Hi Mark. Regarding the reactive load, that was for a different design that would include a tube power section that would subsequently feed a big SS power section.
There's a lot that goes into a design, whether tube, SS, or hybrid, that affects the feel and dynamics of an amp (as well as everything else). So I can make a very stiff, cold sounding tube amp, or a hybrid with a lot of warmth, sag, and compression that folks might interpret as "tubey" sounding. So, to a degree anyway, we can blur the line when it comes to hybrids that encompass the characteristics of a full tube head (if we so choose); things are compounded even more when we factor in what each person's interpretation is of what that should sound like. So I'll try to bound it a bit and take it on a case-by-case basis, because making generalizations is generally useless not to mention inaccurate...
The ICE unit I'm using will sound different than the cheaper, lower power modules that run bridged, but it sounds very close to my QSC PLX3602 in terms of output and slam, so it's doing what it should as a power amp. When I take the unbalanced preamp out of the Studio 1200 into the QSC, versus the tone and response of the internal amp, it's pretty close, but the internal amp actually sounds a bit nicer due to the transformer coupling - adding anything in the signal path affects the tone, and in this case, in addition to improved noise performance, there is a nice musicality that the transformer adds. I could probably come up with a more creative descriptor, but I'm pretty unromantic about this stuff and the whole sonic mojo thing.
So it sounds nice, just like the tubes do.
The preamp circuitry driving the transformer also has a big impact. These are the things that should be addressed by the designer to optimize performance, rather than just dropping the power section in - they are plug n' play for someone with reasonable tech skills, but it's kind of like putting speakers in a box makes sound (but not necessarily a great speaker design), albeit to a much lesser degree. Point being, there are gains to be had from proper integration. The power amp I put together for Mike that you played through had a version of the Jensen transformer front end on it. It sounds great when being driven by an typical unbalanced preamp signal compared to no transformer - I tried it both ways. Mike mentioned that he liked the tone better without the transformer, but that is because he was using the balanced outs of the SF and my BoT, both of which have transformer balanced outs - so one too many transformers in the signal path. I tried the power unit being fed by both the balanced and unbalanced outs on my BoT before I sent it to him, and I agree. That said, I'm sure some folks would prefer it the other way.
In terms of the Studio 1200, the power amp is solid and handles the transients without all the nasty artifacts of the smaller modules which is exactly what I want as a designer. It's a blank canvas. I can control the overall feel of the amp through the rest of the circuit design - voltage levels, filter capacitance, and the driver circuitry. The BoT runs the tubes at very high voltages, and coupled with how the gain stages are configured, translates into a huge dynamic range before the signal is compressed, along with the nice tube edge on top - but it doesn't distort. The Studio 1200 is similar, but obviously the 12au7 front end versus the 6SL7 of the BoT will have a big impact, with the 12au7 being a bit smoother. A 12au7 front end in the BoT would make it a bit cleaner like the SF, but still retain the dynamics and tone that real high voltage provides (I've been meaning to build one in this configuration, along with some other upgrades I have planned). The big challenge of the Studio 1200 was to keep the sonic purity of the BoT, but with a powerful EQ - EQ presents all kinds of challenges, but I came up with something pretty unique that works very well IMO - it's insanely powerful but very musical and intuitive to use at the same time. I've tailored the feel/response/touch sensitivity to provide what I like in an amp regardless of topology - it's not stiff or slow - there is that nice cushion from the subtle compression and harmonics that tubes provide, along with the clarity and dynamic range I want in a bass amp. I've had a lot of great gear over the years, some all tube, some hybrid, some all SS, and they all got me where I wanted to go to some degree - now that I build my own stuff, it's just a matter of getting where I want to go with the parts I have at my disposal.
All I have are some basement rehearsals where I'll use the Studio 1200 with a single Berg CN112. Next gig is March 7th with the loud rock band, so that'll be a proper test. NV610!!!
