I was able to convince Steve Deckert, head Zen of Decware, to send me his Zen CSP2 headphone preamp for review. While the CSP2 is also marketed as a preamp, I did not try it as such. It does have 2 inputs, and trim pots for the preamp outs. The CSP2 is an OTL (Output Transformer-Less) design. Manufacturer's website: DECWARE / High Fidelity Engineering Co. The CSP2 is housed in a nice wood frame, but absolutely everything is top mounted – tubes, inputs and outputs, AC cord, trim pots for the preamp outs. I’m not s sure that’s my favorite configuration – I generally prefer my jacks to be front-and-rear mounted, but the CSP2 does have kind of a cool look – here is a pic: The CSP2’s stock tube configuration consists of three Russian 6N1P dual-triodes (one serving as an input tube for both channels and one as a power tube for each channel) and a 5Y3 rectifier tube. Decware supplies an RCA 5Y3GT that looked OK. I used none of these tubes, however. I used a trio of JAN-Sylvania gray-plate 6DJ8’s and a JAN-GE 5Y3WGTB (6087) for the rectifier, all NOS. The truly excellent manual covers tube rolling in detail, and is in well-written English, as the amps are made by Decware in Illinois. The manual provides some basic info about how the sound will likely change using either a 6DJ8 or 6922 in place of the 6N1P, and also lists that 5U4, 5AR4, GZ34, and 274B rectifier tubes can all be used. Some 5U4 tube types can be VERY expensive, and I did not have any available, so I stuck with the 5Y3WGTB, which is not an expensive tube, but at least in this amp, sounded TERRIFIC. And that is the main thing I have to say about the CSP2 – it is a truly, truly excellent tube amplifier. It has enthralling sonics. Transparent, lush, detailed, dynamic – frankly, I wasn’t really prepared for how good it sounded. It isn’t really a cheap amp, at $795 (and about $80 worth of NOS tubes in my case), but it sounds just fantastic. Bass was deep, powerful, and well defined. It was a little less controlled than my SinglePower Extreme, but still truly excellent. The Midrange was open, transparent, lush, inviting – really ALL the things I hope to get from a tube amp in the mids were delivered in spades. This is truly an amp that lovers of midrange purity will really enjoy. Listening to My Morning Jacket’s “One Big Holiday”, both vocals are guitar were simultaneously clear and distinct. I would characterize the mids as just slightly rich/ripe/fat – what one would expect from a 6DJ8/6922 amp – but certainly not overly so by any means. And dynamics of snare drum hits were still very fast. On top the CSP2 is smooth as silk, and quite extended. Treble detain is also very good. The SinglePower Extreme has a little more treble extension, and a little more detail, but the CSP2 is no slouch. And it has plenty enough detail to keep things interesting to be sure, while being unfailingly smooth. The interesting percussion details on Sheryl Crow’s “There Goes The Neighborhood” was very cleanly represented. Soundstaging was also excellent. The imaging was very holographic. I did feel depth was better than width, and this was again another area where the SP Extreme was a little better, but the soundstaging of the CSP2 was very convincing and notably better than less expensive amps like my Woo Audio WA3. The CSP2 was able to drive my 27 ohm Denon D5000’s extremely well, and equally my 600 ohm Beyer DT990’s. It’s listed as handling headphones from 30-600 ohms. I certainly satisfied myself that this is true. There was plenty of gain for both sets of headphones. Also, and very importantly, the CSP2 is TOTALLY quiet. No hum at ALL. It’s a silent runner, which is really nice. Conclusions: The CSP2 is a truly excellent headphone amp. In fact, of the tube headphone amps I already have, the CSP2 is better than the WA3, the Ming Da 84-C 07, and the TNS Sweet 2. I felt the Darkvoice 337 and SP Extreme were a little more to my personal liking, but only VERY slightly, and the CSP2 is available from a USA maker who is very, very responsive to customers, so it deserves strong consideration in its price range. Color me impressed. I am going to try to score a couple decent 5U4G rectifier tubes, and I will report back on how they sound. In the meantime, I can enthusiastically recommend the CSP2.