As Newbee points out, the answer depends on whether you already have a way to control the volume and to switch between source components (if you're using more than one). If you have an attenuator in the amp or in your source component, that's one piece of the puzzle possibly solved, although there's still a question of the sonic quality of the built-in attenuator versus one that would be in a good separate preamp.
If you have multiple source components, you can either plug and unplug the interconnect cables at the back of the amp to change sources (lots of wear on the connectors with this approach) or you need some switching capability (this would be provided by the preamp).
If you're OK on these points, there then is the question of whether your source can drive your amp to full output (some may be able to, others cannot - you'll hear this in the dynamic range of the output from the amp). For lot's more information, search the archives for "passive" preamps and linestages.
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If you have multiple source components, you can either plug and unplug the interconnect cables at the back of the amp to change sources (lots of wear on the connectors with this approach) or you need some switching capability (this would be provided by the preamp).
If you're OK on these points, there then is the question of whether your source can drive your amp to full output (some may be able to, others cannot - you'll hear this in the dynamic range of the output from the amp). For lot's more information, search the archives for "passive" preamps and linestages.
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