"loudness’ is sooooo misunderstood, back then, and more so now. a ridiculously named feature.
It is not a button or switch per se, but an EQ circuit that is engaged or not, via button/switch/potentiometer connected to the loudness eq circuit.
It should ONLY be engaged below your ’low normal’ volume.
It should be progressively engaged as volume decreases below ’low normal’.
The PROPER coordination of the ’normal volume control’ and the ’loudness volume control’ (or loudness circuit on/off) was/is tricky. Some vintage amps had two volume controls, one to use only for low volume listening.
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The Chase unit I mentioned has been mis-applied by many, they hate, some trickily disable the loudness circuit.
proper setup:
1. Chase at factory default volume (no ’loudness’ is involved at default).
2. Preamp or Integrated volume set to ’your normal low’, i.e. focused listening, just not loud.
3. Use ONLY the Chase for Volume after setting #2 above.
4. Chase UP is simply less attenuation.
5. Chase Down begins and progressively engages their adaptation of ’Fletcher Munson Loudness EQ’ as volume is reduced (further attenuated).
NOTE: If you raise the Preamp or Integrated above ’normal low’, and lower the Chase unit to get ’normal low’, then the ’loudness’ is engaged at normal volumes, thus tubby bass, simply misunderstood, mis-used..