Opera Audio Consonance M800SE is a set of tube monoblocks, 2x75W output based on 4pc. EL34 on each channel. The amplifiers can run in pentode or triode (2x35W), a switched are on the front panel. They are hardwired inside, no printed circuit are used for connecting the topology. Tubes from factory are Electro Harmonics/Sovtec. The amplifier sound really good and give a very good soundstage. The bass is very good for a tube amp. but the high frequency could be a bit dry with the originally tubes. Change to NOS tubes gives the amplifier a nearly high-end sound! I changed to a set Haltron EL34, RCA 6SN7 and Siemens Halske ECC88 (6922) and the sound is so good as you can get from any EL34 based push-pull designed amp.
It dos't sound very "tube like" (nostalgic) but have a modern an defined sound image as in real live.
Switched to triode mode the amplifier lack a bit in the bass but is very beautiful in the mid. and top. Perhaps when use horn speakers with > 100db sensitive, the bass could be no problem in triode mode?
In pentode mode this amp. can drive the most speaker in the market with any problems.
Opera Audio have replaced the M800SE with the newer Cyber 800 set (2x78W) with no triode mode, but now with auto-bias adjustment for the output tubes. (4x EL34 per ch.)
For M800SE you have to adjust the bias for each EL34 tube with a potmeter beside each tube and a phono plug connected to a voltmeter. I will recommend quad matched tube sets, but it's possible to adjust them all to bee even so it not a must for matched tubes.
In the NOS market you will find differ types of the driver-tubes 6SN7, I use RCA or Raytheon but Sylvania is very good. Some 6922 (ECC88) are microphonic, try to get a damper around this input tubes or get non-microphonic tubes. Use Telefunken, Mullard or Siemens E88CC !
I can recommend this amplifiers to all tube-lovers or people who want a really good amp. for a reasonable price, but with super NOS tubes it can be expensive enaught.