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One Vox AC30 vs two Vox AC15s?

Discussion in 'Amp Central Station' started by AJBaker, Sep 6, 2020.

  1. AJBaker

    AJBaker Friend of Leo's

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    So the consensus seems to be that 2 AC15s won't have as much headroom as one AC30. I might eventually try to find an AC30 some day, because I'm still infatuated by the sound of my AC15. I've had it for over five years, and have done many gigs with it (even a few tiny one's where I actually sang through as well!) and it has never let me down. Even a SF Vibrolux or a 5e3 copy which I bought more recently haven't made the Vox redundant.
     
  2. ballynally2

    ballynally2 Tele-Holic

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    well, take both your ac15 AND your Vibrolux to the gig.
    Problem solved and a great combi.
    Point is, slightly different amps often offer a better sound than a bigger single one.
    You will get more juice out of a single ac15 and keep the sound upright with the 2 6L6 Vibrolux.
    You are better off imo than 2x ac15 or 1x ac30.
    Plus, the Vibrolux is not much bigger than an ac15.
    One ac30 is still a somewhat heavy package.
     
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  3. AJBaker

    AJBaker Friend of Leo's

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    You're definitely right about the size of the Vibrolux. Such a convenient package, I wish Vox made a 2x10 AC30 about that size.
     
  4. nathanteal

    nathanteal Tele-Holic

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    How about two AC30S1s?
     
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  5. ballynally2

    ballynally2 Tele-Holic

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    me too. There is really no need for a 2xel84 15w amp to be that heavy.The vibrolux is about 30w and few kilos lighter! Ive played but never owned ac30s. They are just a little too heavy for me as a pickup amp. The Vibrolux is at the ceiling for size/weight at 22kg.
    An ac15 is 24kg while an ac30 is 32kg. To me Twins and ac30s are just over my weight preference and you can never turn them up sufficiently nowadays hence the preference for DRs.
    I love Super amps but cant gig w them.idem w Bassmans. Great amps but they wont get played at optimum volume.
    At least the ac15 can be put at its sweet spot. I would still opt for a head and cab(s) if it was on offer.
    In fact i made my Vibroverb into a head and use 2 10" pine cabs. Lighter and better.
    Your 5E3 Deluxe is about the right size/weight.
     
    Last edited: Sep 7, 2020
  6. etype

    etype Tele-Afflicted

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    Certainly two AC15s would allow you to play louder and cleaner than one AC15. Maybe not as much as an AC30, but hard to know how much more you need. But I think pairing the AC15 with the Vibrolux (35w, 2x10") is maybe an even better option anyway and it costs you nothing!
     
  7. AJBaker

    AJBaker Friend of Leo's

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    I have two issues with that amp:

    1. I almost exclusively pay guitar through the normal channel, so a top boost only amp isn't going to work for me.

    2. I've discovered that I really like the sound of my vocals through the Vox (top boost channel) at small solo gigs. Therefore, I'd like to still have two channels.
     
  8. swervinbob

    swervinbob Tele-Afflicted

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    The big Helix either through a pa or with a frfr or power amp and cab of your choice. You have everything including a mic pre.
     
  9. printer2

    printer2 Poster Extraordinaire

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    On two 15W amps sounding as loud as a 30W amp with two identical speakers as the 15W amps? Yes the pair will sound as loud as the 30W. "Oh but the 30W will have more headroom (going to piss some off here)". Where is the headroom going to come from? Each EL84 can only put out so much power. They do not magically put out more power then there are four in a chassis than if there are two.

    Why does the 30 sound louder than the 15? First you have double the power, 3 dB. Next you have two speakers beside each other. If you had 1W going into one speaker and let us say it has a sensitivity of 100 dB at 1W then you get 100 dB out. You put two of the speakers side by side, split the 1W so each speaker gets 0.5W, you get 103 dB out. The two speakers together act as a single speaker and you get better acoustical coupling to the air. So the 30 has 3 dB more because of the doubled power of a 15, then you get an additional 3 dB because of the two speakers, so the 30 is 6 dB louder than a 15. That is why a stack of speakers is darn loud even with 1W. Every time you double the number of speakers you get 3 dB more sound pressure. As you get closer to the wavelength of the sound you do not gain as much.

    But to get the increase the speakers have to be fairly close to each other. If you widen them to get more of a stereo effect you do not get the additional 3 dB. But at least you can decide if you have the two amps. Stick them beside each other, or if you want spread them apart, or if you do not need as much sound leave one at home.
     
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  10. AJBaker

    AJBaker Friend of Leo's

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    Thanks for the detailed reply.

    I guess at the end a lot will come down to the physics of the tubes and the transformers. Are two pairs of tubes driving two small transformers equal in volume/headroom to 4 tubes driving a large transformer?
     
  11. printer2

    printer2 Poster Extraordinaire

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    And you are right about the tubes and transformer. The transformer has to be able to put out the current when called to. But really the limiting factor is usually the tubes. Sure the Tweed era amps sagged but they tried to get away with the minimum size of transformers then. The design of the 30 as compared to the 15 is no different other than they doubled the current capacity of the transformers.

    Classictone AC replacement

    30
    [email protected] = 152 VA (Volt x Amps)
    http://www.classictone.net/40-18050.pdf

    15
    [email protected] = 72 VA
    http://www.classictone.net/40-18079.pdf

    Hammond

    30
    [email protected] = 152
    https://www.amplifiedparts.com/sites/default/files/associated_files/p-t290nx.pdf

    15
    [email protected] = 72 VA
    https://www.amplifiedparts.com/sites/default/files/associated_files/p-t290cz_specification_sheet.pdf

    The 152 VA as compared to the 72 (2) = 144 VA is pretty close, 5% less VA in two AC15's as compared to a AC30.
     
  12. tubeswell

    tubeswell Friend of Leo's

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    This is an excellent point. 30W won't be 2 x as loud as 15W. It will only be 3dB louder. To be 2 x as loud as a 15W amp, the other amp would have to be 150W
     
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