Spatial Audio Raven Preamp

Hello jc4659,

I have replied to your message a few days ago. I hope you received it.

Thank you.

I've had a Raven for about six months now and am loving it. I've only ever had cheap headphones but I'm about to buy some good ones, so I'd love to know more about the headphone amp capabilities of the Raven. All I've read so far is that the Raven needs 'phones that are 200 ohm or greater. I've settled on the ZMF Atrium Closed as the cans I'll probably buy; they are dynamic driver, 300Ohms and 96dB/mW. Does the Raven have enough power to drive these to a satisfying loudness? I'd love to hear from @lynn_olson  or @donsachs  about the headphone circuit in the Raven. Is it just a chip amp inside, or does it utilize the tubes, etc.  How good is it compared to a dedicated headphone amp. I'm hoping it's quite good so I won't have to complicate my system with a dedicated headphone amp.

Would also love to hear from other Raven owners as to what headphones they've used with the Raven.

There is no headphone circuit in the Raven. There are different taps on the output transformer, like a tiny power amp, and the headphone output is simply a different turns ratio. You could use planar headphones with a 30 ohm impedance ... nothing would harmed ... but distortion would be higher than we would recommend, so we advise against it. But it would certainly work, music would play, nothing would overheat or crash, and no transistors or fuses would short out. The power supply would not care at all.

All that happens is the tubes see a low impedance load, that’s all. Distortion goes up, not catastrophically, but a fair amount. So our advice to stick with 200 ohms or higher isn’t meant to scare anyone. This is not like connecting 1-ohm speakers to your favorite receiver and blowing the protection circuit, or taking out the output stage.

There’s no protection circuit, there are no transistors at all in the signal path, and the 6SN7 is designed to operate with a watt or two on the plate. Unlike transistors, tubes like high temperatures, and don’t need heat sinks. All that happens with low impedance headphones is an increase in distortion, nothing else.

It’s hard to convey just how simple the Raven is. The entire signal path is: input jacks -> input selector -> custom input transformer -> Khozmo balanced volume control -> 6SN7 in balanced mode -> custom output transformer with various output taps -> output jacks. There are no circuit boards in the audio path, all signal wiring is hand-soldered point-to-point.

That’s also why the Raven has a medium price by high-end standards. There’s a lot of labor in every single part, most of all, the transformers, vacuum tubes, and final assembly. By contrast, a circuit board filled with op-amps inserted by pick-and-place robots would be about 1/10th to 1/20th the build cost of a Raven. That's why Shenzen-made products are so inexpensive ... op-amps are cheap, and robots can fill a circuit board in moments.

Lynn, thanks for the info. I see that the Raven specs don't give an output impedance spec for the headphone output. Is it different than the pre-amp's output impedance of 293 ohms?