Preamp/Integrated with Loudness button

Like others stated, all Luxman, many or all Yamaha have them and they have models for most any budget.  It could be my favorite feature on my 509x.  

My t+a has adjustable loudness 

The Lyngdorf TDAI 3400 does everything including room correction, it’s comes with mic and stand, it sounds superb and has bass & treble where you can set the effective frequency, plus multiple preset ‘voicings’ and the ability to create your own. Very comprehensive, very flexible, very cheap for what it does.

I prefer to have a simple push button 'Loudness' ON/OFF solution. Don't want me to customise it. For that, we could use 'Bass/Treble' control or even go for a miniDSP. I have an Yamaha entery level integrated. The variable loudness switch is almost useless for me. It doesn't give the desired 'punch' the way I get from, now retired, B&K pre.

I think the best bet here is Luxman & we should thank them for keeping the legacy.

Check out Vincent Audio Preamps and integrateds. Sold by Audio Advisor.