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[ARSCLIST] RIAA phono EQ and Neumann time constant

I've been thinking about the RIAA phono EQ curve, and realized that
the majority of discs in Europe and many in the USA are cut on 
Neumann lathes.

The Neumann lathes have a fourth time constant of 3.18 microseconds
(50 kHz turnover) which was introduced around 1968 to increase 
cutter life.

When a disc cut on a Neumann lathe is played back on an RIAA phono
preamp, the frequencies between 10 kHz and 20 kHz are more rolled 
off than they should be.  Discs cut on a Neumann lathe will play
-0.2 dB at 10.9 kHz and -0.64 dB at 20 kHz.  If your average phono
preamp is -0.5 dB at 20 kHz, that means that you could be off by as
much as -1 dB or more.

I know there are many more things to think about, like the accuracy 
of the cartridge frequency response, the cartridge loading, the vinyl
wall stiffness, etc. and that the sum of potential errors in phono 
reproduction is fairly inaccurate to begin with.

There's also the bigger unknown of whether the cutting lathe was 
in or out of spec.

I also know that most discs cut in Europe since the late 1960s were
cut on Neumann lathes, but figuring out what was cut on Neumann lathes
in the USA is more difficult - perhaps half of all lathes in the USA
are Neumanns. [visually, you can identify a disc cut on a Scully 
automatic lathe, but that's about it]

What do people on this list think about this Neumann lathe time constant
and it's influence on RIAA playback accuracy?  Is it important, or not?
Should European cut RIAA EQ discs be played back on a phono preamp that 
has RIAA EQ plus the Neumann lathe time constant?

Eric Jacobs

The Audio Archive
tel: 408.221.2128
fax: 408.549.9867

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