Specs 101. Class has started

[GMichael]

I look at the specs for many items before I buy. Listening is good, but I like to know the facts also. Some of these I understand. Some I have an idea on. Some leave me totally guessing. Below are some specs from a 2 channel amp I've been looking at. Please help me fill in the meanings to these specs. It may come in handy to some new comers. Oh OK, it's for ME! But it may help others too.
Extra points to whoever tells me what amp these numbers came from first.


Continuous power output: (OK, we all know that these mean different things to different manufacturers. But it's good to have a starting point for power)
125 watts RMS x 2, 20 Hz - 20 kHz, 8 ohms, both channels driven (continuous power into each channel when your speakers are 8 ohmers)
200 watts RMS x 2, 20 Hz - 20 kHz, 4 ohms, both channels driven (ditto for 4 ohmers)
400 watts RMS x 1, 20 Hz - 20 kHz, 8 ohms (to use this amp as a subwoofer amp)
Current capacity: 45 amperes peak per channel (high current? good for hard to drive speakers with a few dips in resistance?)
Signal-to-noise ratio: > 112 dB, input shorted, IHF A-weighted (more sound than noise?)
Total harmonic distortion: < 0.06 % at full power (Seems great, can I really hear a difference between 0.1% and 0.001%?)
IM distortion: < 0.04 % (huh? Instant messaging? huh?)
Power bandwidth: 5 Hz - 100 kHz, +0/-3 dB at 1 watt (huh?)
Slew rate: >130 V/µsecond (oh come on)
Dynamic headroom: > 1.5 dB (I like the sound of this one)
Interchannel crosstalk: > 80 dB at 1 kHz; > 63 dB at 20 kHz (who?)
Input sensitivity: 1 V for 28.28 V, THX Reference Level (how much the inputs can take?)
Input impedance: 33 k_ (Does this mean that it can't have kids?)
Damping factor: > 800 at 20 Hz (oh oh, does this have something to do with it's ability to control base?)
Voltage: Switchable for 110V – 120V or 220V – 240V operation (ok, you can use it here, or there.)
Dimensions: 17-1/4" w x 4-1/8" h x 13-1/4" d, 3-5/8" h without feet (it's not so big)
Net weight: 28 lbs. (not too heavy either)

[basite]

I look at the specs for many items before I buy. Listening is good, but I like to know the facts also. Some of these I understand. Some I have an idea on. Some leave me totally guessing. Below are some specs from a 2 channel amp I've been looking at. Please help me fill in the meanings to these specs. It may come in handy to some new comers. Oh OK, it's for ME! But it may help others too.
Extra points to whoever tells me what amp these numbers came from first.


Continuous power output: (OK, we all know that these mean different things to different manufacturers. But it's good to have a starting point for power)
125 watts RMS x 2, 20 Hz - 20 kHz, 8 ohms, both channels driven (continuous power into each channel when your speakers are 8 ohmers)
200 watts RMS x 2, 20 Hz - 20 kHz, 4 ohms, both channels driven (ditto for 4 ohmers)
400 watts RMS x 1, 20 Hz - 20 kHz, 8 ohms (to use this amp as a subwoofer amp)
Current capacity: 45 amperes peak per channel (high current? good for hard to drive speakers with a few dips in resistance?)
Signal-to-noise ratio: > 112 dB, input shorted, IHF A-weighted (more sound than noise?)
Total harmonic distortion: < 0.06 % at full power (Seems great, can I really hear a difference between 0.1% and 0.001%?)
IM distortion: < 0.04 % (huh? Instant messaging? huh?)
Power bandwidth: 5 Hz - 100 kHz, +0/-3 dB at 1 watt (huh?)
Slew rate: >130 V/µsecond (oh come on)
Dynamic headroom: > 1.5 dB (I like the sound of this one)
Interchannel crosstalk: > 80 dB at 1 kHz; > 63 dB at 20 kHz (who?)
Input sensitivity: 1 V for 28.28 V, THX Reference Level (how much the inputs can take?)
Input impedance: 33 k_ (Does this mean that it can't have kids?)
Damping factor: > 800 at 20 Hz (oh oh, does this have something to do with it's ability to control base?)
Voltage: Switchable for 110V – 120V or 220V – 240V operation (ok, you can use it here, or there.)
Dimensions: 17-1/4" w x 4-1/8" h x 13-1/4" d, 3-5/8" h without feet (it's not so big)
Net weight: 28 lbs. (not too heavy either)


parasound halo A23 :ihih:

[GMichael]

parasound halo A23 :ihih:

Did you actually READ the specs, or did you just remember that that's the amp I want?

[basite]

Continuous power output: (OK, we all know that these mean different things to different manufacturers. But it's good to have a starting point for power)
125 watts RMS x 2, 20 Hz - 20 kHz, 8 ohms, both channels driven (continuous power into each channel when your speakers are 8 ohmers)
200 watts RMS x 2, 20 Hz - 20 kHz, 4 ohms, both channels driven (ditto for 4 ohmers)
400 watts RMS x 1, 20 Hz - 20 kHz, 8 ohms (to use this amp as a subwoofer amp)
Current capacity: 45 amperes peak per channel (high current? good for hard to drive speakers with a few dips in resistance?)
Signal-to-noise ratio: > 112 dB, input shorted, IHF A-weighted (more sound than noise?)
Total harmonic distortion: < 0.06 % at full power (Seems great, can I really hear a difference between 0.1% and 0.001%?)
IM distortion: < 0.04 % (huh? Instant messaging? huh?)
Power bandwidth: 5 Hz - 100 kHz, +0/-3 dB at 1 watt (huh?)
Slew rate: >130 V/µsecond (oh come on)
Dynamic headroom: > 1.5 dB (I like the sound of this one)
Interchannel crosstalk: > 80 dB at 1 kHz; > 63 dB at 20 kHz (who?)
Input sensitivity: 1 V for 28.28 V, THX Reference Level (how much the inputs can take?)
Input impedance: 33 k_ (Does this mean that it can't have kids?)
Damping factor: > 800 at 20 Hz (oh oh, does this have something to do with it's ability to control base?)
Voltage: Switchable for 110V – 120V or 220V – 240V operation (ok, you can use it here, or there.)
Dimensions: 17-1/4" w x 4-1/8" h x 13-1/4" d, 3-5/8" h without feet (it's not so big)
Net weight: 28 lbs. (not too heavy either)


45 amperes is enough to drive most of the speakers out there, and bridging it to mono doesnt nessesarily mean that you have to use it as a subwoofer power amp, you could (and i'd do that if i bridged an amp) use it as a monoblock too, so then you need 2 amps for stereo, but you'd have very much power.

s/n numbers: the higher the better, you divide the amount of sound by the amount of noise, the higher the s/n number, the less noise.

0.06% THD isn't bad, and will satisfy most of the listeners, some, however want a lower thd...

IM disortion = inter modulaire (or something like that) disortion, or otherwise said, the amount of disortion at 1 khz

power bandwith: the bandwith (between 5hz and 100khz in this case) where the amp can deliver it's full power.

slew rate: not sure, I'll have to research that one...

dyn headroom: how much the amp can deliver for a short amount of time over the maximum output so if your amp has a gain of lessay 28db, and you have a 1.5db headroom, you can have that extra, so you'll have a 29.5db gain for a short period of time.
my upcoming toy will have a dynamic headroom of 2.4 db, good reputation points when you guess which one :)

crosstalk: the 'noise' from one channel that's also in the other channel, but it's not supposed to be there.

input sensetivity: in this case, 1 volt for 28.28 volts, this means that if it gets 1 volt at the inputs, it will give you 28.28 volts of output, which is in this case, the full output. so read as: 1 volt input for full output.

input impedance: same impedance as speakers, only more. there is a rule for this, I think your poweramp's input impedance should be at least 100 times (or more) the preamps output impedance.

damping factor: you are kinda right there, higer damping factor usually means tighter base.

voltage: you were right there too :)

dimensions: no it's not 'big' like a mcintosh, neither is it heavy as a mcintosh, but it's as big/heavy as it's supposed to be.

weight: see above...


this should get you started :)

Keep them spinning,
Bert.

Edit: I think I know again what slew rate means: it's the maximum amount of power running through the amp's circuit at one time.

[basite]

Did you actually READ the specs, or did you just remember that that's the amp I want?


i kinda knew, but the specs confirmed my suspicions :)

[GMichael]

dyn headroom: how much the amp can deliver for a short amount of time over the maximum output so if your amp has a gain of lessay 28db, and you have a 1.5db headroom, you can have that extra, so you'll have a 29.5db gain for a short period of time.
my upcoming toy will have a dynamic headroom of 2.4 db, good reputation points when you guess which one :)

.

a mcintosh?

[basite]

what the? how do you know?

[GMichael]

Just psycho I guess.

[Feanor]

...
IM disortion = inter modulaire (or something like that) disortion, or otherwise said, the amount of disortion at 1 khz
...

slew rate: not sure, I'll have to research that one...
...

Keep them spinning,
Bert.

Edit: I think I know again what slew rate means: it's the maximum amount of power running through the amp's circuit at one time.

Don't have much to add to Bert's input, but ...

IM = intermodular distortion. Input two sine waves at say 8kHz and 10kHz; if you get a response at 9kHz, this is spurrious and its level determines the among of intermodular distortion. High IM is, or used to be, associated with solid state amps.

Slew rate: sometimes referred to as "rise time": the rate at which the amp responds to a change in input voltage. This is the real "speed" of the amp. It's often referred to together with a square wave plot. If an amp can reproduce a square wave well, it is likely to have a high slew rate, because the sharp edges of the square wave represent high harmonics of the base square wave frequency, and their reproduction requires that the amp be able to respond to voltage change very quickly.

[GMichael]

what the? how do you know?

Maybe it had something to do with this.

"dimensions: no it's not 'big' like a mcintosh, neither is it heavy as a mcintosh, but it's as big/heavy as it's supposed to be."

[basite]

Maybe it had something to do with this.

"dimensions: no it's not 'big' like a mcintosh, neither is it heavy as a mcintosh, but it's as big/heavy as it's supposed to be."


ooh I see...

well, you did guess right though...

[jrhymeammo]

Hey GM,

Do you really think A23 would be 3X better than an amp that retails for $300?

JRA

[Rich-n-Texas]

So what happened to the learning aspect of this thread? :ciappa:

Thanks for your input and trying to keep the topic on track Feanor. :thumbsup:

Oh and, you too Bert, for the most part.

[GMichael]

Hey GM,

Do you really think A23 would be 3X better than an amp that retails for $300?

JRA

Not if I could find an A23 on Ebay for $300.:ihih:

[GMichael]

So what happened to the learning aspect of this thread? :ciappa:

Thanks for your input and trying to keep the topic on track Feanor. :thumbsup:

Oh and, you too Bert, for the most part.

I was hoping for a little more input from the techie guys. Calling out Kex. Where are you?

[E-Stat]

0.06% THD isn't bad, and will satisfy most of the listeners, some, however want a lower thd..
The problem with THD is twofold: it is measured with steady state tones (dynamic behavior can be radically different) and it doesn't factor the human element. Minute amounts of high order distortion found in high feedback amps can be highly irritating (Crown amps) where seemingly large amounts of pure second order harmonic (like tubes) falls into a human "blind spot". My VTL amps with 2% distortion sound substantially more like music than an old Crown amp with 0.05% (or at least when its driving a resistor with a test tone) Real world speakers reproducing real world music render this metric essentially useless.


damping factor: you are kinda right there, higer damping factor usually means tighter base.
Anything above 60 or 80 is irrelevant to most speakers. It is quite easy to achieve astronomical DFs - add more negative feedback. Which is contrary to reproducing dynamic musical passages in a natural fashion. Too much is a bad thing unless the amp is delegated to subwoofer duty.

rw

[GMichael]

Anything above 60 or 80 is irrelevant to most speakers. It is quite easy to achieve astronomical DFs - add more negative feedback. Which is contrary to reproducing dynamic musical passages in a natural fashion. Too much is a bad thing unless the amp is delegated to subwoofer duty.

rw

Thanks E. I thought more = better. I was writing off some amps because their numbers were so low. (IE: the non Halo Parasounds.

[Feanor]

...
Anything above 60 or 80 is irrelevant to most speakers. It is quite easy to achieve astronomical DFs - add more negative feedback. Which is contrary to reproducing dynamic musical passages in a natural fashion. Too much is a bad thing unless the amp is delegated to subwoofer duty.

rw

I found this definition of damping factor: "Technically, the damping factor is the specified load impedance (in use, that'd be the speaker system) divided by the amplifier's output impedance." This definition is standard; a fuller explanation can be found here ...
http://www.classic-audio.com/marantz/mdampingfactor.html

A telling point about very high damping factor is this, (same source): "A very high damping factor can tell you something else, and almost always does unless the manufacturer specifically tells you otherwise: Since it tells you that the amplifier has very, very low output impedance, it also tells you that the amplifier design probably has a lot of negative feedback." As I understand it, a lot negative feedback is used deliver the very low THD figures attainable by solid state amps; unfortunately, it is also the sounce of the higher-order HD that, though low in total, is the likely cause of the stereotypicall, harsh S/S sound.

[topspeed]

Terrific answers so far.

Oddly enough, the more experienced I became, the less attention I gave to the specs. Why? There are too many variables and no regulated way to test. Besides, there are new technologies such as switching amps that simply don't fit into the square hole used to measure conventional amps designed 30 years ago.

I will say this, get your speakers before you get your amp. If you're still thinking about the Mini's, allocate funds toward them first. That way, you'll be able to audition amps with your speakers in your room to determine which sounds best. Not all amps sound the same, and specs won't tell you which ones will "lock in" best with your speakers. Synergy is no easy thing.

[dean_martin]

input impedance: same impedance as speakers, only more. there is a rule for this, I think your poweramp's input impedance should be at least 100 times (or more) the preamps output impedance.



this is the one I'm having a hard time with. I have a 2-ch ss power amp sitting in a closet that I'd like to match with a tube preamp. I've read just enough to confuse myself over an amp's input impedence and a preamp's output impedence and whether these are the key specs that will tell you whether the preamp will adequately drive the amp. I think that if there is a mismatch in these specs, no matter how great the amp and the preamp, they just won't perform together. But in comparing the numbers, one is so much greater than the other that I can't get a grasp on what's a good match and what's not. A little elaboration on this would be appreciated.

[basite]

there is some more info in here: http://forums.audioreview.com/showthread.php?t=21414&page=4

[E-Stat]

I think that if there is a mismatch in these specs, no matter how great the amp and the preamp, they just won't perform together. But in comparing the numbers, one is so much greater than the other that I can't get a grasp on what's a good match and what's not. A little elaboration on this would be appreciated.
Primary concern is that of HF roll off. I've used tube preamps with SS amps for years. What are the specific figures for your components?

rw

[dean_martin]

Primary concern is that of HF roll off. I've used tube preamps with SS amps for years. What are the specific figures for your components?

rw

The input impedance of the amp is 20k Ohms.

The preamp I'm considering has an output impedance of "less than 500 Ohms."

There are some more specs I can give, but I'm not sure if they're relevant.

[Feanor]

The input impedance of the amp is 20k Ohms.

The preamp I'm considering has an output impedance of "less than 500 Ohms."

There are some more specs I can give, but I'm not sure if they're relevant.

Your ratio is 20,000/500 = 40. Not the Ideal 100+, but some say as low as 10 can be alright.

[dean_martin]

Your ratio is 20,000/500 = 40. Not the Ideal 100+, but some say as low as 10 can be alright.

Thanks for "showing your work". That helps alot.

Also, that previous thread linked by basite is helpful. I understand the numbers are not the last word on compatability, but I've read reviews that used them to explain why a particular amp did not perform well with a particular preamp.

[E-Stat]

The input impedance of the amp is 20k Ohms. The preamp I'm considering has an output impedance of "less than 500 Ohms."
You should have no issues at all. I am particularly sensitive to this question in that I don't use my preamp at all when playing the CD source. I go direct to amps via precision DACT attenuators. That results in a less favorable impedance multiple although my tube amps help with their 137k input impedance. My situation does, however, require using low capacitance cables.

rw

[hermanv]

According to the data sheet my Levinson DAC has an output impedance of less than 6 Ohms and the Pass Labs an input impedance of 11K (unbalanced) giving a ratio of 1833 to 1, great.

Unfortunately I have a passive pre whose input impedance avarages about 3.9K Ohms and whose output impedance tends to be half that (it depends on volume setting). So I end up with a ratio of more like 11000/1950 or 5.6 to one. The system sounds great, numbers are usefull, don't get too carried away with what is a minimum acceptable number.

THD (Total Harmonic Distortion) has the unfortunate limitation of not telling you which harmonics are most present. SET amps are notorious for having poor THD specs, but all their problems are usually with low order even harmonics such as second, or fourth. SS amps can have the opposite problem, small numbers, but lots of odds of high order such as 5ths, 7ths, 11ths or higer.

Most people think SETs sound relaxed and clean while they find SS gear with high distortion to be grating and fatiguing. It's seems to be these high order harmonics that our ears find most offensive. This could be because it is quite difficult to create these with accoustic instruments, mainly brass and violins tend have high order harmonic content and they are generally considered instruments that have "bite". None of this shows up in the data sheets so THD doesn't provide much help.

IM could help; all amplifiers that distort at all will create sum and difference producs;
suchs as f1 +/- f2
and 2f1 +/- f2
or 2f2 +/- f1
I have seen reviews of amplifiers with very high intermodulation distortion that the reviewer claimed sounded great, but most well regarded SS amps have good IM numbers. Lots of negative feedback helps IM numbers but tend to move single frequency harmonic orders up higher. A trade off. Charts are better than just specs, but require more skill or knowledge to read.

It's all complex enough that your ears are your most reliable guide.

[jrhymeammo]

My situation does, however, require using low capacitance cables.

rw

Hey E-stat,

Could you tell me some ballpark figures on low capacitance cables? I'm in a process of searching for a pair of XLR right now. I havent decided on the length at this moment, but it's be either 1 or 3m. 3m of Silver Streaks could be rather costly. I'm currently using DH Labs BL-1 and they are absolutely the worst sounding cables I've tried in my system. But a pair of Air Matrix could be a different story.

Thanks

[E-Stat]

Could you tell me some ballpark figures on low capacitance cables?
Blue Jeans cable has some low cap interconnects for about $32/meter. I use somewhat pricier JPS Labs cable.


I'm currently using DH Labs BL-1 and they are absolutely the worst sounding cables I've tried in my system.
I have some of those in the single ended flavor. While they are a tad "tizzy" at the top, I find them pretty decent.

rw