Wow, just upgraded the tweeters in my ATC SCM50ASL
I must enthusiastically share my experience, and recommend ATC users to contact relevant distributors to obtain the latest upgrade.
I just upgraded the SCM50ASL with the latest Seas Excel tweeters (with silver coil). The improvement is well worth the cost and about 3 hours of work. BTW, the Excel is the same tweeter in the top of the line SCM70. The only difference between an upgraded SCM50ASL and the SCM70ASL is a fully-discrete power amp in the 70 (op-amp drivers in 50), but ATC told me that the improvement is probably too small to justify the $3K or more.
As you all know, ATC is famous for the mid-range, but uses a cheap Vifa tweeter, but now, the HF is as good as the mid-range, uncompressed dynamic playback in HF is something totally new to me, but the voice and strings just keep going stronger and higher with no sign of stress or breakage.
This is just about 6 hours into the new tweeter, I can't wait for the tweeters to fully break in.
As a sideline, I am also auditing out the CA2 preamp, and it is a killer preamp for its price. I have had many expensive preamp, and my reference is a heavily modified BAT Vk5SE. The CA2 holds itself very well, and the remote control is very nice.
Unlike most other speakers, I am impressed by the continually upgradeability of my ATC SCM50ASL. First, I added the SL woofers, now I have new tweeters.