Preamp and impedance question

So are you sunshine, so are you, in more ways than one.

atmasphere
I think its pretty obvious this isn’t about EPDR...

Yes it was, as this is what I answered to below, saying a 4ohm transformer would be a very good idea as that speaker "5ohm is a nominal figure" you can bet it goes down to 4ohm or even lower, and when combined with any -phase angle (epdr) could be even lower again.

gte357s 2) the transformer is designed for 8 ohm. If I want it to support 4 ohm, I need to upgrade the transformer.

The OP needs a 4ohm tap if not 8ohm also end of story!!!!!!!!!
That MQ300 Lux had one, you two are dreaming to think he only needs an 8ohm tap with that amp he’s getting built, and will have better resale value with both taps.

Like I said anyone to say EPDR (combination of impedance and -phase angle) "does not matter", is dreaming.

The odds are very against you sunshine. Over and out👎

I believe this statement to be entirely fictional
Obviously this phenomena isn’t limited to our amps
So this Stereophile article seems
I believe this statement to be entirely fictional.

Ralph’s gone into product protection mode.
I shouldn’t have use his amps as an example that couldn’t drive those JBL’s 1400 which IS fact and not fiction, "which even he agreed on" way back on the 9-17-2019 and here’s the proof! Ralph's answer https://forum.audiogon.com/posts/1804702 to my post before it https://forum.audiogon.com/posts/1803629
Your slipping Ralph, "one should always remember what one said no matter how old before saying the opposite" Confucius.

And these words "phenomena" "I believe" "seems" are also words that snake oiler’s, and voodoo’ist use, so as not to be held to account, a certain boutique $$$$$ fuse company use them a lot

Taken on board Ralph, with a yawn.
But for anyone to say EPDR (combination of impedance and -phase angle) "does not matter", is dreaming.

Your M60 mono blocks "could not drive the bass" of the JBL 1400 Array’s a 90db speaker without obvious stress playing the bass notes, even at "medium levels" and they were 100% fully functional.
And nowhere! near!! the EPDR load that a Wilson Alexia would present.

https://img.usaudiomart.com/uploads/large/1922864-fcdeac94-atmasphere-m60-mk-33-monoblock-otl-tube-a...

https://www.stereophile.com/floorloudspeakers/jbl_synthesis_1400_array_bg_loudspeaker/index.html

Just keep waffling on, because you still can’t see the forest for the trees.
https://i.pinimg.com/originals/7b/df/d9/7bdfd904dbe2ff73b9de8b8f7d84563d.jpg

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.

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

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

Mistake, get over it, and now the conspiracy theorist!.

Post removed Jun 09, 2020

That's right.
Clean up aisle 4.

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

EPDR is the -phase angle (expressed in -degrees) combined with the low impedance measured, and represents a "far more severe loading" to the amplifier than just the impedance itself, don’t listen to any idiots that says otherwise.

Here is the Wilson Alexia, it's one of the worst bass loads I’ve seen, and so thinks HNRR and Stereophile, it has an EPDR of 0.9ohm!!!!. And the reason why you should get the 4ohm transformer tap as well as 8ohm.

https://ibb.co/stQ44Ry

https://ibb.co/C8d2Zny

Cheers George

I know the X5 use a 12” Eminence driver. I look up their web site, and found the model and curve below. It seems it dips down to 7 ohm

This is definitely not what it will be when it’s in the speaker, as xover will come into it also, plus the -phase angle what ever that might be.
And that if it say -50 degrees in the bass, which is not uncommon, combined that with the "5ohm" of what the manufacture "says" the speaker is, "could" represent a combined EPDR ("equivalent peak dissipation resistance") load even down to 2ohms depending on what the -phase angle is.
Be safe and get the 4ohm tap also, or you could end up with a thick ill defined bass, which will effect the lower mids also. 

To give you an idea the 12" Eminence driver originally in my ML Monolith III’s, was an 8ohm driver but in the Monolith’s they measured with the 3rd order xover a combined EPDR down to 2ohms presented to the amp below 100hz

Cheers George

paying extra to get a 4 ohm tap will not have audible improvement over the 8 ohm tap, am I correct?

Yes it will the bass will be tighter/controlled with the 4ohm than the 8ohm tap, if the speakers are 4-5ohms
Go the $500 extra you can't go backwards once it’s done, and the amp will have far better resale value down the road.
Cheers George

Spatial Audio X5

Na, nothing measured on these, but just by the looks of of them, I'd say a 4ohm tranie tap will be fine for these, btw the real Lux has 16-8-4ohm taps on it's transformer.
Cheers George

gte357s
Can I just add a volume pot to a power amp schematic?

Of course you can, the Lux is 240kohm!! input impedance with 0.49v input sensitivity!!! so absolutely no need for any active preamp with even more gain here.
Just get your tech to use a 20kohm stereo Alps (Blue Velvet) volume pot on the input of the Lux.

The transformer is designed for 8 ohm.  If I want it to support 4 ohm, I need to upgrade the transformer.  I know that the speaker impedance curve can dip to 5 ohm at 30Hz.  Is it important to have 4 ohm support?

A 4ohm tap would be better, you'll halve your wattage though.
Depends on what -phase angle is associated with that 5ohms, what speakers are they? Hopefully there's a phase graph done on them.


Cheers George