Hi all....what do folks think about the ALLNIC A-5000 DHT 300b amps...?? any thoughts..do not hear much about this 300b amp..thx G
300b lovers
I have been an owner of Don Sachs gear since he began, and he modified all my HK Citation gear before he came out with his own creations. I bought a Willsenton 300b integrated amp and was smitten with the sound of it, inexpensive as it is. Don told me that he was designing a 300b amp with the legendary Lynn Olson and lo and behold, I got one of his early pair of pre-production mono-blocks recently, driving Spatial Audio M5 Triode Masters.
Now with a week on the amp, I am eager to say that these 300b amps are simply sensational, creating a sound that brings the musicians right into my listening room with a palpable presence. They create the most open vidid presentation to the music -- they are neither warm nor cool, just uncannily true to the source of the music. They replace his excellent Kootai KT88 which I was dubious about being bettered by anything, but these amps are just outstanding. Don is nearing production of a successor to his highly regard DS2 preamp, which also will have a unique circuitry to mate with his 300b monos via XLR connections. Don explained the sonic benefits of this design and it went over my head, but clearly these designs are well though out.. my ears confirm it.
I have been an audiophile for nearly 50 years having had a boatload of electronics during that time, but I personally have never heard such a realistic presentation to my music as I am hearing with these 300b monos in my system. 300b tubes lend themselves to realistic music reproduction as my Willsenton 300b integrated amps informed me, but Don's 300b amps are in a entirely different realm. Of course, 300b amps favor efficient speakers so carefully component matching is paramount.
Don is working out a business arrangement to have his electronics built by an American audio firm so they will soon be more widely available to the public. Don will be attending the Seattle Audio Show in June in the Spatial Audio room where the speakers will be driven by his 300b monos and his preamp, with digital conversion with the outstanding Lampizator Pacific tube DAC. I will be there to hear what I expect to be an outstanding sonic presentation.
To allay any questions about the cost of Don's 300b mono, I do not have an answer.
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@spazzghettie Looks like a nice amp. LC coupled and they use all DHT tubes. On the downside it is single ended so it won't have the bass punch nor the power of a push pull 300b. Also, I have moved on from LC coupling as I prefer custom interstage transformers, but that is my taste and it doesn't mean that Allnic amp is not a wonderful sounding amp. I also prefer solid state rectification and regulated supplies in power amps, but again, my taste. I am sure that is a very nice amp if your speakers can live with a 10 watt amp and you like the sound of tube rectification in power amps. It also has 6 dB of negative feedback. That isn't necessarily bad, but our amp project has zero feedback and you can tell. So again, they have made a nice compromise with good tubes, obviously good parts and a bit of feedback. I am sure it sounds really nice. |
Don I’m convinced of the merits of zero NFB tube circuit amplifiers implemented appropriately. Is this harder to pull off successfully? Does utilizing some degree of NFB confer a bit of a safety net? I inquire because its use is nearly universal with power amplifiers. Zero NFB amplifiers are a small niche. Charles |
NFB covers a lot of sins. You have to do everything right to have a stable circuit without it. It is actually considerably more complicated than that, but that is a good way to think about it. That allnic amp ad boasts a perfect square wave response. The feedback helps with that. It doesn't mean you cannot build a nice amp that uses NFB, but that "air" and sense of "realism" that you treasure is hindered by NFB. I can see what is inside their amp and have a pretty good idea what it sounds like. It is a dance. We have been working on this amp for quite some time and it will go into production late fall. We have tried many coupling methods and topologies and the fact that there is zero feedback lets you hear major differences between them. Again, there are many great amps in the world, most of which have some amount of NFB to make them really stable and limit distortion. That approach works, but has costs in terms of realism and spaciousness. That said, it doesn't mean those amps sound bad. Just different. I know the sound I value and I cannot get it with NFB, but others have different tastes or the need to drive speakers which are not at all tube friendly. So there are many paths.....and different sounds associated with them. There is no right way, just what we like. |
Negative feedback is the right choice for the vast majority of amps, particularly direct-coupled solid-state, where you can pile on the gain and use that "excess gain" to minimize distortion via feedback. To oversimplify, if you have 20 dB (a 10:1 voltage ratio) of excess gain, you can have 20 dB of feedback, which will reduce the distortion in direct proportion to the feedback ratio ... in this case, ten times. Pretty slick trick. In practice, as the excess gain goes up, and the feedback ratio increases, problems with stability creep in. Marginal problems with stability result in overshoots on square waves, and as it gets worse, brief periods of near-oscillation, and then full-power oscillation, which usually destroys the speaker. So you have to take account of the total phase shift on both ends of the spectrum, which includes the output transformer if it is included in the feedback loop. The phase shift of an output transformer typically limits tube amp feedback to no more than 20 dB, but this can be evaded by having multiple nested loops, as in the Citation amplifier deigned by Stu Hegeman in the early Sixties. But now we get into the (much) deeper waters of both slew-rate limiting and settling time, which are interrelated. That’s beyond the scope of this discussion, but they are limiting factors in any feedback amplifier. Multiple feedback designs can achieve impressively low distortion figures, but settling times can be much longer, since each nested feedback network has to leave saturation, return to controlled operation, and return to zero with its own time constant. These are not trivial design concerns, and made more complex by load dependence ... a reactive loudspeaker load will decrease the phase margin of the amplifier, and that in turn leads to longer settling times. As the phase margin erodes, settling times get longer and longer, until the amplifier breaks into self-oscillation. The other consequence of loss of phase margin is an increase in distortion, mostly at high frequencies, with the limit case of oscillation, which can be considered 100% distortion, with the output effectively decoupled from the input. For obvious reasons, great care is taken in the design phase to avoid oscillation, but there are amplifiers where stability is conditional on the load, with transient overshoots visible under some conditions of load and input stimulus. This was a serious problem with first and second-generation transistor amplifiers. (Which were designed with nothing more than slide rules and nomograms, so you can’t really blame the designers back then.) Nowadays, software modeling programs allow designers to avoid the stability problems of the early transistor amplifiers. If you want to jump down into the rabbit hole, read about "Nyquist Stability Criterion", followed by "Slew Rate Mechanisms" and "Settling Times in Feedback Circuits". For advanced practitioners, read about "Mixed Feedback Designs" and "Combining Feedback and Feedforward".
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