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Dr. Sound - Guilty of Malpratice ????

Discussion in 'Amps and Cabs [BG]' started by rickbass, Dec 5, 2000.


  1. rickbass

    rickbass Supporting Member

    The late outbreak of Carvin threads has begged a question which I posed to their sound tech. guy, Dr. Sound and I want to bounce it off some of you who are more tech knowledgeable than I.

    In short, I asked him about the fact that Carvin spec's THD @ 1kHz and that 1kHz doesn't seem an appropriate spec for bass frequencies, as aopposed to a range of 20Hz-20kHz. So, I asked him if people are correct when they speculate that Carvin's power ratings are inflated by as much as 15%, (as some have alledged).

    Dr. Sound's reply, in part, "The power amps in the R600 and R1000...will deliver their full-rated RMS power. The 1kHz spec is typical for bass amplification. That is a full power spec instead of the typical 1/2 power@0.03% specs you see in pro sound. Actually, I woould be wary of the `fictional' specs I see for other amps out there (some of them publish the 1/2 power spec but don't tell you it's 1/2 power). Most bass amps are well over 1%THD at full power...."

    One of my amps, a Carvin RL1018 is my one of my fread & butter amps. Is this feller greenin' me ???? :confused:

    [Edited by rickbass1 on 12-05-2000 at 05:24 PM]
     
  2. MikeyD

    MikeyD

    Sep 9, 2000
    What he's saying is that the amps will deliver full rated sine wave RMS power (e.g., R600: 600 watts bridged into a 4-ohm load), but this power is achieved with a 1 kHz sine wave and at a distortion (THD) level of up to 1%. I agree that *some* (not all) other bass amps are rated similarly. However, I know of others that are not so rated (they use more conservative figures like 20-20kHz power bandwidth at full rated power at less than .05% THD, for example). The bottom line is, not all manufacturers rate power the same way. They can get into legal trouble, however, if they misrepresent what their amps are capable of. But when one looks at power ratings, one needs to know if that power rating is achieved at one frequency or over a range, at what level of distortion, and into what impedance load. Unfortunately, looking at wattage alone doesn't guarantee one is comparing apples to apples.

    I would not use the word "malpractice" here. He's simply defending Carvin's policy on how they rate their equipment. When *I* estimate Carvin's amps put out maybe 85% of their rated power, I mean with low distortion (under .1%) and over the whole audio spectrum. My disclaimer is that I have not done this with test equipment, so it's relegated to *opinion*, not fact, on my part. I now own both the R600 and R1000, and I honestly believe that their *clean* power output is somewhat less than their claimed wattage figures (in my opinion!). If I ever get my oscilloscope fixed, I might be able to measure it and back it with hard numbers.

    - Mike

    [Edited by MikeyD on 12-06-2000 at 12:13 AM]
     
  3. rickbass

    rickbass Supporting Member

    MikeyD - Not to worry. The term "malpractice" isn't used pejoratively, only as wordplay with the "Dr." bit Carvin uses.

    I was toying with the idea of substituting my R1000 for the R600 with my Cyclops cab and seeing how it might affect headroom. However, since the R1000 isn't offered as an option with the Cyclops, I was concerned it might knock the voice coils through the grill. The good "Dr." told me the R600 drives the Cyclops cab to it's full potential.

    As always, thanks much for sharing your knowledge with me.:D When I first got into bass, (when Precisions and EB3's ruled the earth), amp buying was decided simply by RMS and one's ear. Since then, I've tried to get enough tech in my head to cut through the hype and spare the disappointments caused by naivete.
     
  4. MikeyD

    MikeyD

    Sep 9, 2000
    Yeah - it was late and I was tired, but it occurred to me later. Has to do also with not yet knowing the person behind the words.

    If that's the combo with 1x15, 2x8, etc., it probably won't take all that much power input. The R1000 does put out substantially more than the R600, so one does have to be careful with it.

    That makes two of us! You are welcome; I like to help others and learn more myself in the process. I have lots of engineering background, so I feel a little bit qualified in saying that it is not an easy subject. For a lot of bass players, it's still probably best to check out the amplifiers/speakers in person and to get as much information they can get pertaining to the manufacturers' and products' reputations. Forums such as these can be helpful, as long as people are careful with what they read (i.e., there is also a lot of misinformation going around).

    - Mike

     
  5. rickbass

    rickbass Supporting Member

     
  6. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    The real question is how quickly does the distortion increase?

    Check out these specs from the SWR web site about their Baby Blue amplifier:

    Maximum power at 1KHz under clipping: 120 Watts RMS @ 8 ohms, 160 Watts
    RMS @ 4 ohms

    Power Amp Distortion (1KHz)
    0.02% THD, 100 Watts RMS @ 8 ohms
    0.03% THD, 100 Watts RMS @ 4 ohms

    System Distortion
    (Gain and Master Volume full, enhancer and tone controls set flat,
    1KHz): 0.5% THD

    OK, what does this say?

    1. The power amp THD number gets worse as impedance drops. This is true for almost all solid state amps. They don't even spec the 2 ohm THD, it's probably not too impressive.

    2. The power amp distortion is quite low at 100 watts output but starts to rise rapidly until the system clips.

    3. If they raised the THD number from 0.5% they could probably claim a bit more wattage but as distortion would rise so quickly once you start clipping if they could squeeze out a claim for 5 watts more they would be lucky.

    4. As you start running the amp louder and louder eventually your signal peaks will start to have increased distortion. Since peaks are of short duration, the distortion will not be very noticeable until all the peaks actually cause the amp to go well into clipping (we all know THAT sound).

    5. The "system distortion" figure clearly notes that the EQ is FLAT and suggests that some of the THD is not actually in the power amp but in the PREAMP.

    Just for jollies, I checked out the THD specs for a Sony home theater receiver:


    STR-DE445 $249.95
    - Stereo Mode Power Output, both channels driven, 20 - 20,000 Hz, 0.09% THD:80 w x2 into 8 ohms
    - Surround Mode Power Output, all channels driven, 1000 Hz, 0.7% THD:80 w x5 into 8 ohms

    Hey, they have even worse THD numbers than the SWR amp does and this is a home "hi fi" product!!!

    I bet you didn't know that in surround sound systems, three of the five channels are limited bandwidth and also can use higher distortion amplifiers! Yet noone sits at home watching their DVDs bitching about how the center and rear channels are all distorted, do they?

    Now let's look at the numbers from QSC for one of their RMX series power amplifiers:

    Power per channel
    8 ohms EIA 1 kHz 0.1% THD 200W
    4 ohms EIA 1 kHz 0.1% THD 300W
    2 ohms EIA 1 kHz 1% THD 430W

    Distortion (typical)
    20 Hz-20 kHz: 10 dB below rated power
    Less than 0.03% THD 4 and 8 ohms
    1.0 kHz and below: full rated power
    Less than 0.03% THD 4 and 8 ohms

    Hey the THD is stays the same BELOW 1KHz but not ABOVE once you get within 10 dB of full rated output. Hmmmm...notice that the numbers aren't THAT different than the SWR bass amp, also check out the HUGE increase in distortion at 2 ohms!!!

    Food for thought.

    Anyway, it goes to show that Carvin is not doing anything other than what everyone else is doing in terms of power ratings and claiming that Carvin amps are overrated as much as 15% isn't really a fair statement.


     
  7. MikeyD

    MikeyD

    Sep 9, 2000
     
  8. MikeyD

    MikeyD

    Sep 9, 2000
    A very thought-provoking post. Thanks for your input! You are right about QSC's RMX series; but then take a look at their PLX series. The latter series is rated for power output for the full frequency range with under .05% THD at 4 and 8 ohms. Because of this, when I look at the RMX wattage figures, I personally "derate" them by about 20% (corresponds to only 1 dB lower!) so I can compare more fairly with the PLX and amplifiers by Crown, Yamaha, and others. And check this out: even QSC gives modified figures for the RMX series. For example, the RMX 2450 is rated at 750 w/ch at 4 ohms at 1 kHz and .1% THD, but only 650 w/ch (87%) at the same load 20-20kHz at .1% THD!

    In other words, I'm trying to "level the playing field" when comparing power claims. I had to do this because, like many others, I was comparison shopping by specs recently and I needed to "normalize" power ratings. For the PLX series, for example, I took their 4 and 8 ohm power ratings verbatim, whereas I derated the RMX and Carvin power amps' figures. (Note: I paid much more attention to the 4- and 8-ohm figures than the 2-ohm figures, because of how I anticipated using the amps.)

    Anyway, let me clarify again: when I say 80-85% percent, I mean *clean*, undistorted (at least audibly) power. I stand by that opinion. I was a little disappointed in Carvin's actual clean output compared to their wattage ratings, and I know that I'm by no means the first person having this reaction - many others before me have made similar statements. I'm an engineer, and I read these complaints with healthy skepticism. However, I've since purchased Carvin amps and have done an A/B ear test between them and a Fender amp I own, and I found that people's comments were not that far off the mark. Again, a 1 dB difference is barely audible, but if wattage is a major factor in one's decision, then it's important to make sure the ratings are done under the same loading, distortion, and frequency input conditions. All of the foregoing is my opinion only, and is subject to change if I ever get more detailed test data (either through reading or conducting my own measurements).
    - Mike
     
  9. Skip

    Skip

    Mar 22, 2000
    Bronxville, NY
    First off - Sony is mid-fi, not hi-fi. :)

    Most HT recievers are tested by only driving one channel - because they all use the same transformer they get better measurements with only one channel driven. So buyer beware!

    For real amp measurements of hi-fi amps go to Stereophile Magazine and look in the archives for their amp reviews.

    As for the rise in distortion, most solid state amps clip quickly once they go. Tubes on the other hand usually rise much more slowly into clipping.

    - Chris

     
  10. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    MikeyD and Skip,

    You guys make some good points but are missing the point I was trying to make in the first place: the distortion figures of the Carvin are NOT out of whack with other manufacturer's BASS amplifers. In fact, Carvin is already way more conservative than our pals at Ampeg...check out their "1600 watt" SVT-IV, which is really 1200 watts RMS at 1 KHz (at what THD?). I hear a lot of people complain about solid state Ampegs being overrated.

    It's pretty interesting to me that bass amps today would even be in the same league as typical (call if mid-fi if you want) home stereo gear. Thirty years ago many amps were commonly rated at 5% or even 10% (!!!) THD and wattage was often rated as "EIA music power" or "peak power" rather than RMS (an inflation of 25-50%!!!).

    The claim that tube amps clip more slowly is BS, I've put Fender amps on the bench and watched them clip. Once a sine wave becomes squared off you're generating huge amounts of harmonics (i.e. THD goes through the roof) and tube amps clip for the same reason transistor amps do: the supply rails have been reached.

    As far as the QSC PLX, you bet it's got better specs. It also costs a lot more than the RMX and if you want THD specs with lots of zeroes after the decimal point, open your wallets, folks. There's a reason why a 130 watt Peavey head is $300 and a 120 watt Walter Woods head is $1300.

    If you really want clean, undistorted power for bass, you're best off getting into a preamp/power amp system and buying a good pro audio power amp from Crown, Crest, QSC, etc.

    I'll also go on the record and say if you like the sound of tube bass amps then looking for squeaky clean THD specs on a solid state amp is a waste of time anyway. Most of the tube amp charm IS the high THD.

    In the end, specs don't tell you everything. Go listen, your ears will tell you more than any spec sheet ever can.
     
  11. MikeyD

    MikeyD

    Sep 9, 2000
    I understood the point you were making, but when I was in the market for amplifiers recently, I was considering integrated bass amps as well as separates (power amp + preamp). I needed to "normalize" the wattage figures so I could do a better comparison. I do not agree that ALL bass amplifiers are rated liberally, with the higher distortion figures (my Fender BXR300 being a case in point).

    I agree with this. My old Kustom 200 amp (circa 1969) was rated this way.

    I basically agree with this. However, I believe that the shape of the saturated waveform is different under *mild* clipping: it's more smooth (therefore producing less odd harmonic energy), sounds more like a sine with some even harmonics added, and thereby delivers more power without as much nasty harmonics - which simply SOUNDS louder to our ears (which is why people think they put out more wattage than a similar solid-state amp).

    You missed my point here. I was trying to compare amplifier performance on a level playing field. Once I had the wattage figures normalized to comparable values, then I could see whether it was worth an increment in cost. For example, one might think the RMX series offers a huge dollar-per-watt advantage over the PLX series, but when one normalizes the power ratings, as I have done, the advantage isn't quite as impressive.

    I sort of disagree. Despite what I've said about Carvin, my Carvin amps will most certainly put out clean, undistorted power (I think they are great amps - really!). It's just that one must keep the output level below about 80% (my guesstimate) of Carvin's claimed maximums in order to guarantee truly clean output. And my 80% is probably being generous - 50% is probably more like it to have very low (inaudible) THD.

    I agree. I don't know how many music stores let one run a 1200-watt amp wide-open-throttle, though. Furthermore, some of us are happy to purchase "sight unseen" via mail order (Carvin being the ultimate case in point), if the company's reputation is good and the performance of the product (as claimed by the specs) is satisfactory.

    This is a great discussion. Thanks for your reply, brianrost.
    - Mike