ATC ACTIVE VS PASSIVE

I am a Pass Labs lifetime customer, but I too was enticed by the active atc story.  the amps are a-b not class a like pass so not as liquid sounding.
I had the 15" actiive three ways (5 years ago or so).  it was impressive in many ways but the integration of the drivers just seemed off a bit.  Maybe the newer ones are better.  I bought mine used and sold them in 6 months for what I paid for them so it was a nice adventure.  I would have to say that looking at the amps ( I took them apart) i wasn't impressed by the build quality.  Just the clutter, soldering wires etc. struck me as a bit dated.  I went back to Pass and passive speakers. Pass is known for really clean designs so maybe I am spoiiled.  But the active thing makes a hell of a lot of sense.  Even Nelson Pass made a big active speaker.......few bought it though...........

@sm2727   

I believe ATC actives are biased Class A to 2/3 power. So they are Class A for the most part.

They are dated - discrete components and easy to repair and only minor tweaks over 30 years. Part of the appeal is that ATC got it right from the beginning. 

Unusual that the driver integration did not work for you - maybe your used speakers needed servicing.

Do they make a lot of heat? Do you leave them on all the time or only turn them on when you want to listen to music? Do they have a long warm-up time?

I turn them on just for music - I have not noticed a warm up period but it would take an hour or so to fully warm the massive heat sinks. They do run warm but nowhere near as hot as a Bryston 4B SST just idling (Class AB). Each amp drives only one transducer over a narrow range of frequencies and I believe the active version has a 16 ohm version of their mid range driver - so power is not excessive and heat is quite modest. There are no passve crossovers so all the power of the amp reaches the voice coil.

Hi everyone
Just joined Audiogon.  I've been importing ATC to the US for almost 20 years in pro, just started in Hi FI and few years ago.  Just saw this thread.

The real advantage of active is a practical one from the ATC engineering perspective.
The problems are 
1) losses of a passive crossover, power losses of speaker wire, dampening factor issues with length of speaker wire, etc. 
2) no precise phase adjustment of drivers in a passive crossover design.  
3) as drivers heat up, values of the drivers change and the passive crossover sees a changing load, therefore changing crossover behavior
4) Two well designed 3 ch amps and power supplies within the speakers can be built for less than a large two channel amplifier with pretty chassis, case and feature set and all the connecting cable.  

Brad Lunde
Lone Mountain Audio