With so many stereo valve amplifiers having been designed for the high output of CD players, and phono stages in general outputting 775mV (0dBu) or much less, matching phono stage outputs to valve amplifier inputs has become a problem for valve amplifier users.
Increasing phono stage gain to match levels is often not an option. Much depends on the power rails because they need to allow for sufficient headroom with an analogue signal.
Digital signals don't need any headroom (overload margin) because 0dBfs is the maximum signal level, and they compress the average signal levels to bring them up nearer 0dBfs, and everything sounds loud (but often false).
Vinyl however can peak 14dB above stated output - a 3mV output cartridge can output 15mV on transients (all relative to 1kHz, of course).
In fact most phono stages are able to almost match the volume of CD, but for CDs extra compression. So therefore there is a need for additional gain so the valve amplifier user can enjoy using a great sounding phono stage.
A 5 volt power supply will not clip a 1.75 volt digital signal, but will severely clip a 1.75 volt analogue signal.
And if analogue needs to compete with a 2.3 volt to 2.8 volt digital signal, it needs at least a 40 volt power supply so that transients aren't clipped.
Phono stages usually don't use such high voltage power supplies so the gain cannot be increased.
Therefore a gain box for matching lower level signals to hi-fi valve amplifiers is a good idea.
We recently designed a 48 volt PSU1 power supply especially for high output voltage gain stages. This makes it possible to make a gain box able to swing large output signals suitable to drive the fairly insensitive inputs of stereo valve amplifiers.
It is therefore our intention to manufacture a gain box "matchbox" which the valve amplifier user will find invaluable.
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