I have a luxman R-115, and there are two features I don't understand. The first is a button, next to the tone defeat, labelled "subsonic." The second is a button with a green indicator light labelled "cd-straight" If anyone could explain these to me I'd appreciate it. Thanks
Subsonic filters are typically used for filtering the signal of the phono input. They exist to minimze the amount of power consumed by a poorly matched arm/cartridge combination, motor rumble and warped discs. If you take the grills off your speakers and the woofers are pumping away as you play any source material, you can engage the subsonic filter and that should stop the woofer action.
CD Direct takes the signal from the CD input and bypasses the tone controls and any other ancillary functions of the pre amp beyond just the volume control. It is meant to clean up the signal path though it would be unusual to hear a difference in most cases when the signal is bypassed or run through the pre amp.