RIAA vs Columbia vs Decca

Reissues are most certainly RIAA. I can't imagine any modern recoding engineer using anything else.

Does anyone know of a switchable unit which can fit, say in between a phono stage and a line amplifier, to enable switching between these curves? (I have an Aesthetix phono stage feeding an Audio Research line preamp...)
Or is there an equalisation circuit that anyone knows of which can be adapted for this purpose?

Vintage, Such a device as you propose would have to operate on an already RIAA-equalized signal from the phono section. That's a whole different kettle of fish from applying an alternative equalization curve within the phono stage circuit itself. You'd be better off (less coloration, less noise, etc) just using bass and treble controls on the linestage, IMO.

Chakster, Ralph's post makes a lot of sense. But I was also wondering about the phase issues to which you refer. The very act of equalizing the signal must introduce capacitors, resistors, and, in some phono stages, inductors into the signal path. This will inevitably affect phase, whether the device or the recording is "vintage", or not.

Phase shift is removed by the act of equalizing. It was put there by the pre-emphasis network during the mastering process. So when you play it back its removed.

Vintageaxeman, The curves referred to in this thread are an urban myth, other than the RIAA curve itself. This is why you don't see switchable EQ curves on modern electronics.

Lewm, I think Chakster was referring to "Absolute Polarity". That will open up a can of worms. Some claim that it makes a difference, others claim that they can't hear any difference. I believe JGH was in the latter camp. I definitely reside in the former. That said, older LPs are all over the map when it comes to polarity. Even new releases do not always hew to the standard. Diana Krall's album "Quiet Nights" comes to mind. The new Eva Cassidy releases which are compilations from various sources has some songs recorded in positive polarity and some in inverted.

If you think about it, air is not a linear medium. One glance at the adiabatic pressure/volume curves of an ideal gas will convince one of that. This results in the asymmetric distortion of the sound wave. Common sense would suggest that inverting an asymmetric wave will change the sound. I guess the take away here is if one's system - ear/brain is sensitive to absolute polarity then it is very handy to have polarity invert on remote control.