(...) I have not been able to find this information and do not know how to do so. (...)
That's actually pretty simple, as the input sensitivities for each stage/section are specified, with the input sensitivities telling you the required signal voltages for reaching the rated output power with the volume control fully turned up. So for calculating the phono stage gains you'd simply calculate the gain in dB this way:
gain in dB = 20 x log (line-in sensitivty / phono input sensitivity)
So in case of your Marantz, that would be not quite 38.9 dB for MM and a tad over 59.6 dB for MC.
And of course you could also determine the line-level stage gain the same way with the main-in sensitivity and the line-in sensitivity. The result being a tad over 17.2 dB.
Whereas for calculating the power-amp stage gain you'd first convert the rated output power into a corresponding output voltage (P = U x I = U² / R, so U = (P x R)^0.5), which in case of your Marantz would be (60 W x 8 Ohm)^0.5 = a tad over 21.9 V. And then you can use the same formula once again with that corresponding output voltage and the main-in sensitivity - the result being a tad over 22.7 dB.
(...) I think I should wisely stick to someone suggestion that I just have to crank the volume of my amp. (...)
I was too a bit worried about using an external phono stage to boost the gain further ( like with the Fosi x5) at the expense of loosing headroom, and possibly get distortion and hiss. (...)
Well, regarding the former, you could certainly do that. Which also wouldn't really mean, that your Marantz would need to work harder than with the higher input level from CD, btw, because its volume control acts as a variable voltage divider, so its position simply determines the share of the input voltage delivered by the line-level sources (or respectively the phono stage), that goes into the line-level stage.
And in case you'd wonder about the level difference: In case of digital sources there's a pretty hard limit in form of the 0-dB-full-scale mark, and in case of typical CD players for home use the corresponding output voltage typically is ca. 2 V(eff.) for unbalanced outputs. Whereas in case of records there not only already are at least three somewhat different typical 0 dB marks (namely JIS, NAB and DIN), but in practice so-called "hot cuts" may also exceed these marks pretty considerably. And then phono cartridges also vary pretty considerably in terms of output voltage - like for example in the realm of models intended for MM inputs from ca. 2.5 mV (high output MCs and low output MMs and MIs) up to over 10 mV at 1 kHz and 5 cm/s in 45°/stereo modulation (some DJ/broadcast models). Hence the gain of non-gain-adjustable phono stages is typically chosen somewhat conservatively to provide a reasonable headroom/overload margin.
Anyway, back to your Marantz: If you'd download the service manual for that, you could see, that it's a pretty classic design with electromechanical signal switching via relays in the input section of its pre-amp section - and in case of its line-level inputs there aren't any active stages, before the signals go into the volume control pot in front of the actual line-level stage (except for the CD input, that is, which sports a little unity-gain buffer in form of an OPA2064 opamp, but only for feeding the record outputs - and that is fed with a symmetrical supply voltage of ,+/- 18.2 V, so that it has quite a bit of reserve for pretty hot line-level signals...). Which means, that going for an external phono stage with higher gain(s) wouldn't really be a problem, in case you'd like to reduce the volume control position difference between CD and phono.
Greetings from Munich!
Manfred / lini
it's always something off or needed to tinker with endlessly , I've forgotten about for 25 years ( or cassete tape ? *shrug* )
