Okay, here's the question I'm dying to hear about, how does this thing compare to the Rag? I've been looking for the right tube/hybrid complement to save up for and this looks like it could totally fit the bill!

Can anyone tell me a bit more about this amp. Is this amp like the EHHA? (The EHHA was one of my Cavalli favorites before he started selling stuff.)

As Sachu mentioned, the EHHA LF and LC are an evolution of design. These are obviously not the only ideas and as can be surmised from hints at an EHHA II and the demise of the cobalt, they are windows into Alex’s quest for optimizing a concept. The evolution from low voltage to high voltage to optimized current bias and surrounding circuitry. The basic premise is for the tube to be embedded into the circuitry unlike a typical hybrid in which the tube gain stage is capacitively coupled to the current buffer ala liquid glass. This means that there are no capacitors in the signal path. The tube embedded in this way is thus not the sole gain stage and has a significantly less role in the overall sound but yet still imparts some tonal balance. In theory tube rolling should not affect this amp to the same extent that a tube in the LG would but we all know what happens to these theories.

There is a fair amount of technical discussion on Headwize under the EHHA thread. At a rough guess the LC is the 6th physical incarnation and has progressed quite significantly since the humble EHHA days.

I am glad your thoughts reflect mine in general ..dB

First, thanks to Marv for taking time with the Crimson. 

Nice!  Can you offer any comparisons to the Liquid Fire?  The LF does a magical set-back laid-back enveloping soundstage kind of thing that I really like.  With the right music it makes me melt.  I'm wondering how much of that is in the LC.  I bought a used LF last year.  I'm looking for a more aggressive amp to pair with it, but an amp that sill has that magic.  Would a LC be different enough?

I'd like to elaborate on dBel84's and Marv's answer to this.

The Crimson is, indeed, about 6 generations away from the original EHHA. I call the EHHA, LF and LC embedded or blended hybrids, meaning that the tubes and SS components are blended together in the circuit and totally DC coupled. This is a very different topology from a classic hybrid where the tube voltage gain stage is separated from the SS current gain stage with a HV blocking coupling capacitor. The embedded hybrid topology tends to give a sound quality which blends the tube and SS sound signatures together.

The EHHA amp used low voltage 6GM8 tubes. The multi-step transition to the LF replaced these with 6922s (new production) and added the HV rails necessary to run these properly. It can be a little tricky to have HV rails for the tubes and LV rails for the SS supplying the same circuit at the same time, but the LF solved this problem. The 6922s in the LF operate happily at +/-100V while the SS current buffers operate at +/-30V.

Towards the end of the runs of LFs I had noticed two things about the amp that wanted improvement. Changing these two things led to the Liquid Cobalt first (as a proto) and then the Crimson.

The LF was not really designed as a tube rolling amp (unlike the Glass which is specifically a tube rolling amp and which sounds exactly like the tube in use). But, nearly all of the owners found expensive NOS 6922s to replace the stock tubes. Replacing 4 tubes is an expensive proposition and, of course, some went to the additional expense of having them matched.

The second area for improvement was the qualitative weighting of tube to SS sound. The LF has more tubes in the key positions in the circuit than it has SS. This tilts the sound of the LF in the direction of the tube sound. Many of the owners really like this sound, but in terms of blending the best of tube and SS behavior it was heavier on the tube side.

For both of these reasons the next step involved intelligently reducing the number of tubes. There was an intermediate version with only two double triodes. Not really a design I was comfortable with. The next step came from work on a hybrid power amplifier where only one triode per channel was needed, even though the amp was still an embedded hybrid.

This led to the Cobalt which led to the Crimson. The reduction in triode count with the increase in SS gives (IMHO) a better balanced blending of the tube and SS sounds. The SS has a little more room to make its presence felt which is translating to listeners as higher resolution and slam, while the tube sound is still in the mix. And now, if you want to roll tubes you only need one and the triodes don't really have to be matched.

There are few other design elements in the LC that help the overall behavior of the amp.

Each channel has two bipolar regulated LV supplies. One for the input and driver stages and the second for the output stages. If all stages use the same rails the output voltage swing is limited by the drivers hitting the rails before the O/P devices do. The driver supply is 2-3V higher than the output stage supply (33V for the drivers, 30V for the output stage). The few extra volts ensure that the output is limited by the output stage hitting the rails before the drivers do. This gives a little more maximum power and dynamic range at little extra complexity. This is a commonly used technique. Each channel has separate supplies, meaning that each channel has four regulated LV supplies to itself.

The O/P stages in the LF were biased at 100mA. The LC's are biased at 150mA keeping it in class A longer.

The HV supply for the tube is a unique design (so far as I know). A few years ago John Broskie (www.tubecad.com and brilliant) found a concept for a HV regulator in an old data book. The concept was to make an HV regulator with a tube as the pass device and a LDO nestled between the GK of the tube to do the actual regulation. Since the GK voltage is small the regulator sees no HV. At the same time since the GK voltage is small the regulator has to be LDO in this design. John resurrected this idea using both tubes and depletion MOSFETs.

There are limitations on this concept though. The first is that the GK (or GS) voltage is fairly low and can be close to the dropout voltage of the regulator leaving small margins for stable operation. The second is that this topology doesn't lend itself to negative HV regulators because there are no P-channel tubes and P-channel depletion HV MOSFETs can be hard to come by.

I extended this concept to use enhancement FETs. This solves both problems at the same time. It permits higher voltage across the regulators so that we can use LM317/LM337 class regulators (no need for LDO) AND it makes it possible to create a complementary negative HV regulator because there are readily available HV P enhancement fets.

Our experience is that these are excellent HV regulators using a minimum of components to yield the characteristics of the actual chip regulator in use but at many hundreds of volts far exceeding the maximum regulator voltages.

The LC has one of these to make the 105V that it needs. The Liquid Glass has one of these to make the switchable 200V/300V regulator and the new Lightning has two of these to make the +/-400V rails that it needs.

I guess this was a long story to say that the LF and LC are siblings or maybe grandparent and grandchild, but the LC is a more sophisticated design which is at the same time simpler than its predecessor. The LC will do everything that the LF did and some other things better.

And, it does have a cool looking small enclosure.

There will be two of these at LA CanJam if you want to hear one. If I can get the one back from Marv. 

Alex, can you explain how witchcraft and chicken bones play into the afore mentioned development process? As an actual Ph.D (doctor) in physics, it must be hard to ignore math and science (as some others would like to claim) in favor of the supernatural instead.

Lol, couldn't resist man. I look forward to hearing the LC if its as much an improvement over the LF and LG as Marv says. 

Oh, when designing amps, do you prefer white or dark meat?