And how relevant is that to the OP's issue, the sensitivity of the Sansui, or the price of fish?
Answer: it's not.
He probably needs to consider some much better speakers IMO.
The output level of CD players was an
industry standard (for the 30 Japanese manufacturers in the consortium) of a nominal
2V RMS at 0dBfs. That translates to 5.66V PP. The front end impedance of the AU-9900 is rated at 50K.
Here is a typical CD player loaded with 10K ohms at full output:
View attachment 1295736
You are off on a tangent. Study the schematic.
The front end buffer stage is
after the 250k volume pot. Overload is a non-issue in this particular case- he doesn't have the volume wide open or the amplifier anywhere near being driven to overload, either at the front end, the back end, or in the middle. Also, you have no idea what it will take to overload the AU-9900
front end. Even at the wide-open position- I can assure you it will be a whole lot more than 130mV.
Just for fun, try to overload the
front end of a typical 150mV sensitivity preamplifier line stage and report back here with your findings. I'm happy to do the same with any number of preamplifiers and integrated amplifiers I have here if you cannot.
Where you have a high sensitivity line level buffer/gain stage
before the attenuator/volume pot, overload from CD level sources could conceivably be a problem, but this is
not the case here and is extremely rare except in some really ancient stuff.
Again, he is not talking about overload, in fact quite the opposite, he has to turn the volume pot further than he is used to. That is common with some models of Sansui. Again, it not the sensitivity*, it is the psuedo log/linear taper they used.
I have several AU-xxx series amps and they are the same- it was a Sansui thing.
* most amplifiers of that era had a 100-150mV into 50K for full power into a line (aux) source.
The Sansui concerned also has a three position 'level set' in addition to the -20dB muting cascaded one after the other. Hopefully that is set to the normal position too.