Primaluna dialogue premium HP tube rolling suggestions to reduce brightness
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. Cheers George |
meiatflask 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. Cheers George |
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. http://www.stereophile.com/images/214PLDPfig03.jpg 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. http://www.stereophile.com/images/214PLDPfig04.jpg 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???" http://www.stereophile.com/images/214PLDPfig01.jpg 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. http://www.stereophile.com/images/214PLDPfig02.jpg 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. Cheers George |
