I've always purchased equipment base on the specification. Never on their advisements or the magazine write up.
yes, it does matter to me.
yes, it does matter to me.
Probably the first specification I will look into, is the Watts/channel in 8/4/2 Ohms to validate if power doubles when impedance goes down by half. This will give you a good indication that the amp will not suffer when the speaker impedance varies at different frequencies.
Second spec would be the power transformer kVA specification and total Microfarads of power supply filter capacitors. Again the bigger, the better since it provides an indication of the theorical power handling capability and reserve the amp will have under peak power musical crescendo.
Signal-to-noise ratio would be the last. The higher the figure, better the amp will reproduce clearly low-level details that could hang down near the amp noise floor.
These 3 specifications are nice to have to kind of help you build a mental picture of the seriousness of the amp design especially if you are running innefficient speakers that sound really great.
But at the end, it will be my ears who will prevail regarding the final purchase decision. I will never purchase an amp with excellent specifications which sounds average. I will always go for the best sounding amp with my speakers, regardless of specifications.
As I've said in a number of past threads, IMO the main usefulness of specs is to allow one to identify and RULE OUT from consideration candidates for purchase that would be poor matches to either the surrounding components or to the user's requirements. An example of the latter would be how much power is needed to support desired peak volumes. Examples of the former would be incompatibilities due to impedance issues, gain and sensitivity mismatches, and various issues which can result in amplifier/speaker mismatches (as Russ/Rcprince alluded to above).
Specs are also useful in troubleshooting problems, in getting to understand the priorities of the designer, and in identifying specs that may be TOO good and thereby may signify undesirable design tradeoffs. A classic example of the latter would be an amplifier having unusually good Total Harmonic Distortion numbers relative to other comparable kinds of designs. That will often signify the use of large amounts of feedback, and consequent adverse effects on things like Transient Intermodulation Distortion which arent normally specified or measured, or that are not even measurable in a standardized manner.
Basically, as I see it, if specs are mostly or entirely disregarded and/or are not properly understood the randomness of the process of assembling a satisfactory system, and the likelihood of expensive mistakes, are increased considerably.
Of course they matter, how can anyone say otherwise. Input/output impedance, input sensitivity, gain, number of channels, dimensions, operating voltage, number and type of inputs and color are all critical information. The information won't tell you how the amp will sound, but it will tell if it can operate properly in your system.
Dasign, I would stay away from amplifier that exactly doubles power because in order for this to happen power supply has to be strong enough while output has to be "tightly regulated" which is another word for the "deep negative feedback". In addition many new amplifiers have small amount of power supply caps and tiny transformers since they use ultra quiet line/load regulated SMPS.
Some specs matter and some don't.
An example of a spec that matters is noise. Another is bandwidth (which ideally is 2Hz to 200KHz to reproduce 20Hz to 20KHz properly...)
An example of a spec that hardly matters is THD. The reason this spec has small importance has to do with the way the human ear/brain system interprets harmonic distortion, which is to say it interprets it as tonality. In this regard, the 2nd harmonic is musical and not easily heard by the ear and for that reason quite a lot of it can be present before it becomes objectionable. OTOH, the odd orders (5th, 7th and 9th) are highly objectionable and for that reason trace amounts that are hard to measure can be quite audible (the ear/brain system also uses higher ordered harmonics to interpret sound pressure, so it is very sensitive to these harmonics).
So- when a low THD is seen in the specs, its likely that it will not containing much in the way of the 2nd order and is instead likely to be almost entirely higher orders, on account of the fact that global negative feedback has likely been used to obtain the THD value. Loop feedback, while effective at reducing distortion, is not effective at eliminating it altogether- its use will surely mean that elevated higher orders of harmonic distortion will surely be present.
This is why you will see a debate in high end audio about the use of feedback. Because the ear uses higher harmonic orders as loudness cues, it is essentially more sensitive to their presence than excellent test equipment. Audiophiles have words for such low distortions: bright, harsh, brittle, chalky, etc.
These descriptions will often accompany equipment with low THD values. We have seen these comments around as long as the internet has existed- my point here is certainly not debatable!
Now if the specs showed how the harmonic distortion existed in the amplifier or preamp (showing the lower orders and the odd orders as a separate value), especially in terms of a signal that was in constant change rather than a sine wave, the result would be a distortion spec that told you exactly how that amp or preamp would sound. We are a long ways from that- right now the harmonic distortion spec can be considered vestigial at best.
There are other specs, like damping factor, the are often given a lot more weight than their due- in the case of damping factor, there are no known speakers that need more than 20:1, so why is it important to have a damping factor of 100 or 1000?? But we see this touted all the time... really, a lot of it is marketing and not actual science.
A spec showing that power doubles as the impedance drops from 8 to 4 and then from 4 to 2 may be misleading. I recall a Stereophile test report a few years back of some high-powered solid-state amp, perhaps a Classe, whose ratings indicated just such a doubling. However, the measured power output turned out to be considerably greater at 8 ohms than the rated power, slightly greater than the rating for 4 ohms, and it just barely made the 2 ohm rating. It seemed clear the manufacturer was playing a game with the specs. It had intentionally downplayed the actual output at 8 ohms just to give the appearance of doubling its power for 8/4/2 ohms.
Psaq, In normal test for THD amplifier is fed with pure sinewave ant tested at the output for anything else present. Not only that this test says nothing about THD when driving your speaker but also won't show any high order harmonics manufactured by deep negative feedback in Transient Intermodulation.
40dB of negative feedback means that amp was designed with 100x higher gain that is reduced back to normal by feeding output signal to the input in opposite phase (cancelling 99% of the input signal). This scheme is wonderful and improves everything 100 fold, but when rapidly changing signal (music) is applied amplifier for a moment has higher gain (because of input/output delay) and output overshoots (signal fed back to the input is too late). It can be easily shown when testing amplifier with square wave. This overshoot translates into unpleasant high order odd harmonics. Such amp will have fantastic THD, IMD, DF etc. specifications but it will sound horrible - guaranteed. Even power ratings can be very misleading. Because of all that I think that specifications are pretty much garbage. I would use them only, as Al stated, to exclude certain amps that, for instance, cannot drive my speakers etc.
Kijanki, you appear to have taken a stronger position against use of NF than in the past where you argued results were very implementation specific.
Or are you just pointing out pros and cons, which all approaches always have?
Based on a stated 100X improvement with NF, negative effects would have to be quite significant to eliminate that completely.
The "its all implementation specific" argument still seems to ring true to me based on what I see, read and hear.
Nelson Pass published an excellent article on distortion and feedback:
The bottom line is it does not seem to be implementation specific.
About 50 years earlier, Norman Crowhurst had some similar comments on feedback and showed that harmonics can be added up to the 81st harmonics, with attendant intermodulations at the point of feedback (the feedback node).
This document is an excellent read:
Mapman, there is nothing wrong with use of negative feedback but it has to be done right. Using deep global NGF to achieve better spects at the expense of the sound is what I'm against. Why would anybody need DF=1000 if choke in series with the woofer limits it to less than 100 anyway. Speaker impedance, mostly resistive, already poses limitation. I can understand output impedance 10x lower than 4ohm to provide good damping (DF=20@8ohm) but above it it is just nonsense. Class D amplifiers have very high DF at low frequencies but it wasn't intended IMHO. It comes from the fact that speaker is always shorted between two low impedance points (GND, VCC) by very low impedance Mosfets switches. Some negative feedback, used to linearize output, reduced output impedance even more.
Extending frequency response to >100kHz might be a good thing to avoid phase shift in audio range (poor summing of harmonics) while reducing THD to fraction of percent should be enough. Good design involves quality components combined with very linear topology. Frequency limited input circuit should be followed by extremely fast output stages.
In short it should be very linear and fast to start with instead of fixing it with NGF.
It should be just enough of negative feedback to reduce THD, IMD to fraction of percent (only few times reduction). Bandwidth will increase but you need to reduce it at the input back to one that amp had before feedback was applied. This will prevent TIM completely but amplifier has to be fast to start with.
Yes, specifications are important and do matter, in many ways.
All electronic devices, for example amplifiers are designed and constructed based on specifications first. This is Engineering 101. Design and build an audio power amplifier, with a minimum frequency range of 20 HZ to 20kHZ, power output into 8 Ohms of 250 WPC, harmonic distortion not to exceed 1%, output impedance of x and input impedance of Y. There are other specifications given to the designer, but, these are characteristic.
Specifications with regards to the end user depends on who the end user is. Military useage is different than the average audiophile. For Military, it better meet or exceed the desired specs. For the Audiophile, what exactly do you need to know? 1. Power output over the frequence range, 2 Input impedance, 3. Output impedance, 4 distortion, 5 operating frequency range, 6 load impedance it is designed to handle.
So, yes, specifications are important. If you purchased some relatively inefficient speakers, that have an operating impedance going down to 1 ohm, are you going to pay attention to the specs of the proposed amp? I should hope so. Distortion below 1% is very good in todays standards. But, high distortion is something I want to know about. The amp should be an infinite bus over frequency that amplifies the signal with zero change to the signal. That is what an amplifier is supposed to do. So, yes, distortion ratings are important. However, some manufacturers taylor their designs to a certain sound, read "this adds certain acceptable distortion to the signal" to achieve a certain sound. Too much distortion is just poor design.
I really like Onhighway61s response, particularly
The information won't tell you how the amp will sound, but it will tell if it can operate properly in your system.IOW, use certain specs to rule out an amp in the context of your speakers and pre-amp, but from there, their usefulness is questionable for a variety or reasons.
I also endorse the use of weight when comparing otherwise similar amps because of what it tells you about output xformers and power supply. Of course, its non-scientific and is not applicable to OTLs ;-)
If I may tweek the subject matter just a bit.....I see many conversations here about matching pre-amps to amps based on specs. I hear some claim positive results while others have found unfavorable matches. I guess what I don't understand is why it wouldn't be most favorable to use a pre and amp combination from the same manufacturer. This would seem to lend itself to the highest level of system "synergy". Since (presumably) the same engineering team developed both units to work in conjunction with each other, this would be more favorable than trying to match specs. between different manufacturers especially if there may be different standards used for measurement.
I also endorse the use of weight when comparing otherwise similar amps because of what it tells you about output xformers and power supply.
Seriously, what could the weight tell you about the engineering and design that went into these components of the circuit. Granted, my business partner winds transformers and the outputs tend to be fairly hefty, and depending on the amount of power the amp is spec'ed at so might the power transformer. On the other hand I can carry my Music Reference RM-10 under my arm like a text book, yet it is quite a ballsy little amp. It has held it's own against any amp I've had and I'll further state it has embarrassed a few as well, regardless of weight.
Yes, specs matter, despite all the hype that only listening matters. That being said, few have speakers really able to test the spec limits. I have seen many highly rated amps have a square wave at 30 Hz completely distorted and worse as the frequency drops, and their 120 wpc rating laughable when power output at 50 Hz was a paltry 30wpc....O yes, power ratings are usually at 1khz, an easy load. Your 120wpc amp may only put out a fraction of that at the frequencies needing it the most. The rubber meets the road below 50 Hz. First it has to measure good, then sound good. Transformer quality is paramount, and circuit design. Good transformers come from companies like ARC, CJ, Quicksilver, and many others. Do your research....PT