The Black Shadow 845 (BS845) is a dual mono-block set of Single Ended Triode (SET) Amplification. Unlike many amps that sound fantastic, the BS845s do not require a crane to move. Yes, they are substantial and heavy, but as long as you are careful, these amps can be handled by one person. That is the first physical observation one notes...and in a world of gear, where the Chassis alone can send you to the orthopedic surgeon this is the first think you notice. It takes about 50 hours or so for the 845 tubes to begin to get towards about 90 percent opening up. They rapidly come up to speed in say 20 to 30 hours of play time. All tubes may sound congested at first, but with significant factory burn in, this may not be a problem at all. I have now owned the BS845s for six months and except for being out of town for about a month I play music every day. They are reliable and rock solid in build quality. The gain switch on the front does not degrade the signal quality to my ears and is an asset in the mostly silver wire signal path. The advantage of a gain switch on the front cannot be understated. This feature can be used to properly match to a preamp that one may desire to use for switching capabilities from many sources or other reasons. On the other hand, although I have not done it, I believe one can connect directly and use the mono-blocks without a preamp. Check with the manufacturer to confirm this functionality. Sonically, I have been on a quest for years to acquire "the sound." These amps are considered not only best in their class and a bargain, when compared to some of the overpriced boutique brands out there, but to truly come to understand an amplifier of this caliber has taken me time. I was faced with a variety of trade-offs and I will now tell you about the sonic side of these amps and for anyone looking at these, this I would expect is one of your primary considerations. The sound is nothing short of transporting and an audiophile dream come true. The BS845s will take any system up, but a highly transparent and resolving system can be taken to levels of musicality that are like opening a screen door on a beautiful Spring day to let the light spread into the room. These amplifiers are significantly responsible for bringing a natural sense of tonal harmonic portrayal that will bring you closer to the music than perhaps any other amplifier you may have know. They possess the bottom end shove to move the most stubborn speakers and a rich harmonic palette that brings one not into an excessively syrupy tube land but with just a touch of needed euphonic tint that gives instruments their true to life tonality. All of this is indeed highly addictive and you will find yourself unable to get up and leave the room. These are the kind of additions to a system that put all but the constantly addicted system changer at a point of finality. These are a treasured amplifier that has been brought back with enhancements. They contain under the hood at least eight enormous well sealed depth charge size film and foil capacitors to assure the power supply to this high power tube is never flagging. My personal experience has been the 845B tube is among the most pleasant to listen to... Another real plus is that, while one can use NOS tubes, the designer has chosen readily available tubes that are manufactured today, are not expensive and sound outstanding. This is an accolade indeed in the face of the NOS Tube frenzy. I purchased the base model which is to borrow a word from a trusted audio Guru I consult routinely... "Sensational!" You can drive any real world speakers to plenty loud levels and have body, tonality and the seamless panoramic realism that tubes can deliver. I have a number of amplifiers and the revered AMR CD 77.1 CDP as a source and the sound is nothing short of astonishing. There is no fatigue. You can listen as long as you have time. The Cello is notably rendered with the sound of wood, guitar with strings coherently plucking into the air. Highly sensitive speakers are more revealing, but all sound outstanding. I have two other brands of the best in the world amplifiers and this is my finest amp. I own an approximately 500 Wpc SS amp that has tonality and grip, but does not eclipse the BS845 SET. I own a World Class 300B PSET, which has a different sound and is exceptional in its own right, but again the BS845 still comes out on top. It is worth noting that I am comparing to amplifiers that are nearly in the same class financially and arguably are equivalent contenders, but the most musical to my ears is this amplifier. I consider this amplifier so exceptional as to consider this type of amplification for my musical hobby, something I simply cannot live without. My speakers range from 90 db/W/m**2 sensitivity up to 101 dB W/m**2. ALL of these various speakers sound exceptional and there is absolutely no problem driving them musically, with the entire Pace, Rhythm & Timing (PRAT) you would ever want. These are not cheap, but nothing good ever is... The state of the art engineering that has gone into these amplifiers takes them past the first 85 % of design and enters into the world of the last 15 %, which is where the art of the implementation takes a natural knowledge to portray the music in a way that brings an intimacy and connection, which is so elusive and rare that many audiophiles give up on the idea of simply ever finding it. There is another plus to mention. The nature of these amps is that they will bring the best out any speaker you mate with it. Certainly, high sensitivity speakers are a welcome addition, but if you have 90 dB/W/m**2 speakers do not be put off because the musical enjoyment possible with simply blow your mind. If you get higher sensitivity speakers you will simply be able to see deeper into what these amplifiers are capable of...and trust me...the more sensitive your speaker...it only gets better. In addition, dealing with the professionals at True Audiophile is a pleasure and they are truly not satisfied until you are... I recently had a bad 845 tube that I purchased from an expensive reseller and went it out unexpectedly. The well designed circuit protects you speakers and the amplifier from any such minor incident. I needed some extra fuses and without regard, the importer provided me a source I needed to stock up on a few fuses almost immediately for this normal event that poses absolutely no threat to your amp because of its self protecting design. I was back up in running in only two days!!! That said, know that 845 tubes can last for years and years and typically do, the fact that I had one fail is unusual and they are not expensive to replace and pose no threat due to good circuit design to any or your equipment. Plus, there is a great warranty and great people that stand behind it. I doubt you will ever need that, however. Cheers!!! I recommend this real world amp with my highest recommendation. Buy one now while these are still made, you will never let it go!!!