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. 




Pindac has described the stage Don and I are at now: tuning the subjective balance ... there are a couple of nodes in the circuit where parts selection is quite audible, and we’re fine-tuning that.

I wrote an email to Don a couple of days ago that this topology is uniquely susceptible to parts coloration at the critical nodes. You get the same parts sensitivity in non-feedback SET amplifiers, but the much lower distortion of this circuit, compared to SET, exposes parts coloration more vividly. Fortunately, the right parts are available and are not super-exotic.

The circuit is inherently transparent, so there is almost nothing we can do to take that away, nor would we want to. But subjective tonal balance can be adjusted at the critical nodes. Surprisingly, the tuning has no effect on measurements, since topology, operating points, gain structure, tube loading, and bandwidth all remain the same.

Cloud Sessions asks a good question. Why does it sound this way? The best I can give is:

1) The circuit avoids both local and overall loop feedback, so there are no issues with hard clipping (transient overshoots in the FB network), stability margin (running out of gain and/or phase margin at high frequencies), or sensitivity to load reactance (which decreases phase margin and increases settling time after a large transient).

2) There are no differential stages to current-limit when one tube saturates or clips, taking the other tube along with it ... instead, the paired PP-mode tubes are functionally in parallel, helping each other out when the opposite-phase tube saturates or clips. Avoiding series-mode operation has a big effect on subjective dynamics. No SRPP’s, no split-load inverters, no long-tail pairs, no cathode followers.

3) Last but not least, each stage is individually optimized as much as possible for intrinsic linearity over the audio band. This is a matter of optimizing loads and minimizing the effect of Miller capacitance on the preceding stage.

Interestingly, Class D amps are free of Class AB transition artifacts, so there’s an entire class of coloration that just isn’t there. The big issue for Class D is nanosecond precision of timing for the pulse-width modulation (Class D is pulse-width-modulation, akin to FM, and not PCM), and insensitivity to reactive loads affecting the PWM modulator.

What are some amps you’ve heard with high feedback that you’ve enjoyed? I’ll have to check them out. I’ve seen the measurements for the Purifi and its distortion is incredibly low, to the point it’s at the limits of what the AP analyzer can measure. It does have raising distortion in the treble but if I had to surmise, it is most likely low order as I find the purifi a touch sweet in the treble. I do run it without an input buffer as my preamp is up to the task of driving the Purifi module directly.
I have yet to hear the new Gan stuff that is specifically designed for audio. I know yourself and AGD specifically designed yours for audio applications unlike many of the other brands. Are you guys going to be at the pacific audio fest? I’d love to come hear your Class D amps and hear how it compares to the 300b statement monos.


Our amp of course, which you have to imagine we’ve compared extensively to our class A triode zero feedback OTLs.

The AGD Audion (although I don’t know how much feedback is employed in this design)

Orchard Audio

Digital Amplifier Company (unfortunately the designer passed away last year)

We won’t be at the Pacific Audio Show- I have a prior booking.


Interestingly, Class D amps are free of Class AB transition artifacts, so there’s an entire class of coloration that just isn’t there. The big issue for Class D is nanosecond precision of timing for the pulse-width modulation (Class D is pulse-width-modulation, akin to FM, and not PCM), and insensitivity to reactive loads affecting the PWM modulator.

Yes, crossover distortion artifacts are impossible for any class D using an output filter. Timing issues (which cause an unpleasant hiss) are solved by a self-oscillating topology. This is done by exceeding the phase margin of the amp and the oscillation is used as the switching frequency. This makes for a very high stability amplifier and very large amounts of feedback. Since the feedback is not distorted prior to doing its job, higher ordered harmonic generation is avoided. Essentially the feedback simply reduces the existing distortion (in our circuit this tends to be lower ordered harmonics). Distortion vs frequency winds up being a flat line across the audio band. So it sounds very much like a zero feedback triode amplifier, but more ’focused’ owing to lower distortion, which otherwise obscures detail. You should try it- you make excellent amplifiers and know how they are supposed to sound, so you are in a good position to see how this technology advances the art.

Amplifiers using these tubes run very hot.

Very undesirable given the need for separate air conditioning which affects the sound Quality. super inconvenient situation

It's like running a portable heater in the room continuously which is horrifying.


I would think the majority of people who buy class A amps of any sort are quite well aware of how hot they run and are more than happy to deal with it for the sonic benefits.   As far as separate AC, that notion is absurd