Welcome to Audiocircle and the RWA forum! Thanks for your posting your email here.
MMGs are one of the best sounding speakers out there for the money. They sure LOVE high current amplifiers, which
the Signature 16 is, and it delivers 32 watts per channel into the 4-ohm MMGs. Yes, it CAN drive them (and most other speakers)... as long as you are not looking to play it LOUD. But at lower to "normal" listening levels, the Signature 16 will do fine with them as you have
My question is this: There is all this talk on the forums about how tube amps sound more powerful than solid state with equal specs.
The main reason why some people say this is because when a tube amp starts to clip (distorts), the distortion is softer and not so "grungy" like a solid-state amp distortion, so you don't notice it as much, and by the time you do notice it (when it does get grungy), you are probably outputting more power than what the tube amp is spec's to output ("clean" power rating). This is not the case with all tube amps, but some of them can sound like they have more power than what they are rated for.
I think another reason why some people think they have more power is because they have lower damping factor and the bass tends to be heavier with a tube amp (more quantity
of bass, but not necessarily better quality
of bass). Tube amps with transformer outputs don't have very low output impedance, and this is why the damping factor is usually low, and this can reduce an amp's grip over the drivers. Combine that with a power supply that has high output impedance, and you can get flabby, muddy bass response.
I am NOT saying this is the case with all tube amps - but there are plenty of them that have this issue, just like there are plenty of solid-state amps with their "sonic issues."
My uneducated guess is that the battery in the Signature 16 allows more current draw than the transformer of the moderately priced (but good quality) Chinese amp? At lower volume, (around 70db) the Signature 16 seems a bit more powerful and in control than the Krell.
The LiFePO4 battery pack in the Signature 16 has very low output impedance. There is no power supply transformer and its associated inductance that chokes instantaneous current delivery. There is not rectifier stage adding more impedance to the power supply in its ac/dc conversion process. No need for C-R-C filtering to reduce hum, no voltage regulation needed. So you can get a lot more instantaneous current on demand due to the significantly lower (less than 40 thousandths of 1 ohm) output impedance of the LiFePO4 battery supply, and the low impedance Class AB MOSFET output stage. This is one of the main reasons why the bass has more articulation and control vs. the others you listed, including the much more powerful Krell.
I am not anti-tube, rather I love 'em, so I was pleasantly surprised at the performance of the little Signature 16.
I also love both tubes and solid-state! I just tend to prefer the tubes for the lower voltage signals (source, preamp, amp input stage) and solid state for speaker output stages. When well implemented, I find that this does help get the best of what tubes and solid state topologies offer, and much less of what they don't do as well.
I’m writing this because I am wondering if the Signature 57 is a worthwhile replacement due to its increased power. It seems that most people would still say that it isn’t enough.
The Signature 57 with the tubed input stage will give you all the goodness of the Signature 16 sonic signature, AND MORE! You'll get 115wpc into 4-ohms, way more current, and into speakers like the MMG, that will not only allow for louder playback, but you'll get much better attack and decay, even tighter, snappier bass, and bigger dynamics. I suspect you'll even notice better performance at lower listening levels due to the even lower output impedance of this amplifier. The dual mono design of the tubed Signature 57 also throws an even bigger soundstage (but the Sig 16 is pretty darn good in that regard already
). When the times comes, and if you want a very noticeable upgrade, I would definitely consider trading-in your Sig 16 towards a tubed Signature 57. As always, feel free to call or email me regarding this.
Thanks again for your post - and happy listening!