amplifier's "slam-factor"

I wonder if anyone can explain me why there are differences in the so called "slam-factor" between different amplifiers (with comparable power ratings). It is well known that for example Krell amplifiers have a high slam-factor, while Mark Levinson amplifiers are quite tame in comparison, even the most powerful ones (> 300 watts per channel). Spectral amplifiers are very fast regarding signal amplification and transmission, but I find them not very "powerful" sounding (high slam-factor), assuming speed is one of the factors which determine whether an amplifier has a high slam-factor or not.
That's a good question and one that i would like to know the answer to myself. While one can "tighten" and "stiffen" the bass by going gonzo on the power supply and filter cap reserve, it is not easy to make it "slam". Sean
I cannot provide the answer to your question, however, I do not believe that the 'speed' or 'fast' actions of the transistors and/or high biasing automatically imply slam factor. Although these positive attributes would most certainly help to control and produce a well defined bass region even more than usual.

Even you stated that the Spectrals are known as a 'fast' amp yet lack that high slam-factor as you mentioned.

The Krell's and Levinsons are both known for a solid controlled bass, but I have never heard them known for their speed or being a 'fast' amplifier.

Fast has everything to do with reproducing the initial attack of a note and the ensuing decay of the same note which will also lead to more inter-transient silence between the notes giving the impression of perhaps a blacker background when in fact the listener is hearing more silence between the musical notes as the musician(s) intended.

Those amps lacking this speed will have difficulty reproducing the initial attack properly as well as the ensuing decay. And in the process subdue some of the micro- and macro-dynamics of the note. Even to the point where the notes appear to run together.

As one TAS reviewer asked in the course of a somewhat negative product review 'I wish somebody would explain why the tempo of one cdp appears slower than a competitor when in fact the tempo's of both cdp's are identical when compared to a metrinome'?

I may not be able to explain this very well, but to the best of my knowledge, this is exactly why.

It's a difficult question to answer...

First off, *if* you sit in a recording studio and dork with the control knob of an expander/compressor you'll probably be surprised to find that things have *more* impact when they are *compressed*! That means that when they have *less dynamic range* they sound louder and have more apparent impact.

The second thing is that an amplifier shouldn't have "slam factor" at all, per se. It should merely increase the level of the source signal faithfully - that's the theory.

The difference between two amps that have the same power ratings is often in the implementation. As the complexity and level of the signal increases the demands upon the amplifier goes up. This is where many amplifiers start to fall apart (subjectively).

It's too complex to discuss the inner workings of a given amplifier's circuit, but even for identical circuits, the power supply *does* have a huge effect. As the amp draws more and more power -even instantaneously - the power supply has to respond with enough current to keep the voltage up. Almost NONE do this adequately.

The smaller and lighter the amplifier (except switching supply amps - and then the wall is a major factor) the less likley it can perform equally well at full power as it does at 1 watt. My Symphony No. 1 amplifier uses a huge power supply at >2kva in the iron and 500,000 ufd for filter caps with 140 amp Hexfred rectifiers on 1/4" copper buss bars to keep just this problem to an absolute minimum!

This drives a pair of 180watt per channel modules. At full power, both channels driven simultaneously to heavy clipping the rail voltage ducks less than ONE volt. Most amps drop more like 5 - 10 volts on peaks. Some drop more.

Subjectively, you can think of this as the difference between a drive shaft on a car that is really really stiff and one that is springy. Or maybe a transmission that slips vs. a direct connection.

It's likely that "slam factor" in amps is not really there, while the compression factor comes in to play with tube amps, and the power supply is a major issue with all amps. You can hear this stuff.

Imho, as any type of amp design is implemented better and better, they all start to sound surprisingly similar - meaning the best implementations of the best designs tend to sound very much alike be they SS, Mosfets or tubes...(properly applied, of course).

Now, there is "jump factor" in speakers...
With live, non-amplified music does anyone ever hear slamming bass? I've heard deep, forceful tones that carry a physical impact, but I've never been exposed to that sharp, highly edge defined bass sound except for when I'm listening to high end audio systems. I'm not entirely convinced, but the stereotype Krell/Bryston bass sound could be a form of coloration. Which is not to say that on rock and other strongly rhythmic music that it can't be a very pleasant colorations.
I just replaced my 300wpc Krell FPB-300 with a 150wpc Spectral DMA-150 Mk2 (speakers are Aerial 10T). At first blush it had seemed that I had taken a step backwards in terms of slam. But after further critical listening I realized that the sound had taken a step forward in terms of slam. A great example of how the slam changed could be found by listening to Reiner's Pictures (Classic reissue LP).

The sound of the bass drum on this using the Krell tended to fill the room with a dynamic, fat, "thunk" -- something you could really feel in your belly.

With the Spectral amp the overall sense of slam seemed to take a step backwards because it wasn't as large and as fat. The sound though more closely represented a bass drum being hit with a mallet. The sound of the mallet hitting the hit was sharp and seemingly more dynamic sounding than it had been with the Krell. There also was less of a sense of overhang; the notes seemed to disappear more quickly with the Spectral.

Having played the bass drum before, it seemed to me that the Spectral amp was likely portraying the sound more realistically -- and that the slower Krell was allowing the bass drum sound to hang around a bit longer than it should have been.

I think my observations seem to support the very nicely articulated comments by Stehno above.
What about the slew rate of an amplifier?

Does this play a part in the perception of "slam" factor?

Just throwing out thoughts,
i suggest you look at the control that each amp has on the drivers "damping factor"

Aleph 5 50
SF Power2 100
ML 33H 830
Krell ??? ???

Like Atzen811 slewrate factor I suggest that the ability of the amp to control the drives is very important and likely to affect the sense of slam

aleph very tube like
sf very tube to kinda ss
ml very ss with an incredible sense of control and quiet
krell ?????????

not solving anything here but interested to hear comments and ideas
As a general rule, I have found that MOSFET amps tend to provide "one note" bass that sounds like a wet pillow being struck by a canoe paddle. The sort of bass heard on early Telarc recordings. Bi-polar designs seem to be much better in this respect. Over the years, I have found that the biggest challenge in hi-end audio is getting good, tight, deep, natural sounding bass. Attaining air, depth, detail, extended highs and natural timbre are all easier by comparison.
The trouble with buzzwords like "slam factor" is that they invariably tend to mean somewhat different things to different people. Oh the joy of subjective audio where you have large watts and small watts and where the more murky the explanation the better. One man's slam is another man's unnatural exaggerated bass. Go figure! They all sound the same. They all sound different. Take your pick. It's a free country. Has anyone ever heard the sound of an amp without speakers? Maybe everyone should consider the two as inseparable. Maybe then one would say: "amp a when driving my speakers at exactly matched level, in the same room, playing the same source material sounds, to my ear at least, as producing more natural or more accurate bass than amp b". Good day.
Onhwy61 I think you need to get out more as live music is fast without "sounding" fast.....This is a real trick to reproduce in solid state gear, some can, but most can't.....The odd order higher harmonics normally make the slam come across as hard sounding if the musical peak takes the SS amp out of it's Class A region....The solution is to allow more Class A, enough for the musical peaks.....BEAR runs the Symphony No. 1 to about 40w Class A and we run the JC-1s to almost 30w Class A....Using 89 dB efficient speakers neither amp gets out of Class A on peaks and is one reason that the line between tube and solid state has become blurred in the past decade.....
I witnessed a similar effect when trying out a Classe CA100. The dealer said its damping factor is about 30 and my McIntosh MC7100 is 100. This is not the only difference but the Mc definately has more controlled slam than the Ca100 (the rest of the system was the same for both: Mc C712, Paradigm Ref 100.2, MIT). I have been trying to find a technical definition of damping factor but to no avail. Does anyone know how it is calculated? Arthur
Kennyb, thanks for the kind words.
"Slam-factor" has more to do with the amp and speaker combination than it has to do with the amp alone. I've heard speakers take the slam out of amps that supposedly have a lot of slam. And I've heard speakers make supposedly slam-less amps sound slamming.

It would be nice if we could simply look at specs to determine if an amp has slam, but this is not the case. If you do look at specs also look at the speaker's efficiency and impedence. Usually, high efficient and high impedence speakers with lower powered tube amps or low efficient with low impedence with mega wattage solid state amp produces the right amount of slam.
Pbb, I'm with you brother! Here we go again, Slam by whose standard. One mans slam is another mans flab! An amp is suppose to reproduce the source---exactly. If it doesn't, then it is a coloration. The problem is, who has ever heard a source "Perfectly" reproduced? I guess if we can come up with a definitive definition of slam then we can go from there.
Stehno: J. Peter Moncrieff of IAR showed why one cdp sounds different from the next. He did this many, many years ago to specifically demonstrate that some "golden eared reviewers" really were hearing differences and not imagining things. This is one of the reasons that i like Peter i.e. he not only gives you aural impressions of the gear but also takes the time to actually measure and explain why gear has the sonic personality that it does.

By playing the same identical note on one player and measuring / charting the response and repeating the same procedure on another player, it became quite visible on a waveform that one player had better transient response ( faster rise and fall times, which are what gives us the "attack and decay" characteristics that you mention ), greater dynamic range ( higher positive and negative peaks), lower noise floor i.e. "increased inter-transient silence" ( reduced ringing for greater silence between notes / increased separation of notes), etc...

As you can see, all of these factors could contribute to a very different presentation in terms of "slam", timing, pace, etc... even when using identical source material. I find it both amusing and appalling that a magazine with the stature of TAS could not understand / know why such things occur.

Bear: Your comments intrigue me regarding power supply sag. Does this take place in designs that are fully regulated ? Do you know of any designs that regulate the output section ?

Bob Crump: While i can agree with your comments in theory, who is to say that all music / speaker systems can get by with less than 30 - 40 watts in Class A ? While you did specifically state 89 dB speakers, who is to say how big of a room one has or how loud that they like to listen to specific types of music ? What if the speakers being used were of a low impedance design ? That in itself would change the operational area of the amp in terms of switching from A to AB. Sean
Sean, thanks for validating my previous statement and for adding some of the detail that I overlooked. It is my understanding that Moncrief really knows his stuff about audio.

Two other questions, Sean:

1. You're probably really kicking yourself for not purchasing that Primare P30, aren't you? heh, heh.

2. Why not enter your system into virtual systems here on AG?
Aball, the damping factor is calculated by dividing the resistance of the speaker by the output impedance of the amplifier: DF= Z(load)/Z(out). For an amp to have a damping factor of 100 into an 8 ohm load its output impedance would have to be .08. Since a speakers load/resistance changes with frequency (most anyway) the damping factor of an amplifier varies with frequency too. Above 100 is pretty good. When the numbers start getting really high they kind of get trival/splitting hairs. The difference between a damping factor of 175 and 1750 is a 0.5% change in control over the speaker. Some claim those really high damping factor start becoming marketing hype--particularly if other aspects of the design may have been neglected. Concern rises when an amp has an output impedance of say 2 ohms and into an 8 ohm load we now have a DF of 2, worst case (and it does happen with those SET's) things can actually go into the negative zone. (The equation is simplified: to account for the speaker cable, its resistance is added to the output impedance of the amp and then that sum is divided into the aformentioned equation.)

(Current drive amps are the only time one tries to match the output impedance of the amp directly to the speaker for a DF of 0: this in only done in active systems and rarely to my knowledge. Any other time the amplifier aspires to an ouput impedence of 0)

Slew rates matter: its an important spec. However, their worth has to be interpreted in the context of power and load resistance too. A less powerful amp doesn't need as high a slew rate as a bigger one. Into an 8 ohm load an 11V/us is acceptable for a 32 watt amp; for a 1,000 watt amp 64V/us is appropriate. It does depend on the bandwidth of the amp. And if slew rates get too high it can cause new problems.

This article briefly attempts to correlate some of the electrical/measurable aspects of amplifiers performance to subjective impressions.
An output impedance of 2 into an 8 ohm load gives a DF of 4, not 2 as incorrectly stated. (This is ignoring the change caused by the cable) Although if you look at tube amp specs you'll often see ones claiming DF's of <2. I believe the Cary 300SEI (from mid '90's) actually went up to a 3.8 ohm output impedance.
Sean, I use the Rockport Syzygy speakers in a 16 x 23 x 8'6" room and can hear the transition to Class B on musical peaks when running just 10w of Class A and can't hear the transition with about 30w of Class A via a switch on the JC-1s....
Stehno: As to the Primare piece, i would have liked to have grabbed it, especially at that price, but i'm not upset about it. Then again, i don't know what i missed either : )

As to listing my systems, i had done that at one time on AA and had one of them listed here. Quite honestly, i pulled them down for security reasons. I and several others discussed this privately and came to the same conclusion i.e. we didn't need to advertise what we had. Quite honestly, i do not live in what is the best part of town, hence my desire to relocate. Two houses on our block have been burglarized in the last year, so no sense in pushing the matter if you know what i mean.

Bob: Thanks for the response. The point i was trying to make was that others may have different ideas of what they think is "loud" and have lower efficiency speakers AND have bigger rooms. While that is a tough situation ( big room, low efficiency speakers, high spl requirement ) for sure, i'm sure that it does exist. Just as i would have laughed if someone would have told me that i needed 1200 wpc to power a set of speakers before owning a set of them, i no longer rule things like that out anymore. Each situation is different and we all have different goals / priorities as to what is most important to us within our own systems. Sean