Earphones driven by preamp RCAs?

What are the advantages/disadvantages of driving headphones off the preamp RCAs (my pre has no earphone jack)?

The eaphones have an impedance of 300 ohms. The preamp has an output impedance of 325 ohms, SE. For good listening, I need to turn the preamp volume to about 12:00.

Would a preamp with a phono jack, or a dedicated preamp do a better job?
I have a 'phone amp. It has rca inputs-- I would just guess this is why they make HP amps. I'm curious to see what others say.
The jack ain't the issue; it's what's driving the jack. You preamp has a relatively low output impedance and does a fair job of driving the phones. However, the fact that you have to set the VC at 12 o'clock suggests that there's not much power output available.

A dedicated phone stage, regardless of the output jack, will have more power and a lower impedance. The result will probably be lower distortion.
Thks,Kr; I kinda knew it had to be something like that.
I believe matching the pre output and headphone input impedances will maximize the power transfer. So, anything else different between a pre with headphone jacks and one without?
I am also interested in finding out more on the topic....lately I find myself browsing through the for-sale ads for headphones, but my current setup (pre, cdp or amp) does not have a headphone jack. It would be great if I could avoid buying a separate HD amp. I'll be keeping an eye on this thread...
It may maximise the power transfer but if there isn't enought drive power to begin with it won't matter.
Antique Sound Labs (ASL) makes an impedence matching device specifically for driving headphones from a high voltage pre-amp RCA output. If anyone wants more info, email me off-forum.
I have plenty of volume at 12:00 - that is not the really what I am interested in here.

What about the quality of the sound? What if I compare my headphones on the pre, to my headphones on a headphone amp RCA, to my headphones on a pre with a headphone jack? Sure, the answer will depend on the specific units compared, but how do they compare in general? What are the pros and cons? If I wanted to get the best sound, which direction would I go? Or are all three just as capable?

If I already own a fantastic pre (RCA out only), would there by any reason to add a headphone amp?

1. In general, a well constructed purpose-designed device, like a headphone amp, will be superior, for driving headphones. Note, they have a much lower input impedance than that of the average amp. Of course, such a general statement is irrelevant when you get to real-world specifics.

2. Just because it's loud enough does not mean that it has enough power to work into that load without distortion. A 12 o'clock setting is pretty high (in general and without knowledge of your preamp or the gain curve of the pot). Is that where you set it to feed the amp/speakers?

3. Why not just try a decent headphone amp and see for yourself if it is better? Surely, there are web dealers with a useful return policy.
Kr4: For the same volume, the speakers are at 9:00.

Lets get more specific. My pre is an ARC LS 25 MKII. Can I do better with a headphone amp?
Hard to answer as I've never used one. However, ARs tube units have more than decent line driving.

My advice stands: Try a good headphone amp.