it so well except weak. The computer will make the stereo light and MPX sputter or just howl as well between channels. Mono is solid if you are tuned in good, the lack of a manual muting switch is a pain. Right now I'm using the tape out and monitoring it from my Pioneer SA-6500 II. I'm using a simple dipole made with speaker wire, I use the Pioneer, it's tuner sister and some Akai components in my recording setup in the second bedroom work desk.

Yeah, there is the bare minimum to this to do some basic task but it's rather barren to me. I use a small Pioneer receiver from the early eighties and an audio time for an alarm clock. at least it has more stuff. It is a nice sounding set though. Old Shack stuff is fun in it's own special way, warts and all.

re: STA-20

The excessive noise I mentioned was caused by unshielded signal cables (tape out, phono from preamp to source switch and back etc.) and overall bad state of the unit caused by age and previous repairs. Full recap, replacing cables and some transistors helped greatly: the unit`s own noise (mains hum mostly) on aux setting starts to be heard at the volume turned up to 3/4, before it was pretty noisy at 1/4. The tuner section still needs work, since previous "repairman" damaged ferrite cores in two tuning coils and misaligned it badly. I`ll get around to it, eventually.

re: STA-20

In addition to "TinkerTom"'s good comments, there is a schematic diagram on page 11 of the STA-20 user's manual posted on this site. Although service manuals are difficult to come by for the Realistic receivers, at least many of the user manuals of that vintage contain a schematic on the last pages, although they may be hard to read because of the paper size.

Also, there were actually three STA-20's built: catalog #31-2025 (1966-67); catalog #31-2055 (1975-76); and last, catalog #31-1979 (1990-) under the "Optimus" brand.

re: STA-20

The schematic in the user manual for the STA-20 has no voltages on it, so it`s rather limited in terms of troubleshooting, especially for someone not very experienced as myself. However, having it I realized that the STA-21 is almost identical in the amp and preamp sections, the PCB layouts apply to the STA-20 and were of great help to me. If not for that, my attempts at repairing it would be even more disheartening than they already were. Servicing the preamp board was a tedious nightmare beyond economical sense.

re: STA-20

It's gonna take some elfin magic to get that schematic in a state that I can save as one page and get up to a size I can read.

re: STA-20

I know what you mean, I just extract pages with parts of schematics to images, then join them manually in an image manipulation program and save as one image. Most of the time I also cut out sections of the schematic I work on at the time, say amp or preamp, and save as separate files. Tedious, but saves a lot of frustration later.

re: STA-20

That newer STA-20 was an OPTIMUS. and I'd sure like to have the service manual for it, it needs at FM alignment. It's a doozy, AM sound is nothing to write home about like you'd expect for such a thing but the amp is pretty nice and the FM is also pretty good for weaker stations, once you get a simple wide dipole on it. I use it with one of my computers and cannot complain at all.

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