My amps respond well to changing the input tubes.....a lot of guitar amp guys say the same thing....best thing with a prima luna is to call Upscale they are the distributor
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I don’t believe output tube rolling is the answer to the OP’s problem, as the below will still be there and explain.
One must remember speaker and the speaker wire introduce not only a resistive load to the amp but a capacitive one as well. ESL’s even more so capacitive, so all amps theoretically should be unconditionally stable, eg no ringing whatever the load on bench square wave tests.
In Ultra linear mode this amp is a little unstable into 10khz 8ohm pure resistive loading, even without any speaker/wire capacitive loading which would exaggerate this ringing even more which may cause the brightness heard.
But in triode mode it seems to be a bit more stable, and should not sound as bright, but still we don’t get to see it with some capacitive loading just 8ohm pure resistive.
Even JA "Stereophile) who did the above measurements said this
" PrimaLuna DiaLogue Premium performs at its best with tubes operated in Triode mode."
One can clearly see in ultralinear mode the sharp rising frequency response after 20k this is the rigging seen on the 10khz square waves. "It a bit like an uncontrolled resonance peak of some metal dome tweeters" "brightness???"
It seems to me that in Ultralinear mode they’ve gone for too much bandwidth (70khz) at the sacrifice of stability.
But in triode mode all is far better behaved, with no peak after 20k.
If I owned this amp I would only use it in triode mode, and if that didn’t have enough power, I’d get another amp that was.
The stock Primaluna Preamp tubes in the 2 middle slots were way too bright for me. So if you want to go with new production tubes. I would suggest the reissue Mullard 12au7's. If you want to experiment with old American tubes. You might want to seek some Baldwin or Conn organ pulls for less than $30 a pair. Triode mode will help as suggested.
George HiFi- since you seem to have a better understanding to the technical concepts, perhaps you can explain this to me. The amp has output terminals for 4, 8 and 16 ohms. While my proacs are 8 ohm, when I run them using the 4 ohm terminals, they sound better - bigger soundstage, more air around the instruments. If it matters in the equation, my set up requires me to run about 4 meters of speaker cable (I cant place the amp next to the speakers)- which I am using Kimber 8TC bi-wired.
Everyone Else - I have reached out to Kevin at Upscale about the V11&12 tubes and will see what he recommends. I will check out aniwolfe's source, too. When you say the re-issue Mullards- are these the Russian made tubes?
Yes the Mullard reissues are Russian. Jared is usually my go to guy at Upscale when it comes to tube recommendations. Kevin can be difficult to get an good answer from. Just my personally experience.
Also I want to add. You shouldn't be forced to use only Triode mode with your amp. If so, then what's the point of owning it? I prefer to use UL most of the time.
If you are sure about which impedance terminals sound the best you can try some very inexpensive new stock JJ tubes in the 12AU7 spots.
The JJs come stock on the Cronus Magnum and are a dark sounding tube but still capable of great sound. This will be an inexpensive way to see if you are headed in the right direction. You can get JJs 10 bucks each.
part of the brightness in the PL Dialogue and HP are the use of the SCR coupling caps. If you swap those out for Jensen Copper foil, you will get a midrange to die for and a 3 dimensional and airy top end.
The first AU7 (center two tubes) will have the largest affect on sonics, so maybe start there first with some Mullards. The 2nd and 3rd position sockets will have a lesser effect on tonal balance. Perhaps as some others suggested, use some RCA clear tops (used by many organ mfgrs back in the day) in those other slots.
Hi, to answer that properly without guesswork, I tried to find an impedance graph of your "proac tablette anniversary" speakers, but with no luck.
While they are factory rated at 8ohms there could be dip/s maybe to 4ohms maybe in the power regions, and the 4ohm tap from your amp then has a better damping factor (output impedance) to control them at that frequency.
Just go with the 4ohm tap in Triode mode, as this amp is questionable for capacitive stability in Ultra-linear mode. As Stereophile has stated, if you find you don't have enough power, look to either more efficient speakers or a bigger amp. Don't go wasting money on different tubes they will not fix the instability in Ultra-linear mode.
I would listen to Aniwolfe. He and I both have been rolling tubes. He is more experienced than myself in the 12AU7 area so he is a good source of information. Also there is a review of the Dialogue Premium in Stereophile talking about the upper midrange glare and the reviewer swapped out the stock tubes to combat this problem. I don't agree with his KT120 power tube choice but to each his own. I can't remember the 12AU7's he tried. I would start with cheaper tubes and/or call Upscale and let them guide you.
One of the great things about owning a tube amp is altering the sound with different tubes. Especially ones with auto biasing. All you need is 2 12au7’s to start. I would call Jared at Upscale to get his advice on what would make the biggest impact.
As far cryo goes. I don't have much experience. I would imagine it would be a subtle difference from what I have read.
Meiatflask... The Naim kit has been known to add a bit of treble emphasis in some applications. With that said,I would try a pair of the NOS Mullard 4003’s as already mentioned. They definitely can tame the highs a bit and also add a pleasant...smooth as honey coated flavor to the mix...though admittedly,not to everybody’s liking. It would be the first thing I would do for the improvement you are looking for.
I just ordered the British mullard 12au7/cv4003 from upscale, a matched pair for the v11-12 positions. I thank you for all of your comments, and I'll let you know how things turn out after a have had some time for serious listening.
I am am going to open a new string on cryo treatment (later today) , as that has me curious. Jared at upscale said the cryo makes the tubes break in faster, so for 8 bucks I went ahead with it.
Recommendations seem to be all over the place. Whatever your ears end up liking, the PL DP preamp would be the optimal setup.
With that in mind, the suggestions of NOS RCA,GE,Raytheon. ..
American tubes instead of the Euro/Brit tubes have made my PL HP sing like a VERY expensive amp. IME, a decent(not necessarily $$) also add to refining these great amps.
With a little searching, you can find 2 decent US tubes for the price of 1 popular Euro/Brit tube.
leotis107 posts05-20-2017 1:28pmHey George,Yeah for a tube amp, their not very stable in ultralinear mode as JA of Stereophile found when doing his bench tests measurements, and Art Dudley heard.
No amount of tube rolling will cure this, as it’s circuit/feedback/output transformer related, best to keep it in triode mode for better stablity.