Best power amp for Quad 63

+1 fortepiano50

Re:Shrill... Yes.. what you said...

Keep loving your Quads and I would echo the recommendation for Quad amps.

@fortepiano50

I’ve been meaning to add my .02 here for a few days, but have been busy.

I’m sure that many of the recommendations above will sound good. The OTL amps, in particular, will have a certain magic. I auditioned a pair of well-regarded Futtermans and thought they were great. But I was put off by the potential hassle of re-tubing those amps.

I also owned, and really loved, a Sanders Innersound Electrostatic amp. This was a circa ~2000 version of his current Magtech amp. It sounded awesome.

However, I caution folks about using a Sanders amp with any Quad ESL which has the "crowbar" protection circuit. The protection circuit is basically a dead short. It results in the amplifier dumping its prodigious power into the dead short in an instant, which basically can destroy the amp. Ask me how I know. This requires sending the amp to Coda for repair and service.

My very strong recommendation is to use one of the Quad amps - I’m now using a 909 and am very satisfied. It’s the only amp in the world designed to work with the protection circuit. It isn’t flashy. Not expensive. But an extremely fine all-rounder. Won’t have the transparency of the OTL amps, but substitutes rock solid reliability for that last little tiny bit of detail. That tradeoff is worth it, in my book.

The advantage of an OTL on this speaker is due to the very high impedance the speaker has in the bass. This peak is not due to resonance. Solid state amps will throttle back their power into this impedance and so getting the speaker to play bass with solid state is problematic.

OTLs OTOH can make power easily into this higher impedance, which works well with the electrostatic characteristic. A lot of our customers have commented that with our amps they don't need subs to make convincing bass.

ESLs in general do not obey the same design rules that box speakers do. Most box speakers are designed around the idea of being 'voltage driven' which is to say that the amp driving them can act as a 'voltage source'; being able to make the same voltage regardless of the load impedance. ESLs work better with an amp that makes constant power with respect to load impedance. For that you need a tube amp with no feedback so its output impedance is high enough for this to occur (you can also do this if voltage and current feedback in the amplifier are done in equal amounts, but this is very rare in amplifiers!).

For more on this topic see:

http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html