Possible impedance matching issue with subwoofer?

Al, the builder told me if the plate amp has the negative high level input grounded or in common with another connector (left minus connected to right minus, then I would need to do a special connection from the Atlas. Connect only one phase of each channel ( presemably the plus) to the high level input.

I will look at the back plates tonight.

Yes, but in addition to connecting the + output of the Atlas to the + high level input of the sub (for each channel; I believe you are using two subs), you also need a ground or signal return connection between the sub(s) and the amp. Otherwise you'll most likely get a BIG hum.

Best regards,
-- Al

Ha, ya a BIG hum is the last thing I need1

Ok, one last question so I can make my final decision. I am not sure I want to go the high level hook up route as I simply don't know how the plate amps are wired. Can't see anything as all the sub binding posts are hooked together on a circuit board with the traces hidden from view. I would have to take boards off etc and I don't want to do all that. My amp is fully balanced and I fear causing an issue due to the way the sub high level inputs may well be wired -Keiga KG 5150.

Bottom line. Is the line level hook up going to cause an issue in terms of impedance mismatch or not? Al comments as well as Nsgarch suggest I will not have an issue in terms of sound degregation. Here are the facts on my gear.

Preamps output impedance is 5k ohms
Plate amps input impedance is 22k ohms
My stereo Atlas amp has an input impedance of 470k ohms
My sub cable is very, very low capacitance -Al referred to it above and they 10 feet long. I run two subs.
My ic's between the pre and amp are 3 feet long

While the music sounds good I do wonder if I am rolling off in the bass area and possibly compromising the sound of my main speakers. Again, both Al and Nsgarch seem to suggest no issue. But some other comments suggest otherwise? I would buy a Buson buffer to place between my pre and subs if that is deemed as best. I understand that such a buffer would reduce what the subs see as output impedance down to under 600 ohms and perhaps as low as 100 ohms.

I would rather not spend the money if there is nothing here to be concerned with. I set my subs to play 40 hertz and below only. Since I have 2 I set the volume very low - near the minimum really.

What do you expert say.

I would add to the key facts that you listed for your gear that the output coupling capacitor in your preamp is 3.3 uf. Many tube preamps use somewhat smaller coupling capacitors, which would increase the likelihood of deep bass rolloff. Many tube preamps also have much lower output impedance at mid and high frequencies, which would further increase deep bass rolloff when used with a smaller coupling capacitor, because it would result in more of a DIFFERENCE between the low frequency and mid/hi frequency output impedances.

Per my earlier analysis, my feeling is that you are certainly not experiencing any major deep bass rolloff, and at most any deep bass rolloff would be extremely slight and would only occur on material containing spectral components approaching 20 Hz.

As I indicated earlier, if it were practicable to go to the high-level sub connections probably the most significant difference would be due to putting the sonic effects of the amplifier in the path to the sub. And that difference, while standing a good chance of being significant, is probably unpredictable in terms of being better or worse.

Best regards,
-- Al