So, have been putting the new amp through its paces, learning its voice and how it interacts with the MC5 and the Line6 Pod HD effects unit. Tonally, it's a lot different sounding than the first amp ("Scarlett"), of course: much more mid-frequency focused, no doubt due to the cathode bypass capacitor and coupling capacitor values that reduce the low end, and the cool-biased, all-12AY7 (tube type) pre-amp seems to compress the dynamics a bit, so note attacks and articulations are a bit softer. And while it is bright enough sounding, it doesn't have Ruby's sparkliness in clean settings. The range of tone settings of the preamp feels a bit limited compared to Ruby, but that may have more to do with the aforementioned bypass and coupling caps, than the components of the tone section of the circuit. Nevertheless, I may try reducing the value of the capacitor governing the mid pot, to roll off a bit less of the low end there. At about 7 on the preamp "gain" dial, the clean tone develops a nice edge to it, and progressing up to 10 adds a slight crunch when I dig in to a string, especially in humbucker setting on the MC5. That said, I'd still characterize it as remaining quite inside the realm of "clean" for single coil and non-aggressive playing. Just as I hoped it would.
The OD (overdrive) circuit is fascinating, though I'm still figuring out how to consistently get sounds I like from it. As you may recall, it is a cascading pair of triodes (again, 12AY7) which takes its signal input from the output of the preamp. When the preamp gain is high, the OD input is also high and can drive the first OD triode to the point of clipping, or flattening, the highest amplitude portions of the audio signal. But with the preamp at lower gain settings - below 50% - the first OD triode gain remains mostly linear and simply shapes the tone of the signal, further reducing low frequency content and softening the highs. The "drive" dial controls the amplitude of the signal coming from the first OD triode and presented to the second, and allows fine control over further distortion of the signal, from a very clipped high gain sound (depending to a large extent on the shape of the incoming signal) to a fairly clean punchy mid-boosted sound. After that, a single "tone" dial allows for attenuating the high frequencies and preserving the lows, and a "level" dial adjusts the final signal strength passed back into the main circuit.
Using the Line 6 HD-500x signal processor for adding effects such as stereo reverb, delay, L/R panning, etc., in the FX loop part of the circuit has worked well so far, especially considering the range of input voltages is has to handle, from a few hundred millivolts to a couple of volts. The HD apparently adjusts automatically to the incoming signal impedance. This is not true of the pedal effects I have, and they do not work well in the FX loop. I can run the single channel "send" to the HD and return a right and left stereo signal to the power section, or return just one channel from the HD as a mono effect, and leave the other channel dry (un-effected). Both methods work well, and as planned.
The power section stays quite clean and crisp up through reasonable volumes and only begins to break up at ear-splitting levels. With the attenuator (Fryette PS2) in place to keep the final output volume down, I can activate one channel and dial the power section up to the point of near break-up, which is a nice sound - probably one I would use for recording, but not in a live setting because it's requires too much fiddling around. Here's the circuit in its current implementation (without the power supply):
I recently received a new speaker to try in place of one of the stock 12" Fenders that came with the FM212 salvage amp. Based on my positive past experience with a 2x10 stereo combo, I opted for a 10" speaker that is shown to have a relatively balanced response: the Eminence Cannabis Rex. I created and installed a second baffle behind the existing one on the right side of the amp, mounted the speaker, and have been playing it on its own and in combination with either the stock 12" Fender mounted in the left side of the amp, or an EV-L 12" mounted in a separate Thile-optimized cabinet. I like the new speaker so far, but I'll have to do some recording and listening back to be sure it's what I'm aiming for.
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