Apogee Diva bi-amping

Pschall, you can also try the Apogee Users fourm and they can help you out at Apogeespeakers.com

This is the forum link.

I am living blissfully with Apogee Divas driven by two Audio Research D-250 Mk II Servo amps in a vertical bi-amplifying arrangement. I use a heavily modified Apogee DAX 3 crossover (OPA627 opamps with output current sinks for class “A” operation, power supply improvements, etc.). When changing the power supply caps in the D-250s, I was able to double the capacitance within the same can volume, raising energy storage to near ARC REF 750 joule levels. I will be trying a fully passive line-level crossover and maybe a tube-buffered version if required, to rid my system of the many opamps in the DAX, although the OPA627 is about as good as opamps get, IMO.

I think big Apogees thrive on big tube amps despite conventional wisdom to the contrary. The word on the street, repeated endlessly by people who probably have never tried any of this, is that Apogees are all difficult loads and require Krell amps, and only Krells. The one-ohm Scintilla was indeed a difficult load, but the Diva and many other later models were actually pretty benign. The Apogee load seen by my amps is mostly resistive at around 3 ohms, much easier to drive (by the 4-ohm tap) than the load presented by some electrostatic speakers such as my also-beloved Quads, which dip down to Scintilla levels at the highest frequencies. The difference between Apogees and most other speakers is that Apogees are not very sensitive ("efficient", if you prefer). But they can handle prodigious amounts of power without compression or distortion. What big Apogees need is clean and pure musical power and lots of it. To me that calls for big tube amps.

I would not consider vintage Krells for any serious rig of mine, with any speakers, because of a “whiteness" that many of us hear. Ditto for many/most of the other vintage solid-state amps. Some people like that sound, but to me it's not what live music sounds like. In fact, if Apogees really only worked with Krells, I would move back to Quads so I could keep using tubes. Fortunately, that's not necessary.

With a kilowatt of tube power on tap, the sound is effortless, majestic, spacious and detailed. No whiteness or zippiness, but plenty of air and space like you hear at live events. The sound is relaxed while still being powerful. The "slam" that you hear and feel at a live concert is there in spades. I've never heard this effect reproduced in the same manner from any other speakers besides the big Apogees. It is exciting and even frightening at times. The Divas can present you with the most delicate voices deep in the soundstage while thundering with drums and bass. The sounds don't seem to interfere with each other in the least; there is none of the intermodulation or thermal compression that you get too often with voice coils. Bi-amping helps here for sure. I have monitored power levels with voltmeters to see how much is needed in my room. At fairly loud levels approaching 90 dB, I'm seeing about 8 watts average from each of the four channels into the ribbons (16 watts per channel). Peaks demand much more power of course. So, I think Apogee's recommendation of 100 watts per channel minimum is probably about spot on. By the way, at present I am using Apogee's recommended Symo LS5-SX cables, in about 6 foot runs.

You do not need not go to the extremes with tube amps that I did to enjoy big Apogees. For fun, I am modifying (slowly, as time permits) two pairs of HK Citation II amps and I will try those on the Divas. I expect they'll do fine at 120 watts per channel (60 times four).