What Spectral gear specifically, so I have a mental note. I always wanted to try a Spectral DAC (the older one with the UltraAnalog DAC chips).
Stereophile | January 2017 Issue
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What Spectral gear specifically, so I have a mental note. I always wanted to try a Spectral DAC (the older one with the UltraAnalog DAC chips).
Spectral DMC-30SV preamp, DMA-400 monoblocks (the DMA-300 RS stereo amp is also excellent on that preamp). Cables MIT/Spectral (appears to be essential because otherwise the amps go into oscillation).
I understand, the cable issue was also a problem for me a few years ago when I contemplated purchase of the DMC-15 SS pre-amp/DMA-260 amp (very good, but not as free of electronic artifacts as their top gear). The tonal balance in my system, by the way, was almost identical to that of my push-pull triode amps.
I think I heard the predecessors to these models (DMA-360 monos...not sure about the pre). Tube like is not what I would have described either.
Also, how can amps that go into oscillation unless they use specific cables be a good design philosophy?
A similar line of caution was thrown my way when I owned my Naim rig. You could only - only - use NACA4, and then - and only then - use NACA5 when you had passed the rite of passage and were invited to upgrade to the superior cable.
Me? I used Chord Company cables and liked it a whole lot better. That was of course when the warts started appearing on my stomach and I was continually denied the promotion I was promised. Weird.
The answer is simple: they are unfiltered extreme designs
To clarify: every solid state amp devoid of any input and output stabilization filtration stands a good chance of oscillation, assuming they are of wide enough bandwidth; this is why just about all of them feature input chokes and output inductors. But some manufacturers elect to put those filters outside the chassis, either in networks along the cables and/or in the inherent inductance of the wire itself. There are good reasons for having those filters outside the chassis, like moving the magnetic fields inevitably generated away from the sensitive circuit board. It is an extreme design approach, but when one is engineering driven - like Spectral - you do extreme things. In addition, I feel Spectral has selected cables with extreme linearity to mirror their own designs. This is all part of a "system approach", which doesn't really appeal to everyone - but there is fundamentally nothing wrong with this approach, from an absolute engineering perspective. To go to more extremes, you can imagine that the inductance required to stabilize an amplifier and still provide bandwidth out to MHz may be split between the inductance of a network box and the wire itself, meaning, you can keep the inductance constant for varying lengths of cable purchased.
I have posted the following before, it is taken from the Spectral DMA-300RS web page http://www.spectralaudio.com/DMA300/DMA300.htm and it's referring to the subject of input/output filtration and how the internal wiring (never mind external) is designed to replace that:
This is an example of extreme engineering.
The truth is that, before MIT came into the picture, you will find older Spectral amps from the 80's that do in fact feature input chokes and output inductors, like the DMA-80 and others from the 1980's - and in those designs which did not require specific cables, you will find the output inductors mounted at the speaker terminals - a small optimization because the magnetic fields are away from the circuit board, but close to the speaker wires. Trade offs and optimizations, like everywhere else in this hobby.
Regarding the sound, I would not agree with KeithR even on older Spectral designs. The Halcros were and remain exceptionally dry, and the very bad definition of solid state (BTW, google images of Halcro amps to see those big-ass output inductors over the boards). The Spectrals and other high speed designs do face challenges not found in more conventional amplifier designs; thermal tails (memory effects) is one of them, which are more evident as the speed increases. The big leap in the DMA-300 and 400s and 30SV is the elimination of these distortions, and I know of no other high-speed designs that make such claims. To solve these problems, from what we are reading, they have gone (as always) to extremes, building custom amplification devices, and in the case of the output transistors, to using video devices of extreme bandwidth. There is no doubt that every generation of product improved upon the previous, and the exuberance we are now expressing is only referring to these latest designs. Personally, I have always said that I have the greatest respect for the tube device for its extreme linearity, and that I like Spectral for attempting to achieve tube behavior and performance in solid state designs without the tubes' shortcomings; the road has been long, but I feel they finally solved the problem.
The proof is obviously always in the listening, and if you were to listen to the 30SV->300/400 system with MIT cabling, you just maybe stunned. The problem in such aural evaluations is to find a system with equally worthy sources and speakers and room. I've been upgrading and modifying my components around them obviously in order to get the best out of them. On the other hand, you may not like the sound at all, and that's OK. I've heard people claim many times that Spectral (and others) is analytical - well, I'd say it's because the recording contains all of that information. Frankly, the best of tubes that I have heard are analytical too, and I just love that. Others yet will claim they like their Spectrals without MIT cables - all the power to them. However, it's probably no coincidence that Spectral owners on this forum are gaga over the latest offerings...
Morricab:
KR isn't as warm as those three - but I confess I have not heard it in my home. Typical SET warmth is pretty much 2nd harmonic, let's call a spade a spade.
I would agree with you that most systems get piano strike or sustain correct, but rarely both.
"darTZeel is not completely feedback free. They use nested local feedback. Quads use feedback. I think it was Bruno Putzeys who demonstrated mathematically that nested local feedback is in effect no different than global feedback. Shindo's SETs are probably without feedback but their push/pull amps probably have some. BAT does not use feedback but if you look at the measurements, their transformers are clearly undersized and the distortion shoots up in the bass...this will color the sound of what is otherwise and interesting design."
OK- here are the amps I've owned or had 7 day+ in-home demos with high efficiency speakers. To imply I don't have experience with negative feedback is odd. (I think you over focus on the subject - and now that your position has changed to no local feedback its even more peculiar). And Quads sound like SET to 9/10 people that hear them, so to criticize Peter Walker's classic circuit for using a very small bit of NFB doesn't matter.
Since 2010:
BAT VK300se
McIntosh MA6600
McIntosh MC601s
Almarro 318B
Mastersound Due Venti
Shindo Haut Brion
Shindo Montille (EL84 version)
DeHavilland 845Gs
Audion Black Shadows
FirstWatt SIT 1 and 2
Sophia Electric 845s
Ayre VX-5
Valvet A3 Class A monos
DarTZeel CTH-8550
Vac Phi 200
Vac Phi Beta (integrated)
Melody AN845
Quad ii Jubilees (yes, the gold plated beauties not the cheap Chinese crap)
Line Magnetic 219 (not my room, but on my speaker at dealer's)
Luxman 590ax
To clarify, I had BAT VK-75SE on Wilson Sophias in 2005, which I don't deem a HE speaker. I would say that lack of global negative feedback on SS amps is much more important than tube.
KR isn't as warm as those three - but I confess I have not heard it in my home. Typical SET warmth is pretty much 2nd harmonic, let's call a spade a spade.
I would agree with you that most systems get piano strike or sustain correct, but rarely both.
"darTZeel is not completely feedback free. They use nested local feedback. Quads use feedback. I think it was Bruno Putzeys who demonstrated mathematically that nested local feedback is in effect no different than global feedback. Shindo's SETs are probably without feedback but their push/pull amps probably have some. BAT does not use feedback but if you look at the measurements, their transformers are clearly undersized and the distortion shoots up in the bass...this will color the sound of what is otherwise and interesting design."
OK- here are the amps I've owned or had 7 day+ in-home demos with high efficiency speakers. To imply I don't have experience with negative feedback is odd. (I think you over focus on the subject - and now that your position has changed to no local feedback its even more peculiar). And Quads sound like SET to 9/10 people that hear them, so to criticize Peter Walker's classic circuit for using a very small bit of NFB doesn't matter.
Since 2010:
BAT VK300se
McIntosh MA6600
McIntosh MC601s
Almarro 318B
Mastersound Due Venti
Shindo Haut Brion
Shindo Montille (EL84 version)
DeHavilland 845Gs
Audion Black Shadows
FirstWatt SIT 1 and 2
Sophia Electric 845s
Ayre VX-5
Valvet A3 Class A monos
DarTZeel CTH-8550
Vac Phi 200
Vac Phi Beta (integrated)
Melody AN845
Quad ii Jubilees (yes, the gold plated beauties not the cheap Chinese crap)
Line Magnetic 219 (not my room, but on my speaker at dealer's)
Luxman 590ax
To clarify, I had BAT VK-75SE on Wilson Sophias in 2005, which I don't deem a HE speaker. I would say that lack of global negative feedback on SS amps is much more important than tube.
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Honestly Brad, what I'm gleaning from our discussion is that KR isn't typical SET and doesn't perhaps have a lot of the flaws I've heard on them (bass, 2nd harmonic creating a weird in space midrange, and muddy transients).
I heard a full Viva setup on T&F speakers last year play Chopin - I wanted to churn butter in the room with all that piano creaminess
I heard a full Viva setup on T&F speakers last year play Chopin - I wanted to churn butter in the room with all that piano creaminess
Thanks for the clarification I guess until I hear the newest stuff I will reserve judgment but the older stuff never sounded particularly tube like let alone SET like. I also don't see the logic of putting an important aspect of your amp in a third party cable. That filter may not be in the amp but it is important to the amp's correct function nonetheless. Why leave to chance that the end user can screw up? The could put the same circuit right at the amp outputs, no?
"KR isn't as warm as those three - but I confess I have not heard it in my home. Typical SET warmth is pretty much 2nd harmonic, let's call a spade a spade."
I am not sure where you got this from but I am sorry to say that what research has been done on psychoacoustics doesn't really support this premise. Most good SETs will only make a few tenths of a percent 2nd harmonic with a moderate output (say < 5 watts for a 20 watt amp) and this is inaudible by basically every study I have seen. A dominant 2nd harmonic with exponential decay with increasing harmonic order is exactly what your ear/brain will perceive as natural and undistorted (below a certain level of course). Dominant odd order harmonics happens mostly in a synthetic environment like electronics. You are confusing this 2nd vs 3rd order with the reality that is a lot more complex.
My research into this matter (because it is one of those things in audio that I think i worth being concerned about...not frequency response) indicates that for tube amps the problem lies in 4 areas:
1) Output transformer quality. Normally it is too small and saturates...this is to balance with good HF extension sometimes or more likely to save money. As you can see from many online measurements avvailable, many tube amps (like the Dehavilland GM70 and BAT VK60) have a sharp increase in distortion in the bass...particularly as the power goes up. This creates a whole spectrum of harmonics that are most certainly audible and will contaminate the whole frequency range leading to audible coloration.
2) Underperforming driver sections that are overloaded long before the output tube itself is overloaded.
3) Cheap parts quality. In amps with no negative feedback parts quality is paramount for getting good sound (this is a strong Audio Note and Kondo Philosophy but it holds true). Parts cannot fix bad designs but they can reduce the quality of a good design
4) Power supply robustness and cleanliness. This is pretty true for all electronics but I include it here especially because of potential IM distortion issues with power supply modulation.
SS amps have other issues:
1) Rising distortion with frequency, which can be seen often in measurements of THD vs. Frequency. This also plagues PP tube amps with negative feedback. This makes sound more fatiguing and hurts tone and dimensionality of stereo.
2) Completely out of whack distortion pattern. Dominates on odd and high order harmonics and even though they are low in level they are often audible and add unpleasant artifacts to the sound. One of the main causes of unnatural "synthetic" or fatiguing sound. Also kills soundstage and image 3d and palpability
3) Overdamped bass. Not such a problem if one has underdamped speakers (common) but with critically damped speakers or horns the sound becomes overly tight and lacking texture
4) Susceptibility to back EMF from highly reactive speakers giving IM distortion, which leads again to issues with point 2).
For the record, Quad amps sound nothing like a good SET...that 1 out of 10 was sadly right...no push pull amps do as it is sort of inherent in push/pull to cancel even harmonics...this changes the character.
Interestingly, BAT's white paper on the VK60 indicates that even as little as 3db of negative feedback had a detrimental impact on the sound according to them. Pity they didn't take care of business and put serious iron on the output or they might have had an even better amp. The VK60 and 75 were always good but not great and that might have been why. I had a VAC 30/30 with adjustable feedback (from 0 to 6db) and it ALWAYS sounded better with 0, clicking on even 2db dried out the sound of the mids and highs...not a good thing.
How much iron is enough? Well, the Aries Cerat Diana (one of the cleanest sounding amps I have heard) has 18Kg output transformers (big part of why this amp is over 100kg total)! The ones in my Ayon are probably over 10kg each and in my lowly JJ they are well over 10Kg each (it measures quite good in this regard...). More common sizes though are 3-8Kg and this is probably too small for anything other than a single 300B. The problem with large transformers is that they have difficulties with high frequencies unless wound very carefully and thoughtfully.
I think I made explicit points as to why they don't want anything at the amp outputs, as you said. But to clarify, they do not want circuits - the stabilization comes from the cable's and the amp's overall capacitance and inductance, IN the construction of the copper WIRE, much less in the MIT box. FM Acoustics is very similar, in that they force you to buy their Forcelines speaker cables with every amp purchase - in both cases, whatever cables are used, they are part of the amp's design.
And they don't care if the user screws up; the dealers are there to guide, and there are Spectral-branded MIT cables to use, although they are not much different than regular MIT. They build for performance, not for user friendliness, and you either buy into it or you don't. They are not the easiest pill to swallow.
I get that you are passionate about the brand and i don't really want to argue with you about what Spectral's logic for design an amp this way is; however, if you look at this from a distance you will see two things:
1) They didn't elimnate the need for some kind of compensation network at the end of the amp (which BTW limits the bandwidth of the amp to a couple hundred Khz rather than Mhz), it is clear that without something there the amp can become unstable with "difficult" speakers.
2) They simply "outsourced" this network and integrated it into the cable. The construction of the wire is probably not as important as whats in the MIT "box". Either way, there is compensation and bandwidth restriction. If you put it inside the amp or at the end of a cable there is not so much difference in the end.
"The UL-38 is a dedicated Spectral cable network which assures the precision time alignment, critical termination and tuned roll-off required for stable operation of Spectral’s megahertz amplifier designs"
I guess it is a valid choice but a curious one and I guess it obviates the need for cables coming after your tuning network...that is possibly an advantage assuming the MIT is otherwise THE perfect speaker cable choice for the amp beyond it's functional duties...if...
Agreed, but the point is that no one can eliminate this type of filtering. As I said earlier, any solid state amplifier without filtering and with adequate bandwidth and power WILL oscillate. It's an inevitable evil for all SS designs. So they aim to address in a different way.
Not entirely correct; the wire itself is important. The box, for the most part, addresses other issues as per MIT patents - ie. those articulation poles. Think about FM Acoustics' approach as well, which features no box.
Correct - and all SS amps have to limit bandwidth, for stability at least - you see that behavior in the various frequency response measurements. At the same time, they also avoid amplifying high frequency grunge.
Not correct. Revisit the points about magnetic fields.
Hi morricab,
Enjoyed your post. That’s nicely put.
When I first abandoned a very tweaked and elaborate digital, high powered tubes, and hard-to-drive dynamic driver system that I could not get to play music not matter what I tried, I assembled a less-rigid system philosophy allowing me to compare and contrast the world of idlers, SETs and higher-sensitivity speakers. Begging, borrowing and… well, everything short of stealing components from friends, dealers and distributors with whom I had good relationships, I soon discovered a topology can only ever be as good as its conception and implementation/execution (although in some ways this was always obvious, it came home to roost here). Perhaps unsurprisingly, the much-vaunted qualities of lower-powered amplification was in very many cases missing in action, and most often, due to the issues you mention above. It’s part of the process of articulating the problem in terms of the bathwater and not the baby.
The other thing I discovered is that too often the strength of an individual variable is used to disguise the inherent weaknesses of the collective performance. I’d be encouraged to listen for the incredible liveliness of a particular range of frequencies, or lead to marvel at the see-through transparency of the front-to-back depth but in a way that was almost in an attempt to dissuade me from probing too far and questioning the fact that while there were indeed many outstanding individual qualities, the sum of the parts was considerably less, and the musical whole was often the victim of a number of compromises made in order to claim superiority in a single domain. To be fair, this doesn’t just apply to SETs - the fixation with über-speakers that trade dynamics and rhythmic agility for ultra resolution is a sacrifice on the altar of coherence and holistic musicality that’s easy to be swayed by but fundamentally proves unrewarding.
It wasn’t until I began talking to builders from both low-volume one and two-person boutique manufacturers and the DIY community I was able to understand many of the obstacles needing to be overcome. And although cost per se was not always the answer, the reason I ended up seeking out the sensibilities of JC Morrison, Dave Slagle, Jeffrey Jackson, Aldo D’Urso, Thomas Mayer, and since hearing the AC stuff, Stavros Danos was that I came to appreciate the quality of the result is actually almost always proportionately a reflection on the designer/builder in the same way it is with musical instruments. Too often a product is marketed based solely on the selection of topology rather than the designer’s understanding of the topology - the latter is so much more critical in my experience.
Ultimately, I came to realise when it comes to idlers, SETs and higher-efficiency speakers I was buying the builder much more than the product, and have stuck to this philosophy since (albeit in concept, not practice - we’re still “in between” systems). It’s saved me a lot of needless expenditure, and a lot of dashed expectations.