Dave,
The Quad II circuit combines a long measure of the holistic presentation and tonal purity of a fine SET amp, with some of the bottom end discipline of a push-pull amplifier, without the excesses of either. My Audion 300B PSET mono blocks are the Golden Dreams -- their top amp. The Quad Jubilee mono blocks are not better than the sensational Audions, but they are much closer than the price disparity suggests. The Quad II was a very simple circuit -- there are only 13 caps and resistors in each mono block signal path, the rest of the componentry being tubes, transformers, choke and power supply filtering. They are the most SET-like push-pull amps I've heard, ever. The Quad II also is optimized for a 16 ohms load, so Druids or Superfly are perfect for them. Definitions less so.
I'm not enthusiastic about most 300B SET amps. Most are sweet and rich but also slow and euphonic. Audion's SET amps are an exception, being fast, transparent and beautiful. There are some others too. I haven't heard Dignity Audio, so can't directly comment. The Quad II circuit has some bass bloat compared to many more contemporary tube designs, especially those using diode rectification. But compared to the majority of SET and PSET amps, they are relatively controlled. The Quad II is also very quiet compared to most SET. For someone with Zu levels of efficiency who also wishes to avoid the noise, bass euphonia and tube exotica of SET, I think Quad II reissue amps are both a great buy (assuming a good preamp) and aurally beautiful. The reissue QII mono blocks are faithful in circuit and execution, plus there are reasonably good KT66s again, along with good 5881 subs.
If you can find a pair of Jubilee amps, their price may be off-putting, but that is the most convincing Quad II version I've heard -- some cryptically dismissive reviewer comments notwithstanding. But that's no reason not to buy the current ~$3000 Asian-built reissue. It's excellent in it's own right. And anyone fearing 15w just won't do it for them, the KT88 Quad Two-Forty emulates the II's simple clarity with more punch.
I haven't yet connected my Quad II Jubilees to my friend's Superfly speakers. I should get a chance to do that soon. But I know intimately how well they do on Druid 4-08 so extrapolating to Superfly isn't difficult. They will do even better. My Audion Golden Dream mono blocks are out for service. I'll have them back i. A week or so, at which point I can resume hearing the Quad IIs surprising me. I recommend the Quad II in reissue, Jubilee or rehabbed original form, for Zu higher impedance models, without reservation. The match to Definitions is more conditional due to the 6ohms speaker impedance. I'll be digging into that match, against 845 mono blocks, over the next week or two.
A pair of Quad II with good tubes will sound less "vintage-in-a-bad-way" than a stock Dyna Stereo 70. You can tune the sound somewhat via tube substitutions: more reticent with 5881 output tubes; a little more assertive with a GZ34 rectifier tube. I'm anxious to try the Shuguang carbon/polymer KT66, which should sound vivid and incisive. The Quad II has input sensitivity I'd 1.4v for full power, so put a strong line stage or preamp in front of it. I've been listening to the Jubilee amps in my Druids system for over a month. They could keep me happy indefinitely in that speaker.
Phil
Phil
