How broken is my NAD Vox AC4 ?

Discussion in 'Glowing Bottle Tube Amp Forum' started by Mike_LA, Sep 21, 2021.

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  1. Mike_LA

    Mike_LA Tele-Afflicted

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    Greetings Gang,

    Well, I didn't need this amp but I've always wanted a Vox AC4C1.

    I have an AC4TVH but that has an attenuator and the AC4C1 has a master volume, which I find more useful. After watching CL for a while, I found one for $200

    However; when I was testing it I noticed the the treble pot cuts the bass and thins out the amp so I have to run it, bass at 8 treble at 2. It was a good deal so I snagged it hoping it is an easy fix.

    Am I imagining things?
    Is it more of a bass cut instead of adding treble?

    CVC Tele Neck Pup
    Vol and tone on 10
    The amp knobs
    Gain Bass Treble Volume
     
  2. Mexitele Blues

    Mexitele Blues Tele-Afflicted

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    I don't know about the AC4 specifically, but the AC15 and AC10 tone controls are interactive. As the treble is increased past noon, the less bass makes it through.

    I will guess your amp is working as designed.
     
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  3. The Angle

    The Angle Tele-Afflicted

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    I have no experience with the AC4, but I have played bigger Voxes. Vox tone controls are always weirdly interactive. Not like that, though. It sounds as if the treble pot is dumping signal to ground as it's turned up, which is the opposite of what it should do. That strikes me as something being wired wrong.
     
  4. Mike_LA

    Mike_LA Tele-Afflicted

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    I looked inside and it looks unmolested, the tubes still have shrink-wrap holding the tips in the cages. Perhaps a bad pot then? I always suspect a cap going out since they seem to fail the most but a bad pot would be a possibility.

    I will attempt to put a meter on it.


    20210921_130203.jpg
    20210921_125838.jpg
     
    Last edited: Sep 21, 2021
  5. MuddyWolf

    MuddyWolf Tele-Holic

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    In your video the tone controls straight up sounded pretty good. You may find that you get the amp "fixed" but now the amp doesn't sound as good. Dont get compulsive and mess with the amp if it sounds good. I made that mistake many years ago and screwed up an amazing sounding amp.
     
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  6. The Angle

    The Angle Tele-Afflicted

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    There's an AC4 section in the Owner's Clubs forum. Someone there might be able to compare your experience with how their amp behaves.
     
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  7. Mike_LA

    Mike_LA Tele-Afflicted

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    Yup, going to wait for someone who owns one to comment before I do anything....
    I know they're out there . . .
     
  8. dan40

    dan40 Friend of Leo's

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  9. Dukex

    Dukex Tele-Afflicted

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    I used to have one and liked it a lot. The tone controls are interactive (so are the gain/volume controls). I wouldn't mess with the circuit but instead just start twisting the four knobs.

    I'd also start with my guitar tone at 5 not 10.
     
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  10. Mike_LA

    Mike_LA Tele-Afflicted

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  11. Mike_LA

    Mike_LA Tele-Afflicted

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    Ha ha I'm a marshall guy, everything
    at 11
     
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  12. MuddyWolf

    MuddyWolf Tele-Holic

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    On old Marshalls I agree. Every knob full up. On Fenders...no. More like every knob on 5. They sound great like that. They sound flabby and or ice picky with the knobs on 10. Voxes....IDK, somewhere in between.
     
    Last edited: Sep 21, 2021
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  13. Mike_LA

    Mike_LA Tele-Afflicted

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    Yup, as long as it's not broken I can work with it fine.

    Just never had an amp react like this, the AC4TVH only has 1 tone knob so I can't compare
     
  14. Mike_LA

    Mike_LA Tele-Afflicted

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    Come on TDPRI . . . . . . .

    Rollin the dice again . . .

    Someone out there haaaas to own an AC4 and can tell me if theirs sounds like mine . . .

    :D
     
  15. gusfinley

    gusfinley Tele-Afflicted

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    Remember that this a "top boost" channel, so don't expect gut-thumping bass out of it - especially with a tele!

    Oddly enough, The second C in the AC4C1 stands for custom - meaning a less interactive top boost circuit. On a "classic" top boost channel if you crank the treble and bass controls you get a severe mid-cut. I have helped a few people mod their AC4C1s back to "classic" specs.

    Also, there is a bright cap on the gain control, so if you want more bass you need to turn up the gain and perhaps use you volume on the guitar - or find a good balance.

    I like my top boost channel with the following settings: Gain/Volume = 6 o'clock, Treble = 2-3 o'clock and Bass = 10 o'clock.

    Also, keep in mind that the volume control also has a bright cap on it. Many have removed this cap to get a more consistent sound at the full volume range. So the amp will sound thinner with the master volume down. Many AC4C1s have been unappreciated due to the Master Volume Bright cap.

    I helps to know how you amp works in order to use it correctly.
     
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  16. voskarp

    voskarp Tele-Holic

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    In a (OK, modern custom) Top Boost circuit the tone controls should be kept around noon for a "normal" sound. I always kept the Bass at 11 o'clock and Treble at 1 on my AC4, until I rebuilt it as a non Top Boost.
     
    Last edited: Sep 24, 2021
  17. voskarp

    voskarp Tele-Holic

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    I have that exact one (the blue with a 10" speaker), but I rebuilt it. The tone controls worked as you describe them, that's partly why I rebuilt it, and keep modifying it.

    Not to hijack the thread, but my current rebuild (and it has a preamp inspired by the AC4TV, which is "top boost sounding" and AC30 + my own weird ideas) will look like this:

    •VOPAC4v.3.1.png

    Just as an example of what you can do if you wanna go crazy on the thing. I ripped out the original circuit as it was, and only used the transformers, cab and speaker, so it can easily reversed if desired.
     
    Last edited: Sep 24, 2021
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  18. Mike_LA

    Mike_LA Tele-Afflicted

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    Thanks for that.
    I have enough amps that I can work with it and don't need to mod it.
    Just knowing it's right is all I need.
    Thnx again
     
  19. nathan5782

    nathan5782 Tele-Meister

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    I had one last year for a few months and didn’t care for how it sounded on my Nashville telecaster. I had picked it up in a trade with some other gear and that’s how it left.
     
  20. Mad Kiwi

    Mad Kiwi Friend of Leo's

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    I haven't listened to your clip yet, as it's early here but I have been playing with my AC4C1-12 a bit lately. The tone controls are very interactive as most Vox amps are. I use an ACc30 CCH a lot so am used to this.

    A Marshall it is not. the AC4c1 is weird in that the volume is best used as the secondary knob, while you use the gain knob as the main knob. Full or high volume with mid or less gain sounds pretty crappy usually. Set the gain to taste and as you increase Gain in particular but also volume to suit, the bass and sound comes back. This is why most amp demos of it sound bad as they are always volume-centric.

    Vox AC amps do weird things to the mids by adjusting the tone and bass controls. My bet is that yours is not faulty, it will just take a bit to get used to.

    Another thing to note is that Vox amps, especially in the crunch to gain levels always sound harsh in a standalone / bedroom environment. This is what is usually called the "chime" when played in a band or the "mix". Many many times people come here and say how terrible their Vox amp sounds without understanding or appreciating that harshness is exactly what cuts through in a mix and provides the chime they are known for. My guess is that if you stood a few feet away from REM, Mike Campbell, or the Beatles Amps while being played, they would sound exactly the same (harsh, bright) before the mixing desk, ribbon mic, etc.

    Admittedly it's a hard balance to achieve in a standalone situation but it is what it is. Having just bought an SV20 a few months ago, I think it's a bit like a real Plexi IMO.
     
    Last edited: Sep 24, 2021
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