Don posted this explanation concerning his Model 2 preamp and the new Raven on Agon:
"The older preamp is a nice, but conventional single ended tube SRPP circuit with Akido buffer (extra tube per channel). It uses dual regulated power supplies and dual regulated filament supplies and really good signal path parts, and the wonderful Khozmo attenuator. The Raven is a completely different approach and circuit. It is fully balanced and transformer coupled at both input and output with custom wound transformers from Dave Geren at Cinemag. It will take either xlr input or rca input, and will happily provide xlr or rca, or even headphone output, and will drive even a 10K power amp impedance. The Khozmo setup is dual mono because you have to control both halves of the xlr on each channel. The power supply uses two damper diodes, very high quality transformer and is a true C_- L - C (cap, choke, then cap) that feeds a much higher quality regulator that is used in the previous preamp and also feeds a pair of gas regulator tubes after that. It is dead quiet, fully balanced, and has very little sonic signature, but provides great drive for the power amp. I really like it, and those who have been to the show have heard it driving the 300b mono amps."
https://forum.audiogon.com/discussions/300b-lovers?page=7
Don expounded on the differences between his current preamp and the new Raven:
The sonic differences between the old Akido circuit and the Raven are fairly dramatic. The Akido circuit sounds like one of the best darn traditional tube preamps I had ever heard, and that is why I built it for years and kept trying to squeeze another few percent out of it with every improvement. The Raven is part of the 300b project. Both the amps and the Raven will happily play with the rest of the world, either single-ended RCA or XLR, but together they can form a complete balanced chain with a balanced source. The Raven can drive the input tube grids of the Blackbird amps directly via XLR because it has an output transformer. I would not do that with a solid state preamp or DAC output stage, only something with an output transformer or coupling cap to protect the amps from DC input. A solid-state device would be fine for possibly many years until one instant that it isn’t, and then DC can come flooding into the amp. That would not destroy the Blackbird, but the input tube would be really unhappy, and some nasty noises could arise from the speakers. The Raven simply cannot do that because it is transformer coupled. The RCA input on the Blackbird amps is transformer coupled, so that is always safe, but the XLR inputs can bypass that input transformer. So the Raven is made to mate with the Blackbird.
The sound of the Raven vs. the older Model 2...? Well, as much as I like that circuit and build, it sounds slightly slow and veiled compared to the Raven. The Model 2 is a great preamp and I have maybe 150+ of them out in the world in one form or another, but the Raven is a step up. There is just more resolution of fine detail, with what sounds like effortless and unlimited drive. It is not bright in any way at all, but it is highly detailed. The whole 300b system is like the iron fist in the velvet glove to my ear. It has all the subtle detail and shadings of a flea-watt SET amp, but serious grunt and drive at the bottom and extension to 34KHz at the top end and a very subtle roll-off after that. I suspect the final version of the amps may make it out to 50 KHz before the roll-off begins. So HF is extended and airy, but again, never bright sounding. The Raven is definitely part of that experience because I built the amps first and used them with RCA inputs and my old preamp, and then I built the Raven. Like the amps, once I heard the Raven there was no going back. So then Lynn and I experimented with several power supply variations before deciding on the final topology. They all sounded quite good, but the final choice was clearly the best to my ear. At any rate, the Raven is a big part of the sound people heard at the show. My old preamp was good, but not in the same league. My 2 cents.....
