dsavitsk

Meet the Fonkens

It is probably not ideal, but it is also not necessarily a huge concern. My experience says that the lower the Z out the better for Grados, but anything up to about 8 or 9 ohms will have a decent damping factor, and assuming enough current will perform fine. You could, of course, use a stepdown transformer/autoformer of some sort to improve things.

Output impedance for a cathode follower is approximately ra/mu, or 1/Gm. For the standard 6080 used in a headphone amp, this is about 150 ohms (the reason they work at all is because there is a ton of current -- here's a good article on this). Less than warmth, this high Z out really just leads to flabby bass and lack of control for Low Z phones. OTL does often have warmth, but note the 3 signal path caps (output, interstage, and Rk bypass for the driver) in the standard design, plus the several PS caps that are also in the current loop.

Sorry I didn't quote that very well. I was attacking the article, not the messenger. The increased 2nd harmonic theory is stated over and over and has come to be accepted as truth. But, as I say, there really isn't any good evidence that it's true, and indeed, there are lots of reasons to think it is false. The cap theory is mine, and my experience seems to be that if you get the caps out of a circuit, you lose that sheen and bloat, but it could certainly be something else, too. -d

Better? http://www.youtube.com/watch?v=RzOQbmtzw2U

Thanks for the welcome!

Tubes do not "add warmth". Tubes are very linear devices -- much more so than transistors. The most likely culprit of the "added warmth" in many tube circuits are the multiple capacitors in the signal path, which do add warmth and distortion in spades. These can be designed out in many cases, but doing so is exceedingly rare. I've almost never seen it done in commercial gear. Also, the 2nd harmonic distortion thing is a dumb myth. If you want to convince yourself of this, use your computer to add 2nd harmonic distortion while you listen. It will not make your solid state gear sound like tube gear. It will make your solid state gear sound like solid state gear with a high 2nd harmonic component. Tube gear often sounds good in spite of the 2nd harmonic distortion, not because of it.

None of these (other than the EL34's) appear particularly valuable. These are about equivalent to the 6CD6GA. Decent power tube, but has a lowish screen grid limit. Could be used for a few watts in a power amp -- I wouldn't both for headphone duty. http://frank.pocnet.net/sheets/127/7/7867.pdf Here's a schematic using one, which you'll notice uses a lot of your tubes which may not be coincidence: http://www.triodeel.com/du1a475.gif Another low power output pentode (much lower power than the one above). Might be useful for a transformer coupled SE amp of some sort -- good for a couple of watts pentode, or less than a watt triode. http://frank.pocnet.net/sheets/127/2/25C5.pdf Close to an EL84, lower plate voltage iirc -- one of them is not going to do much for you.