also for reference, the entire challenge:
THE $10,000 AMPLIFIER CHALLENGE RULES {April 21, 2000}
By Richard Clark
There is no question that all amps are not the same. It is very easy to measure large differences in the performance of amplifiers. This is true in nearly every known specification, including power, noise, distortion, etc. My experience has led me to believe that even though these differences can be easily measured, hearing those differences may not be so easy. Given the relatively small magnitude of performance differences, there is a giant step between amplifier performance and our ability to hear performance differences.
It is claimed by designers, manufacturers and especially salespersons that differences in amplifiers are clearly audible. Reasons include "obvious" advantages of one type of circuit topology over another. For example, it is claimed that certain designs have a smoother midrange response whereas other amplifiers exhibit tighter bass. Tube fanatics claim that tube amplifiers have that "warm" sound we all need in our systems.
Such descriptive terms are certainly subject to personal interpretation. It is not my intention to determine if one particular amplifier is better than another amplifier. Differences in the quality of the discrete components and constructions are more appropriate for settling the issue of "good - better - best." The sole purpose of my amplifier challenge is to determine if the differences in amplifiers are audible.
What differences are Audible?
I believe the perceived differences in amplifiers are all due to various factors that can be explained with basic physics and elementary psycho-acoustics. For instance, if two amplifiers are not carefully matched in volume, and one amp is slightly louder than the other, then it would be a simple matter to detect such a difference. In such an example it is important to understand that it is not the circuit topology, quality of the component, design excellence, or superb marketing and packaging that caused the noticeable difference - it was an error in the test setup! It is my present belief that as long as a modern amplifier is operated within its linear range (below overload), the differences between amps are inaudible to the human ear.
Comparing Amps
The idea here is for a test subject to scientifically demonstrate his/her ability to hear differences in amplifiers. It is our job to carefully match the amps so that we are comparing "apples to apples" instead of "oranges to frogs." This means that we sure wouldn't want to compare one amplifier that had + 12 dB of high frequency boost against another amplifier that was adjusted for + 12 dB of bass boost. Such a test would be easy to pass - even on identical amplifiers with consecutive serial numbers.
For our comparison test, we aren't concerned with which amplifier sounds best to the test subject. We only require that the listener be able to identify each amplifier when it is powering the speakers. Since many folks seem to believe that amplifiers have some kind of distinctive sonic character, this test should be easy to pass. Right? After all, we're talking about comparing those harsh sounding, high distortion, squeaky "widget As" to those warm sounding, smooth, bass hog "widget Bs."
Now pay particular attention to the following sections. Since we're looking for differences in amplifiers, and we already know that those differences are probably going to be very, very small, it is important that the parameters under our control be carefully adjusted so as to be equal as possible. This means that we must be cognizant of differences we might unknowingly introduce between amp A and amp B. They must be adjusted as identical as possible. We already mentioned the importance of volume. The same goes for the L and R balance. It sure would be easy to choose an amplifier that exhibited left side bias over a balanced amp. Right?
Well, in order to keep this amplifier comparison test fair, there are a few other parameters that must be considered. I'll list them all in the following section.
Amplifier Comparison Test Conditions
1. Amplifier gain controls - of both channels - are matched to within +- .05 dB.
2. Speaker wires on both amps are properly wired with respect to polarity. (+ and -)
3. That neither amp has signal phase inversion. If so correction will be made in #2 above.
4. That neither amp is loaded beyond its rated impedance.
5. That all amplifiers with signal processors have those circuits bypassed. This includes bass boost circuits, filters, etc. If frequency tailoring circuits cannot be completely bypassed an equalizer will be inserted in the signal path of one (only one and the listener can decide which) of the amps to compensate for the difference. Compensation will also be made for input and output loading that affects frequency response. Since we are only listening for differences in the sonic signature of circuit topology, the addition of an EQ in one signal path only should make the test even easier.
6. That neither amp exhibits excessive noise (including RFI).
7. That each amp can be properly driven by the test setup. Not normally a problem but it is theoretically a problem.
8. That the L and R channels are not reversed in one amp.
9. That neither amp has excessive physical noise or other indicators that can be observed by the listener.
10. That neither amp has DC OFFSET that causes audible pops when its output is switched.
11. That the channel separation of all amps in the test is at least 30 dB from 20Hz to 20kHz.
In addition to these requirements the test will be conducted according to the following rules.
Amplifier Test Comparison Rules
1. To make things easy we would prefer to use high quality home type loudspeakers for the test. If our speakers are not acceptable, the listener can provide any commercially available speaker system as long as it uses dynamic drivers. The actual measured impedance cannot exceed the rated load impedance of the amplifiers tested. If, however, the tester would like to perform the test in a car, we will use a car, however, it will have to be provided by the test subject. For practicality we will have to limit the number of amplifier channels to four or less.
2. Amplifiers will be powered from the same power supply at a nominal 14 volts DC. (any voltage is OK as long as it is the same for both amps)
3. The test can be conducted at any volume desired; however, the amps will not be allowed to clip. In other words, listening volume can not exceed the power capacity of the smallest amp of the pair being tested. (power capacity will be defined as clipping or 2%THD 20Hz to 10kHz, whichever is less)
4. No test signals can be used - only commercially available music.
5. The listener can compare two amps at a time for as long as desired. For practical reasons we would like to keep this at least no more than a few hours. A test session will consist of 12 A/B sequences. Passing the test will require a positive identification of each amp for all 12 sequences. Remember, guessing will get you about 6 out of 12. If the differences are so great, and a subject can really hear the difference, then he/she should be able to do so for all 12 sequences.
6. To win the $10,000.00, the listener must pass two complete sessions of 12 comparisons. Passing the test means 24 correct responses.* The amp of choice can be compared to the same or a different amp in each session - challengers choice. We have many amplifiers in our demo inventory such as, but not limited to, Alpine, Rockford, Kicker, Phoenix Gold, Precision Power, MTX, Adcom, Kenwood, Pioneer, Sony, etc. You can pick any of them or bring your own.
7. All amps must be brand name, standard production, linear voltage amplifiers. This does not exclude high current amps. Amps can not be modified and must meet factory specs. They must be "car audio amplifiers designed to be powered from a car's electrical system."
8. Failure of an amp (this includes thermal shutdown) during the test will require that the test be repeated after repair or replacement or cooling of the amp. This means that the entire test session will have to be repeated.
9. The amps will not be overloaded during the session from either a voltage or current requirement.
10. To save time the listener will have to pass a quick 8 trial session to qualify for the extended 2 session test for the money prize. Any 2 amps can be used for this test. Passing this qualifying test will require at least 6 out of 8 correct answers.
11. The amplifier power up and/or power down sequence will not be acceptable for comparison. (The turn on/off noises of some amplifiers would give it away.)
12. Although anyone is welcome to take the test, only subjects employed in the car audio industry or Car Sound subscribers are eligible for the $10,000.00 prize.
13. Cost to take the test is $100.00. $300.00 for people representing companies. Payable in advance, scheduled appointments only. Done correctly the test takes several hours and I don't have the time if you aren't serious.
* Twelve correct responses in a row is certainly a lot of correct listening but $10,000 is also a lot of money for a few hours of easy listening. The way people describe the differences is that they are like night and day. I would certainly not have any trouble choosing between an apple and an orange 12 times in a row. When compared fairly I believe the differences in amps are much too small to audibly detect and certainly too small to pay large sums of extra money for. If I am wrong someone should be able to carefully take this test and win my money. Even if I am right, if enough people take the test eventually someone will take my money due to random chance. This is the reason for the large sample requirement. If you feel that you can easily pass this test but 12 sequences will give you "listening fatigue" I am willing to modify the requirements. Since the way it is being offered is a challenge and only my money is at risk I am willing to let a confident challenger "put his money where his ears are". If we are willing to make this a bet instead of a challenge, I am willing to drop 1 sequence for every thousand dollars put up by the challenger against my money. This would mean:
____My___________ _ _Your________Trails Required to win__
$10,000 to $0 = 12 Tries
$9,000 to $1,000 = 11 Tries
$8,000 to $2,000 = 10 Tries
$7,000 to $3,000 = 9 Tries
$6,000 to $4,000 = 8 Tries
$5,000 to $5,000 = 7 Tries
$4,000 to $6,000 = 6 Tries
I will not do the test with less than 6 trails. It would be statistically meaningless and reduce the challenge to mere gambling.
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of course my challenge includes tube amps---thats what got it started to begin with----while most tube amps have more distortion than transistor amps it is still usually below the audible level of a couple percent---the biggest audible difference is like Big T said---the higher output impedance created by the transformer windings causes a slight frequency dependant amplitude difference---while this is usually less than a db or so except in the worst designs (the "super" amps without negative feedback really have this problem big time)the effect is subtle but audible-----and since it naturally happens at the resonant places of the speaker it is sometimes very pronounced----it is easily duplicated with a small value resistor in series with the speaker-----RC-
and just to show you how people misunderstand my challenge someone recently told me he could pass the test if he didn't have to be "blindfolded"----thats what his understanding of a "double blind" test was---so much for scientific understanding.....
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guys my testing procedures are more than fair--and they are set up to help the listener--all you have to do to get the details is to e-mail me at
[email protected] and request the amp challenge rules--you can provide any CD player--any speakers you want--you can do the switching--you can provide the CD's and on and on and on---i want to see somebody do it--i will be happy to write the check--it will bring back a new realm of audio to me--and remember it is not a bet--you don't lose 10K if you lose--that is why i call it a challenge--a bet would require you to put up an equal amount--there are conditions i am willing to accept if you only want to do it 6 out of 6 times but because it increases the odds of guessing i require it to be a bet at that level--now before you continue to mis-quote me FIRST read the challenge rules!!!!!!!!!!!!!!!!--and if you think you can do it then come on and prove it and stop talking about it
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I wil not disagree with that assumption as I have found it to be true--thats why I exclude that condition from the testing conditions--but the real issue is that there are no amps that really sound better than others unless you drive them into a condition where they all sound bad--and the difference comes down to which sounds the "LEAST WORSE"--and remember that it is the "sound quality" that is supposed to be the reason to pay large sums of money for those "sweet sounding amps"--well the simple fact is that a modestly priced amp with more power than an overpriced "exotic" amp will surely sound the best under those important "real world conditions with dynamic music" so the bottom line is still what I have been saying all along---when buying an amp buy reliability and POWER--forget about the nonsense of "sound quality"
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guys--it always circles back to the same old thing--i have never said or even inferred that there is no meaningful difference in amps--of course there are differences--some amps cost more because they are built better--perhaps they will last longer--or play longer without overheating--or have better resale value because they have more "brand appeal" or do more because they have more features--all I ever said was that WHEN THEY ARE COMPARED EVENLY THE SONIC DIFFERENCES BETWEEN AMPLIFIERS IS BELOW THE AUDIBLE THRESHOLD OF HUMAN HEARING-- as for what we actually hear consider that if we compare two identical amps but turn the bass boost up on one and leave the other flat we will be able to hear the difference between two identical amps that have consecutive serial numbers--read my challenge rules--it should make sense
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i don't have a power limit for the test--the rules just say that the listening cannot exceed the clipping limit of the smallest amp of the pair being compared--i don't care if you compare a 500 watt amp with a 50 watt amp--you would just have to keep the listening below whatever caused the smallest amp to clip
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Blkout---tube amps are a serious waste of money--an obsolete technology like wooden wheels and horse drawn buggys-i can make any good quality solid state amp sound exactly like a tube amp with less than 5 dollars worth of parts---i have done it on many ocaasions for my amp challenge---but why would anyone want to degrade a good solid state amp to make it sound like a tube unit??? sure confuses me...........RC
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the actual components depend on each amp but rarely does it involve more than a resistor or couple of small caps-----90% of the time all it takes is a small value resistor in series with the output----the faults of tube amps are pretty much the same regardless of price---some are just worse than others-----but i have to have the amps to do an actual measurement.........RC
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guys---an L pad is designed so it presents the smallest possible resistance in series to the load for a given amount of loss-----that is why there are L pads and not just resistors----do they have an effect??----of course they do BUT THE EFFECT IS MINIMAL----is the effect the same as having a high source impedance (ie low damping factor) ----yes it is but as i have always said---the negative effects of low damping are overstated as well as the benefits of tube amps--------its all just audio nonsense........RC
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Colin, the output impedance of an amp doesn't have nearly the effect at midrange and high frequencies as it does with bass.
you can compensate for lpads because they just change QES of the speaker. usually letting you get a little more low end out of a speaker at the expense of efficiency.
you see very few setups(outside of guitar) where tubes are driving the woofers. This is not by choice, more necessity. (I dont think you need to worry about this with the butler amps, because if i remember correctly, they just use tubes in the preamp stages)
It is of course better to have all drivers matched to the same efficiency, but if they are unmatched, especially in the mid+high range, the L-pad solution is the lesser of two evils. I dont know if winISD lets you model generator resistance, LspCAD does. The main reason it is better to use Lpads on midranges instead of woofers is the power involved. You may need a 50 or 100W resistor in the woofer setup, where a 5 or 10W will work with midrange.
To obtain new QES and QTS, you simply use the following equation
QES' = (1+Rg/RE)*QES
where Rg is the output impedance of the amp or Lpad
RE is the DC voice coil resistance
QES is electrical Quality Factor
then for new QTS
QTS' = QMS*QES' / (QES'+QMS)
If your midrange is less efficient than your woofer, the best option is to add another midrange.
jt
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RC's amp challenge is the source of much debate but I have found it to be very helpful. The challenge simply proves that 100 (or insert whatever number pleases you) unclipped, unmanipulated watts from a less expensive amp will sound the same as 100 unclipped, unmanipulated watts from an expensive one. Does this mean everyone should run out and buy the cheaper amp? No. If the expensive amp is constructed with a higher quality of parts, is designed with a heat sink that functions better, has a nice crossover with more user functions, a better warranty, etc. then clearly it is more desirable. Furthermore if you only want 100 watts and the expensive amp can produce 130 watts before clipping compared to 105 watts before clipping for the less expensive one, this is an added bonus. I have seen some post on this forum expressing dislike for the challenge because (A) it states the obvious and (B) it doesen't tell you which amp is better for the end user. Both of these statements are true. For those of us who are just learning about car audio, however, RC's challenge serves a good purpose. It helps us to see past the marketing hype that wants us to believe that 100 unclipped, unmanipulated watts will sound different from one amp to the other (like when they compare distortion specs from two amps that are both well beyond the range of human hearing).The amp challenge will not tell you what you should buy, this is not it's intended purpose. It helps to educate consumers like me. The amp challenge helped me to understand what I really need to look at when considering an amp. To me this seems to be it's intended purpose and it serves this purpose well.
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guys---the sound quality issue of amps once again raises its ugly head----i ahve no reservations of including class D amps in my amp challenge and have done so in the past---for years dave and i have been strong proponents of class D as it just makes sense---yes it is harder to do class D at higher frequencies but not impossible---its just not as important as we usually reserve most of our power for the lows anyhow----and as for actual efficiencies i have posted such numbers in earlier threads---they are probably in the archives by now but at full power 70 to 85 is typical for class D and 55 to 60 is normal for class a/b-----at one third power (the most important due to the nature of duty cycle of music) the a/b is usually about 25 to 30% and the class d is about 50 to 60 percent........RC
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spliff--the audio world is full of guys who feel they could beat that challenge with no problem--that particular guy was a very keen listner--i would have to place him in the top 1% of challengers--he aced the qualifying test--very few have ever done that--after passing the qualifying round he was extremely confident--but once we started the real listening test he knew within minutes that he was going to lose---he looked at me with extreme dissapointment and said he wanted to continue just in case he got lucky
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colin----you can't hear less than 3% distortion no matter what kind it is---IM--TIM--THD---and in the amp challenge i don't worry about the 2ond order thing---it means nothing to audibility---the only thing that matters audibly is frequency response-----and for the resistor i just put a small value resistor in series with the speaker---usually one or two tenths of an ohm will make any transistor have the same response errors as a tube amp--------and WASTE if you want an amp with little damping factor use a resistor equal to the nominal impedance of the speaker---such as a 4 ohm with a 4 ohm speaker---you will then have a damping factor of ONE--------yes you will lose half your power but at least you can hear how it sounds------------RC
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guys ---have any of you ever heard cd 103 from autosound----it has tones and music at various distortion levels from .01% to 10%----it is easy to see what you can hear----no one can hear less than 2 or 3% on any kind of music-----but on a reasonable system it is easy to hear fractions of a percent on pure single tones-------check out the cd.........RC
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There is an ABX tester available and tons of clips (# of bits, distortion, etc.) for you to test your ears with. Also has guidelines for doing listening tests.
http://www.pcabx.com/
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as i stated in the tube amp thread i spent the last several nights doing some tests on the "sound" of amps when overdriven or "clipped"--------seems this has become the "best excuse" to surface on why one amp may be sonically superior to another-----i have always excluded overloading the amps in my challenge since the issue started out as a search for what specs really contrubuted to sound quality-------and since it seemed silly to listen to amps producing double digit distortion in a quest for sound quality this requirement made perfect sense to me-----in my first round of tests I compared a JL, a Jensen, and a high quality home/studio tube amp (4 El-34's per channel in a classic push pull output) ------i considered the JL as representative of the best car audio has to offer----the Jensen as a brand that most "sophisticated" audiophiles look down on and the tube amp as a good example of high quality tube design----meaning it is a real honest to goodness tube amp unlike the market driven hybrid nonsense that is sold in the car audio market---------the car amps were powered by a motor driven GM alternator wired to a yellow top battery------the home amp was of course plugged into the wall outlet-------i tested the amps at the following levels-------driven right to the edge of clipping (0 dB overdrive)------6 dB overdrive------12 dB overdrive------18 dB overdrive------and finally 24 dB overdrive-------the amps were connected to a 8 speaker (4 per channel) JL array wired to 4 ohms so the power could be safely absorbed without damaging the speakers------the signal was tapped directly off the speaker lines with a lab grade bridging coil and fed into a digital workstation------the signals were then "normalized" for the same loudness since the amps all had different power outputs-------i then edited the tracks into a single easy to compare CD-------here is my first impression-------the JL and the Jensen sound the same at all drive levels--------ie their distortion is equally bad------the tube amp sounds a little worse at the higher over drive levels-------i don't hear any speacial sonic character from any of the amps and sure can't hear any "tube magic" that is so touted by tube fanatics-------no soft clipping or pleasing harmonics------just nasty distortion-------i was going to do a few more amps in the test but after this i believe it is about as futile as trying to find survivors in the WTC------at this point i believe i am willing to modify my amp challenge to allow any ampunt of clipping as long as the amps have power ratings (actual not advertised) within 10% of each other----this would have to exclude tube amps as they seem to sound much worse and it is obvious-----------anyone want to listen to the CD send me and e-mail and i will send it to you as long as you agree to send it on to someone else that is interested in also hearing the results in a timely manner----when i send it to you you will be given the name and address of the next person to send it to--------the music is copyrighted and i don't want to make lots of copies...........RC
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manville------i don't follow you but here is a try----are you saying to set the overall amp gains the same??? ie --the sensitivity so a given input voltage will achieve a given output voltage????------if so thats what i always do in my amp challenge------but if one amp is more powerful than the other the difference is obvious if one amp clips and the other doesn't--------the unclipped amp will always sound better----somehow i doubt that is what you are asking???????-------what are you getting at by specifying the "cars" charging system-----in my test we actually powered the system from a alternator/battery combo-----and since an amps overall gain is not affected by the supply voltage i don't see the reason for this request------i will send the CD out monday---------i look forward to your comments..........RC
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I'll stop there... that's only 400 characters under the limit for a post
I've only included stuff that is relevant and not bickering. If you're just going to post yet another silly flame then don't bother, if however you want to ask/discuss then go ahead, whatever your opinion.
