On 17/01/17 19:53, Roger Hayter wrote:
The Natural Philosopher wrote:

On 17/01/17 13:51, Andy Burns wrote:
Dave Plowman wrote:

DerbyBorn wrote:

You can now buy a turntable for about £50 to output to a MP3 file.

Neighbours had to send back two, to get a third working one, I haven't
heard the results.

it was never simple making a good sounding RIAA preamp.

Do that in software on the PC.

still got to do a proper input buffer-with-gain stage though.

As I vaguely understood it, it was necessary to do the correction in the
first stage for noise reasons. BICBW, and that might only have been a
practical limitation at the time.

well if you do it at too high a level, you may end up clipping before
filtering.

IN general the input stage boosted form a nominal 2mV or so at 50K ohm
impedance, to a corrected few hundred mV. You could have put the RIAA
filter after that, but why bother? Wrap it as feedback on the input
stage so the output of that is neat and normalised with respect to
volume and frequency response.

It was just the neatest way to do it.

There was only a 65dB S/N ratio on a typical pickup anyway, due to
thermal noise in the wires. You could generally design carefully for a
couple more dB of front end noise at the worst.

Hardly CD quality.




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"In our post-modern world, climate science is not powerful because it is
true: it is true because it is powerful."

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