Tube Preamp/ McCormack Amp impedance matching

My concern is the effect of impedance on HF or low end roll off. Newbee, my speakers are the Ohm Walsh 5000. I also have 2 powered subs that would be connected to the 2nd set of pre outs on the VTL so that plays into impedance as well.

Foster 9, To add to your burden - some pre-amps with 2 outputs have them configured so that both outputs cannot be used at the same time to drive two different amps at the same time. I have a pre-amp configured as such and when you add a 2d system you load down the other output and change the impedence relationship.

I have another pre-amp with two outputs which will correctly drive 2 amps etc at the same time with out loading each other down. With the former, I compensate by using one set of outputs and using a Y connector splitting the signal between the two amps. If you are experiencing a roll off when you are driving two amps, etc, off two outputs, check with the pre-amp manufacturer to see how the outputs are configured, don't make an assumpion that something that you can fix is a problem.

While I agree with Bob's comments, this falls under the "but there is other information we do not know", I wouldn't be overly concerned with the actual impedence curve unless you are trying to solve a problem. I have a pre-amp with 600 ohm output which sounds fine with an amp with 10K input even though the manufacturer recommends 20K, and conversely I have a pre-amp with a 3500ohm output which doesn't interface well even though the amp has a 47K input. "On paper" they both should be fine but the mismatch (or lack of a mismatch) shows up on listening. Also, SS amp output impedence curves matching speaker impedence curves are not usually a problem for a high quality SS amp unless you are driving a substantial sub 4ohm load at certain frequencies in the speaker, a problem usually solved by getting amps with high current (and possibly power out put as well depending on the speakers efficiency) and the concurrent ability to drive 2 ohm loads.

FWIW.

Emerson -- Apart from the issue of the powered subs, I think that your original question has been well answered (and we are very fortunate to have Steve participating here at Audiogon).

Re the powered subs, there are three key questions:

1)What is their input impedance?
2)Does the VTL 2.5 have separate buffer stages on the two sets of outputs, or are the two sets of jacks simply wired together inside the rear panel (which is probably how the majority of preamps with two sets of outputs provide them)?
3)How long will the interconnect cables be, and if you are intent on using specific interconnects, what is their capacitance?

Regards,
-- Al

Thanks Newbee and Al. Al,I'm using 20ft runs of Blue Jeans LC1 cables which I learned from you are low capacitance. I believe the input impedance on the sub amps are 6k ohms.