Realistic STA-19 tone section??? Help!

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I wonder if anyone has the schematic for Radio Shack's Realistic STA-19?
There are two tone sections:
On front is a loudness contour switch.
On back is a deep bass eq switch, with excellent results.

Of particular interest is that the input, chip amplifiers and bass eq are arranged for high quality bass. The STA-19 input + tone circuits can fix a PC or Chromecast-audio. Very useful!

I would like to try making an efficient, diy version of the power amplifier + at least the fun bass eq and input section(s). Those are good!

If you don't happen to have the schematic, then do you know where I could buy the schematic?
That's design to learn from. I'd like to find it.
 
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The older model showing the System 7 bass shelf.
It is the system/flat switch
 

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No response in 15 hours? funny thing.
As R****S**** products hardly ever lived long useful productive lives, none of us have the desire to replicate them. I bought a few in my teens & twenties, but always noticed the speakers, with "20 to 20000 cyc/sec" response, sounded like ****. I bought a set of RS headphones in a hurry, the builder let the secret out. Below the 20-20000 spec there was "production tolerance +-20 db". So if any sound came out, it was a good product.
On the schematic you post, notice the transistor # are proprietary. Helpful aren't they.
I found the RS parts were the worst available on the scrap market, too. I quit buying any about 1970 and moved to the TV repair supply, which was no paragon of virtue but at least the stuff worked all of the time. A while, got a lot of short life caps there.
I dived into dynaco in 1970 because the college library had some that played records 18 hours a day.The used ones I bought then still work, many e-caps later. Ratchet up a notch or two and study something successful, not the garbage of the electronic world. Say HH Scott, Macintosh, parasound, marantz, peavey, crown? For line level stuff like tone circuits, Allen & Heath mixers? You can get free schematics on eserviceinfo.com or many repair threads here or on PA systems.
Note RS of the UK and commonweath countries is a respected supplier of genuine factory parts. R****S**** of the US was part of the Tandy corp and known IMHO mostly for lowest first cost sleaze.
The 1.2 w RS amplifier you posted over on the single supply amp schematic thread, those were really funny. I thought you were talking RS of UK. My '59 Fomoco car radio had more power than that with one transistor, but a bigger heat sink I bet.
 
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PRR

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> No response in 15 hours?

Takes hours to trace that drawing. Would have been nice if Daniel had marked it up.

"Flat" is your basic amplifier. NFB is 33K, 470r, 220uFd. Gain is 71, flat to 0.1Hz (other networks will limit bass extension).

"System" takes NFB from both speaker + and speaker -, sensing the return current, thus responsive to speaker impedance. Much of the speaker side is cropped on Daniel's snip, so I don't know all the details, nor would I really care. It is surely optimized for the specific speakers sold for it. "Enhancement" on other speakers will be hit-or-miss.
 

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..."System" takes NFB from both speaker + and speaker -, sensing the return current, thus responsive to speaker impedance....
Thanks for focusing my search!

Sure enough, it blurs instead of audibly clip. So, mystery solved on how they got bass from the Minimus 7 speakers. Partial Current Drive.

There's a similar curiosity at the input. Design is from Panasonic, Technics, NEC. Thanks again--it really helps to know what to look for.
 
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