As Viridian suggested initially, be wary of that old cartridge. If the cartridge has been sitting unused for a decade or more, it's very possible that the cartridge suspension has stiffened to the point that the it is no longer useable. Not only will the sound be bad, you risk damaging your LPs. Viridian's suggestions for a replacement are cost effective possibilities.
If you're think the cartridge is fine, you may have a some short in the connecting cables from cartridge to phono stage or phono stage to preamp that is shorting the signal and reducing the volume. Check your cables and connections carefully to ensure that they are clean, tight and don't have any stray wires touching a ground.
If you can try the phono stage in someone else's system, that will give you confidence it's not a factor (or confirm it's defective).
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If you're think the cartridge is fine, you may have a some short in the connecting cables from cartridge to phono stage or phono stage to preamp that is shorting the signal and reducing the volume. Check your cables and connections carefully to ensure that they are clean, tight and don't have any stray wires touching a ground.
If you can try the phono stage in someone else's system, that will give you confidence it's not a factor (or confirm it's defective).
.