Subwoofer for classical music listener

@steakster
That sounds MUCH more promising. I would expect a reasonably well designed transformer coupled output stage to not have much variation in output impedance over the frequency range. Consequently I would expect that even if the output impedance is 630 ohms there would be no problem even if the overall load impedance is much less than 12K, and certainly less than the parallel combination of 12K and 50K which is 9.7K. (The 100K balanced input impedance of the power amp probably represents a load of 50K on each of the signals in the balanced signal pair).

And capacitance won’t be an issue either, given the short length of the cable to the power amp, and its exceptionally low capacitance per foot.

The one thing I’m left wondering, though, is if separate transformers are used for the RCA and XLR outputs, or if the circuit is somehow configured such that the same transformer is used for both. Or even if separate transformers are used, if there might be interactions between the two outputs as a result of effects that occur on the primary (input) side of the transformers. For example, effects that might result in a slight impedance imbalance between the balanced pair of signals going to the main power amp. An experiment that might be worth doing would be to turn the level controls on the subs all the way down, and seeing if there is any difference in the sound coming from the main speakers when the cables to the sub are disconnected from the preamp vs. when they are connected. (Of course, have everything turned off when changing connections).

Best regards,
-- Al

@almarg Whew! Glad to hear the better prognosis. The reason for the question is that there definitely is a difference in SQ between the original built-in Bash (digital) and the new Dayton (AB). The Bash seemed to go lower - more thunderous - it shook the room (suspended flooring). The Dayton seems to be subtler - smoother and more controlled - no room shaking. I was never able to compare them side by side. I’m under the impression that the Bash had less wattage because it didn’t have any heatsinks. From the photo below, I suspect that the RCA & XLR’s share the same transformers.

Here’s a preamp photo of the wiring including the transformers.
Here’s a preamp photo of the RCA & XLR outputs.The connectors on the right are toggle switches for ground on/off and XLR/RCA.
Here’s a preamp photo of both the input & output jacks.

I’ll try the experiment that you suggest sometime when I have the courage to change the gain settings. It took a long time to find those settings for a seamless integration. Thx mucho for your help.

@bob_reynolds On the SVS, does it do an AD/DA conversion to do the processing digitally, particularly for the high-pass?  I thought some subs do that.  I have an SB13, and may have misunderstood or overthought it.

@bob_reynolds . Interesting. Thanks. Maybe that's worth a shot on the SB2000.

I thought the SB13 had the highpass go through processing and through AD/DA, so I’ve been too stubborn, fundamentally, to even try it. We spend all this time and money trying to get our DACs right, just the thought of taking that and going back through what would have to be a lesser "quality" AD/DA kills me. Less so on the actual sub processing though...to me, the benefits seem to outweigh any compromises for the sub, itself.

But, I generally agree with you on DSP, but on the digital signal--before any analog conversion. Although I haven’t personally tried DSP in stereo.