[chadh]

I've noticed that, often, headphone amps are capable of being used a pre-amps.  I'm wondering, then, whether (in general) a pre-amp can be modified slightly to be usable as a headphone amp?  Obviously, one might need to add a headphone jack.  But, other than that, what else needs to happen?  Or does this depend significantly on the topology?

I'm wondering this as I have a tubes pre-amp that I hope to replace at some stage.  But if I could convert it to use as a headphone amp, I might be interested in pursuing that option.

Chad

[peranders]

The answer to your question is yes....

Pre amp used as headphone amp => the amp must be able to cope with 30-100 ohms load with low distortion

Headphone amp used as preamp => the amp must be able to have low noice and low gain.

All my headphone amp designs can be used as preamps

[chadh]

Thanks. 

Pre amp used as headphone amp => the amp must be able to cope with 30-100 ohms load with low distortion

What determines whether the amp can cope with this sort of load with low distortion?  i.e.  How do I know whether the pre-amp I own is a good candidate for adapting for use as a headphone amp?

Chad

[peranders]

The driving capability determines that and this can be found in a datasheet if opamps are used, otherwise you must have some design skills to get a picture of that.