Al, your suggestion to call Jensen resulted in some good information. I spoke to their designer, Bill Whitlock, who informed me the specifications shown on the website are referenced to a typically worst-case scenario where they considered a load (amp impedance) of only 10K ohms. The good news for me is that when the input impedance of the amp is higher, the load seen at the input of the transformer is also higher. Therefore, when using the transformers with amps having an input impedance higher than 10K ohms, the recommended 2K ohm preamp output impedance becomes less of an issue. Bill said, since the input impedance of my amps is 100K ohms, there would be no sonic penalty with regards to bass response resulting from my single-ended tubed preamp's higher output impedance into lower frequencies (3.3K ohms at 20Hz).
Ralph, I agree entirely that a fully differential and balanced preamp would be the best solution for my amps. However, by only looking for preamps that are fully differential and balanced, the field of available contenders has been significantly reduced. I do currently have a pretty good sounding differential balanced solid state preamp I am using, but the field for balanced tubed preamps is much smaller. Therefore, since I like the sound of my single-ended tubed preamp, and can apparently use it with the Jensen transformers without a sonic penalty, I believe (at least for now) that using the transformers is a good solution for me, and possibly also for the OP (depending on his preamp/amp impedances).
