Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Tube vs. SS Watts - How do you compare

Discussion in 'Amps and Cabs [BG]' started by degroove, Mar 6, 2003.


  1. degroove

    degroove

    Jun 5, 2002
    Wilmington, DE
    I was curious as to how to compare wattage ratings on a tube amp to wattage ratings on a solid state amp.

    Is there a rule of thumb - say 50 Tube to 100 SS?

    I am wondering becuase I play a 350 Watt SS head and was wondering how much tube power I would need to play at a comparable volume.

    If you do know of a rule of thumb, is it based on your experience or something more factually based like from a book?

    Thanks,
    Matt
     
  2. Rule of thumb is usually a factor of 2. Supposedly a 100 Watt tube amp can get as loud as a 200 Watt SS amp since the tube amp can be run farther into distortion and compress the signal making it sound louder than a clean signal of the same wattage.

    If you're playing with a 350Watt SS amp, you could probably get the same volume level with a 100 or 200 Watt tube amp, provided you like the sound of a tube amp distorting a little bit (the greatest bass sound in the world as far as I'm concerned.)

    Chris

    (edited brainfart)
     
  3. Not really. Here is how I view the tube vs SS issue. A SS amp rated at 350 watts at 1% at 1k. Isn't going to put out much more usable power under any circumstances. Once it starts clipping the sound is going to go south real fast. A tube amp rated at 300 watts on the other hand will still only produce 300 undistorted watts but it can work beyond the 300 watt barrier in 2 ways. 1st of all when it goes into clipping the sound while distorted is still musical and therefore usable, maybe even desirable. 2nd tubes produce a natural compression when overdriven which gives you more usable average continous power. A good compressor with a SS amp should produce the same effect. All in all I don't think one is better than the other, only different. If your looking for sound volume per dollar, SS is the only way to go. If your looking at watts per lb, SS is still the only way to go. If you like the sound of an all tube amp better than SS or hybried than you have no choice but to go with all tubes. jmho
     
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    1 watt = 1 watt.

    Amps are rated using a continuous-level sine wave at maximum output voltage at the threshold of clipping. Tube amps tend to have more gradual clipping characteristics than solid state amps, so pushing a tube amp beyond its power rating is less harsh than doing the same with a solid state amp.

    Thus, with a tube amp you might be able to get peaks that are substantially higher than the amp's power rating, albeit somewhat compressed. Trying the same thing with a solid state power amp, you might get some noticeable distortion due to clipping.

    In its favor, though, solid state power is relatively cheap. For just $500 to $600, you can buy up to a couple kilowatts of decent, reliable power, so you can avoid the clipping problems almost altogether.
     
  5. Fuzzbass

    Fuzzbass P5 with overdrive Supporting Member

    If you're into totally clean tone, then there won't be a whole lot of difference between tube and SS amps of the same wattage. If however you dig the warmth (harmonic distortion) that comes from running a tube amp in the "sweet spot" (roughly the point where clipping begins), then yeah, the tube amp will seem to be noticeably louder. I can't put that into numbers because the sweet spot is purely subjective.
     
  6. degroove

    degroove

    Jun 5, 2002
    Wilmington, DE
    First, I love Vonnegut. Slaughterhouse 5 is one of my favorties. Tramalfadore.

    Also, Thanks. I am looking at amps that put out 200 Watts tube and the next class seem to be 300 Watts. I am trying to estimate how much power I would need to play at my current ss volume.

    It appears that a 200 Watter would do the trick based on your answer. Of course, more is always nicer!;) Nonetheless, I do like the overdriven tone of the likes of Allan Woody, Jack Bruce, etc. I play in a classic rock cover band, so overdriving would be pleasant, not repugnant to my ears.

    I am thinking I will just have to go out and try tube amps depite the brand of this wattage range and guage loudness myself.

    Thanks, so much.
     
  7. degroove

    degroove

    Jun 5, 2002
    Wilmington, DE
    Yeah, SS clipping is UGLY. My amp clips if I play too physically. I get some peaks that make my LED flash on and off. I have to turn down so I got some headroom.

    I would like to hear Tube clipping. I will have to go to a store and try some tube out.

    Then I can make my decision.

    Thanks for the input.
     
  8. degroove

    degroove

    Jun 5, 2002
    Wilmington, DE
    Great descrition of the tube process and why it can be louder than a SS amp. Good points.
     
  9. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    1 watt does equal 1 watt. FWIW:The formula is Watts=Volts x Amps. Given that, I'd like to point out the following:

    1 Volt x 10 Amps = 10 Watts.
    10 Volts x 1 Amp = 10 Watts.
    5 Volts x 2 Amps = 10 Watts.

    So there are 3 of the infinite numbers of ways to achieve 10 watts. The product is the same but the means to that end is totally different. What does that mean to us? Well, do you think that the given 10 watts is going to sound the same in all 3 situations? I don't know, I've never tried it in an experimental way where results could be measured, subjectively or otherwise. But my hunch is: I don't think so. Its just something I've kicked around in my head for a long time.

    Bottom line: when an amp's (regardless of the type of output devices) power is expressed in watts, that just ain't enough info. Even when expressed in the generally accepted terms of bandwidth, THD, and frequency variation (ie, 10 watts from 20Hz to 20kHz, + or - .1dB at 1% THD, its still incomplete.
     
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    They would probably sound very different because there would be three very different speakers involved; the first would have an impedance of 0.1 ohm, the second, an impedance of 10 ohms, and the third, 2.5 ohms.
     
  11. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    That's correct, and those impedance figures are similar to what actually happens in a reactive load, such as a speaker, over a range of frequencies. It also proves my point that, at least as far as sound is concerned, power ratings mean diddly. The only thing that a power rating on an amp is really good for, IMO is to get you in the ballpark. It gives lay people a way, flawed as it is, to compare amps.

    As you know Bob, this is a very complicated subject that requires technical knowledge to fully understand. I respect your knowledge and knew you would understand what I was trying to say. I have in the past been critical of the way amp manufacturers manipulate specs in order to sell amps and I still maintain my critique of them; OTOH I do realize that manufacturers have to have some way to help lay people make a choice. IMO its a bittersweet tradeoff. :cool: :cool:
     
  12. i think 200W of tube power would compare favorably to your 350W SS head in terms of useable volume.

    i know this is my first post here at TB, but i'm going to take a risk with what i say. i believe a little education will illuminate this discussion.

    i know that P=VI, and that a watt is a watt, but that doesn't mean that QSC measures watts in the same way that stewart does, or that aguilar, crown, ampeg, walter woods, EA, mackie, or anyone else measures theirs the same way, either.

    so just because an amp is advertised as "300W into 4ohms at .1% THD" doesn't mean it has the same kind of headroom, dynamic capability, or bass handling of any other "300W into 4ohms at .1% THD" amp might have.

    so good luck comparing SS watts to SS watts.

    amps are not rated dynamically for power or performance. power is specified at 1kHz typically, but even when it is specified 20Hz to 20kHz, it is still inadequate to judge things like sound quality and volume in terms of dBs.

    any amp that has a 15A IEC plug can't realisitically create more than about 850W for any appreciable amount of time without either shutting down or tripping a breaker in your wall. 15A * 120V = 1800 VA. at 67% efficiency (a very good number for a switching amp supplied by a switching power supply), that's about 1200W maximum peak, which is about 850Wrms continuous. and that's for one channel. if you're running two channels dual mono or bridged, it will be even less efficient.

    so, yeah. sorry if this reads angry. it's not meant to be. like i said, "i believe a little education will illuminate this discussion."

    robb.
     
  13. Dude, welcome to Talkbass, and being from Meridian, you must be a Peavey engineer. :D

    Chris
     
  14. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    er...a...bump:bassist:
     
  15. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    No, a Peavey engineer would know what power specs mean. ;)
     
  16. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    0.1 ohms doesn't resemble a speaker impedance. 2.5 ohms could resemble a 4-ohm speaker load at certain frequency points, and a 10-ohm load could be an 8-ohm speaker a little above or below resonance, or up in the frequency range where the impedance becomes more inductive. But I don't see what your example was supposed to demonstrate.

    I agree with you to some extent. IMHO, it's unfortunate that power amp specs are expressed as power and not voltage, but that's the way it's been for ages and it's not likely to change anytime soon.

    After all, amplifiers put out voltage, and power is just incidental to the voltage and the impedance. A solid state power amp putting out 40 volts will put out the same 40 volts into an open circuit, into 16 ohms, into 8 ohms, and if it's capable of doing so, into 4 ohms or 2 ohms, all with no more than a minuscule amount of variation from one load impedance to another. Thus, into an open circuit, the amp puts out 0 watts; into 16 ohms, 100 watts; into 8 ohms, 200 watts; into 4 ohms, 400 watts, and into 2 ohms, 800 watts. That's because the current delivered into the load is exactly proportional to the voltage and inversely proportional to the impedance.

    Speakers vary in impedance over their frequency range. That means that at a given output voltage, at some frequencies their impedances are lower and they'll draw more current from the amp than at others, and thus more power. The speakers might or might not be louder at those frequencies where the impedance dips. There's more to speaker performance than just impedance.

    There is no "typical" speaker load that can represent anything but a small slice of all the speakers ever sold, used, or invented. So rather than try to define an amp by the power it can put into an arbitrary simulated speaker load, manufacturers measure power amp output voltages into 8-, 4-, and 2-ohm resistors so at least they'll be partly appropriate and partly inappropriate for all speakers. But the figures derived from these measurements can give you a decent picture of what the amp can do.
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    This is interesting. Reminds me of the days when I was shoppping for a car audio amp, where wattage ratings are virtually meaningless. The generally adopted rule there is to look at the fuse holders. The higher the ampre rating, the more powerful the amp. How does this hold up in relation to the voltage?

    I don't think I've ever seen voltage listed on the spec sheet of an amp? Maybe that should be the next question we ask after "how many watts ?"
     
  18. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    C'mon, now you're going to tell us that cars' horsepower specs don't give an accurate picture of their comfort, sound system quality, and cornering ability. ;)

    Uh, no. You seem to be saying that a power amp's plug rating should be tied to what it can do in a test situation instead of what it will do in real-world usage. That's unrealistic. Very few power amp owners use them for test bench applications running continuous-level test signals at full power. Those who do probably know to have an adequate AC supply on the bench. For example, in my department we service everything from old model 1080's (40W/ch @ 8 ohms) to PowerLight 9.0PFC's (4500W/ch @ 2 ohms), and we have AC circuits adequate for testing them for continuous full power performance. That's far more demanding on the AC than any kind of normal audio program, such as music. Amplifiers in normal usage don't have to put out full power for minutes at a time, only for tenths of seconds at a time; therefore, they have plugs that are suitable for that usage.

    Not true.
     
  19. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    If that gets out, Pete, you might see car audio amp manufacturers putting higher-rated fuseholders on their amps, whether they need it or not. ;)

    [/QUOTE]I don't think I've ever seen voltage listed on the spec sheet of an amp? Maybe that should be the next question we ask after "how many watts ?" [/QUOTE]

    Since power specs are calculated from RMS voltage, maybe it should be the first question. ;)

    You can work it backwards: V = SQRT (P * Z)

    So if an amp does 400W into 4 ohms, take the square root of 400 * 4, which would be 40 volts.
     
  20. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    :) Good point. Capitalism sucks sometimes!

    Thanks Bob, you just happened to pick the exact specs of my bass amp :)

    But if it's a set formula, does that mean ALL 400w, 4 ohm amps have 40 volts? Pardon my ignorance/curiosity - I'm struggling to see how using voltages makes for more accurate camparisons than using watts.