Balanced Zen Line Stage

Here is my Balanced Zen Line Stage preamp, completed after 1.5 years: 1 week to assemble the BZLS boards, and a lot of laziness to design, build, and debug the rest. Preamp PCBs were purchased from Kristijan Kljucaric of Croatia, and were assembled with the basic schematic and parts values from the Nelson's PDF manual. The input and output attenuators are self-assembled Alps ladder switches with the recommended 10k and 5k impedences, respectively. The power supply was modified to accomodate the 300VA 40-0-40 toroid transformer that I had laying around. Input source selection using relays and control for a front panel VFD display (from NewHaven Display) is handled by a simple 8-bit ATMEL AT90S8515 microcontroller. The circuit design and PCB layout were done by myself, and the PCB was fabricated by Olimex of Bulgaria for their low one-off price. A separate toroid is used for the digital power supply. The chassis is from the 20 series of Par-Metal. Par-Metal made the chassis to custom specifications with cutouts and hole punches, which made this project much easier due to the lack of access to a machine shop. You'll notice that the chassis matches that of my AKSA 100 amplifier (bottom of my audio rack) - that is not a coincidence. Major quirks I've had that delayed completion of the project for the last half year were from the VFD, RF noise, and slight hum. The slight hum was fixed by tying the preamp's signal ground directly to the chassis ground (earth), rather than through the thermistor. RF noise was on the wires feeding the preamp boards, and was eliminated by adding ferrite cores (not pictured) to these wires - altered wire length could possibly have helped. I only use preamp is only used for unbalanced audio. Since this is my first component preamp, I have no reference for comparison, but the sound is definitely great when combined with my AKSA 100 amp. My goal when choosing a preamp to build was to select one which will satisfy me for a lifetime. I believe this one will do! Thank you Nelson for your excellent design! I have much respect for your vast analog knowledge and commitment to the DIY community. Sincerely, Gregory Peng, .(JavaScript must be enabled to view this email address)