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First One - mosFET amplifier module

Hi Walkalone

Because there was never an input cap present in VSSA, in any variant. VSSA had AC coupled feedback and DC coupled input, so global DC voltage gain was 0 dB, meaning +1 Vdc on the input resulted in +1 Vdc on the output. If someone likes to have an input cap - no problem, free choice, personally would recommend 10 uF Mundorf or Jantzen film cap.
 
I try to understand tendency of grilling the output transistors, but it is impossible to find reasonable purpose. Maybe this is usable for headphones or in 3-way active system for direct tweeter driving. If you carefully study the thermal transfer characteristic data, maybe Exicon ECW20N(P), you will see, with higher temperatures in term very high bias, without fan cooling, you will be soon on thin ice. The main quality in sound are fastness and low output impedance, linear transfer up to 100kHz or more, with no more than 2° phase shift, to maintain all harmonics to stay in phase with main carrier tone and not 20° after it. Fortunately, the FO contains all the excellence. Every time I heard low level debate about 20Hz-20 kHz limited sound I am horrified. Maybe someone expect music will be pure sinusoidal characteristic, but this is a miles from truth. Sinus signal is only backbone for all distortions, implemented in form of triangles, grass and all other micro disturbances inside sinusoidal signal, that mean real very high frequencies. Human ear, like Mr. Linkwitz said on last session, in all years of evolution depend on detection these distortions, to separate distance, direction, recognize cello from violin with same tone and not the last, how you can recognize voice of your own children in the crowd. Mentioned this phenomenal characteristic and high level sensitivity on distortions and echoes is template for realistic hearing. How good you can feel the stage depend on good end amplifier with a lack of nonsense improvement, frequency limited input or sharp limited feedback and has capability of very fast delivery the current to loudspeakers, with in real time fighting with induced currents back from loudspeaker. In term of these you need fast as possible amplifier. I will never try any electronic attenuator in term of strangulation fastness of signal throughput, limited to mentioned 20-30 kHz. One will say, what about CD quality with limited throughput, yes this is true, but one more strangulation in front of end amplifier is too much for living stage reproduction. Now a day is many good sources to enjoy in music like DSD, PCM, also goldsmith Vinyl... Few weeks ago I have heard pair of this FO amplifier in active system with excellent level of quality and I was impressed.
 
Hi joztom,

Good write-up there to think about but think your focus on speed strangulation will fall apart in reality, only FO in theory has possibility to pass a perfect 20kHz squarewave, not only CD quality will fall apart there also the higher resolution sources you reference can't pass a 20kHz square wave and also total forget about Vinyl, and then further on think about recording process where microphones will always heavy strangulate speed domain. Also your post don't mention speaker domain at all and here everything will fall total apart in don't expect any normal minimum phase domain loudspeaker to pass real square waves above 6kHz area and if its a multiway speaker that includes phase distorting XO points forget any real square waves being passed, so this domain is a heavy real speed strangulator.

Its a yes to seen isolated on paper FO is non strangulating chain device for speeds but it would not correct errors for the rest of chain, to do this hole system including cables and location would need to be locked and analyzed from input to output and DSP corrected and one should probably accept that this correction will add CPU cycle system delay in DSP to get output correct improved.

In critics for CD quality remember in mastering and mix there is taking special care for its sound domain so play them back as they meant to using 44,1kHz converters to get hear what was meant to, and think same is case for other source rates.

Think in the wish to get any system reproduce any more accurate or real correct in speed domain than other is very complicated based the various source formats over time and also the various pass band limitations that always exist on recording and reproducing devices.
 
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There is a main problem. No matter, how I am qualified, I can't express what I am hearing in fact. I only have possibility to explain, express with words and nothing more and no one is better. There is much better situation in picture environment; you have resolution tests, color tables and normalization cards (Kodak grey card reference). In term of lack all these basic etalons in hearing environment, every audiophile is under weight of suggestion all kind of critics and evaluators, snake oil researchers, maybe paid from manufacturers. Everyone has duty to consolidate his own stand with connection with stand of own education. We are able to fighting to infinity, real results will fail. We are anytime on own page of river. All debate over comparisons will worth null, especially in close circles are every time some differences, depend on own wife's mood, humidity, temperature, personal mood etc.
I have implemented current feedback in my amplifiers 30 years ago (1987) with success, but only for personal use. I do not know FO constructor personally, but on many presentation with compare other products, is very advanced and every time in first line in quality reproduction.