Has anyone purchased a set of the Blackbirds? Kind of surprising there still hasn’t really been any real world feedback on them yet (tho maybe I missed something).
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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Hi @atmasphere I just found schematics with a cathode follower 12BH7 300B driver. Is it similar to the schematics you were talking about? https://www.diyaudio.com/community/threads/300b-schematic-recommendations.340133/page-2 Just don't need pentode input and global feedback thought input tube cathode. |
@alexberger Yes, that's how its done. Note that the EF86 input tube is wired in triode mode. Its quite linear that way; my Neumann U67 microphones use the same tube in the same manner sans feedback. |
Interesting SET that harks back to the original Western Electric 91A, which also used feedback to get the desired performance. I have mixed feelings about cathode follower drive: the output impedance of the CF is low (probably 100 ohms or so), but the peak current available is no different than anode drive. Considering the load is dominated by the Miller capacitance of the 300B (about 80 pF), the CF will definitely extend the small-signal bandwidth, but will have no effect on the large-signal bandwidth (also known as slew rate) which is determined by the (linear) current available to charge a capacitive load. The small-signal benefits would be useful in a high-gain feedback topology as shown above, since it would improve phase margin at high frequencies, which in turn improves distortion at high frequencies. And the circuit shown above is definitely high gain compared to typical zero-feedback SET amplifiers; performance would be dominated by the feedback loop, not the 300B. (Note for those puzzled by the schematic: there are two ground lines, not one, with the upper ground line at the top of the schematic. It winds its way down to the lower ground line, which ultimately connects to chassis ground at the RCA input at the lower left side of the schematic.) |
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