Consonance M10S Tube Integrated/Headphone Amplifier
Background and Design
Opera Audio is among the oldest and largest Chinese audio firms. In the English speaking world they go by the name Consonance and have been steadily garnishing praise from the hi-fi press for over a decade. They make a variety of gear but the focus seems to be tube amps, and to that end they offer a wide selection of amps ranging from integrated units to monoblocks in various sizes and power ratings. Sadly, they only make a single headphone amp, one of their earliest products which hasn't changed in the 10 years since it was released. I've kept an eye on their speaker amps for years but had never spotted anything with a headphone jack - until now.
The Consonance M10S ($1,100) is a relatively compact single ended Class A integrated amplifier with built-in headphone amp driven straight from the output tubes. It measures 12.5" wide, 10" deep, and 6" tall and weights well over 20 pounds. It uses a complement of 12AU7 and 12AX7 valves in the gain stage, and comes stock with a set of EL34 driver tubes which can be swapped out for KT88 or 6550 tubes by means of a simple bias adjustment. This requires opening the case which isn't as difficult as it sounds. This transformer coupled design uses solid-state rectification which may cause some eyebrows to raise. A lot of tube headphone amp makers such as Woo Audio and Eddie Current use tube rectification, but solid state rectification is not unheard of. For example tube legend Pete Millett uses solid state rectification in his cost-no-object Apex Pinnacle which is the most expensive headphone amp I can think of. True, he uses exotic Silicone Carbide rectifiers in place of the more pedestrian materials in the Consonance unit, but the point remains.
Consonance keeps things very simple on the front panel - volume knob, input selection knob, headphone jack, and a switch to select headphone mode (which conveniently mutes the speaker output). Around back we find quality speaker posts, 3 pairs of RCA inputs, and a single 1/8th inch input for use with portable devices. Build quality seems bomb-proof - this thing is built like the proverbial tank and notably features a removable tube cage that actually works - helpful for someone like me with small children in the house. A lot of companies will slap on a small bit of metal that looks more decorative than functional, leaving the delicate and potentially very warm tubes exposed for curious little hands to explore.
Despite the fairly traditional tube amp styling on display, Consonance spices things up a little with wood accents on the upper side portions. I had mixed feelings about these - they looked fine on their own and actually matched my A/V stand perfectly. Yet next to a pair of Salk Sound monitors I'm currently using, the finish looked a bit "unconvincing" for lack of a better word. The Salk monitors are beautifully crafted so perhaps it's an unfair comparison.
As long as I'm complaining about relatively inconsequential things: what is it with audiophile companies and remote controls? Apparently they think we want our remotes as heavy and chunky as possible even at the expense of ergonomics. The M10S remote clearly comes from a different Consonance model as it has numerous functions like transport controls which don't apply to this device. The only thing it does here is control volume through the motorized pot, which actually works quite well. Just take care not to drop it on a glass coffee table or a bare foot as there will most certainly be consequences.
One interesting thing about the M10S that I don't commonly see on other amps is the ability to change from ultra-linear mode to triode mode using a top mounted switch. The EL34 is a pentode tube with a somewhat unique feature - the screen grid is not tied to the cathode. This means it can be wired in "true" triode mode where the screen-grid has all of the plate's output signal voltage impressed on it. I'm not aware of any other pentode valves having that ability. Ultra-linear mode taps the primary winding of the output transformer to impress some, but not all, of the plate's output signal onto the screen-grid. So it's somewhere in between pentode and triode operation. Normally an amp based around the EL34 uses one method or the other but in this case we get to try both. Ultra-linear mode boasts an output increase of roughly 60%, with an available 12.5 watts RMS versus 8 watts RMS in triode mode. Consonance recommends powering down for 5 minutes before making the change and very much frowns upon switching on the fly.
The headphone output is rated at 1 full watt per channel into a 32 ohm load and has an output impedance of 30 ohms. This makes it more ideally suited for higher impedance headphones from Sennheiser and Beyerdynamic. I tried quite a few headphones and, as I'll discuss, some low impedance models worked better than others.