Rebbi, Ive had a chance to get some listening in over the last couple days. I have a lot of thoughts, but I will try to confine them to the relevant questions.
1. Can an SET amp satisfactorily drive the deCapo Bes ?
2. Would such an amp represent a substantial improvement over your Mahis?
I have some preliminary impressions to share. First of all, let me give you a brief summary of the system into which the 3 amps were inserted for comparison.
The source was a ModWright Sony HAPZ1, feeding a Coincident Statement Line Stage preamp via VH audio Symmetry ICs. The preamp fed signal to the amps via a VH audio Spectrum Ag IC. Signal out to the speakers was via Coincident CST 1 cables. My Coincident Triumph Extreme II monitors were available for reference. The 3 amps available were Coincident Frankenstein 300B monoblocks, a Coincident Dynamo stereo amp, and a Dennis Had Inspire KT66 amp. In addition, I have recent memory of the deCapos driven in the same system by my now departed Cary 500.1 SS monoblocks, which are 500 WPC into 8 Ohms.
Music used for the evaluation were the following albums played back via the MW Sony HAPZ1. Shostakovich, Symphony No 13, Babi Yar, Mahler Symphony No 3, Neil Young, Live at Massie Hall.
At the outset, let me say that the Inspire KT66 isn't going to be suitable for anything but low dynamic range acoustical music with the deCapos. I evaluated both the KT66s and EL34s, and both 6SN7 and 6SL7 inputs. The 6SL7 was certainly a better choice. The KT66 tubes were better than the EL34s, but really, no matter what I did, mid bass and below was very soft. It is not an SET, but it was around, so I threw it into the mix. The amp mated well with the speaker above the mid-bass, producing some heavenly tones utterly incoherent with the soft, slow, muddy lower registers. It gave a plausible presentation with the Neil Young, but utterly failed on the Mahler and Shostakovich.
The Dynamo was a much different story. Keep in mind that the dynamo is brand new. Last night was its first time out of the box, so there is still some break in to be had. Keep in mind also, that this amp is using the cheap Chinese new production tubes that are supplied, and they also have no break in time. All that said, I immediately perceived some synergy between the dynamo and the deCapos. I am pretty excited about this pairing for my bedroom system, especially since the dynamo has volume control and won't require a preamp for a single source system. There were some issues. The upper registers became hard and unpleasant when driven too hard, say, 94 dB+, and there were indications that the Dynamo fell short in the lower registers at high volume, although the low strings were generally well reproduced. I suspect the harshness in the upper registers will be addressed with burn in and tube selection. Perhaps the lower register issues can be mitigated also with better tubes (especially the rectifier). That said, the Dynamo drove the deCapos well through the first movement of the Mahler 3. The sharp, quick, tympani attacks were handled well. Of more concern were the sustained low strings passages. These were not handled as satisfactorily as when the deCapos were driven by the Franks or the Cary SS amps. There were some stunningly beautiful moments. At about 10 minutes into the final movement of Babi Yar, there is a bassoon solo followed by a violin solo. The Dynamo/deCapo combo reproduced this with a harmonic sophistication unmatched by any other combination of amps and speakers I tried. Yes, even the Franks with the deCapos or the Triumphs with either the Franks or the Dynamo, did not match the level of shear beauty in this short passage. It is important to reflect on this, in that it underscores the importance of system synergy. It is also important to note that the beauty of this passage hit my emotional response button in a big way. It is that response that fuels my obsessive expenditure of cash, so this was a big deal for me. It is also important to not take this out of context. For most of the rest of the music, the Franks were far superior to the Dynamo.
My very preliminary listen to the deCapos driven by the Coincident 300b Frankensteins was more than satisfactory. Again, this was a quick preliminary listen, but the Franks drove some clean 99 dB peaks in the treble with no distress. My thinking with the Dynamo is that one should probably go no louder than 95 dB peaks at the listening position, in my case, back about 11 ft from the speakers.
So can a flee watt SET drive the deCapos? I would argue yes, based on my limited experience in driving them with the Coincident Frankensteins and Coincident Dynamo. Some of this will depend on music preference, room size, listening levels, and ancillary equipment, but it is something that can work very nicely.
I could make a case that the Franks drove the deCapos better than the Cary 500.1s. This is not just a simple case of WPC. The Triumphs were clearly better than the deCapos with the Cary SS amp, but the gap closed substantially when the two speakers were driven by the Coincident tube amps.
