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AC4TV - No Bass?

Discussion in 'Amp Central Station' started by markw51, Feb 1, 2012.

  1. markw51

    markw51 Tele-Afflicted

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    Just plugged my AC4TV MINI, (which I think is the same amp as the other versions,) into a cab and there seems to be no bass at all. Very trebley sounding.

    Is that typical of low power tube amps or just this one?
     
  2. teleamp

    teleamp Friend of Leo's

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    Vox AC = very trebly, do you have any other cabinets to try it through.
     
  3. markw51

    markw51 Tele-Afflicted

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    Yes and its the same trebly sound. So that's a signature sound of Vox AC?
     
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  5. teleamp

    teleamp Friend of Leo's

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    Where do you have the volume at on the amp? What type guitar and pickups? What volume do you have the guitar set at?

    The amp will amplify the signal it receives... there is a chance it will be more "bassy" with a different guitar.

    What type of cab/speakers are you trying.

    Is yours the head, or combo, if combo, use it with the stock speaker... if you can't get a good tone for you, then I suggest trading the amp off.
     
  6. teleamp

    teleamp Friend of Leo's

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    To someone that has played big amps with big sound, they may never be happy with a low wattage amp, it's not that they don't have as much bass, it's just not what you are use to hearing.
     
  7. markw51

    markw51 Tele-Afflicted

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    Looking at the schematic the capacitors in the first stage appear to be quite small in value so that may be where the brightness is coming from. Sounds fine through the small speaker in the combo but too bright on anything bigger IMO.

    I was using playing a very bright sounding Stratocaster but this is extremely bright.
     

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  8. Scotty 2

    Scotty 2 Tele-Holic

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    True,,the audiance will probably .:grin:never notice it
     
  9. Hiker

    Hiker Friend of Leo's

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    Considering it's a smaller practice amp, if you don't set your expectations too high, you'll enjoy the characteristics. I concur with the idea of trying a different guitar, and fiddling with the tone knob(s) on the guitar, and the amp's single tone knob.

    The Internet reviews stated that it likes pedals, and some users report that it sounds good through a 'bass' cab.
     
  10. teleamp

    teleamp Friend of Leo's

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    I don't know how to explain it, but it sounds as if your experiencing the Fletcher-Munson effect.
     
  11. theGecko71

    theGecko71 Tele-Holic

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    Mine with the 10" speaker has ok bass. I mean, I can't feel it in my chest or anything, but it sounds great.
     
  12. KellyCaster71

    KellyCaster71 Tele-Meister

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    I have the mini too. The bass seems ok to me through the stock speaker.
     
  13. markw51

    markw51 Tele-Afflicted

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    Found this on the Strat Talk Forum which addresses what I'm talking about:

    I'm modifying a couple of these for customers, and have a couple of suggestions for inexpensive mods.

    Usual disclaimers apply: even though this is a cute little amp, there are lethal voltages inside. Take it to a tech for modification, unless you're 100% certain of your skills and safety training.

    1. Lack of bass response:
    The AC4TV is pretty bass-shy, even when plugged into a larger cab. When the internal circuitry is choking off the low end, tube and speaker swaps can only have a limited effect. Improving the bass response increases the clean headroom slightly, reduces the boxy effect from the combo cabinet, and generally makes the amp sound more "grown up". I consider it a must-have mod, even before upgrading the OEM tubes.

    Cap C5 is unusually small, at 4.7nF. Upping it to 22nF (use 400v SOZO Mustard.) opens up the low end nicely, without spoiling the trademark Vox chime. C5 is just to the right of the volume control, and a 400 volt Sozo mustard cap fits nicely, stood on end. Parts cost is only a couple of bucks.

    22nF is a median value. It improves the bass without affecting the distortion very much. Crunch fans might prefer a 10nF. People looking for warmer clean tones can take it a step further by sticking with 22nf, but also upping C6 to 47nF. However, modding both caps will take the distortion out of Vox territory- the resulting woody, fat breakup sounds more like a tweed Champ.

    2. Odd tone control behaviour:
    This one is more a matter of taste than a "must-have". Various components in this amp are voiced fairly bright, for that chimey, Vox tone. However, the tone control goes too far IMO. Cap C4 is much smaller than normal, voicing the tone control so high that it barely affects the midrange. At low volume with dark-sounding humbuckers, it can be difficult to tell if it's working at all.

    Increasing C4 to 470pF will improve the range of the tone control. Simple mod, and once again, parts cost is minimal.

    Even with professional installation, both modifications should cost well under $100. The overall tone is still very much Vox, and neither mod has much effect on gain staging, so the way the amp responds to volume and dynamics is largely unchanged. These mods form a good foundation for further changes, but I suspect that a lot of users will be perfectly happy with the amp as-is, once they hear an AC4TV with this setup.

    The good news is that there is still more improvement available from speaker and tube swaps...
     
  14. markw51

    markw51 Tele-Afflicted

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    Plug it into something else and tell me what you think.
     
  15. jjkrause84

    jjkrause84 Poster Extraordinaire

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    Thanks for that mod list...seems pretty cool!
     
  16. jefrs

    jefrs Doctor of Teleocity

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    No.

    The AC4 is quite different to the AC15 is quite different to the AC30.

    The common characteristic is no negative feedback, otherwise they are very different amp circuits. The AC30 is not a 30W version of the AC15 (although it started out as two AC15 in one box :) This no-NFB gives richer harmonics and a characteristic mid-range, definitely not hi-fi. A number of British amps went this way.

    The AC30 is the one that got the Top Boost (TB), it can give it a breaking-glass quality but it does not lack bass. The AC15 was always intended as a stage amp, the AC4 as a little practice amp. Part of the AC4 problem is lack of grunt, at higher volume we need far less bass boost (it's our hearing). It is a perennial problem of small amps, the better ones don't suffer it - they are voiced correctly.

    One thing that may be important is the speaker. An ext cab is generally designed to be played loud and not voiced to bottom-end at low volume. A trebly little amp may benefit from a woofy speaker like the Greenback, which is unusual in that it is rich and plummy at low volume but tightens up and has a clear top-end at high volume. Makers generally fit a cheapish high-volume sound-reinforcement stage speaker, which sound great at stage volume but have little bottom-end at low volume.
     
  17. tacomamc

    tacomamc Tele-Afflicted

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    I have no problems with my ac4tv 8... especially after I built a pine cabinet with slightly larger dimensions... plenty of bass response to me.
     
  18. Jaybird

    Jaybird Tele-Meister

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    I once had a ACTV4 and found it too bright. A word of caution if you decide to change caps or any other component. The PCB trace is extremely thin and can be burned out very easily. My advice...sell it and get something else.
     
  19. Phil_tre

    Phil_tre Tele-Holic

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    Mark,

    can I use "Orange Drop Sprague" cap instead of Sozo ?
    I plan to replace C5 and I already have a couple
    of Orange drop caps... I know someone suggest
    agains tantalum caps for audio signal ???

    Phil.
     
  20. jefrs

    jefrs Doctor of Teleocity

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    Orange Drop are just radial polyester
    - from 15p each e.g. http://www.cricklewoodelectronics.com/Cricklewood/home.php?cat=150

    Tantalum are generally used to replace small electrolytic e.g. on the cathode, but watch the voltage - they tend to be low voltage rated. About 30p ea e.g. http://www.cricklewoodelectronics.com/Cricklewood/home.php?cat=171

    The only differences in frequency response between capacitor types occur at radio frequency esp micro-wave. However some types like ceramic and paper are notoriously unstable and should only be used where their actual value does not matter e.g. DC-blocking.
     
  21. Phil_tre

    Phil_tre Tele-Holic

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