I agree with clio9 that the transformers (and associated circuits/parts) have a tremendous impact on the quality of sound through electrostats. In my many pairs of Acoustats I have Spectra’s, which of the Acoustats are more like Finals (electrically segmented) which were only available using transformer based interfaces, earlier interface driven models that aren’t electrically segmented (like the Model 3), and original direct drive servo amplifier driven Acoustats (Model X and the Monitors). Amongst my sets of those direct drive servo amplifiers I have fairly stock and highly modified amplifiers. Modern amplifiers can make those Spectras sing. The middle generation interface driven models can play extremely well. The direct drive amplifiers are magic.
A fellow I bought a pair of Spectra 33’s from had never heard the servo amps, but was a big electrostatic and horn lover. He actually ran Sound Labs for some years before switching back to Acoustats. Curiousity eventually got to him enough to buy a pair of very nice, highly modified servo amps to drive some Model 6’s. He was blown away by how great they sounded.
Those servo amps got some bad early press that was really undeserved. They are fine. Stock amps aren’t bad. The direct drive part is their magic. The later builds were better than the earlier ones, but with a little work they can be greatly improved. If you want to go crazy it’s kind of amazing how far they can be taken and there are folks out there still coming up with improvements. To me, the most amazing thing that stands out for Acoustats vs other electrostats is the panel reliability. The newest Acoustat panels are maybe 30 years old. The oldest are approaching 50. And nobody is rebuilding the panels. They just keep trucking. They are certainly NOT perfect panels. It’s easy to pick out things I wish were better, but it’s hard to argue against demonstrated long term reliability.
To bring this back around to the Finals — part of what got me to order a pair are some of the details that I think are going to make these long life panels. The teonex, the low bias voltage, and the process and coating used to deposit the conductive layer. I’m hoping these turn out to be as long lasting.
The arcing report above catches my attention. I’m hoping to find out more.

