Electrostatics and tubes

Let's clear up something here. Roger's direct drive amplifiers were made for either the Acoustat ESLs (non-hybrids) or his own ESLs. None were made for the Quad ESLs (the voltage was too high). The RM-10 was manufactured during the time Roger owned Vandersteen and Quad ESL speakers so those are the speakers he tested the amp on. By his own account he was surprised how well the RM-10 behaved on the Quad ESL. The key was that the output of the RM-10 was 35V which was the maximum tolerated output of the Quad ESLs so the amp wouldn't overdrive the bass panels. By his own admission Roger acknowledged in my presence while listening to the RM-10 on my Quad ESLs that while it was a nice amp for the speaker, and pretty flat, the bass was a bit lean.

The Quad ESL (57) has been getting a bad rap for it's bass production for years. The speaker has quite good bass response down to 40 Hz. In most music, that would suffice. If you listen to rap/hip hop, electronic/dance, some of the newer movie soundtracks, and organ music, then the speaker will certainly not reach to those depths. The Quad ESL will even go below 40 Hz but at that point while the bass is still pleasing, it's more of the one not bass variety. I use a distributed bass array with two open baffle bass units next to the speakers and and additional two sealed boxes spread asymmetrically about the room. All bass drivers are 10", active crossover set to 100 Hz low and high pass with 24 dB slope. I use a Music Reference OTL-1 on the Quads and Bel Canto Ref 1000M monoblocks for the bass drivers. Works quite well.