Member's recommendations for tube amplification

And here I thought I was asking a simple question. : )

 @grannyring  @clio09  @charles1dad  @larryi  @atmasphere 

Thanks to all for the vigorous discussion. It has been immensely helpful. It's good to be back in school. 

I've followed convention and general norms on the issue of how much power is "right" by speaker sensitivity, etc.

Terry's findings with the LTA MZ2S with the Double Impact were difficult to accept when he first posted them. It's obvious it worked for him, his music choices, listening levels, his room, etc. though he did augment with slightly more power, though much lower than those 'norms' would dictate. Others followed and tested the same with replicated results, but also acknowledged that a few more watts of power was advisable.

It appears that there are clearly exceptions to the 'rule' and perhaps more than we would think or have tried. @clio09 's example being one that really stands out. Finale another. LTA/Triode one more, etc. etc. based on very specific speaker pairings from yours and others' posts in this thread.

In my case, your posts and the back and forth have made me much more comfortable taking a "risk" with a lower powered SET amp. That's good news, I think,...though it does widen the choices to consider. 

I'm looking forward to @teajay reporting on the Double Impact SEs ... his take will likely help and direct a possible choice. 

No decisions as of yet. I've had to start a Google Sheet to keep track of all the amp choices and who made the recommendations so I can reach out more specifically when I get closer to doing so.

Having the Pass XA-30.8 makes the wait very easy.

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If there are other recommendations out there, please post!!!

I'm back for a moment as Ralph contacted me about the thread.

For Bill, first of all I was not upset with your comments. I think Charles summed it up nicely. I left here a while ago because of the misinformation I kept seeing over and over again and how audiophiles were being influenced by it. Again, I come back every once in while because of something interesting I see. Your mentioning the Music Reference RM-10 was just that, as you rarely see that amp mentioned at all, let alone a discussion like this. A true injustice to the amp in my opinion and I owned one long before I started working with Roger Modjeski, the amps designer.

As I read over my last post it dawned on me that I could add a bit more to it to make it clearer. Again, Ralph's comment on SET power is not being disputed. It's true and something I have seen occur on test equipment in Jack Elliano's (Electra-Print) shop. It's not easy to get around the cold hard facts of how SET amps typically behave. Quite frankly some people like the distortion, it gives them the warm and fuzzies, and that's great. Until you know what to listen for, and when those nasty harmonics start to rear their ugly heads, as they will eventually as the power rises, then you should not find things so pleasant.

Jack Elliano developed a set of output transformers that allows two series triodes (in this case an EL-45) to provide about 12 watts of power. He also designed a summing loop that tapered off the rise in the distortion (IMD), which in no NFB SET amps happens pretty quickly after the first watt or two (when power to handle peaks in music is generally needed). So for this circuit IMD is less than 1.5% up to 3 watts (25% of full power). It will rise to 10% at about 7 watts (still extremely clean at greater than 50% of full power). The distortion finally causes the amp to clip at 12 watts (full power). That's why such a design (which we used in 45 and 300B designs as well) can push a 6 ohm speaker like Fritz's Carbon 7's to bliss, or as Charles noted those 4 ohm Hornings.

In a typical circuit without such a summing loop IMD distortion will rise to nearly 30% at 7 watts, and at this level you anyone should be able hear it (although the rise up to that point could be challenging). The first few watts will be fine for the most part (the 20 - 25% of full power Ralph alludes to), but the amp will turn out the nasties quickly after that. However, that's not to say such an amp can't be enjoyable in a given room with a given set of speakers at low listening levels, as I've heard it happen. On the other hand in the A/B testing of these two circuits I could hear the distortion as we cranked it up past 80 dB (on 94 dB 8 ohm speakers). You learn where your limits are pretty quickly.

There are a lot of nice folks here still, but I really would be doing myself a disservice if I hang around. That could change but for now life beckons and I'm knee deep enjoying life in my new surroundings in the Bay Area while still fiddling around with my system when time permits. I hope I answered your question Bill, take care everyone.

Perfect. Thanks @clio09

Funny thing is I am feeling the same as you regarding these Agon threads and sense hibernation is right around the corner for me. Things have changed over the years, discourse is rough and angry often times, and I have grown weary.  I am sure my fuse is short and sensitive for this reason. I have a few posts left in me and then will most likely hibernate.  I stay pretty fit and do not have the fat cover I should for this season of change😁   I remember our shared experience with passives, TRL, and general audio years ago.

Enjoy life, loved ones, and your passions!

David,
You’re in a good situation, speakers that have made you happy and a top notch Pass Labs XA 30.8 as  your amplifier reference point. Your approach is very rational, taking time to learn more about the "many" fine choices available to you. I believe that your quest will end very successfully. Your thread has generated informative commentary and perspective.
Charles

Jack Elliano developed a technique to reduce distortion he called 'Class A3' (as opposed to class A or class A2). As a result, his SET amps were the exception to the 20-25% rule to which most SETs adhere. Jack had a patent filed on the concept.

Regarding discourse on the threads, I find for the most part that the best approach is to not take things personally regardless of the conversation. I see it as not really being my problem when someone makes personal attacks. Occasionally I'll get trolled; however the site is moderated, but in order to invoke the moderation you have to report the offending post. I find that its really important to not respond to a post that offends you. Occasionally the thread gets taken over by trolls and at that point I stop posting on such a thread- there is no further point.

These tactics work pretty well regardless of what site I post. There is one site, hydrogenaud.io, that is very much all about objective measurement and also has an unusually high troll content; on that site you have to have a pretty thick skin. But the same ideas apply even there.

When you take all the weirdness and such that are part of the internet forum experience personally, that's when it stops being fun. And the fact of the matter is that there isn't a good reason to take anything said here personally!