Preamp and impedance question

Zu Omen Def is actually 6 ohm nominal! No wonder I hear better sound with the 4 ohm tap!

And if that’s nominal, you can bet you b****s, they dip down even further than that.! And even further again when you bring in the -phase angle into the equation as well if it’s high.
So what does that tell you? get the optional 4ohm tap on the MQ-300 output transformer.

Here again is something JA of Stereophile says about combined low impedance with -phase angle (EPDR)
This is on the Emotiva Airmotiv T2 review just put up to read on the web.   Nominal impedance: 4 ohms by the manufacturer. 
https://www.stereophile.com/content/emotiva-audio-airmotiv-t2-loudspeaker-measurements

John Atkinson : Stereophile
  Fig.1 shows that the T2's impedance magnitude does average close to 4 ohms, though the minimum value is 2.85 ohms at 112Hz, and there is an amplifier-taxing combination of 4 ohms and –53° electrical phase angle at 78Hz.

Cheers George

@georgehifi , Maybe you could explain to gte357s, exactly how this EPDR is "taxing" a tube amplifier knowing that being frequency based, and real music, the time at any of these EPDR minimums is very short.

@gte357s , changing the tap from 8 to 4 ohms will have minor changes on the frequency response, distortion, and damping primarily of the woofer (which also shows as frequency response). There are likely as many who would like the 8 ohm tap as the 4 ohm tap, but of course best to use the one you like.

gte357s OP
@georgehifi Please excuse my limited knowledge, I don’t fully understand the phase angle and stuff.

Don’t listen to the conspiracy theorists here, just read this article in Stereophile "How Loudspeakers Torture Amplifiers" used by Stereophile in all speaker measurements they do, with comments always on "how combined impedance with -phase angle (EPDR)" is the real total load that the amplifier will see.

Look nearer the bottom of page 1 with the paragraph that starts of with

" But loudspeaker loads are not, in general, resistive. They comprise complex impedance’s with both resistive and reactive (capacitive and inductive) elements,"

https://www.stereophile.com/reference/707heavy/index.html

Then go to page 2 where they get right into EPDR
https://www.stereophile.com/content/heavy-load-how-loudspeakers-torture-amplifiers-page-2

Then also page 3
https://www.stereophile.com/content/heavy-load-how-loudspeakers-torture-amplifiers-page-3

And this is the reason why Ralph Karsten’s big Atmasphere’s monoblocks that my friend had, could not drive the bass of the "so say" easy load, high efficiency (90db), easy impedance load (8ohms) of the JBL 1400 Array speakers, because of the added -phase angle of the EPDR combination.
I circled In the red circle https://ibb.co/SKbkF4t

JBL 1400 Array. Its minimum modulus of 4.9 ohms occurs at 92Hz. Its minimum EPDR is 1.9 ohms!!!

Then read about the B&W 802D’s EPDR load to the amps

Cheers George

@georgehifi , all you did is regurgitate what you already said, without in any way relating EPDR to a tube amplifier, except in the way you used it, it is wrong. EPDR is not impedance and-does-not impact frequency response w.r.t. output damping factor. That is not how it works ... at all.

How does EPDR specifically impact a tube amplifier??  This is a discussion on tube amplifiers. Just saying "It could not drive" is at best an opinion based on your friends listening preference, but without any hard data ....     EPDR does not impact current delivery, it impacts power dissipation in the amplifier. Do you refute that? The highest current will be delivered at the impedance minimum. Do you refute that?

@atmasphere may wish to jump in based on the comments made about his amplifier.

The proofs above from guys infinitely more savvy than you, like Matti Otala, Eric Benjimin, Keith Howard 

Atmasphere stick his neck out for you. That’s a low percentage ask.

Atmasphere was the one that said the JBL 1400 are a difficult load for the tube amps, when we were talking about the Wilson Alexia’s 0.9ohm load with his amps, because I stated the Alexia’s are even worse than the JBL’s.
do a search and find it.