A matched pair of The Mastering Lab ML-1 microphone preamplifiers. I built these units from parts left from the original run of ML-1 mic preamps built in the 90's. The parts were purchased from a retired technician from The Mastering Lab. That technician (who was deeply involved with the original design and manufacturing) graciously provided a massive amount of guidance and advice to ensure I built them perfectly. We emailed or spoke nearly every day. He even inspected and tested a couple to approve my work. I also rented an original to study to compare construction and sonics. Mine are built more cleanly and sound identical.These things get pretty warm during operation. Thus, units built in the 90's are now due to have all the electrolytic caps and zener diodes replaced. The tubes (especially the cathode follower) are definitely in need of replacement. You'll have none of those worries. I used the best available Nichicon, Panasonic, Sprague Atom, and UCC electrolytic and film caps, and Reliable Capacitor AudioCap polystyrene audio coupling caps. 1% resistors. Solid core wire. Just like the originals. The originals used input transformers from Reichenbach, Sescom and UTC. After much testing and comparison, I selected a particular input transformer that sounds indistinguishable from the originals. NOS (not used) GE 5751 and RCA 6922 tubes. Original units were prone to the B+ zener diode regulators failing, so I used zeners with twice the current rating and doubled them up (the benefit of observing failures over the last 25 years). Also, a push pull trim pot was added to allow the engineer use to the 10dB variable trim, or disengage it entirely to achieve an unloaded input transformer secondary (a desirable feature, read up on it). No expense was spared and no detail overlooked.I spent over a year chasing this dragon. I co-own a high level electronics repair shop in Austin, TX, and have professionally built and repaired TONS of studio gear and tube microphones in the last 30 years. I'm a fastidious, perfectionist kind of guy. I did all of the work myself. Feel free to ask questions - I want the buyer to be 100% confident with their purchase. These units are built right, and I'm quite proud of that fact. I built several that I'm keeping. The ONLY reason I'm selling these two is I went crazy spending money to build these, so could stand to recoup some of my investment.THD at 1kHz is .009% at +30dBu! 

IEC power cord for 120V operation is included. Photos are of the actual unit(s) you'll be purchasing, so look at the high resolution pictures carefully. These units are new, rack mounted once with washers.