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B&K amps = slow!?


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#1 of 12 OFFLINE   DanielSmi

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Posted November 19 2002 - 06:03 PM

Now, I don't want anyone to yell at me but I was just looking at the specs of the B&K amps and they didn't look to fast. Yes, it's true I've never heard them before but I was wondering if this was true? I'll give some examples:

Damping Factor: 450 at 50Hz
Dynamic Headroom: 1.2dB
Slew Rate: 14v/µs.

Now I'll comare it to a similiarly priced Parasound 2205at:

Damping factor : >1000 at 20Hz
Dynamic Headroom: >1.5dB
Slew rate: 130 V/µs

Now I'll give you definitions of these terms if you don't know them so you'll understand where I'm coming from. (terms from www.audiovideo101.com)

Damping- An audio system's ability to stop playing a signal after it has ended. For instance, a sharp drum thump should not drag on for too long a time. If it does, the system is exhibiting poor damping meaning that it is not properly ending the sound production associated with the drum thump. Such a system is generally muddy and not well refined making individual musical nuances difficult to make out.

The damping factor relates to how well an amplifier is able to control the movement of a speaker driver, stopping its motion after the signal has stopped. If the driver motion is not halted, the driver will continue to move creating back-EMF (voltages sent back into the amplifier from the speaker's voice coil moving in the magnetic field) and unpleasant, distorted sounds. Look for an amplifier with a high damping factor when you go to purchase audio equipment. The damping factor should be at least 300.

Dynamic Headroom- An amplifier's ability to go beyond its rated average power for a short time in order to recreate loud or explosive audio signals that rise very quickly, without distorting or clipping. In order to have high headroom (an ability to achieve loud peak levels without distorting), and amplifier must have a solid power supply with a good amount of reserve energy on which it can call. Headroom, also referred to as dynamic headroom, is measured in decibels (dB). An amplifier with a rating of 3 dB can double its output power for peaks. Look for an amplifier with a rating of 1.5 dB or higher. It is important to have an amplifier with a strong power supply.

Slew Rate- Fastest rate at which an amplifier can change the amplitude of its output signal measured in volts per microsecond with a higher figure being better (meaning that the amplifier can change more voltage in a given period of time, one microsecond). An amplifier with a good slew rate can quickly alter the amplitude, or power/volume, of a signal. This is an important characteristic for reproducing sudden, extreme changes in a signal such as those developed with an explosion or similar loud, powerful, sudden sound. Slew rate is the response rate to an increase in amplitude.

Now notice that the damping factor for the 2 are measured at different frequencies. The Parasound at 20Hz and B&K at 50Hz. I think it's safe to assume that stopping a 20Hz signal is harder than stopping a 50Hz signal. Now the B&K doesn't have the lowest damping factor I've seen in fact it is similiar to the Rotel, but the worst I've seen was actually from a McIntosh 5 channel amp my friend has and that's at like 150 or something, it's really low. Also notice that www.AudioVideo101.com says that the dynamic headroom should be at least 1.5dB and that B&K doesn't meet that, but it does have a damping factor higher than 300.

Again I'd like to say that I've never heard these amps before, but from looking at the stats it doesn't appear to have a very powerful power supply. I also don't own a Parasound. These are just observation of stats. So, whad'ya think?

Daniel Smith

#2 of 12 OFFLINE   James R. Geib

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Posted November 19 2002 - 08:09 PM

Here is a link elaborating on the damping factor value, and how it relates to the amplifiers performance. Slew rate and dynamic headroom are significantly more important when looking at an amps specs!


http://www.trueaudio.com/post_013.htm
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#3 of 12 OFFLINE   Haris Ellahi

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Posted November 19 2002 - 10:50 PM

Thanks for the info! Posted Image

The Parasound HCA-2205AT looks VERY nice.

#4 of 12 OFFLINE   Haris Ellahi

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Posted November 19 2002 - 10:54 PM

By the way, what is the slew rate of the Rotel RMB-1095?

#5 of 12 OFFLINE   James R. Geib

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Posted November 19 2002 - 11:12 PM

Rotel does not list the 1095's slew rate on it's spec. sheet, so you'd have to contact them to find out
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#6 of 12 OFFLINE   Charles Gurganus

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Posted November 20 2002 - 12:19 AM

Which amp SOUNDS better for your setup? I wouldn't get too carried away with some of these specs. They are all measured differently makeing comparisons meaningless in most cases. I looked at amps power supply and design and considered which ones would work better with my NHT speakers. With that in mind, Parasound, B&K, Rotel and Sherbourn were all in the running.

I am not saying to ignore these specs, but when you start talking about $2000 amps, they are all pretty good. Some are better suited for different speakers.
Charles

#7 of 12 OFFLINE   Yogi

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Posted November 20 2002 - 03:01 AM

I have a B&K multichannel amp and I have compared it to other amps in the same $$$ range. Parasound, Rotel (damping factor 400) are all excellent but the B&K has one of the best low end response and one of the smoothest treble. Its hard not to like B&K sound. Its smooth, effortless and uncongested at any levels. So I dont think you should be worried about those specs but more concerned with how an amp mates with your speakers and your room. In that regard, I think B&K is the most forgiving (of all the above amps) of what speakers you mate it with. It sound fabulous with any speaker: from Vienna Acoustics (very warm) to Klipsch (very bright). Now thats something not every amp can boast of. Parasound would be second in that regard and Rotel a close third. Any amp that is neutral to bright cant be mated with a whole lot of speakers. If you dont believe me try mating an ATI/Outlaw with Klipsch.
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#8 of 12 OFFLINE   Chu Gai

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Posted November 20 2002 - 04:15 AM

You're making a bit more out of the the possible audible differences in damping factor and slew rate between these two amps than there is.
With regards to damping factor, take a look a little less than 1/2 down at this link and think a bit just how the Parasound's greater damping factor is going to result in improved (diminished) distortion numbers. You don't need a lot of 'damping factor' to control the movement of the speakers and both amps are significantly above what's required. The difference in part are due to marketing decisions with a bigger # being looked upon as better.

The higher slew rate amp has the capability of changing faster than one with a lower value. As far as low frequencies go, it's a non issue. They don't require fast changes. For higher frequencies played at louder levels it 'might' be a problem if it was terribly low. Neither amp has issues in this area though. The slew rate is also a game played by marketing largely because the source signal itself has source has an inherently limited and low slew rate.

So long as either amp is capable of driving your speakers to the levels you like I wouldn't sweat these specifications much.

#9 of 12 OFFLINE   Chip E

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Posted November 20 2002 - 04:59 AM

I just bought my first multichannel amp a couple weeks ago. A B&K 200.5
I didn't look at any spec, numbers, yada,yada,yada. It sounds incredibly good. Posted Image
- Chip

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#10 of 12 OFFLINE   randy bessinger

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Posted November 20 2002 - 05:33 AM

BK amps=slow?

Mine (7270) is very slow. Since I put it in my rack it has not moved an inch.Posted Image

#11 of 12 OFFLINE   DanaA

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Posted November 20 2002 - 05:45 AM

Chu,

You are a walking encyclopedia of knowledge of electronics. Whether everyone always agrees with you or not, I always read your posts. I will never know the technical side as well as you, but you do know your stuff . Thanks for sharing your insights.Posted Image

#12 of 12 OFFLINE   Chu Gai

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Posted November 20 2002 - 09:02 AM

I understand that people take a very personal shine to their equipment and that an attack or a perceived attack on that choice is taken like you've attacked them, their beliefs, their taste, their ability to arrive at an accurate assessment, etc. Trying to stay on the topic of amps all I can say is that there are a ton of great amps out there, new and especially used. Not only are there a ton of great amps but one can buy them anywhere from the hundreds (and even below if you get lucky!) to the thousands. If for you high slew rates or rise times or sub 0.02% THD, or a frequency response out to 40 or a 100K is important (I call it a preference) then they are out there. We've all got our special needs and some of us even have finite budgets (imagine that). Hey look, right now i'm pissed off at the German gov't for political reasons and I'll excercise my protest with my wallet by making sure nothing I buy comes from that country. Don't even get me started with France! The thing with amps, whether you want to subscribe to the position of unsighted testing or not, is that the results very strongly suggest there's far more commonality than there are audible differences. That doesn't mean you buy the cheapest one but it does mean that you can look at the vast majority of the claims that are out there and put them in the shoebox marked claims. That shoebox has got other claims like ionized bracelets, vitamin supplements, the tens of thousands of guaranteed diet programs, and all that. Unless there are glaring issues with a receiver or an amp it's really making the proverbial mountains out of molehills. I think it's important that people identify first what their power requirements are either presently or for the foreseeable future. Then if you're a monoblock kind of person, get those. The idea of two amps, one three channel the other two turns you on, then go for that. An all in one solution meets your needs, then by all means go for it. You find the methodology of a Class A amp best defines you then buy one. Budget's really really tight, investigate the pro area at your local music store. It's really very hard these days to buy a poorly made amp.
I think required viewing for everyone should be 'Crazy People' with Dudley Moore as that movie hit adverstising pretty dead on. Just my $0.02...take out a five and have a cup of Starbuck's on me Posted Image