Preamp and impedance question

@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.

Savvy how? I am sure I can match them in patents and AES papers. Really doesn't matter, since they would all agree with ME, not with you. You don't even realize that you have not made any arguments to support your claim and have done nothing to show the impact of EPDR on a tube amp. You just keep repeating the talking points that illustrate either a lack of understanding of EPDR or of amplifier architecture and operation. I really couldn't care less that what you believe, but when you come on here and give bad information, I will point it out.  I called out to @atmasphere as he appears to have a solid understanding of amplifier operation.

Here is what @atmasphere said,

**Any** 60 watt OTL will be uncomfortable with a load like that (see JA's comments in the review at the link). This is a great example of how *not* to do it- you always want a tube amp to play loads for which it is intended!

I don't know atmasphere's OTL specs, but normally they have a somewhat high output impedance. The huge resonant spike with voltage drive on the JBL would cause a significant level change at that frequency.

We also noted that particular customer was going through power tubes faster, which is no surprise since a lower impedance will cause more of the power generated by the output section to be dissipated in the output section- and that's hard on tubes. We finally got him to install a pair of ZEROs and then the tubes stopped failing, plus he had more power. The Wilsons traditionally have been fairly efficient so none of this should come as any surprise. The national sales manager at Wilson (John Giolas) had our amps for several years.

Note this is --average-- impedance, not EPDR minimums, which will increase the instantaneous power dissipation in the output section of a tube amplifer (exactly as I said) based on music content, which does not have much impact on tube life at all (also what I stated). 

Here is another point, at the same volume level, whether you use the 4 ohm or 8 ohm tap, the instantaneous power dissipation in the amplifier output section will be almost exactly the same at the EPDR minimum.  Then again, I believe the MQ-300 is ClassA, in which EPDR does not have any meaning.