My first (noob) attempt with speaker amps and Abyss Phi TC
I have recently sold my XI Audio stack (Formula S w/ Powerman) in order to move to an amp which I can use for both my Phi TC and high sensitivity loudspeakers.
I have already booked / planned a few auditions in the next few weeks, but in the meantime, I decided to give a chance to my 25 years old Audio Note OTO, a push-pull (4x EL84) class A tube amplifier with 12W on 8 Ohm.
I am sure the Oto designer never thought it could be used for driving a headphone, and that was apparent as soon as I plugged in the Abyss – via an XLR > banana adapter – into the speaker taps, and I was welcomed by a clearly audible background noise even at zero volume.
I tried grounding the amp and, while the buzz I could hear from the outside disappeared almost completely, the background noise through the drivers remained.
First lesson learned: don’t take for granted that the relatively low sensitivity of the AB-1266 is a protection against background noise. Hopefully, modern speaker tube amps will perform better than my Oto in this respect.
Second lesson learned for me: even with a modest 12W on 8Ohm, I had relatively small volume knob rotation available before getting to excessive loudness levels. With the DAVE in pre mode (-3dB fixed volume, 3V output over RCA), I could only use less than 20% of volume.
Obviously, there is more than W and Ohms to consider to project the driving capabilities of a speaker amp to the Abyss. I mean, by simply scaling 12W on 8ohm to 47Ohm (Phi TC impedance) I estimated about 2W of power, i.e. less than the Formula S, but this is obviously not the case ...
Can you experts out there please explain what is going on to this noob here?
Coming to the sound, the presentation via the Oto was apparently different, with a thicker, denser character, especially in the lower midrange down to sub-bass region.
Significantly less air but, strangely, an additional perceived depth and (slightly) width of the soundstage.
The upper midrange / lower treble smoothening from the vintage tube amp design was actually not there as I expected. Vocals were a bit sweeter but not much different from DAVE direct.
The most dramatic change in tonal balance was the bass response, with an emphasized mass and longer decay. A slower bass, less defined, whereas very enjoyable with certain tracks.
Dynamic changes are generally slower, but with a few tracks where the Formula S and the DAVE alone clipped (e.g. Funeral March for Rikard Nordraak - Reference Recordings - my go-to track for visceral dynamics), the Oto had no issues. Actually, the thunderous tympani strokes at 1:10 are the best I have heard from headphones to date.
Anyway, I definitely prefer the DAVE direct over the Oto overall, plus the background noise is not tolerable for longer listening sessions, so I am afraid my good old audio companion from my University times has to move out of my rack again
.