Re: Pre-amp for Linsley-Hood?
The original Cambridge Audio P40 used shunt feedback on a flat frequency response buffer input stage, with the volume control in the feedback arm. It does indeed sacrifice 14dB of S/N, but it meant that nothing in the preamp could overload before the power amp clipped.
That was important because a series feedback input stage with RIAA correction wrapped around it has very little loop gain left once the +20dB bass lift is in place. So warps in particular can push the input stage into overload.
When P40's were supplied for trial by the main Swedish radio station, they came back and asked what the frequency of the rumble filter was. There wasn't one. What was being interpreted as rumble in a conventional circuit was low frequency distortion artifacts resulting from warps in the record.
Which was actually a pretty radical design for the late 60's - a two transistor virtual earth shunt feedback buffer with volume control. And sure the noise was higher, but still OK as compared with noise from the vinyl itself.
Craig
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