I recently had the opportunity to check out the Seventh Circle Audio N72 mic preamp with the CH01 chassis and PS01 power supply. The N72 is available fully assembled or in various kit forms. With the help of the instructions from the webpage and the schematics, I assembled my kit in six hours. The PCB board was well labeled, but the instructions indicate a few incorrect component values on the board. Therefore, it would be prudent to study the instructions before soldering down your parts. This kit isn't a project for an absolute novice, but if you have some soldering experience and can tell the difference between a resistor and capacitor, you should be able to handle it. Initial biasing of the circuit was simple, but fine biasing requires an oscilloscope. If you run into trouble, you can call or email Tim Ryan at Seventh Circle. If you really screw up or otherwise end up with a dead preamp, you can return the kit for repair (although no one yet has needed to do so).
Once assembled, I did some initial testing of the N72 with an MXL 2001 large-diaphragm condenser mic and a set of headphones. I noticed a nice, full bottom and an open-sounding top end when singing and talking into the MXL. The N72 definitely has a sound to it- you can hear the effect of the big transformers. I then continued my evaluation by comparing the N72 to a "real" Neve 1272 and a Chandler Limited 1272ex. (Thanks to Dave from Vintage King for the loan!) Using a single SM57, I recorded vocals through each of the mic preamps. Although the Neve exhibited the most saturation and top end (and won the blindfold test with the vocalist), the N72 and the Chandler were both very close in sound quality to the Neve. It was very hard to tell the difference between the Chandler and the N72. The Chandler seemed just a bit more like the Neve, but all three were very good sounding mic preamps. Keep in mind that the N72 is a fraction of the cost of the Neve and Chandler preamps, and there's great variability in the sound of vintage components.
I've since used the N72 with great success on guitar, bass, drum overhead, and vocals, using many different mics. With my tube-modified MXL 2001 as a mono overhead, I was able to get a really huge drum sound. The floor tom was especially big. The preamp sounded great even when I cranked up the input and backed off the output trim. It gave me that really cool Flaming Lips' drum distortion. It worked well with my Earthworks TC30K right up on the speaker cone of a guitar amp, handling the hot signal without problems. The transformer saturation is quite apparent, and it's a welcomed effect when recording to digital. The noise floor of the N72 is low enough for ribbon mics that need more gain. I would highly suggest purchasing an N72 if you are looking to add a mic preamp to your collection that "has a sound." I am definitely purchasing more channels to fill up my CH01 chassis. (starting prices for kits with parts: $349 per channel; minimal kits: $85; fully-assembled preamps with chassis and power supply: $799; www.seventhcircleaudio.com)