Preamp and impedance question

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.

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

I have not even once changed what I have wrote about EPDR. I have addressed your specific arguments in every case, while I have yet to see you make even one deep technical analysis w.r.t. the discussion  you raised on EPDR.  I have also used my own words, while you have only linked to articles.  Would you like some Maple Syrup with those waffles? Perhaps it will go well with those sour grapes.

georgehifi7,226 posts06-10-2020 1:21amJust keep waffling on,

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 believe this statement to be entirely fictional. Our bigger amps (MA-2 and MA-3) drive that speaker with ease, although I would hesitate to call it an 8 ohm load. A customer of mine has that speaker and having spent a week at his house, I can say the two work very well together. He owns the MA-3s, but the MA-3 has a unique bank-switched power tube setup that allows you to shut off 1/3 or 2/3rds of the power tubes (such that they are not even lit up) thus allowing the amp to run with much less power. The speaker and the amps worked fine together in all three modes.


Tubes are a bit different from transistors in a number of ways as we all know :) One of the ways they are different is the Safe Operating Area (SOA). With tubes you can exceed the SOA without damage to the tube if the tube is allowed to cool off afterwards. A tube dramatically overtaxed, such as in a loss of bias, can turn cherry red from heat, but if allowed to cool off, and the problem corrected, can continue to give normal service. You simply can’t do this with semiconductors- Very Bad Things happen- exceed the SOA and the device is likely damaged immediately! Now the output section of the MA-1 amplifier (140 watt monoblock) can sustain enough current in a pinch that it can easily knock out a 15 amp circuit breaker in the wall. Of course we fuse the amplifier in such a way that this can’t happen in practice, but the interesting bit is that in this situation, while the tubes are obviously outside their SOA, they can survive this sort of thing easily.

During WW2, To get more power out of an 807 (which is basically a 6L6 with a plate cap to prevent arcing), some transmitters placed the tube in a water jacket to cool it- and thus got an astonishing amount of power out of it (around 500 watts- but keeping in mind it was also class C). So this concept is well-known and been used to advantage for a long time.


This simple fact is why a tube amp can drive loads that you would not expect possible (which is why the later Wilsons, despite their low impedance in the bass, seem to work fine with our gear). I’ve had to learn it through experience myself- when I was first approached decades ago to see if our original M-50 (immediate predecessor to our M-60) would drive a Quad ESL63, I thought the amp would fall flat on its face. Turned out to do the job quite well- better than an RM-9 owned by that customer.


Obviously this phenomena isn’t limited to our amps- all power tubes have this aspect of a ’soft’ SOA. So this Stereophile article seems to have more relevance to solid state amps, where semiconductors are simply going to punish you with failure if you don’t observe their limits.