Switching the stock EL34's to KT88's, KT120 or KT150 will result in more bass.
The trade off is losing the EL34 midrange.
KT77 will retain the EL34 mids with increased bass, not as pronounced, but you may find it to be a good compromise.
New speakers or new tubes
I am running a Prima Luna Dialouge HP into Thiel 1.5s with a Rythmik 12 inch sub in a fairly large room with a vaulted ceiling. One of the features I like on the Prima Luna is the ultralinear/triode option.I first heard this ption on a Manley amp years ago that I couldn't afford but then saw it on the Prima Luna and I like changing it up. When I first brought home the amp I was using Tekton Lores with an efficiency in the upper 90s and the switch from ultralinear to triode was very apparent and enjoyable. At the time my Thiels were in the basement with blown tweeters. I decided to have them rebuilt by Rob at Coherent Sound and when they came home I put them in the system and decided I prefer them to the Tekton Lores. The Tekton has better bass, which was addressed with adding a subwoofer to the Theils, and bigger soundstage but the Thiels are so smooth to my ears in the midrange it's overall more enjoyable to listen to. However, maybe due to the lower efficiency of the Thiels, they don't sound great in triode mode. When the sound mellows out as it does in that mode it is now too flat and lifeless, whereas with the Tekton it was relaxed but still had dynamics, soundstage, etc.
My question is, if I'm going to make a change do I roll bigger tubes, KT 120s work in this amp, for higher watts, would go from 70 to 90 ultralinear and from 40 to 50 in triode, or do I look for a high efficient new speaker, perhaps bookshelf, that bring me the great midrange of the Thiels, the enjoyable sound of triode mode from the amp and perhaps a bigger soundstage than the Theils, more like the Tektons. Thanks for your thoughts.
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I am running the Rythmik sub from the sub out on the Prima Luna. Eythmik recommends this first in its set up instructions. Also, I was looking at Rel also and although Rel typically recommends running the speakers full range they have an instruction video particular to the Prima Luna and for this amp they recommend using the sub out. So for those reasons that's what I'm doing and the crossover is 80 hz I think. |
Yeah, Thiels are a tough load for a tube amp and your Prima Luna sounds like it just doesn’t have the juice to let the 1.5s fully open, so I’d vote for more tube-friendly monitors with good midrange like ProAc, Joseph Audio, Usher, Fritz, etc. Also, when funds allow adding a second sub will yield a nice improvement. Hope this helps, and best of luck. |
Typically, what I find is changing Amplifiers has an overstated and underwhelming impact on sound quality. Especially when you start with something that has a lot of power. That said, the Prima Luna seems to have a decent amplifier, that shouldn't struggle with the 1.5s. I suspect your problems lie elsewhere, and I would probably encourage most people to look at room correction. |
+1 @tablejockey, complements about your post. Highlighting it. One of the more accurate descriptions I’ve ever seen by a member sharing thoughts on 34s, mids, bass with the big tubes, including hybrid benefits of the 77s. Nice, Agree! 👍 |
Do you notice it’s quite a bit worse at lower volume levels ...Kinda flat, not engaging, not dynamic and more lifeless? A few reasons for the question. When you mentioned triode, caught my eye. @soix note too, the comment "to let the 1.5s fully open". Brought a memory. I read your post and wanted to share something for what it’s worth. For several years I played around building several sets of speakers using the exact same drivers Thiel used from the same parts mfg. Even with quality crossover parts they kinda lacked some presence and body with some amps (not all) and different modes of operation. If I turned up the volume a little it helped some, but not enough with any of my lower watt (10 to 50w) tube amps in triode. Not good at lower volume levels. I too ran subs with my Thiel-like custom speakers. Lower power triode was not a match. Found other ways to make them work a little better - for a while at least, until I discovered different drivers and more efficient / higher impedance speaker designs. I found this though driving these 86db/4ohm'ers:
While it might be be intriguing the whole idea of "triode" mode with your PL HP amp, and yes you heard something different with your Tektons, there are some speakers including your Thiel 1.5s that might actually sound better in ultralinear mode for reasons I won’t attempt to try and explain about your speakers. Forget the elusive deep sound stage of triode for a moment. Your speakers need to be lit up some. btw, my new mono tube amps are not triode, full pentode, and they do sound better when listening closely when paired with lower impedance / less efficient speakers more similar to yours. Question: Did you try UL mode with your PL amp and Theil 1.5s, and truly sit and listen for a good long while, multiple listening sessions? What did you hear? Maybe worth trying again since you upgraded the 1.5s. Turn your subs off for a bit too, you’ll hear the differences in a different way too between UL/Triode. Then turn them back on, listen again. Hope this helps in some way, fwiw. Best of Luck.
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What’s wrong with staying in Ultralinear? You should prefer one mode over the other. I use Triode in my setup, Dynaudio 1.8’s which are also a 2 way + passive radiator small tower. They are probably your polar opposite in terms of voicing. I don’t really worry that it doesn’t sound as good in UL. The differences that you are describing are exactly what you should hear when switching from one mode to the other, and the one that sounds better will depend upon the speaker. Clearly the extra dynamics of UL work well w/ the 1.5’s. I think if you liked both modes equally it wouldn’t be as good of a match. You can try the KT120’s and see what happens but I doubt it will change your preference towards triode. Actually for not much more than an Octet of KT120’s you can probably find the 1.8 mk2’s. Then just think of that button as the Dynaudio/Thiel switch. |
Decooney and perkadin: Thanks you for your posts. Yes the issue is more noticeable at lower volumes. Yes I've done many close listening sessions with both speakers and with sub engaged and not. Triode just isn't good with the Thiels so I am staying in UL. It sounds great, very happy with the Thiel Rythmk combo. Like everyone else, I'm always looking for an improvement so I'm considering standmlunt speakers, Pro Ac Response D2R I think caught my attention. 8 ohm speakers with 90 db efficiency. |