Meridian America 562 Additional technical information, Clipping and overload, User Guide

Technical information 31

Additional technical information

Understanding input sensitivity in a digital preamplifier

There is no variation of sensitivity for digital inputs. The consumer SPDIF interface defines full-scale in terms of the digital word coming in.

In a conventional analogue preamplifier the input sensitivity is normally quoted as that level required to give rated output when the volume (i.e. gain) is turned full up. In 562 this figure is less important than the maximum input that can be fed to the preamplifier without distortion. This level is sometimes given for analogue preamps as the overload level.

For the analogue inputs of 562, the input sensitivity you select in Gain (see page Error! Bookmark not defined.) is the voltage at which the analogue–digital converter will overload. For some sources – e.g. Radio, Tape or Video this can be very closely defined and the nominal output of the source will be within 3dB of its maximum. For other sources – e.g. turntables, the maximum signal is less well defined and some experimentation may be beneficial. See the section following on ‘How to get the best out of LP’.

Clipping and overload

Input overload occurs for analogue signals that overdrive the analogue– digital converter. We have fitted a Level light to the front panel of 562. If you are close to overload on analogue sources this will flash. The threshold for this light is 3dB below clipping. Ideally you will use a combination of 562 input sensitivity and source output that is as much as possible consistent with this light never – or only very rarely – flashing. An obvious exception to the ‘never’ rule would be on interference signals like ignition noise on a tuner or bad scratches on a record.

How to get the best out of LP

The turntable source is quite unique in the problems it presents to getting optimum sound quality. Obviously the turntable itself must be correctly setup and we recommend you have your dealer check it from time-to- time.

562 has several adjustments that affect the sound quality of turntable sources. Here is a starting checklist.

1.Is the 562 installed far enough away from components which contain mains transformers to ensure that you get no hum induced?

2.Is your cartridge Moving-coil or Moving magnet. Ensure you have the right module fitted.

Pickup cartridges tend to have their output specified at 5cm/s recorded velocity. Normally the maximum velocity found on an LP is 25cm/sec at the outside and around 18cm/s in the inner grooves. 25cm/sec is about the maximum tracking ability of audiophile MC cartridges. Certain moving- magnet cartridges can track up to 35cm/sec but there are rarely these velocities to be found.

On the face of it we could adjust the LP input sensitivity to 5 times the rated output of the cartridge. If we do this then as expected the overload Level light very rarely illuminates. This kind of setting gives three benefits:

∙The maximum digital level for any recording.

562 User Guide