(Note- this is related to my earlier post http://www.audioasylum.com/cgi/vt.mpl?f=amp&m=115930 )
I've got a triamped system (see my profile if you want to know details) the high frequencies go to a pair of Fountek CD2.0 which are a 5-inch ribbon. I have a DEQX as the crossover and I am always experimenting, but I tend to cross over to these drivers around 2500 Hz with a slope of 100 dB per octave minimum. (I've tried as low as 1000 and as high as 4 kHz) I use a linear-phase filter topology.
Anyway, I have found that there is quite a difference in sound depending on which amplifier I use to drive the Founteks. There seems to be a greater difference with the tweeters here than with the SEAS Excels I'm using for bass/mids, or the subwoofers. In other words, I've tried various amps on the mids and the subs, and as long as they have the required power, they sound good. Not much difference (except the Dynaco ST70, it added some "darkness" and "warmth" to the mids which sounds great on my Quad ESL-57's but is unwelcome on the SEAS mids)
So, I'm looking for the right amp. Here's what I've tried and how they sounded to me:
Marantz 240 - had to pad down the output, amp was too noisy to use directly into these high-sensitivity drivers. Sound was harsh. Highs had a "grating" sound- hard to describe- some kind of nonlinearity.
Dynaco Stereo 70 (with MIT multicaps and other good parts, but stock topology) - sounded good but somewhat lacking in detail and attack.
Power amp section of Yamaha CA-800 integrated, set to "CLASS A" operation- very good sound. Detail, attack, and nicely extended highs. Sounds like it might be running out of steam on loud passages- seems this amp produces about 5 watts / ch in Class A. Best overall sound, though, so far. Really great; no glare, no harshness. Needs about 6 dB more "oomph" though.
Yamaha A-700, in "DIRECT" - "AUTO CLASS A" mode- harsh sound. Again, "grating" - a very irritating sound. Ick.
AMC CVT2030 hybrid MOSFET / tube amp - this amp had great SHEEN and never added harshness to the highs, sounded better than the Dynaco ST-70 but softened the attack and seems to roll off at the very top end. Musical, and actually very nice but lacking that attack and clarity of the solid state amps.
SO - what amp is suggested? So far the champ is the Yamaha CA-800 power amp section, run in Class A mode. Perhaps I should get a Monarchy 70, which is a 25-watt/ch Calss A zero-feedback design that is highly regarded. Or a Pass Aleph 3, but the Aleph 3 is too expensive for me, I need to stay below about $500 unless you know someone who wants to buy a Yamaha A-700 and a Marantz 240.....
FOOTNOTE: I'm a guy who beleives that, aside from the way they sound when clipping, all good amps sound about the same- EXCEPT the way the amp interacts with the speakers' reactance can cause some definite variations in sound. So, given the amp has enough power, my thinking is that the "sound" of the amp is due to electricial interaction with the speakers' impedance, which is usually pretty complex due to the crossovers, multiple drivers, etc. SO- according my my theory here, all amps sound sound about the same on these ribbon tweeters, because their impedance is very simple and flat, with just a little inductive reactance. They are about as close to driving an 8 ohm non-inductive resistor as you can get with a transducer, as far as I can tell. And they are so sensitive (98 dB 1 watt 1 M) that no amp should be clipping when driving it. Yet- here I am, hearing VERY discernable differences between these amps. These differences are NOT subtle! OK, so the tube amps, maybe the output transformers don't work well at the upper end of the audio spectrum, that might explain that. (Maybe I should try a Harman Kardon Citation II or V - they were pretty flat to 50 Kc/s at full power) But why does this old Yamaha sound so GOOD??? It's really very puzzling.
