What are ideal impedences between tube and ss?

My thanks to Herman and Clueless for the valuable info. I went to a vocational high school many moons ago and while trying to stay up on hardware these days the theory aspect of this hobby seemed to slip away from me.

I think it is the latter. Sensitivity doesn't pertain to your original question.

Your setup, like most, is designed to transfer voltage from the pre to the power, not current. Some current will flow. But if the input impedance of the power amp is high enough, and yours is, then this current will be minimal and everything will be fine.

Hi South:
Does this help or is it too arcane?

I remain

Thanks for your reply. Tell me this, if the pre has a high amount of gain and the amps sensitivity is low enough would that help with the current transfer you mentioned. I don't listen very loud and my spkrs are 89db(Meadowlark Kestrals).Or does this have anything to do with my question. I'm trying to get a handle on this in case I want to change pre's or amps. Thanks again.

Your preamp output impedance is very typical. The input impedance of you amp is on the low side of normal. Typical for a SS amp is 50K and for a tube amp 100K even though some like yours and I believe the Nelson Pass amps are a little lower.

A general rule of thumb says the goal is an input impedance at least 100 times higher than the output. This, of course, is open for debate. Yours is closer to 50, but that should not be a problem as you attest to with your observation that it sounds great.

There are several issues. At the pre-power interface your goal is to transfer voltage from the pre to the power. As the power input impedance drops it draws more current from the pre. Some pre amps don't like this and become non-linear. You also drop more voltage across the output impedance of the pre amp so less is available to the power amp. You then have to turn the volume knob up higher. Depending on the overall gain of the amplification, this could be a problem if you run out of voltage before you get it as loud as you want.

On the other hand, a higher input impedance makes it easier for noise to makes it's way into the power amp. So you want a high input impedance to make it easy on the pre amp and low impedance to minimize noise. You can't have both so a compromise is made.

There is also a camp that advocates matched impedances including the interconnects and another that uses a current transfer design rather than a voltage transfer like your more typical design.