I've narrowed it down...
When all is said and done I believe the need/advantage for feedback comes down to amp design and certainly the speaker involved. Some speakers simply don`t need the additional damping feedback provides, other speaker types would benefit. The proof is in listening, my amp has no loose bass or undisciplined problems,there`s good control,articulation and nuance, so feedback is`nt always mandatory. In the end what matters is proper amplifier-speaker compatability. Regards, |
I 2nd Clio9s recommedation of Audiokinesis for a speaker line to consider. A great sounding speaker with the lower powered Atma-sphere S30s (30 watts, Class A, Triode, OTLs) - a killer combination at a relatively low price (for this hobby). I think the speaker was actually developed with the amp which goes a long way to ensuring amplifier/speaker compatability. If I did not own the Merlin VSMs, it is a speaker line that I really would be interested in; it caught my attention at RMAF. |
Yes the Atma-Sphere S-30 was used in the voicing of Audiokinesis designs, but IIRC so was NuForce. Duke happens to be a dealer for both brands so he certainly had access to each. My reasons for recommending these speakers is really about the flexibility and the fact that you can audition many types of amps with little worry as to compatibility. I have run 2 watt 45 and 12 watt EM7 SET amps, 35 watt EL-84 push pull, 70 watt KT-88/EL34 push pull, and 300 watt solid state amps with my speakers and the sound has always been pleasing, if not somewhat different. I'm sure there are other flexible speaker designs out there and if I were the Op these would be the types of speakers I would focus on. I for one am in the camp that the system should be built around the speakers. |
Unsound, you used the phrase numerous requests Your request for links which I provided does not constitute the above and my response also satisfied your lone request. So your statement above is clearly misleading. With regards to Norman Crowhurst, he does imply that negative feedback is beneficial. I pointed to him because he supports my claim about odd orders being distorted in a small degree by the presence of negative feedback. IOW he does not make a value judgment- that is made elsewhere, for example by Nelson Pass. However in Crowhurst's text if one is familiar with Chaos Theory http://en.wikipedia.org/wiki/Chaos_theory we see that Crowhurst shows the formula for feedback; compared with that of a classic chaotic system that the two are nearly identical. He also mapped the Strange Attractor that is characteristic of the resulting Chaotic system that an amplifier is when using feedback. These things are not coincidental; the presence of bifurcation (distortion) is predicted by Chaos Theory and Crowhurst, despite Crowhurst's writings preceding the formation of the branch of science we call Chaos Theory. Now the fact that Chaos Theory predicts negative feedback to be a destabilizing factor in amplifier design is something that should not be ignored (BTW, many designers will mistakenly claim that negative feedback is a stabilizing factor). However no value judgment is made, simply the expression of what is. It is other studies including the rather simple and repeatable test (to which I have already referred) that make the value judgment. That judgment is not entirely mine, BTW, but a fairly large consensus in the audio community which agrees that odd orders are unpleasant to the human ear (and is the reason that over 50 years after the introduction of transistors, tubes have failed to become a footnote in audio history). All I have done is outline what is. |
Atmasphere, the requests I made were for articles you have referenced before that are other than the Crowhurst. Since my previous post was not specific please refrain from making misleading statements regarding me. You generously provided a lengthy Crowhurst link in the past. In that article, Crowhurst suggested that negative feedback could be usefull, but it was important not to abuse it. Once again, I will remind you that according to Nelson Pass some people prefer the odd 3rd order. Once again, we seem to be straying off topic. |
It has gotten some what off topic yet very interesting and informative,good thread IMO. Atmasphere do DHT tubes behave differently from IDHT(Pentode) type tubes and would their response to feedback be the same? is one type more linear than the other? could that explain why some SET amps with DHT tubes can perform well without the need for feedback. Suprisingly the Yamamoto DAC I use is SS yet the builder uses zero feedback(he claims even 1 db of feedback is noticeable in the circuit). Regards, |
Unsound, The 3rd harmonic is one of the lower orders and is the only one considered musical with relation to the fundamental by the human ear. So Nelson's comment is spot-on. When Crowhurst was writing, it was not generally understood at the time that the odd orders (above the 3rd) were the distortions that the ear finds unpleasant, although you will see Crowhurst refer to 'listener fatigue' with respect to the use of feedback. IOW he knew something was up, but some of the aspects of the human ear simply were not understood at the time. Charles1dad, the DHTs are far more linear than tetrodes or pentodes. In fact all triode tubes (whether directly-heated or not) are quite linear, enough so that is is fairly easy to build an amplifier with them that does not need feedback. Triodes in general will generate distortion that favors the lower orders while the tetrodes and pentodes generate more distortion and also more of the higher orders and so tend to sound harsher, thus the need for feedback with them. If you speak to almost any SET designer, they will likely tell you that the lower orders that their amps tend to make are not objectionable to the human ear, which is true. They do color the sound though- the ear hears distortion as tonality- so the lower orders contribute to the 'rich' or 'lush' sound of SETs. |
I was doing more research prior to purchase today and saw that one manufacturer recommended an hour heatup of the tubes prior to listening... Are they all like that? Is there a down side to leaving the amp on (other than shorter tube life) which brings me to the next question. What is the expected tube life? |
They are all like that, but 15 minutes is more than enough to warm them up unless you really want to get paranoid about it. Tube life is very dependent on the tube used and the ciruit it is in - some output tubes in some amps will go 2,000 hours, the ones in my Music Reference RM10 MKII are said to go 10,000 - you need to ask the manufacturer of your particular amp, and the input and driver tubes usually last longer than the output tubes. |
Hey, you haven't lived til you experience a catastrophic tube failure. In my experience, you simultaneously get loud crackling and spitting noises from your speakers as a light show appears from the offending amp. This is much better if the lights are dimmed. Smoke will often rise from the amp's chassis, but with a little luck, the fuse will blow before any serious damage is done. As you bolt from your easy chair to turn things off, heart racing of course, you'll no doubt get that familiar smell of burnt electrical parts. Gee, it doesn't get any better than that! Lest anyone think I shy away from tubes on the mere chance one might fail, there are 68 tubes employed between my two systems and I never worry about it. |
