Impedance Question?

jmcgrogan2 has the best answer +1

Our tube preamps don't have an output coupling cap- so they can drive 600 ohms let along 10,000 ohms with ease. The output impedance is the same at 5Hz as it is at 1KHz or 30KHz.

Generally speaking though, most tube preamps are likely not to play bass right driving 10K, simply because of the output coupling cap being too small.

That said, I have a Dared MC7P (there’s a dash in there somewhere..) and it played nicely with a Crown amp that had in input impedance of 10k and currently plays well with ICEpower monoblocks. The Dared apparently has a low input impedance.

It’s all so freaking variable!

The Dared apparently has a low input impedance.

Yes as you stated 100ohms in your previous post, which will drive any poweramp.

But being a tube it will be capacitor coupled, and if that cap is not big enough in uF, that 100ohms output impedance can start to rise in the bass and increase that 100ohms, and if it rises enough, into a 10kohm amp you could get bass rolloff.

The cap needs to be at least 5uF into 10kohm, to be rolling off the bass -3db at 3hz which just starting to rolloff at 20hz

This is why direct coupling is so good, no cap to **** things up and to colour the sound.
Best cap is no cap.

Cheers George

And that is why I'm leaning towards a direct coupled SLP-98 with some 50's JAN tubes.

@georgehifi oh man, sorry. I didn't mean to repeat myself. I've the schematics for my pre somewhere, I'll see if I can figure out what value the coupling cap is. 
What formulae are you using to calculate low frequency roll off?