Pure class A amplifiers = "slow" amplifiers?

Hi folks, I know this is subject of controversy. In general pure class A has been regarded as the best way in solid state amplification to get the purest sound. In my experience many pure class A solid state amplifiers (Accuphase, Pass Labs, Plinius) sound "slow" and are lacking "dynamics". Do they sound that way because they have less distortion than class A/B amplifiers, I mean sometimes a signal is so pure that one is increasing the volume adjustment knob to get a louder sound. With a very pure sound it seems like music goes slower too (= psychoacoustic phenomenon).

No. Some of the fastest rise times are from class A.

So if this perceived slowness you think you hear from pure class a, its something else in the system

What i have experienced from class A/AB (Pass x250.5) and class A, sa102, is an incredibly dynamic and lucid presentation. A fine example of a class AB (though it is biased for about up to 5 watts in class a) was my dna 225. Also good dynamics and sense of rhythm, but outclassed by the more expensive amps ive had.

Both the pass and plinius have very "black" backgrounds upon which the musical event is built. The 225 has higher noise floor and dynamic contrasts not as extreme. I think what you are hearing is the purity of the event and maybe used to a more hyped sound from lesser amps.

just my 2 cents
do you know for sure that the slow sound you have heard was attributed to the amplifiers?

I have never heard a system with a Class A amplifier sound slow. Slow sound is usually a result of overripe, fat and bloated bass. If the amps you heard possess that quality, then I guess it is what you heard.

Systems that overemphasize bass usually sound slower. Although there are amps that sound heavier in bass with softer highs than other amps, but it hardly is a characteristic of a pure Class A amplifier sound.

If I recall correctly from your previous posts, you own digital amps. Sound of digital amps is different. If you are used to one type of sound, you need to readjust and get used to a different sonic presentation if you switch to Class A amps. The sound is just different. Which is right, it's for you to decide.
The thing that makes this comparison tough is that in order to be valid, the amps you're comparing (class A to class AB, etc.) have to be the same in other ways as well . . . and this may not be the case in your experience.

I would hypothesize that the class A designs you're associating the "slow" sound with also are single-ended or zero-feedback designs that have a comparitively high output impedance, which will definately affect most loudspeakers' response in such a way as to change the way you percieve timing information.

I think I understand where you are coming from. When I first heard my Nagra VPA tube amps (which are Class A), I experienced the same thing. In fact, when I first inserted them into the system, the music seemed less dense, and slow...there was no sense of urgency to the music. But there was a sense of "rightness" to the music that I cannot describe.

Your hunch about the lack of distortion is what my hunch is...of course over time, once my ears adjusted to the new sound, and now I no longer experience the "slowness".

it's too easy to generalize. i am auditioning a class a amp with my magnepan 1.6s. i would not use the word "slow" to describe what i hear. my "reference" amplifier(s) is the vtl deluxe 120.

while an amplifier may have a peak in the bass, it may also be extended in the treble. depnednding upon the frequency response, such a situation may be described as "boom and sizzle".

the combination of attenuated treble response combined with an over emphasis in the region 80 to say 150 hz is rare in a class a amp, in my opinion.
In the Black and Blue books of the the great German or was Austrian Oh that's right Vienese Philosoper Wittengstein explained at length . The only thing which anything tells you of itself, is limited to what it can tell you. Further you can't whistle about it either. In plain old Austrian if the thing called Class A amplification tells you it sounds slow -it does indeed sound slow. Logic will tell you that if A does not depends on how it's circuit. then you can count on A always being A. His obversations being limited to the fin de Ciecle or Saichel, when there was no abundance of anything, especially class A, so could he know? We are left to ponder.
Finally if it sounds slow is that so terrible?
Slowness is a function of the source. What are you using?
If you want to know if the amp in question is slow of fast - just look its bandwidth. Wide bandwidth is a property of the fast amp ( If I am not mistaken: BW = 1/Slew Rate) and vice versa.

All The Best
Stevecham writes:

Slowness is a function of the source.
Not completely.

Band width and slew rate are not a function of eachother only potentially limited by one or the other parameter. In any event the slew rate is ridiculously quick, some other elements must account for percieved slowness. I don't percieve it in my class A tube amp at all. I think it is not physics but pycho acoustics with cues telling some listeners the sound is rich dense, or heavy and therefore slower.
If you're just telling us that you don't prefer the 'Class A' sound, that's understandable. Class A is not the only way to good sound or else it would be the only type of amplifier people would buy. Just because you prefer one over he other doesn't mean you're missing the bus or it's a design issue - there are plenty of A/AB's out there that outperform single-ended Class A. But then again, substituting a better amplifier shows up downstream equipment. Maybe it's the preamplifier slowing things down.
What are your speakers?? Pre?? Source???
Dave, I have Soundlab A-1's, Accuphase C-290V preamplifier and MBL/Accustic Arts digital front end.

Dazzdax, there should be little or no correlation between what seems to be a slower tempo and the purity of the signal.

You are correct that the cleaner the signal the more you want to crank it because it does not sound as loud as previously. That's because we historically have associated loudness with distortion. The greater the volume the greater the distortion. So when a more pure output is generated we have a tendency to think it is not as loud.

As for slower tempo, this generally has much to do with the speed of the transistors (and perhaps other innards).

Amazing how one component made by two different manufacturers can make the tempo sound slow as molasses or lightening quick.

Always something to look out for when purchasing gear. I suggest staying far, far away from any component that you deem to be 'slow'. It's a huge step in the wrong direction as it has nothing to do with musicality no matter what other benefits the component may offer.

Hi Chris,

I notice that you are using Furutech wall outlets (cryoed)...are they the gold version?

In my set up, i used to have the top of the line Gold outlets...they kind of "muddied" the low end which kind of resulted in a slower sound...

When i changed over to Hubbell 5362 (normal and uncroyed), the sound seemed to lighten up.

SO you may want to consider changing one or two of your wall outlets to some other brand to test.

Also, i have found power cords to slow down the sound of a component. For example, when i use a warmer cord (copper) versus silver, on the Pre or the source, the dynamics slowed...

On the amps, i used to use Black Sands Silver Ref Mk5 and they sped up the amps...

What this showed me that if you use warm (cord) and warm (components), things sound richer (maybe quiet) but could slow things down....this is where the synergy thing works i suppose.
Oh wow, you guys mean that I can really change the time signature on a song by getting a different amp? I always thought that Bernstein takes Dvorak a bit too slowly. . . what amp should I select to speed up playing time by about 20%?
My experience is that Class A amps provide a fuller sound which I believe is more realistic to the original performance. Class AB or Class B amps add crossover distortion when they transition from Class A to B. I believe this sounds like adding an edge to the music, especially transients, which accentuates the leading edge of the transient at the expense of the follow-thru. This sounds "sharper" or faster. However this leads to listener fatigue over time and is particularly noticable on "hot" recordings which can sound almost unlistenable in some instances. Obviously there are more variables which make an amp sound different than another one. I heard a demonstration once of amps whose only difference was at what point they transitioned to Class B i.e. at 5 watts or full Class A. Class AB sounded as I described above. I much preferred the Class A. It wasn't a night and day difference but was noticable.
Guidocorona, LOL.
Other than making sure your power is enough to command the A1's, maybe the accuphase pre is adding some fudge...nice sounding but not speed racer! Try a used Krell stereo amp with a KCT...should be warm and fast.
Guidocorona...Believe it or not audio can be speeded up without the tonal change that results from overspeeded playback...but no using a simple amplifier. It takes some digital processing.

It is a fact that our sense of hearing can recieve and understand speech faster than our tongues can wag. Alarm messages, for example to airplane pilots, can be speeded up.
Class A (in general) will produce less distortion than any other form of operation. The human ear uses odd-ordered harmonics as loudness cues; in particular the 5th, 7th and 9th. Although only found in trace amounts in most amplifiers, even very subtle increases in these harmonics are readily noticed due to the way our ears work.

We perceive the increase as brightness/hardness.

I would not surprise me in the least to find that some people hear that as 'speed' (to me the word speed refers to the risetime or slew rate of the amp) or bandwidth.

If those harmonics are not altered the amplifier will be more relaxed or 'laid back', which is **not** to say that there is a coloration- in fact. there is *less* coloration.

In transistor amplifiers some of the fastest risetimes are manifested in Class A amplifiers. This is true of tubes too, although to really get the same speed as transistors you have to get rid of the output transformer, but then they can be every bit as fast as the fastest transistors.
"Speed" or more properly "rise time" should never be a problem for audio amps. After all, both tubes and transistors are used at radio frequencies.

I know Guidocorona was just joking with his post. ... but ... I just would like to clarify for those who may not know. The tempo of a song ( how fast or slow it is played ) has nothing to do with the time signature. Two totally different things.

Thank you Tom, sadly, you are correct. Performers often take obscene liberties with clearly specified time signatures or stylistic practices, resulting in totally bizarre tempos of performances and recordings.
Rythmic signatures are a different matter all together, and are subject to their own special kind of manglings.
Eldartford, you are right of course, about time domain compression/expansion. I have played with analog time domain compression of speech streams since the mid 70s. . . . and in those days results were pretty horrendous. Now days, using advanced algorithms, reasonable intellegibility can be achieved by speeding up digital recordings of speech up to 3X. Text to speech engines (TTS) can yield intelligible speech upwards of 500WPM by adopting differing compression scales for different phonemes. I have heard formant-based TTS engine actually running at 1200WPM, but do not pretend to understand them at such speech rates. G.
After reading G's jibberish I am confident that someday there will be time travel:)
Thank you Dave I have no information on upcoming breakthroughs in time travel, nor on the ability of an amplifier to speed up the tempo of a musical performance. On the much more mundane topic of the application of time domain compression/expansion in formant-based and concatenative speech synthesis, I invite you to experiment with the open source NVDA screen reader:
You will discover that you can make significant changes in speech rate. G.
G, you are an organic based lifeform right? Not cybernetic! Maybe your from KAPAX...anyway, I'll check out the sight.

Apologies Dave, I have no information on 'KAPAX' either.
FWIW, IMHO, in my experience, pure Class A amps TEND to be less forward than Class AB amps. Perhaps to some that might be percieved as "Pure class A amplifiers="slow"amplifiers". I have met a very few individuals who profess a preference for Class AB over class A amplifiers. On the other hand, I have met many who profess a preference for Class A over Class AB amplifiers. I prefer high powered Class A amplifiers. My budget constraints have led me to high powered (as determined by speakers, rooom, etc..), high biased Class A/AB amplifiers.
Hi Unsound, Krel are Class A SS amp. . . how would you characterize them? Aren't they caracterized to be relatively forward sounding? G.
The bug-a-boo about A/B amps is crossover distortion where, as the waveform crosses zero and changes polarity, one output transistor turns off and the other turns on. The very first transistor power amps caused distortion of the waveform as this happened. It was largely responsible for their poor sound quality. Once this effect was recognized designers have taken pains to minimize crossover distortion. Not all A/B amps are created equal. Good ones exhibit little or no crossover distortion, although they may have other problems, most of which could affect class A amps also. However, crossover distortion is easy to understand, and is often cited in criticisms of A/B amps.
Class A amps are not slower or faster than class A/B and do not inherantly have more distortion. Class A actually potentially has less distortion because the active device is biased in a manner so that it conducts the through the entire cycle of the input signal. Of course can drive the active device too far in one direction or the other and end up with a distorted waveform - distorted sound. A Class A device avoids the distortion caused when you process something less than the entire cycle with one active device and the remainder with a second active device, because the point where the conduction crosses over causes a glitch. However, this is not really a problem if the system is properly designed. Why would anyone want to use less than Class A topology ? Because you save on the size of the active devices, if you are only conducting current half the time you create less heat and can use a lower wattage component. A well designed CLass A should sound no better or no worse and no different than a well designed Class A/B. Now there are a host of reasons that one amplifier may sound different than another but whether the design is CLass A or Class A/B is too limited of a criterion to say how an amp will sound or how well it will be able to drive a load.
Guidocorona, my impression of real Krell amps (pure class A power only amps, no HT or integrateds) is that they are warm, deep, and excell at both micro and macro dynamics. I'm a big fan.
In my opinion dynamic range is more loudspeaker related than amplifier. For if you rely on massive power to get dynamics you are forcing your loudspeakers to perform, requiring massive cone excursions and much heat to crossover parts and voice coils all detrimental to sound quality and loudspeaker life span. I find loudspeakers that are efficent and need little power to provide far far better dynamic range and speed than conventional loudspeakers that need huge power just to sqeak out limited SPL. Since the driver cones are hardly moving in hi-eff designs they reveal hidden details that are lost to massive excurtion designs. Plus hi-eff are at ease at almost all SPL levels since these designs are never forced or pushed they dont heat up as much or sound fatiging like convetional designs do at HI-SPL. Once you hear proper replicated dynamic range conventional loudspeakers with massive power sound slow and compressed. CLass A is not the cause at all its the loudspeakers.
Johnk...Although Maggies aren't high efficiency speakers, they do have very small diaphragm excursion, and I believe this may be a lot of the reason they sound good. When I designed a cone driver subwoofer system to go with my Maggies a prime criteria was minimal cone excursion. What happens to the typical subwoofer cone is obscene!! I ended up with three subwoofer systems, for my three front channels, each including a 15" driver and a 12" driver. I get very strong bass with quite modest cone excursion.
I spent over a decade with dipoles most models including maggies. For me HI-EFF been the better sound. Now with HI-EFF ribbons about this frees up design. I have a few med to hi-eff hybrid ribbon loudspeakers about. Gives the best of both worlds. No need for HI-Eff to be all horn but still my mains for now are giant 3 way front horns. Ive built a few bass systems for Maggie, ML, SL, Quad owners and the fostex 31.5in is the best I heard matched to 20.1 3.6 and other electrostatics.31.5 can be used in OB so dipole bass. But very large and costly...No free lunch. I have also used 31.5 with oris 250 fostex f200a a few dif ribbons and comp tweeters set up as OB even mid horn is dipole but -6db down over front and to me;) a good step up from the maggies and other electrostatics Ive owned mess about with for customers. I do hear why folks enjoy the maggie sound you can build good systems arround them. As with all things YMMV,and we all dont have the same tastes.
Johnk...Fostex 31.5 = cone area!
Also, Fostex 31.5 = $2535.75
as of April 07. Probably more now.
At least you didnt look at the fostex w400a hr price. Iam working out a design using these with a ribbon;) in a 2 way......
JohnK I respectfully disagree. Under-powered loudspeakers tend to lack dynamics. Different speakers have different amplification requirements. There are pros and cons for each speaker design. I have yet to hear highly sensitive loudspeakers that perform to my satisfaction.
Hi folks, I know this is subject of controversy. In general pure class A has been regarded as the best way in solid state amplification to get the purest sound. In my experience many pure class A solid state amplifiers (Accuphase, Pass Labs, Plinius) sound "slow" and are lacking "dynamics".

What you may be observing is simply a lack of distortion. A very high priced Class A amp is likely to be top notch. Furthermore, the design eliminates crossover distortion which is responsible for very high order harmonic disortion (in very small amounts but perhaps audible in some cases).

If you remove higher order harmonics (distortion) then music will indeed sound more laid back and natural - it will lack that edgy sound that you hear with most pop music today such as Red Hot Chilli Peppers, Green Day, Arctic Monkeys etc. (where distortion has been deliberately added in the mastering stage to make it sound "loud" - see CD loudness wars on google).

My speakers run Class A to two thirds power and I am very familiar with the harsh sound of modern pop CD's. The modern hypercompressed CD effect is such that they sound "fast" or "edgy" or "snappy" at low volumes (perceptively this sounds better to many people which is why the mastering engineers do it) - however - at higher volumes the sound is noticeably harsh and unpleasant compared to a properly mastered CD with proper dynamic range and without "hard-clipped" square signals (often, on a modern CD, a single track is clipped or flat-lined over 10,000 times!! I am not joking! If someone tried to sell you a towel and you got home and found it full of holes then you would take it back and demand your money back - this whole thing perpetrated by the recording industry is totally scandalous).

So laid back slow or natural sounding amplifier is GOOD, at least in this context, IMHO!!
Absolutely agree with Shadorne's reasoning.

We are surrounded by mass media broadcast sounds that are reproduced with compressed software/inferior equipment to begin with so it sounds good on bulk of the mass produced home and car stereos, radios and TVs. A shadorne says: Fast, edgy, snappy, punchy, grainy, thin, boom and sizzle sound is what we are used to in our everyday life.

So when we hear live sound or pure signal (from superior software of course) being reproduced it sounds so different than mass media delivered sound that you question your sanity (;-)) and your equipment (Class A amps for example). At times you almost want that punchy and edgy definition sound back where faster sounding leading edges are IN your face.
I have always preferred a fast, lively sound since owning a Linn LP-12 and discovering the British "PRAT" sound.

Electronics, generally speaking, with ultra-wide bandwidth will have a faster presentation for a more accurate portayal of musical transits and phase. Faster is better and conveys the musical energy far better than slower designs although some may prefer that type of sound. Remember, it's all subjective what each of us enjoy.

That said, the sound can be smooth or it can be edgy - speed has nothing to do with tonality. The Delta Sigma Italian amps & preamps we distribute are flat to 3Mhz, lightning fast with the tonal purity of a great OTL design.

So we can have speed and harmonic purity - it simply takes some searching for the special designs.

Jim Ricketts/tmh audio
Jim, is there an info page on Delta Sigma amps? And what type of amps are they? Tubes, SS, switching? Class A, A/B, D, T, other? Thanks G.

Our website has information - surf over to http://www.tmhaudio.com/DeltaSigma.htm

I visited the factory last November to meet the designer is most unique in his creativity. Good guy, too! We expect the Reference "North Pole" linestage to arrive in a few weeks - also flat to 3Mhz.

I was always a tube person...until the visit to Italy and heard Delta Sigma.

Jim Ricketts/tmh audio
Thank you Jim. . . did not really find the info I was looking for about underlying technology, class of operation, single ended vs symmetrically balanced, damping factor. Interesting about the Kosmos conductor. . . more conductive than Silver? What is its resistivity value at 20C? Will DS be shown at RMAF in the Fall? Thanks, G.
Yeah, I did the same thing and could not find the Amp's topology on your website. I know you and I have talked about this, Jim, and you think highly of these amps designed by ex employee of MBL, and you might have mentioned which type Delta Amps are but it escapes my memory at this time.
Symphonic Line Kraft amps are pure class A and maybe the fastest sounding solid state amps out there. It all depends on the implementation.

Dealer Disclosure

The SINE "Kosmos" conductor is an alloy of metals including silver. It goes through an 8-step process that alternates annealing and deep cryo (4 each) to achieve a conductivity higher than silver (and of course copper and gold).

Extraordinary sound.

We are receiving some other models ("Coliseum II" and "Cassio") that use some of the technology in the Kosmos series including carbon powder to absorb micro vibrations and in-line RFI/EMI. Also will receive a batch of the wall outlets w/platinum plating using a ultra high grade outlet. All is deep cryoed.

I expect SINE will become a reference in power and cable products...I'm that imprressed!

Jim Ricketts/tmh audio
Thank you Jim, unfortunately 'greater than Silver' does not mean anything to me. I am glad the product also uses graphite powder to its advantage. Graphite is naturally abundant,
inexpensive, and easy to work with. Any more hard info you can share about Sigma Delta Amps?

The SINE "Kosmos" custom alloy conductor's higher conductivity should relate to faster, easier flow of current or signal. Sonically, it has the vivid, liquid transparency of the Delta Sigma amps & preamps & BOW ZZ-8 CD player we are re-introducing to US market.

Re: the Delta Sigma electronics, obviously much is proprietary. The 3Mhz circuit (flat within 1db) is amazingly fast thanks to the ultra wide bandwidth. But that liquid transparency I mentioned above is so like a great OTL amp...but with strong, vice-like grip on bass dynamics and an upper end that is so airy and delicate. I've simply never heard anything as pure and powerful as the Delta Sigma...including $350k monoblocks.

During CES2008 where we introduced Delta Sigma NP Integrated and Manger's 109-AG ultimate monitor, we received numerous compliments on how lifelike piano sounded. Some people in the hallway entered thinking we had a real piano playing.

After the "North Pole" reference linestage arrives later this month, I'll post some additional comments. After hearing it in Italy, I can't wait!

Jim Ricketts/tmh audio