• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube Amp for Headphones

I'm going to have to say you are correct. I'm not sure why I did that t-pad originally, it was a while ago. 😱 It worked for me. But I'll have to agree with you, no reason for the 30R resistor. Of course as someone else mentioned, those values need to be calculated for the particular amp and attenuation needed.

I'm just trying to understand the logic of the 30r resistor. Protection ?
 
Long ago the IHF standard for headphone outputs had some series resistance added for some reason or another. For the practical purposes of that circuit, if you plugged in 32 ohm headphones, we would all assume that they are very likely quite sensitive, and the 30R resistor would pad them down a lot more than your not so sensitive Beyerdynamic 600 ohm headphones.

That all falls apart when you have low impedance planar headphones, but that wasn't really a product that existed when these ideas were originally being thrown around.
 
> the 30R resistor would pad them down a lot more than your not so sensitive Beyerdynamic 600 ohm headphones.

Long ago I plotted a LOT of late 20th century headphones, SPL vs Z, and came up with "27 Ohms" as a best-fit to equalize SPL from all models. And 27==30==32 for any practical purpose.

The second consideration is how this interacts with impedance bumps. At that time my mild investigation suggested that while some hi-Z cans had significant bumps, the "32r" buds were mostly very flat Z. So another 27r was no big deal. Of course your mileage may vary. I was working on headphones amps which could be designed for 27r large signal internally to limit output on lo-Z phones and still give low-Z on small signal.