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Vox Experts: adding a bit more "fatness" to an AC15HW

Discussion in 'Amp Central Station' started by JamesAM, Apr 21, 2021.

  1. JamesAM

    JamesAM Tele-Meister

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    Hi all,

    I'm looking to see if it's possible to modify the AC15 circuit to get a bit more of a thick matchless or even plexi sound out of it at higher volumes. The top boost channel has the right amount of gain, but doesn't have enough thump in the bass. The normal channel has the right amount of bass, but lacks the gain of the TB channel. Jumping the channels muddies up the low end too much with my ES-335. This amp is SO CLOSE to the sound I'm chasing in my head, but falls just a bit short.

    What are some ways to squeeze a bit more bass or gain out of this circuit? I know coupling cap value changes are one way, but has anyone tried anything else? I'd prefer easier changes as opposed to something like adding a pentode in the preamp, but I'm open to any ideas you might have. Or, is this a fools errand, and I should just build an 18 watt or a 6v6 plexi?
     
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  2. Whatizitman

    Whatizitman Friend of Leo's

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    The classic Plexi and Matchless sounds are typically from far larger amps. Bigger cabs and more speakers make a huge difference in low end response. The DC30 in particular is IMO one of the best sounding amps ever made, period. And a plexi through a proper 4x12 is.... well, a plexi through a proper 4x12.

    Not sure if the lack of EF86 also makes a difference, though. But it's typically considered a "high gain" tube circuit, though higher fidelity with less distortion. OTOH, how that translates to tone that hits your ears is based on far more factors than tube complement.

    EDIT: Also, top boost is just that. A top boost. You can use the cut knob to fine tune things a bit. The tone cut is typically misunderstood in how it is supposed to work, BTW. Just sayin'.
     
    Last edited: Apr 21, 2021
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  3. DeepDangler

    DeepDangler Tele-Meister

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    Short answer: fool’s errand.

    I used to have one of those amps. It’s going to be locked into that old Vox sound because it’s running just one greenback speaker (or alnico depending on your model). You could try a higher output speaker like a Celestion Creamback or Redback.

    I would try every pedal on the market before modifying that circuit. Those amps sound excellent. If you really want it to sound like a Marshall, you should sell it and just get a Marshall.

    If you’re willing to play pedals instead of speakers, the Boss DS-1X and JHS Angry Charlie would be good pedals to look at for Marshall tones into the clean channel.
     
  4. Peegoo

    Peegoo Poster Extraordinaire

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    Modifying an amp into something else (beyond the tinkering/hobby aspects) is a waste of money.

    An amp circuit is designed to generate sound a certain way. All the components chosen by the designer contribute to this.

    Think about it this way: "I'd like my Dodge truck to feel more like a Ford truck."

    Get a Ford.

    If you like the amp other than the lack of thump, run it through a closed-back cabinet. That will get you most--or all--of the way there.
     
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  5. sax4blues

    sax4blues Friend of Leo's

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    I played AC15C1 for many years. For me the top boost needed the controls significantly adjusted as volume changed. At higher volume and gain I would have T way down, B 12, and adjust Cut. This made more mid/low mid focus.

    There is a reason C30 and the like exist. I sold the Vox for Dr Z ZWreck Jr and it does the low mid thing like the Vox never could. Flip side,... it doesn’t do Vox.
     
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  6. Chandlerman

    Chandlerman Tele-Meister

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    A TC Electronic Mimiq pedal provides multi-tracking which might give you the extra little bit of thickness you seek.
     
  7. Marc Morfei

    Marc Morfei Friend of Leo's Silver Supporter

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    Timmy pedal.
    Tone cut knob.
     
  8. JamesAM

    JamesAM Tele-Meister

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    Thanks! that's what i was worried about. I've got a naga viper that sounds awesome on the normal channel, and is probably as close as I'm going to get, but I'd prefer a non-pedal solution if at all possible.

    I definitely agree: the amp does sound glorious. It just isn't quite the gloriousness I'm after - i was hoping that there was a non-pedal way to fix it from within the circuit, but I don't think there is.
     
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  9. JamesAM

    JamesAM Tele-Meister

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    yeah, the tone cut only takes away treble, it doesnt add bass. The naga viper I've been using sounds good, but only on the normal channel - it just shifts the frequency hump of the boost, so it doesn't really tighten up the bass of the top boost channel.

    I guess an EQ pedal might get me to where I need to be, and I guess it's cheap enough to try.
     
  10. JamesAM

    JamesAM Tele-Meister

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    Thanks! yeah, I hear you on the cut knob. Unfortunately the way Denny designed it is kind of the opposite of what I'm after - I'm hoping to not only remove harshness from excessive treble, but also add some bass for fullness. Might just be time to go get the hoffman schematic for a 6v6 plexi and start sourcing components.
     
  11. gusfinley

    gusfinley Tele-Afflicted

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    What amp do you own (there are many HW series - date of manufacture would help)?

    What setting are you using?

    If you have a "classic" Top Boost circuit there is an interaction with the Bass control, where if you turn the bass all the way up it also turns the mids all the way down. Some Vox based circuits "fixed" this (like the new "Custom" series) but it is retained in most of the HW series amps. Ironically, if you turn the Bass down a bit, sometimes you can get more bass.
     
  12. JamesAM

    JamesAM Tele-Meister

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    Sure, it's the AC15HW1 with the greenback - not the heritage one from about 15 years ago (with an EF86).

    Settings with an ES-335:

    -Top Boost only: master defeated, channel volume 4 oclock, T/B in the "V for Vox" positions, with Bass at about 2:00 and Treble at about 10:00, cut has to be roughly at noon to reduce harshness. very high-mid heavy, but sounds good. lacks bass response.

    - Normal: volume dimed, bright switch on, master defeated, no cut. juuuuust short of the gain level I'm after, but the naga viper helps. Bass is a bit muddy, but naga viper helps.

    - Jumpered: I've tried all over the dial here, but i've found it best with treble up 100%, bass at about 3:00, cut at about 8:00, blend the channel volumes to get a good balance (roughly 100% top boost with about 3:30 normal). This gives the fullest, most bass heavy sound with reduced high mids and a bit more scoop. The bass is unfortunately muddy and not tight, but it's an ES-335 so I'm realistic in terms of what's possible.
     
  13. Dukex

    Dukex Tele-Afflicted

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    I'd buy an inexpensive seven band eq pedal and give that a try.
     
  14. gusfinley

    gusfinley Tele-Afflicted

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    I can't fault your settings. It looks like you are using the amp right.

    What tubes are you using in it? If they are the stock Chinese types, there are improvements to be made there.
     
  15. JamesAM

    JamesAM Tele-Meister

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    I hear ya, they’re all JJs. If you know of any that will give a bit more oomph, I’m open to trying them!
     
  16. KC

    KC Friend of Leo's

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    The best thing about the Timmy pedal is how much control it gives you over bass response. The Distortron has more of a Marshall flavor and also has a bass response switch.
     
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  17. DrBGood

    DrBGood Tele-Holic

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    Have you tried an external cab with more/bigger speakers ? I'm pretty sure a 2X12" closed cab would give you tons of oomph.
     
  18. DeepDangler

    DeepDangler Tele-Meister

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    Circuit mod would be risky and you’d take away from what the amp is anyways. A pedal solution that could help is going to involve 1 or 2 and some experimentation. To increase fatness on the amp, you may have to cut bass first. If you push a bass heavy sound to the amp, the bass frequencies clip and distort differently and get too loose sounding.

    Try running an Overdrive with a decent bass cut and mid hump like a Boss SD1 (like a clean boost with volume max and 25% drive) into the top boost channel. Run the overdrive trebly and use the bass and treble controls on the amp top boost channel to boost bass and cut treble. You want the amp to do the heavy lifting.

    If that’s still too loose, run a clean sound in the normal channel and use two pedals. Run a Boss SD1 on clean boost settings into a distortion pedal that can be bassy. Tell us what you find!
     
  19. Dacious

    Dacious Poster Extraordinaire

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    Can't add what's not there to start with. That design is what it is.
     
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  20. derekwarner

    derekwarner Tele-Meister

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    Sell the ~~335 & purchase an old Telecaster? ...........not as silly as it sounds ........

    Next step, throwing out the Chinese tubes & install Slovakian replacements into the VOX.......
    Next step, then you may want to consider selling the AC15 & purchasing a Boss Katana Artist
    Next step, then you may want to repurchase the ~~335 bask as a standby for the Tele

    Could be a near perfect scenario...the old ~~335, the old Tele & the new Katana Artist

    Derek
     
    Last edited: Apr 23, 2021
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