The difference between preamps and power amps

September 2, 2021
 by Paul McGowan

29 comments on “The difference between preamps and power amps”

  1. I only know that a magnifying lens or a simple lever directly amplify the “input”- the magnifying lens inherently adding already distortions. An amplifier (!) as discussed here can only use the input signal as a control or governing factor to create a bigger output signal (energy flow) derived from a new energy storage other than the source energy. And this transformation process is inherently associated with all kind of distortions and phase shifts. Thus I prefer a passive “preamplifier” TVC better classified as transformer based volume control. I also rarely see modern preamps “amplifying” anything unless they have an integrated equalizer or phono preamp the latter however should be placed as close as possible at the phono cartridge (there are even tiny digital phono “preamps” placed on the head shell of the tonearm).

  2. The word “valve” was used…
    Colloquially, this word denotes a vacuum tube, but this is a little broad.

    The original valve idea is that there is a potentially unlimited source of energy available and the tube acts as a valve – closing and opening accordingly with a controlling lever or wheel.

    The cathode (in a triode) has this unlimited quantity of electrons, and a high potential (voltage) on the plate (the B+) awaiting to attract these electrons -again, in a virtually unlimited way.

    The gatekeeper which is the hand on the valve is the grid placed between – and +.

    This idea moved into the age of the transistor (another valve).

    Meanderings: off

    1. In British English, we normally use “Valve” to refer to a thermionic vacuum tube. It’s not colloquial; that’s the normal and correct name for the device.

    2. Good morning Mr. Willox!
      All that is true, except for one thing.
      Not all power and preamp tubes are made alike.
      I believe you were talking about pentodes and tetrodes.
      But there is the one tube that doesn’t have the grid electrode in it.
      This tube, is referred to, as a triode tube.
      It only has a plate, a screen, and a directly heated cathode.
      It works on a slightly different principle.
      The screen, is where the small audio signal is applied.
      The electrons that are standing still on the cathode, are then excited by the small audio signal on the screen, then multiplied to a grater signal on the plate.
      In these kinds of tubes, there is no grid.
      These are tubes like the 2A3, 6A3, and 300B.
      Other tubes are, 45, 845, 211, and 213.
      All of these tubes, are power triode tubes.
      And what I wrote up above, is how they all work.

      1. I was basically referring to a triode…
        Simple stuff, and basic electronics.
        I never did get deep into the study and function of the extra elements – and thus my comments about “valves”.

  3. For one thing, Paul was some what, correct in how he explained it.
    Audiophile Dad, no disrespect.
    But this is where you dropped the ball at.
    The voltage amp, cannot drive a speaker without some currant.
    You’re correct about that.
    But where I think you lost him at, is the power amp.
    A power amp, has both a currant, and a voltage amplifier.
    The voltage that comes in from the preamp, is met with both a voltage and currant amplifier, at the same time.
    I don’t fully understand how this is done with a single ended input from a preamp, but I do have a pretty good understanding of how balanced inputs do this.
    Lets just say, we have a balanced power amp, and a balanced preamp.
    On one leg, is the voltage.
    On the other leg, is the currant that’s sent out as a load to drive a speaker.
    Without using too many technical words, this is what happens.
    When both the voltage and currant meet up together at the output of the amplifier, you have the watts to drive a speaker now.
    That’s what both a preamp and a power amp, works together with a loud speaker.
    Some people don’t get how this works inside of the very first amplifier.
    The tube amp.

    1. John: A power amplifier is normally a voltage amplifier with a voltage gain of about 30, a very low output impedance, and a very high output current capability. In many designs based on bipolar transistors, the amplifier consists of a first section providing the voltage gain and necessary voltage swing, followed by a second section which is a unity gain buffer capable of delivering the required output current, all within a single feedback loop.

      I prefer to avoid the term “current amplifier” because in general usage this implies an amplifier that creates an output current that is an exact (but magnified) replica of the input current. An ideal current amplifier would have a low input impedance and a high output impedance. It’s not useful for driving speakers.

      1. Good morning Mark!
        You’re correct about that.
        In spite of the fact that I can build a transistor amplifier, and do it with my eyes closed, there are many parts of that kind of an amplifier, that are a bit over my head.
        I understand tubes a whole lot better then I understand transistors.
        But if you know what you’re doing, you can make a tube amp, out perform a transistor amp.

  4. Here’s an observation (made by others) that extends the pre/amp discussion in both directions:

    A speaker is just a ‘microphone in reverse’. 🙂 Analog waves are converted into electrical signals, then back again.

    (1) We all know how important speakers are to our sound quality. Heck, we’re supposed to spend two-thirds of our budget on speakers. This is the “back end” of the signal chain and speakers’ impact can be very crucial, very complex, and very personal.

    (2) But think about the lowly microphone. The statement above makes me appreciate how important everything is BEFORE the signal reaches the preamp. Especially the recording technique — capturing the magic of the music in a studio or live environment so that it sounds “real.” What kind of microphone is used? What kind of mike with what kind of music works best? How many are used? How are they positioned? How are the different signals mixed? On and on… Just as important as picking your speaker.

    What is your favorite microphone for music? 🙂

  5. Why not just put a volume control on the amplifier along with some inputs to connect a CD player and Turntable? I think they call that an integrated amplifier 🙂 Something I prefer over a separate amplifier and preamplifier. I think when you go to separates you need to spend a lot on the preamplifier in most cases or it won’t sound as good as a well designed integrated. If I want to use my amplifiers I can always use the pre outs on my integrated amplifiers, though I do have separate Proton preamplifiers and even a highly regarded Adcom preamp/tuner. There are some good cheapskate preamplifiers out there but then you need a high quality cable to connect it to the amplifier and more shelf space. I have a good Proton D1200 amplifier and also a B&K ST140 amplifier and many other components that I don’t use because I’m using my Creek 5350SE. I have to ask myself why I bought so many components? Am I starting an audio museum? Or is being an audiophile a sickness? LOL.

    1. Hey Joe,
      My DENON POA-4400 monoblocs were the best, as they had a gain control on the
      front panel so I could connect my Audio Alchemy DDE v1.0 DAC straight into them
      without the unnecessary pre-amp screwing with the sound on the way through.
      I’d love to find a similar product today with the same sonic quality & at the same
      (x3.5 inflation) price.

    1. Some preamps can be very heavy, even heavier than some amplifiers. PS Audios Sprout for example is 100 watts per channel and weighs less than 10 pounds. These are mainly class D amplifiers that are lighter for the watts they deliver compared to much heavier Class AB and A amplifiers that use large and heavy heat sinking.

      1. The smiley emoji was my way of saying that I was being a smartass 😉
        The PS Audio – ‘Sprout’ is an integrated; it is neither a pre nor is it a power amp.

        1. FR I know that you enjoy Being a smart ass…lol. Being that the Sprout is an integrated amplifier it would way even less If you removed the preamp section. 🙂

  6. FR, all preamps mess up the sound unless you keep all the contacts and pots clean. When clean some are still better than others.

    My Creek integrated amplifier has a well designed passive preamplifer and an excellent amplifier. It has active preamp capability but I never tried it. Creek designed it to sound best in passive mode and those who used the active option don’t like it from what I hear.

    Most source components have enough output voltage to drive the Creek amplifier to its maximum output with the Creeks and an active preamp section if not perfect could only color the sound.

    If the amplifier doesn’t have the right input sensitivity or the source component has a low voltage output that’s not a great match for a passive preamplifer. My source components sound as they are with gain.

    The Creek is transparent in the chain. If you have a high quality Stereophile class A source component the quality of sound will only be limited by the quality of the recording and speakers.

    The Creek does have a high current output and is stable into loads as low as 2 ohms but it only has 90 watts per channel into 8 ohms which increases into lower impedance speakers which isn’t a problem unless your speakers are very inefficient but even then it still pumps out decent levels of sound even past its sweet zone Paul talks about.

    Most amps start coloring the sound and losing their linearity outside of the sweet zone that’s more of a problem with inefficient speakers.

    No matter how great your system sounds at high levels it gets tiring at those levels for long listening sessions especially with digital components. Bob Weir of the Grateful Dead talks about that in a recent interview when comparing Digital and analog. You can find that interview on YouTube.

    Analog is still King as long as you find the original first pressings in good shape. Digital transferred to vinyl sounds terrible.

    1. I’m currently using a Musical Fidelity – ‘M6i’ dual mono stereo integrated.
      Rotary gain control & input switches…that’s it.
      An absolutely stunning piece of kit…everyone says so 🙂

        1. I had the Harbeths from 1993 to 1999, when I had the DENON monoblocs…what seems like a lifetime ago now.
          Google: KRIX – ‘Harmonix Mk2’ (Australian made floorstanders) & check out the test results, etc.

            1. I know that it’s only a small part of the story, but since they are made here locally you’ve virtually no chance of listening to them, so the KRIX website (pretty pictures) & measurements & test figures is all that I got for ya…but only if you’re interested. 🙂

              1. I’m pretty happy with what I have now. But as audiophiles we always want something else to compare to what we have. Sometimes I look at a speaker and read the reviews and I say I got to hear those. It’s not always possible so I rarely do hear them. I just file them in my head and when I find a great deal on the used market I just buy them. Rarely am I disappointed and if I strike out I can get my money back reselling them. Pay full price its hard to get your money back. There are some good values in used audio.

              2. I’m a fan of sealed speakers. I don’t hate reflex designs and generally the order I put them is transmission line, passive radiator, and ported. But it doesn’t me I cannot like a ported over a transmission line. It depends on the speaker. My first choice has always been sealed speakers even if efficiency is a trade off.

                1. I know, you mentioned that you’re a sealed box man before.
                  I can plug the ports on the KRIX’s but I lose too much of the deep bass for Rock ‘n Roll.
                  There have always been 5 Harbeth models & 4 of the 5 are ported.
                  You still have your NHT 2.9 floorstanders don’t you?
                  How’s the foam surround on your bass drivers?

                  1. Yes I still have the 2.9 speakers. Would like to upgrade to the 3.3 someday to get that last whollop of bass. No subwoofers needed. The 2.9 and 3.3 are very close in sound character and use the same drivers except for the side firing subwoofer in the 3.3 is 12″ in a deeper and slightly taller cabinet versus the 10″ in the 2.9. The tweeters are aluminum. I don’t have to worry about foam deterioration since all of the drivers use butyl rubber. I love the 2.9 and they are only 75 pounds versus the 123 pound 3.3. But still I want the 3.3 someday. I will probably keep both sets or give my son the 2.9. As for the bass I will put my 2.9 up against any reflex system. You don’t lose the low end but the efficiency is only 87db. That has no effect on how loud they will play if you have the power. Your amplifier will run out of power before the speakers do. And the midrange on them is gorgeous.

                    1. My old Celestion – ‘Ditton 66 Studio Monitors’, that I had for 38 years, were also a sweet & very detailed legendary loudspeaker.
                      I had 4 of them (2 pairs) that I bought in March 1981 & sold in December 2018, something that I regret but because of parts unavailability & resale value (high) I decided to get my money back on them & move on (both pairs sold within 3 days of being advertised).
                      They had one of the best designed & manufactured 2.25 inch dome midrange drivers ever made.

                      https://www.youtube.com/watch?v=0S9MAszBieU

  7. I had vintage Mac MC2205 amp and plugged CD player directly into it. Man did it amplify to loud levels. I now added the C2500 preamp which I presume is the better way to condition the low level cd source. Is my thinking correct? The sound quality is much better with preamp.

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