Both the KT-2A/2A-KT and LA-3A versions are subtly optimized to the hardware in those units. There are differences in how the T4B operates in those units due to the properties of both the input transformers and sidechains. When the KT-2A first came out I bought one, and was immediately underwhelmed by the stock T4B. So, I grabbed a bunch of my reference T4B's and tried them all in my new KT-2A. I found a couple that I especially liked and went about measuring why those T4B's worked particularly well in that unit. After determining the pertinent specs for both the photocells and EL panel I began building T4B's to those specs and thus the KT-2A version was born.
The LA-3A story is similar but also different. I have rebuilt quite a few LA-3A's for customers in the past, and as a part of that I performed extensive measurements and performance tests on their units, both before and after the rebuilds. The front end of the LA-3A presents a different impedance to the T4B and therefore requires a different attenuation curve from the photocells in order to sound best. Also, LA-3A sidechains have a tendency to become unstable when they get some age on them, (which results in oscillations, both audible and ultrasonic) so the components in the LA-3A version are selected to try to mitigate this instability somewhat. Both the KT-2A and LA-3A sound demonstrably better with the bespoke T4B's in them.
Regarding the T4C, the original Urei T4C was installed only in the Urei BL-40 Modulimiter, which is an LA-3A style opto limiter and an FET peak limiter (not very similar to the 1176 though) in one chassis. It was originally designed for broadcast use, as an RMS leveler and peak limiter in one box, for use in front a transmitter. They were sold in the early to mid seventies, and were rendered obsolete overnight when the Orban Optimods came out. While the T4C was supposed to have a slower attack and slower release than the T4B, the T4C's I've had in house were all over the place. Many were actually faster than what we now call the "Classic" T4B response. Since the BL-40 was designed with the Opto section ahead of the FET section, the result is that the Opto section handled more of the peaks than it should have, and the performance of the FET section was compromised. I designed the Kenetek T4C to have a genuinely slower attack and release, as well as a smoother compression curve (e.g. lower ratio during hard compression) than the original T4C's, and different than any of the T4B's I offer. This allows the FET section of the BL-40 to do its job of peak limiting more effectively, the way it was originally envisioned.
That's all fine and good, but how many functional BL-40's are left out in the wild? Not enough to cost justify the development of a new product, that's for sure. But how many people out there use an LA-2A or LA-3A in combination with an 1176 to do parallel or series compression? Quite a few, I'm betting! The T4C is optimized for this kind of use, to give the 1176 a little more breathing room and let the LA-2A do the more subtle opto thing it does so well. So, if you use parallel or series compression you might like to try a T4C. Also, if you use LA-2A's or LA-3A's across your mix buss and just 'kiss' the signal with 2 or 3 dB max of compression, you might like what the T4C does to your mix.
I'm still finalizing the specs of the T4C and figuring out how to manufacture them consisitently, so we're probably a month or two away from them actually shipping, but I would be happy to contact anybody who's interested when they are actually available. Just PM me and I'll be back in touch.
Thanks!!!
Bill
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