300b lovers

Whitestix,

What the heck is a VTV EVO 1200 class D amp with Purifi modules?  Never heard of such an animal....he he.  You must have your nomenclature confused.  What VTV product did you REALLY have?  Yes, I mod the VTV amps (Purifi, VTV D300 digital amp and Ncore Nilai).....so am very familiar with all the types and possibilities.  Maybe I modded yours......but it was not an EVO 1200.....he he......it don't exist. 

Sounds like that 300B amp is killer......me...enjoying the heck out of my modded VTV D300 amp pure digital amp......no DAC, no normal analog stages.....just....very pure sound.

Show Update: Don, myself, and Spatial team will be at the Seattle show. What you will see and hear will be pre-production prototypes, sonically close to what we plan to manufacture. I can tell you neither Don, nor I, will tolerate any backward steps in sonics. I’ve lived with original Karna amps since 2003, and they remain my personal reference standard. The production amps must match or exceed that standard.

Prices, and names, are still up in the air. I call the preamp the Raven, and the amps Karna Mk II’s, or Blackbird, depending on my mood. Don calls them the Statement 300B’s. Spatial will probably come up with own names for the preamp/amp combo. Don and I are encouraging people to buy the set, but they are flexible enough to interface with industry-standard components.

At the expense of a small technical quibble, I don’t see Class D as entirely analog. Without the pulse-width modulator, it is a 100~500 kHz AM transmitter that transmits a silent carrier. The pulse-width modulator is what makes the whole thing possible ... the pulse widths are precisely (and I mean very precisely, down to parts per million) 50% positive and 50% negative, if the input is zero.

Deviations from exactly 50/50 alter the pulse widths (to 51%/49% or any other ratio) but the pulses themselves are rail-to-rail, and the output devices are purely switches. It is a modulation system like AM or FM, which are also analog, but it is a modulation system nonetheless. Without the PWM modulator, there is no signal that can get through the amplifier.

Class D has been around commercially since the early Seventies. The trick is extremely fast switching with no overhang, resistance to load reactance, and a (very) low-distortion modulator. An FM transmission chain that achieves less than 0.1% distortion is at the limit of the art, and PWM modulators inevitably have their own set of distortions. PWM is not inherently distortionless, any more than AM or FM. Yes, it can be transmitted, but it would be very sensitive to multipath and group-delay errors ... both would cause distortion. With both FM and PWM, small time errors translate into amplitude distortion after demodulation.

Interestingly, SACD/DSD, at the native 2.8 MHz switching rate, is a type of quantized PWM. Since the pulses of true PWM are variable width, they cannot be recorded on digital media. DSD uses dither encoding and digital feedback (noise shaping) to quantize the PWM pulse train into fixed widths and provide the closest approximation to true PWM on playback.

@whitestix 

A friend has owned the Cube Audio Nenuphars for over 4 years and simply loves them. They’ve taken full range single driver speakers to a very high standard of performance.

Charles 

Charles,

As a 300b amp owner yourself,  you know whereof I speak.  Expect a report back on this thread in due time when the Cube speakers are run in.  Some folks agree that Cube's driver technology is one of the biggest leaps forward in speaker design in a long time.  I heard them at Axpona and was compelled to have them in my system.  

@whitestix 

Now, with another 100 hours on the amps, I will amplify the comments I made in my OP--- these amps are the most stunning addition to my 50 year quest for more accurate and pleasant sound in my system

I believe you. These amplifiers with your Cube Audio Jazzon is going to be a sublime pairing.

Charles

Gents,

I have had several Class D amps in my system in the past 10 years, and the earlier versions of them were dry and lifeless after extended listening sessions.  In the last couple of years, I had the VTV Audio EVO 1200 Class D amp with the Purifi module, with the aftermarket ministrations of Ric Schultz, and while the sound was as Ralph describes it, there was something missing in the sound after extended listening sessions.  It may clearly be due for my inherent biases, I will readily admit that.  After listening to the VTV amp for few months, I swapped back into the rack my McCormick DNA .05 which had their Platinum upgrades and after a few minutes of listening to it, I said to myself... "Ah, what was missing with the VTV amp has all been restored."  That is what I experienced, plain as day. I later got the stellar Wells Audio Innamorata SS amp, lovely both in its looks and more importantly in its sonic excellence -- easily the best SS amp I have ever had in my system.  After a few months of enjoying the Wells amp, I swapped Don's KT88 tube amp back in the rack and it was easy to hear the difference in SQ... back was the liquid sound of tubes with amazing extension on both ends and a soundstage that mesmerized my ears.  None of the sluggishness in sound of my old CJ gear, which was appealing to my ears, but far from an accurate sound reproduction, so Don's KT88 amp had all the advantages of a SS amp but had the warmth, richness and liquid sound that I desire which serves to envelope me in the listening experience (which I agree my VTV amp did to a degree initially) but here is the difference:  after hours and hours of listening, I loved even more the sound for the KT88 amp, whereas in extended listening sessions, there was a lacuna in the sound with the VTV amp that I clearly sensed and missed.  

That said, my new 300b monos are a quantum leap forward in SQ even compared to Don's KT88 amp in all respects and most noticeably this:  it sounds as if there is no amp at all... just glorious music enveloping the room, with pure tonal and timbre correctness that astonishes me... and absolutely dead quiet.  As good as the Kootenai is, and it is a stunning and powerful 65wpc tube amp, the 300b monos are in a whole different realm. 

I have not heard the fairly-price AtmaSphere Class D mono's at any audio show, but as Ralph has come from a tube-centric point of view, I must acknowledge that he might have be on to something with his design, surely he is. There are lots of advantages to using a Class D amp and God bless those that love them.  

This erudite conversion with Lynn, Don and others has been a deep dive into tube design philosophy and I personally am hearing the splendor of their creation moment by moment, lucky me, for darn sure.  Again, and not to be disputatious on this wonderful thread, for the liquid euphonic and most natural presentation musical reproduction with my new 300b monos, I am still firmly in the tube amplification realm as it recreates music in such a realistic way, so pleasing to my ears.  The hell with the heat the 300b monos throw off!

Now, with another 100 hours on the amps, I will amplify the comments I made in my OP--- these amps are the most stunning addition to my 50 year quest for more accurate and pleasant sound in my system.

I am driving my 86db efficient CSS Audio Criton 1TD-X speakers with the 300b amps at the moment and I can play music as loud as I can possibly tolerate it with no sense of distortion or clipping.  I have a 8 wpc Willsenton 300b integrated amp which I drove the same speakers with and it got pretty distorted as I rotated the volume knob to the right.  I recall that Don said that his mono's sounds "like a 100 wpc amplifier" and he is exactly right.

Boys, you are going to have to pay to play with Don/Lynn's new monos, but it is clear to my ears that if you are looking for an end game in amplification... and have the appropriate synergy with your speakers, then I hope you get a chance to hear them, which I will in the Spatial Audio room at the Pacific Audio Fest this month in Seattle, along with Don's new companion tube preamp.  

I have a pair of Cube Audio Jazzon single-driver speakers arriving on Monday which I think will be a stellar match for the 300b monos, but still the the mono's have made my Spatial Audio Triode Masters sound the best they have ever sounded, by far.  To be candid, if I had had the new 300b monos, driving my Triode Masters, before I ordered the Cube Audio speakers, I don't think I would have ordered them so as the Triode Masters sound so fantastic.  Don Sachs encouraged me to buy them ~6 years ago and now he has as his reference speakers the Spatial X- speakers, clearly an upgrade from my Triode Masters.

I live in Sacramento and would be happy to invite music lovers to come and hear my Don Sachs gear and my Cube Audio speakers.  Send me a private message and let's hear them together.    Cheers!

Ralph,

I understand that you are referring to the approach you use with judicious application of negative feedback. I was referring to Lynn’s comparison to the “golden age “ PP amplifier which typically used 20db of NFB. Your current class D amplifiers do not fit this description.

Charles

Zero NFB seems to uncover a masking effect.

@charles1dad That's not quite correct. It depends on how well the feedback is executed and as I've been pointing out a lot recently, with most amps made in the last 70 years or more that's not happened.

But if its done correctly, amps using it can be amazing- no hint of dryness, nice soundstage; everything you want in an amp.

I've described what's needed often enough, no need to repeat it here.

That’s why I am agreeing with what Lynn wrote. Zero NFB seems to uncover a masking effect. The subtleties and nuance of virtually everything is revealed as noted.

Charles

The difference is Class D switches at 100 kHz or higher, with pulse width translating to signal level, while Class A is non-switching and like a preamp, fully analog from start to finish.

@lynn_olson most quality class D amps switch at 500KHz or more. Also to be absolutely clear, class D is 'like a preamp, fully analog from start to finish.' A very different type of circuit, but analog nonetheless. 

I do not have the resources to confirm this via test bench measurements as you do. I can only rely upon listening experiences with my own audio system.

@charles1dad Lynn is correct- if you are not running feedback then everything in the amplifier design right down to the component quality, wire and solder makes a difference. When you run lots of feedback you get rejection of things like that- often including sensitivity to line voltage.

@lynn_olson

Another factor is sensitivity to parts quality. An amp with 20 dB of feedback (which is nearly all Golden Age amps) tends to wash out differences in the sonics of different parts. This is exactly what feedback is meant to do ... 20 dB of feedback is a 10:1 reduction of all sources of coloration. A zero-feedback amp, by contrast, reveals the sonics of every single part, particularly at critical nodes in the circuit. This raises costs compared to the PP KT88 equivalent.

I do not have the resources to confirm this via test bench measurements as you do. I can only rely upon listening experiences with my own audio system. When I placed my 300bSET zero NFB amplifier in my system the first time (2009) the immediate difference/improvement was the sense of naturalness. Very stark and unequivocal. In my system realism and authenticity took a step (Or two) forward.

Charles

Although a glance at a schematic might lead you to think it is simpler than a classical (Golden Age) PP KT88, the parts are more expensive. Way more expensive, just as 300B’s (as a group) are more expensive than KT88’s (as a group).

Another factor is sensitivity to parts quality. An amp with 20 dB of feedback (which is nearly all Golden Age amps) tends to wash out differences in the sonics of different parts. This is exactly what feedback is meant to do ... 20 dB of feedback is a 10:1 reduction of all sources of coloration. A zero-feedback amp, by contrast, reveals the sonics of every single part, particularly at critical nodes in the circuit. This raises costs compared to the PP KT88 equivalent.

Depending how you feel about the sonics of solid-state and feedback, you can travel a continuum between modern Class D, with sophisticated and complex feedback, to Class AB transistor or MOSFET with 20 to 40 dB of feedback, to Class AB push-pull pentode with 20 dB, to Class A with zero feedback. Each type sounds different and has different distortion spectra.

Comparisons between modern Class D and all-triode Class A are not absurd, despite radically different technologies. Class D and Class A both skip over the many difficulties with Class AB device switching, whether bipolar transistor, MOSFET, or pentode (each device type has different artifacts associated with the AB transition). The difference is Class D switches at 100 kHz or higher, with pulse width translating to signal level, while Class A is non-switching and like a preamp, fully analog from start to finish.

I just have the first production one running  in now in prep for Seattle show.  It will be at least $5000 as it is cost and labour intensive and all very high end parts.  

Any indication on target preamp pricing?

I agree with Atmasphere. Some things cannot be accurately modeled. Put it on a bench, attach a dummy load, light it up, and measure square waves. Tune for nice-looking leading (and trailing) edges. Measure both low-level (below 1 watt) and also just below clipping.

There is a simple and inexpensive means of dealing with heat due to amplification. Ducts in the ceiling above the amplifier(s) can be added, along with dryer style hose the connects via a squirrel fan to the outside. This can be installed for a few hundred dollars (mostly labor), is quieter and far less power draw than air conditioning. 

Do you use load a resistor after the interstage transformer? What kind resistors do you use?

@alexberger If any audio transformer is not loaded it can 'ring' (which is to say it will generate harmonic distortion, which can be quite profound). The correct loading will cause a state of 'critical damping' in the transformer, where when a square wave is put thru the device, it will have little or no 'overshoot'. Since the grid of a tube tends to be very high impedance (other than its capacitance) some form of resistive loading is a good idea to explore!

Since you sound like you are up to something with your own design, I recommend an empirical approach, which might be to drive the transformer with a square wave and have it drive in turn a power tube which is operating normally. A potentiometer and oscilloscope's probe across the output of the transformer would then allow you to vary the potentiometer and observe the result on the square wave. In this manner you can exactly dial in the correct loading value.

@alexberger 

Hi

I am sorry, but I am not giving anything about the design of the amp away.  I had ITs custom wound for the project.   My amp is PP, but if you need a load resistor with your circuit then I would try two kinds.  A good quality wirewound of sufficient rating, and a good old Kiwame 2W or 5W depending on what you need.   I usually use wirewounds, and not cheap ones, but Ohmite or Vishay or something else of quality.  Which you prefer will depend on the circuit, your ear, and the Hashimoto iron.  The resistors are cheap so try both kinds and see what you think.

Hi @donsachs ​​​​@lynn_olson ,

I have 300B SET with 6f6 driver in triode mode. I did 2nd harmonic distortion calculation using 3 point method and 6f6 plate characteristic graph. So with RC coupling that I have right now I get more than 2% distortions with voltage swing 140v pick to pick and when I go to interstage transformer coupling I can get around 0.7% distortions with 160v pick to pick. The difference is huge!

I have a couple of question about using transformer. Do you use load a resistor after the interstage transformer? What kind resistors do you use? I'm going to use Hashimoto A-305 transformers. As I understand Hashimoto recommends 100K load resistor for this transformer.

Regards,

Alex.

Very good article about how the brain distinguishes between reality and imagination. Since audiophiles are endlessly arguing about perception and reality, this is a useful read:

Quanta Magazine

I use Tubes that also run quite hot, the Amp's these tunes are utilised in are positioned in free space away from other Structures within the room.

I have in the past owned a Portable Air Conditioner Unit, that produced Icy Cold Air, this has been reserved for use when the External Temp's are getting up to the +25 Centigrade to help with sleeping. When using the room the system is set up in during these periods of high Temp's, I have never felt there was a need to run the Portable AC Unit during a listening session.

If increasing Room Temp's are a concern, as a result of a Tube Amp' being used, and a Cooling Device is at hand, cooling the Room in advance of the listening session is certainly going to cool the room and not impact on the Sound being produced. 

My cautionary advice to an individual interested in using Tube Devices is no different to the advisories I was given many years past, which is to make sure there is always 'eyes on' the devices in use for the bulk of the time they are Powered On, and have a revisit shortly after being Powered Off. After approx' 30 Years of using Tube Devices, I have not had a concerning experience, only the oddity of a electrical glitch, a spent Valve or a blown fuse.     

@drbarney1

I agree with Lynn in that I won’t work with power supplies over 550-600V. The teflon mil spec wire is all rated at 600-630V so you would have to source 1200V wire for headroom. All normal parts are rated at 630V so you would have to source special caps, resistors, etc... You don’t mess around with 1000V or you will have a fire. Also the transformer set in these mono amps including the custom interstage transformers and choke would eat up most of your budget. I like some Lundahl iron, but I found that their IT started ringing above 15KHz in my circuit, so you would most likely have to get custom iron to do your project as I did. So yes, you could certainly build the project you discuss, but it isn’t simple, there are lots of issues and sourcing of custom parts rated for 1kV and if you use Edcor or Hammond iron you or something else of that ilk you will get medium grade amp, not one that has incredible detail and sounds alive. So if you build that amp with $2000 worth of parts you may be able to do it, but if you spend a lot more you will get a much better amplifier. You will still have a fire risk if you don’t make sure every single part in there that sees high voltage is running at no more that 70-75% of its rating. Easy to do at 500V, but a lot harder at 1000V.

@dz13

Just outside of Las Cruces.

Wig

@wig Where do you live? I live in Tucson so I'm guessing Phoenix area? 

Not going anywhere near an 833 or those Eimac transmitter tubes. No thank you. Those things light up a room with a dazzling white light and get serious, room-heater hot. They are designed for transmitter use, with forced-air cooling that ducts to the outside.

And if somebody chooses speakers that are 0.2% efficient, well, what did you expect? Class D or Class AB for you, as well as a dedicated AC power outlet that goes straight to the circuit-breaker box.

45 is indeed very very nice sounding.

Cost has gone up quite a bit though. $2k will be barely enough these days for a high quality 45SET DIY project, assuming no fancy enclosures and not using big name irons like ISO or Hashimoto.

Stereophile published an article on the Westinghouse 300B, which, unlike cheap modern 300B triodes, had a triple coated cathode which lasted longer and was the secret to the better sound. If you can tolerate less power the NOS 45 globe tubes were made the same way and many people find them richer sounding than the cheap modern 300B. 

Around 2005 there was a Japanese 833A SET amplifier driven by 300B transformer coupled to the grid of the 833A and rumor had it the 833A was run on only 1000 Volts with a positive grid bias to force it to draw more plate current. It sold for $350,000, but the parts and labor could scarcely cost a percent or two to manufacture it. You would not need high sensitivity speakers for it, you can use planar magnetic speakers if you want. Lundahl has probably the best coupling transformer there is for coupling a globe 45 to the 833A grid which can run on zero or ground bias for eliminating a bias supply capacitor from the signal path and this is more than enough power for driving less sensitive speakers. Either a globe 45 or a WE 300B will work for this. Hammond makes a more robust air-gapped output transformer rated at higher DC current than smaller more expensive big-name brands and it is perfect for the 833A. 

This is relatively easy to build yourself for less than $2000 retail in parts if you know how to be careful with the 1000 Volt power supplies it needs. 

If a cool room is important, you want Class D (90% efficient or better) and speakers that are more than 1% efficient (a true Theile/Small 92 dB/meter/watt), as well as switching (not linear) supplies for all the other audio components. That’ll make no more heat than a transistor radio.

Class A vacuum tube is the exact opposite. Constant power draw regardless of signal, from silence to clipping, plus heater current of a few watts per tube, and a few watts of excess heat from the linear regulators. Similar to a 1963 all-tube color TV. My Panasonic 58" plasma HDTV consumes 500 watts, a bit more than a pair of Statements.

To put that in perspective, the same as four or five 100-watt conventional light bulbs, or the heat emitted by two people at rest. A light to moderate additional load on the A/C system, less than 1/10 of its capacity. Of course, if your A/C is running more than 50% to 70% of the time (a 50~70% duty cycle), probably not a good time of day to use the oven or turn on vacuum tubes.

I live in the desert where it reaches over 115 degrees and run my KT88 tube amp nightly and did the same thing when I had my coke bottle 845 and 300b tube integrated amplifier. No issues with heat in my room 😁

Wig

@donsachs 

+1.
Exceedingly absurd and silly.

Charles

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

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.

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.

@cloudsessions1

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.

@lynn_olson

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.

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.

@cloudsessions1

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

That would be terrific!! Even if not heard in the same system. Still worthwhile to hear the GAN class D amplifiers and how they compare with the new 300b push-pull amplifiers. My sense is that Don and Lynn’s amplifier is something quite special.

Charles

@atmasphere  very interesting Ralph. 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. 

@pindac   Exactly my friend, exactly.   Once the power supply is right,  all the operating points are right and there is some serious listening, then the tuning begins.   We are almost there...

When I was having a Bespoke Valve Input/Output Phonostage Built for me.

The designer builder was running two builds parallel, with the only differences being one had more RCA Inputs and my one had a Single RCA Input.

The Designer Builder invited me to listen once more to the design, but I could not get my head around it, there was still too much perception of weight, which was a a assessment put forward during the demo's done prior to what was supposed to be the final demo' prior to completing. 

I told the designer/builder, it was time to introduce Foil Resistors and Alternative Cap's. After some toing and froing, we got there in principle. Z Foils and a selection of Copper Foil Cap's was bought in.

The impact these had on the Sonic was from my assessment something very very special, even the designer /builder was on board and had their eye on this as a Upgrade Package on the Phon's if they were to be produced in increased numbers My later investigations which resulted in the addition of Vintage Tubes selected as a outcome of Tube Rolling experiences, was the addition that is the Cherry Garnish on Top.

The Tuning/Tweaking has the capacity to produce a sonic that is very different in the attraction/likeability generated to a earlier version. 

These amps are still prototypes and being tuned as we speak.  So what Cloud wrote was in reference to the first prototype a year ago.  Spatial Audio Lab had that amp for maybe 6 months.   The mono amps are probably 25-30% better at least.  @whitestix  has a pair, and Lynn and I are still tuning them and have improved them since that pair went out.  What will be shown at the Pacific Audio Fest in Seattle will be very close to the final circuit, but there will probably still be a bit of tweaking after that.  I would expect production and sales to be Q4 of this year and maybe Q1 of next.  We have to see how it goes.   Again, I hope lots of people can hear them in Seattle and give an honest opinion.  They will come to market, I promise, but we want them to sound as good as they can first.

Maybe.  Except that there are things we cannot measure.

@donsachs That was true back in the 1980s. It really isn't now. Measurement technology has really advanced in the last 40 years!

Its the distortion of any amplifier that is its 'sonic signature'.

There are many class D amps I've heard over the years that I had to struggle to take seriously. But I've heard some now that sound every bit like a very good tube amp; just like in a tube amp where arcane subtleties can make or break a design, the same is true in class D (or any design for that matter). I pointed to what is needed to make a successful amplifier (if you're going to use feedback) in my prior post. Most amps using feedback fall short of the GBP needed so distortion is much higher at higher frequencies than the THD measurement suggests!

THD by itself, if that is the only harmonic distortion metric used, allows a lot of problems to be swept under the carpet. When it is the sole metric, it leads to the myth that 'there are things we cannot measure.' The reality is if the harmonic spectra is measured at several frequencies (including above 1KHz) and if distortion is graphed vs frequency, then we start to be able to predict the 'sound' of the amplifier.

Both the 'measurement only' guys and the subjectivist guys hate this! But Daniel von Recklinghausen was right- if it measures well but sounds bad, you measured the wrong thing.

I’m convinced that no feedback plays a role as every amp I’ve heard with feedback doesn’t have that super inky back blackground or perfectly rendered transients.

@cloudsessions1 That is because in most amps employing feedback, its poorly applied- so my surmise is you've yet to hear one where the feedback was really right. Norman Crowhurst pointed this problem out 65 years ago, describing how the feedback node (the point in the amplifier where the feedback signal is mixed with the incoming signal) isn't linear; therefore the feedback signal gets distorted before it can do its job, thus creating higher ordered harmonics that have given feedback a bad rap. Its not the fault of feedback so much as poor application. Amazingly, little has been done in the last 6 decades to fix this; IMO mostly out of ignorance and a lack of will to do so.

I've heard amps with very high feedback that sound utterly relaxed in the mids and highs and portray depth with ease.

@cloudsessions1 

I have a purifi amp and it couldn’t hold a candle to the original 300b statement prototype. I love new class D as when you get the synergy right I find it to top any SS class AB I’ve heard. But the 300b just makes everything right

That is quite a tribute and observation.

Charles

I’m not sure how the 300b statements could achieve such great technical performance over some of the “state of the art” amplifiers I’ve had in. Maybe Lynn, Don or Ralph could comment on that. It’s put things into perspective that maybe just maybe we don’t know every way to quantify all measurements to what we hear. 
I’m convinced that no feedback plays a role as every amp I’ve heard with feedback doesn’t have that super inky back blackground or perfectly rendered transients. Although the amps I’ve heard with no feedback trade that off for less extension on both ends of the spectrum and a lack of power/effortlessness. The 300b statement is the outlier in this regard. 

I have a purifi amp and it couldn’t hold a candle to the original 300b statement prototype. I love new class D as when you get the synergy right I find it to top any SS class AB I’ve heard. But the 300b just makes everything right. I find it odd because it does even the technical attributes better. The blackground is soooooo black, the details precisely rendered, and the soundstage depth of the charts. The only system I’ve heard that could compete was a magico paired with ClassE mono blocks. But even that system while the soundstage was mind melting it was very polished sounding. The 300b statement has much more realistic tone with great texture. 
I still snicker 🤭 when bringing a friend over who’s never been a big fan of tubes and putting on Pot by Tool cranking it to 11 and watching his mouth drop. The sheer power and realism the 300b’s presented!

donsachs:

When do you think your new 300b mono-blocks will be available for order? I would want to buy them independently of a package with the Spatial Audio speakers as I have a pair of Daedalus Apollos (sensitivity about 96db) that I am super pleased with. I want to upgrade an integrated tube amp and have been patiently looking for the right 300b amp to drive them.

@atmasphere 

"There are now class D amplifiers that have a distortion spectra that if you had one on the bench you would be completely convinced you were measuring a really well-behaved triode tube amplifier."

Maybe.  Except that there are things we cannot measure.  I prefer the sound of a good tube to any SS device I have heard to date.  Personal preference.  I would not be at all surprised if that Class D amp measures better than my tube amp in every regard.   I bet in a blindfold test I would choose to listen to the tube amp.  Again, personal preference.  Other people would make other choices, as it should be.

I hate the sound of solid state devices.

@donsachs There are now class D amplifiers that have a distortion spectra that if you had one on the bench you would be completely convinced you were measuring a really well-behaved triode tube amplifier.

There are three reasons for this:

1) its really easy to get really high Gain Bandwidth Product values, such as 20MHz with class D, so feedback can be supported across the entire audio band (no rising distortion with frequency- like a zero feedback amplifier in this regard)

2) the feedback node can be very linear so the feedback signal does not get distorted prior to doing its job.

3) the things that cause non-linearities in the circuit tend to generate lower ordered harmonics.

Despite inexpensive power being available, I still prefer higher efficiency loudspeakers for the reasons Lynn outlined above. In addition, the harder you make any amplifier work the higher the distortion. For this reason I feel that higher efficiency and higher load impedance is an advantage to all audiophiles.

@donsachs

I wouldn’t own an inefficient speaker because I would be doomed to SS amps, and I hate the sound of solid state devices

It seems that the latest generation class D/GAN may be addressing this. Time will tell.

Charles

You don't have to convince me, my speakers are 97 dB 8 ohm:)

I wouldn't own an inefficient speaker because I would be doomed to SS amps, and I hate the sound of solid state devices.

@donsachs

I would stick to speakers that are 88+ dB and very well behaved. The spatial audio X4 current model is 88 dB 4 ohm (and very well behaved) and the amps will happily drive them to ear splitting levels in reasonable room

As @atmasphere has made the point eloquently on past occasions, easy load impedance (Higher ohms and less fluctuations ) speakers are less stressful on amplifiers. In addition he has pointed out that they are lower in distortion compared with low impedance speakers.

Charles

As Lynn said, the amps have dual regulated supplies, one for the 300b and one for the input and driver tubes.   IF the specs on that KEF speaker above are really what the review said, then the amp would drive them.   Also, as I said far above somewhere, the first stereo prototype of this circuit with only one power supply per channel drove a pair of experimental Spatial Audio Labs X4 prototype speakers that were approximately 87 dB 4 ohm to insane levels, much as what Thom was describing above.  The monos have dual supplies in each amp, so would be even more capable.  All that said, I would stick to speakers that are 88+ dB and very well behaved.  The spatial audio X4 current model is 88 dB 4 ohm (and very well behaved) and the amps will happily drive them to ear splitting levels in reasonable room.