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Power-Amp vs. Pre-Amp?

Discussion in 'Amps and Cabs [BG]' started by GreyBeard, Oct 31, 2002.


  1. pre-amp

    34 vote(s)
    91.9%
  2. power-amp

    1 vote(s)
    2.7%
  3. both are equal

    2 vote(s)
    5.4%
  1. Which one has more effect on the overall tonal balance. Can this be corrected with EQ or is it more. I've been using a Alembic pre-amp for the last 6 years and I've used several different power-amps with it. It always seems to sound pretty much the same to me no matter which power amp I use. I must admit however, that the power amps I've used have been Solid State Analog PA type deals. I haven't used a Power Amp specifically designed for bass or an all tube power amp so my opinion is lacking somewhat in practical experience. What has been your experience?
     
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    The poweramp only marginally attributes to the sound, especially when it's solid state.
     
  3. ldiezman

    ldiezman

    Jul 11, 2001
    Nashville
    yeap what JMX said.. your preamp is going to shape your tone more than you power amp... power amps are to provide transparent power as not to color your tone
     
  4. BFunk

    BFunk Supporting Member

    Pre-amps obviously color your tone, but power amps play an important role too. I think they contribute a lot to the dynamic response of the amp. When you are playing in a group, dynamics can play an important role in how the bass fits and supports the group's sound.
     
  5. Matthias

    Matthias

    May 30, 2000
    Vienna, Austria
    As the others said, the power amp should not (and usually does not) colour the sound.
    But from what I've learned here, the quality of the amp, especially of the power supply, has an effect on low end performance and 'tightness' of the sound.

    Matthias
     
  6. vanselus

    vanselus

    Sep 20, 2000
    Boulder, CO
    None
    That's ridiculous. If I want my poweramp to color my sound, my poweramp is gonna color the sound DAMN IT! ;)

    Seriously though, I didn't find the tone I was looking for until I found the Ag DB728, which really colors the tone. I went from a Stewart 2.1 to the Ag & the difference was night & day. Before that I had a Mackie 1400i which sounded completely different from the Stewart, but not quite as different as the Ag vs. Stew. Believe me, when I heard the difference between poweramps I was floored. Up until then I thought like you - poweramps for power, preamps for tone. Check it out and see - you'll be shocked.

    Aggie Stew? Longhorns love it!
     
  7. 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
    Power amps aren't designed to add or subtract or in any way change the tone of the signal, just like a camera body is not meant to add sepia tone, soft focus, or other effects to every image you shoot. A preamp is analogous to the lens of the camera; if you want filtering or focus or depth-of-field effects, you get them in the lens, not the camera body. Similarly, the best place to get the sound you want is in your instrument and your preamp, and use the power amp to amplify what you put into it.

    That doesn't mean that no power amp will color your sound. Some amps are poorly designed or made and add distortion. It might even be a nice, pleasant-sounding distortion. However, such power amps never seem to have a knob for controlling the amount of "niceness" they add, so if you like that distortion on everything, then go ahead with a power amp that adds coloration; if you want control over your sound, get a versatile pre and a transparent power amp.
     
  8. boogiebass

    boogiebass

    Aug 16, 2000
    Well-said, Bob.
     
  9. vanselus

    vanselus

    Sep 20, 2000
    Boulder, CO
    None
    The point is not what they're "designed to do" but more what they ACTUALLY do. Thanks for ripping on my amp, BTW. I happen to love it, but it's a tough love. Sometimes it craps on the carpet, and I have to rub its nose in it.

    Oh, so now my Aguilar is poorly made? :D

    Well, the question in the first place was "which has more effect on tonal balance" so your theories on how poweramps "should" be made have nothing to do with it. The simple fact is, all poweramps color the sound, but some so minutely that you can call it "transparent" - but we've been led to believe that "transparent" is always a good thing. In my opinion it CAN be, depending on what you're looking for - but a lot of people "searching for a transparent sound" don't really realize that's not what they want to hear. I can't tell you how many times i've been told "i want a transparent sound, not this trebly stuff..." ugh.
     
  10. After reading these responses I see that I have posed a rather controversial question. The fact is, that a power amp should not by definition add or subtract anything from the signal. It should only amplify it. But, however, power amps do in fact sound different different from one another. (according to these responses) What is important to me is to know why they sound different. Is it the way different designs work with varying speaker loads? For instance, a tube amp is designed to work ideally at say 8 ohms. That is why tube amps have different settings for different ohm cabinets. Ohmage (there is that word again) can vary greatly over the frequency range of a speaker. No 2 tube power amps are gonna work exactly the same way even bacause of variation in tube biasing etc. Does this account for the fact that tube power amps sound different the solid state power amps? As I understand it, solid state amps can work at a wider range of ohmage* In fact, the lower the ohms the more power they produce (to the point of overheating!) again do to the fact that speaker ohmage* varies over the frequency range of the drivers and the way this interacts with the power amp could color the sound and account for the sonic differences in power amps. What I think we are all looking for is the perfect power amp. One that neither adds nor takes away anything. One that lets the pre-amp color the sound.
     
  11. vanselus

    vanselus

    Sep 20, 2000
    Boulder, CO
    None
    I try to pay ohmage to my amp every day.
     
  12. 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
    "Why" is the big question, and it's been the subject of a lot of both study and factual findings on one side and marketing hype and nonsense on the other. If you delve into the study of psychoacoustics—into perception, biases, aural memory, etc.—you learn that it's not even all that easy to reliably tell what sounds different and what sounds the same.

    It's long been said that the ideal power amp is one that acts like a straight wire with gain—that is, Voltage out = Voltage in × gain. In my message above I only addressed the nonlinearities that cause the output voltage do be a less-than-accurate reproduction of the input voltage. But even changes in gain change how we perceive sound. You could put two identical, very transparent amps into identical systems in identical environments, and they'll sound the same. Turn one amp up a little bit, and it'll sound fuller, with better bass and high end, even though it's not adding or taking away from the sonic nature of the signal; it's just amplifying it more. That's just how we hear; even Golden Ears folks do, regardless of whether they think of their ears as lab instruments or not. Understand some of these tricks of human hearing, and you might also catch on to some sales tricks, like the 200-watt Spiffbait 2000 amp being turned up louder than the 1000-watt Superaccurate One-Triple-Zero so that it sounds better and punchier when you compare them.
     
  13. 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
    IMHO, if an amp doesn't do what it's designed to do, then the design was faulty.

    And I don't recall ever saying anything about your amp.

    Go with whatever you like and suits your situation. A car that turns better to the left than to the right would be better suited to a NASCAR oval than to an F1 Grand Prix track. If you want coloration in your power amp, go ahead and buy one. I was just pointing out that transparency is a desired design goal in power amps, and tonal control is a desired design goal in preamps, so if you're looking for tonal control in a preamp and transparency in a power amp, at least you're looking in the places where you're most likely to find them.
     
  14. vanselus

    vanselus

    Sep 20, 2000
    Boulder, CO
    None
    so Bob, you're a pretty serious guy then, right?

    I was JOKING.

    However, I disagree with you in that "transparency is a desired design goal in power amps" because it might be to YOU, but not to everyone.

    Transparency does not always = good.

    "so if you're looking for tonal control in a preamp and transparency in a power amp, at least you're looking in the places where you're most likely to find them."

    But to reiterate - if you're not specifically looking for this combination, but just looking for tone, transparent power amps are NOT the only way. Just look at how few pros use transparent solid state poweramps. (uh oh, flame war coming i can feel it)
     
  15. Hmmm... I thought the DB728 was pretty transparent, until I drove it hard.

    The big differences between the "sounds" of SS and tube amps lie in how they operate beyond their linear ranges. The output transformers in tube amps lend some colouration, but not all that much. Tubes and transistors don't inherently sound different when operated within their linear ranges. There have been lots of studies where people with trained ears couldn't tell the difference between tube amps and SS amps when they were run clean. Now, overdrive them and the differences become obvious because of the differing overdrive characteristics.

    There's no such thing as a "bass specific" power amp, BTW.
     
  16. It is almost like saying "if you can't measure it, then it doesn't exist". :confused:
     
  17. vanselus

    vanselus

    Sep 20, 2000
    Boulder, CO
    None
    Which brings us right on back to my first comment, that [no matter WHAT the reason] different poweramps sound completely different, and have the ability to completely change a rig's tone. Anyone that's A/B'd a bunch of poweramps will tell you that - no matter what the intentions of the manufacturer, or what SHOULD happen, or even a bunch of bench tests - they sound different.
     
  18. Do you think it might be the difference in the class of operation for each amp. A/B G and Tube?
     
  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
    No, it's pretty much universal. Anyone who wants to sell power amps to other than a tiny, narrow niche knows that the output signal has to be faithful to the input signal under all the conditions that the amp is designed for, and not add arbitrary manipulations on their own. That's why power amps have few knobs and switches, while preamps, mixers, effects devices, EQs, and other processors have many.

    Okay, not always. If you're okay with relinquishing that much control, then seeking non-transparency and non-accuracy is fine.
     
  20. 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
    How's that?