darTZeel NHB-108 model one User Manual

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darTZeel NHB-108 model one User Manual Manual pdf 23 page image

darTZeel NHB-108 model one User Manual, version B 1.0 Page 23 of 35ally is. It is one of our favourite subjects for discus-sion, since it is here that we can find the key to theproblem.Since the CD came on the scene, lots of water hasflowed under bridges. In the ‘nineties, a big bugreared its ugly head on the "perfect sound for ever"road. Its name is "Jitter", and it is, more scientifi-cally speaking, an "uncertainty of chronometerprecision".Jitter is nowadays well known, and well explainswhy temporal errors, even when small, lead to am-plitude distortion. Effectively, a "0" or a "1" notarriving on time will be translated into output am-plitude which will not be proportional to the inputamplitude of the signal. We all know how jitter"sounds", when not cured.Thanks to – or because of – this famous jitter, atruly digital calamity, we can better understand thattemporal distortion will alter the precious and deli-cate analog, musical signal. In the analog world,though, TD is more subtle and more difficult totreat and cure.In the darTZeel NHB-108 model one, everythinghas been done to preserve the temporal integrity ofthe music.There are two principal means for reducing, or eveneliminating, TD.The first is to use several small but local NFBloops, instead of a bigger and slower, global NFBloop. This approach greatly improves signal trans-fer speed and propagation delay time.The second is based on the principle that temporalerror is equivalent to phase shift. So if one canenlarge the frequency response by a factor of ten(say 200 kHz), phase shift will be also greatly re-duced.Ideally, the best would be to apply both means de-scribed above. The only problem is that they con-tradict each other. High bandwidth generally re-quires higher global NFB, while low NFB leads topoorer frequency response.Here is where the darTZeel NHB-108 model onecomes in, the first very low NFB and high band-width power amplifier. No global NFB is used, andboth 1 st and 3 rd stages are even open loop! So whatabout the frequency response? Everything is okayup to the Megahertz range (1,000,000 Hertz), sayfifty times the audio range!T5.2. What application field?The electronic schematics of the darTZeel NHB-108 model one's audio circuit, as we will soonsee, is astonishingly simple."It's because the NHB-108 has high THD and IMDvalues", would say our well-meaning detractors.If you have read us from the beginning, you arenow perfectly aware that harmonics are not directlyresponsible for the sonic signature of an amplifier.The apparent simplicity of our audio circuit hasbeen effectively made possible through our choiceof semiconductors technology.If the THD and IMD produced by the amplifier arekept low enough, say lower than the audibilitythreshold, then no further correction will be needed,and the audio circuit can remain simple.At the start of this new century, 3 main technolo-gies coexist in the construction of transistors, thesebeing in chronological order:- Bipolar, in the early 1950s.- Field effect, in 1962.- IGBT, a mix of the previous two, in the ‘eight-ies.At darTZeel, we strongly believe in new technolo-gies. On the other hand, we readily admit that noth-ing can replace experience.So, "our" winner is…Bipolar technology!T5.2.1. IGBTsFor your own information, we are ready to tell youan old secret. What does the word "transistor"mean?It comes quite simply from the contraction of trans-fer and resistor.IGBT stands for "Insulate Gate Bipolar Transis-tor". It behaves like a bipolar transistor at its output,while being driven like a FET at its input.IGBTs are mostly used in power applications, likeinverters, switching power supplies, heart defibril-lators, and… for some audio power amplifiers.We do not have any preconceived notion about theuse, and more specifically, the sound of IGBTs.Results can vary with the samples used.Their linearity is close to FETs, which is, alas, notenough for us.IGBT technology is by far the youngest, and welack time to fairly judge them as to their long-termsound quality, reliability and availability.