100 watts Class D = 10 watts in a tube amp?

Discussion in 'Amps and Cabs' started by Metallicdream91, Jul 28, 2013.

  1. Eminor7

    Eminor7 Member

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    The Trademark 60 (TM60) is only a 60W amp when plugged into a 4-Ohm load. The TM60 is based on the LM3886, which is rated at 38W peak when plugged into an 8-Ohm load. http://www.ti.com/lit/ds/symlink/lm3886.pdf
     
  2. germs

    germs Member

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    i always thought of measurable watts as "clean" watts.

    so, a 18w tube amp CAN go louder than a 18w SS counter part, but how much of that is dirty sound?

    i would suppose that it all depends on how you're going to use the amp - and that's why the JC120 has it's fans, as does the Bluesbreaker.
     
  3. Sirloin

    Sirloin Supporting Member

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    Yep, plus the Celestion Seventy 80 is rated at 98db. Stick a V30 or G12H30 at 100db in that thing and it would seem like it has twice the wattage. Then put one of the Eminence 103db rated speakers and stand back. In order to compare SS and Tube amps you MUST run them through the same speakers/cabs to have anythiing close to a valid comparison.
     
  4. 5881

    5881 Member

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    I used to sell hi fi gear in the late 70's and all manufacturers were required to rate gear based on 20~20,000 hz at a certain % of distortion with an 8 ohm load. This was either a trade association agreement or a law instituted by the Federal Trade Commission or FCC. Previously manufactures would make wild claims on watts per channel for stereo receivers, etc.
    The amount of power (watts) need to drive a speaker at 20hz (really low bass note), given the amount of air that requires movement from the speaker "motor" to push the cone excursion to it's max is far greater than that needed to make a tweeter move a 128th" to get high end. After all, sound and speakers are all about movement of air. By rating across the entire "listenable" frequency range evens out the playing field.
    Same with distortion; an amp will make more watts when pushed beyond it's "normal" listening level, but will sound like crap, especially a SS amp.
    Impedance is also a factor, as it basically represents the load the speaker is putting in front of the amp. Think in terms of how much water can be pushed through a given diameter pipe. The larger the pipe the more water can be pushed through. The lower the impedance, the less back-pressure the speaker presents to the amp (larger pipe). An amp rated at 60 watts at 8 ohms will put out maybe 75 into 4 ohms.
    Hopefully I got this right, and if not I'm sure I'll know in 5 minutes or less!
     
  5. chervokas

    chervokas Member

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    Not true with tube amps, where the impedance of the load is reflected through the OT to the output tubes. In that case, the amp will deliver maximum power in a load matched to the design (the output stage and the OT's turns ratio). So a tube amp with an output of 8 ohms will transfer maximum power and deliver maximum headroom into an 8 ohm load, match it to a 16 ohm load or a 4 ohm load and you get less power and less headroom.
     
  6. drbob1

    drbob1 Silver Supporting Member

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    I guess the design point is well taken. That said, almost all SS amps are designed in such a way that they "hard clip" when they exceed their nominal power output, which tends to be nasty and hard on speakers. Tube amps, OTOH, almost always clip in a softer manner because tubes don't go into hard cutoff at the peak of the voltage excursion (one tube is in soft maximum output the other is in cutoff for nearly 1/2 the cycle no matter how loud the note is). For at least guitar amps it's fair to say that it's safer and usually better to exceed the rated power output for a tube amp.

    Ratings by manufacturer are all over the place for amp output, frequency response, speaker sensitivity... Just no way to know how something will sound till you try it out.

    Comparing class D to tubes, it's worth noting that a 300w tube amp vs a 300w class D amp will likely be able to sustain a much sharper attack on a note due to the power storing ability of the OT and the power supply.
     
  7. teemuk

    teemuk Member

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    Care to actually prove any of those statements? I find it hard to agree with most of them because in the light of my research...

    - Many solid-state amps today are not designed to hard clip. In fact, designers have greatly concentrated on this design issue for a long, long time. The engineers are not blind to it and totally will exploit benefits of soft clipping, assuming there really are such. The behaviour of an overdriven tube power section is also very well researched and techniques to emulate its characteristics in both analog and digital realm have been refined to a great degree.
    - Most tube power amps actually hard clip and no one even notices (or cares).
    - Hard clipping doesn't sound nasty. Yes, it sounds like clipping but there's very little audible difference to softer clipping (they are both very, very audible).
    - Hard clipping actually has many useful applications, including -uh - tube power amp overdrive and tube preamp overdrive. Also, modern hi-gain tones wouldn't exist if there wasn't hard clipping.
    - There's a great difference between amp clipping "hard" and amp clipping and misbehaving while doing so (ringing, hysteresis, saturation, etc.)

    I agree. When we speak about musical instrument amplifiers (especially guitar amps) one amp is hardly comparable to another because there are tons of variables that make them different. If there weren't we would all be happy with just a single amp. Output power or being tube or solid-state are from the bottom of the list of variables that actually mean anything. One tube amp will sound different (in various imaginable ways) from another tube amp just as much as it will sound different from a solid-state amp. So really, what's the point of comparison?

    I encourage everyone to stop obsessing about this issue and to do their own research on the topic instead of believing and parroting the same tired old catch phrases and misinformation this topic always brings out.
     
  8. Jason417

    Jason417 Member

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    Correct.


    Wattage is current^2 x resistance

    Sound Pressure Level is a product of wattage, proximity to speaker, directivity, atmospheric and room conditions, boundary coupling, total harmonic distortion, damping factor, frequency, and about 50 other things.

    ***The main reason a class A amp will usually produce more volume than a class D is because the digital power amp isn't capable of distortion or overload. You can push a class A into clipping until the total harmonic distortion is 1000x beyond the class D. This will give you a ton of extra volume (along with distortion)

    Guitarists live with this phenomenon every day, but you can also see it in light bulbs. We all know that LED lights use less power to make the same light level as incandescent bulbs, and that's because the power (wattage) is only a small part of the luminosity (efficiency, SPL?) of the bulb.



    Or you could ask the uneducated kid at GC and he'll tell you that wattage isn't wattage, and that 10 = 100.
     
    Last edited: Jul 30, 2013
  9. Jason417

    Jason417 Member

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    This is an appropriate analogy: a watt is a watt, just like a pound is a pound, or a mile is a mile. It's a unit of measure that applies to power.

    "Loudness" is measured in decibels, not watts, or pounds, or miles.

    So... there are more factors involved in Loudness than just watts. Tube amps are capable of pushing beyond spec, so they are louder than the same spec D amp.
     
  10. GCDEF

    GCDEF Supporting Member

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    We're not talking about solid state amps that emulate tube amps. We're talking about when a transistor hits the wall it starts generating square waves. Tubes don't. They also add third order harmonics, where tubes add second order, which are much more musically pleasing.

    It boggles the mind that somebody could actually argue that tubes and transistors act the same way when they're pushed hard.
     
  11. Jason417

    Jason417 Member

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    Here's some articles about power handling, tubes, speaker sensitivity, and such.

    Slimy Speaker Sales and Misleading Numbers
    http://www.peavey.com/support/technotes/concepts/THE_LOUDSPEAKER_SPEC_SHEET_GAME_2005.pdf

    Tube amps
    http://www.peavey.com/support/technotes/hartley/chapter_6.pdf

    Peavey invented a technology to prevent hard clipping of the power amp. Hard clipping destroys speakers and transformers, and is avoided at all costs by responsible amp designers. So yeah, soft clipping is pursued.
    http://www.peavey.com/support/technotes/concepts/clippingrevisited.cfm

    Some people might turn their noses at Peavey, but no company is as transparent about the science behind sound as they are. You can get the same info from any sound engineering book, like this one:
    http://tinyurl.com/kmktsf2
     
  12. drbob1

    drbob1 Silver Supporting Member

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    Um, teemuk, you sound educated but it doesn't sound like you've looked at the response curves of transistors vs tubes when driven past the voltage rails?

    A transistor simply stops increasing output and the sharpness of the cutoff is determined by the slew rate of the amp. With a decent power supply, at a frequency the amp can reasonably handle, it approaches a square wave. Which IS hard on a speaker, does sound like an unfiltered fuzz (worked for the Beatles in one song, otherwise not something we often use-plugging a fuzz directly into a FR power amp and speaker). The solution has been not to somehow change the function of output transistors but to manipulate the input to allow it to compress more gracefully, to shape the output wave to simulate overdrive distortion and so on. None of which changes the fact that if you drive the output transistors past the power rails, you get square wave distortion, unfiltered. A class D amp with a 100w output is not going to be good sounding or safe at 110w.

    A tube output stage on the other hand has many factors that make it react more gracefully. As you approach maximum output the attack on each "sine wave" is generally rounded off, which means no square wave. Plus the presence of an OT ALSO reduces slew rate and rounds off the tops of signals that exceed the maximum output swing. Bottom line is that the output curve of a tube amp filters out many of the odd and high order harmonics that are pecieved as harsh. On the downside of the swing, the cutoff is sharper, but here it's masked by the other power tube's positive swing. Properly biased for minimal crossover distortion, you can push the duty cycle to get nearly double the output of the clean signal without a lot of harsh artifacts. So a 100w tube amp, properly designed, can sound great at 160 or 170w (the maximums that I've heard mentioned with Marshall Super Leads for example).

    Now, you could engineer your SS amp so that a 100w amp is NOT approaching the rails at 100w, if it's designed so that the output section doesn't clip till 200w, but you call it a 100w amp and let your signal processing introduce pleasing harmonics and compression between 100w and 200w, then you're absolutely right, it could sound just as good. Unfortunately, you'd then be paying for the engineering of a 200w amp but only able to sell it for 100w prices. While the cutting edge of SS amp builders might be able to do that (say Pritchard, although I don't know how he rates his amps), most class D amps are built to a price point and therefore most will not overdrive their stated rating gracefully!
     
  13. Jason417

    Jason417 Member

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    There's so much bad information in guitar land. 99% of what we "know" is anecdotal and comes from our idiot uncles, the kid at the guitar store, or a badly written article in a magazine with Vai on the cover, again.
     
  14. teemuk

    teemuk Member

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    Interesting....

    ...yet, I don't see it happening in this highly praised vintage Fender. ...on that note, the lack of soft clipping is equally evident in most other tube amps as well.

    [​IMG]

    :huh

    Exactly. Tubey soft clipping being a good example.

    Quilter makes an on point reference about this issue in his patent concerning soft clipping tube power amp emulation employed in his amps. (I bet some folks want to argue no such thing exists, right...) Anyway, employing a 400W class-D design to produce 100 watts clean is still likely cheaper and more efficient than a 100W tube amp, which also wastes an ungodly amount of power to produce its rated (clean) output. What's really the difference?
     
  15. teemuk

    teemuk Member

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    What transistor? In what type of design/circuit?

    It's not just transistors. It's CIRCUITS.

    CIRCUITS

    CIRCUITS

    Get it?

    Something like a MOSFET in an open loop design will clip very softly. It won't just stop producing output and flat out hard clip. A differential BJT stage is also a very good example of a transistor design that has very soft clipping characteristics. You need to evaluate this issue on circuit basis. Devices alone are meaningless. They are always part of a circuit.

    Shouldn't this be a basic concept? I'm seriously starting to feel that I'm probably wasting my time on this. :bkw


    Though, I do agree that pre-limiting before a "standard" linear amp is another perfectly viable solution to achieve the very same goal. ...And at least seems to be more popular design choice as well.
     
  16. tech21nyc

    tech21nyc Member

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    I think I can speak to this as I owned a Club Deluxe and I also use a Power Engine which is the same amp as the TM60. The difference in "clean" power between these two amps is not that great. The difference you heard was most likely due to the efficiency of the speaker and tonality. The G12H30 that Brian uses in the Club Series is a 100dB sensitivity speaker and the 70/80 in the Power Engine is 98dB. Doubling the wattage all things being equal will yield you a 3dB difference in volume. Plus the Club series is based around a Vox circuit and has a very pronounced midrange whereas the clean channel of the TM60 is more Fendery and has a more scooped midrange. A forward mid sound will always seem to cut more which is why rock guys have typically liked Marshalls over Fenders. The Marshall always seems to cut more and this is irrespective of wattage.

    The Power Engine I use has an original Celestion G12 Century which is a 102dB sensitivity speaker. I can tell you first hand that my Club Deluxe could not compete as I was going for a clean tone and the Club Deluxe gets dirty very quickly. It's supposed to. It wasn't designed to be a big headroom clean platform. If you want that you buy the 100 watt. Top Hat Ambassador.

    Having said all that watts are watts, and we like everyone else measure "clean" power with a 500Hz sine wave and test equipment. There are too many factors to consider to make a blanket statement that one amp is louder than the other. Speaker efficiency, cab design, amount of speakers, frequency response etc. Tube amps can "seem" to be louder as we don't perceive the onset of clipping in those designs to be actually distorted. It sounds good which is why we like those amps.

    Where does this leave you as the player? If you prefer your Club Royale, and you think it seems louder then use it.
     
  17. ekp

    ekp Member

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    Instead of rating my amps at 5% distortion, which involves a bit of clipping, I give them four ratings: They produce 60 watts clean and continuous; 90 watts clean attack; 90 watts dirty continuous; and 180 watts dirty attack.

    Roughly speaking my 60 watts is akin to industry 75 watts. However, my attack is so big, that my amps will hang quite well with 100 watt tube amps.

    And then there is the Watts Knob that lets you turn the power down to a few watts with circuitry that maintains the amp's character. This is a remarkable feature as Duffy Kane found one night when his gig shifted from an outdoor venue to a rather small room. Even turned down the amp had lots of tone. He was such a happy player, his band played on an extra hour.

    Have a great day, Eric
     
  18. Guinness Lad

    Guinness Lad Member

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    I just got a BadCat unleash, this is 100 watts class D. When it goes through my 12 watt Aiken Tomcat the biggest thing I notice is more headroom. Volume doesn't appear to change too drastically but it's really loud anyway so there probably is a leveling off.

    I think speaker and amp voicing makes an amp sound louder than what it really is. Pump a bunch of bass through any amp, it will give out right away.
     
  19. michael.e

    michael.e Supporting Member

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    Problem is, you blow the physics issue out the door with the "sound like SH$# factor". Physics and getting a nice tone at a gig, to me, are two very different things.
     
  20. michael.e

    michael.e Supporting Member

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    Where it leaves "me" as a player is that I found it far preferable to play my old Tophat at a gig. It cut much better, the quality of the tones, to me, were superior. The sensitivity and response of the amp, for my personal needs were superior.

    In a live setting, I found the Tophat a much better choice for me. I also went for similar feeling and sounding tones.

    There was no comparison.
     

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