Mods for AC15?

Discussion in 'Amp Central Station' started by AJBaker, Mar 24, 2021.

  1. AJBaker

    AJBaker Friend of Leo's

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    I've found the Vox AC15 to be a fine gigging amp for a wide range of applications.
    I've read about various mods that people have done over the years, but I've only ever done a single one: remove the bright caps.
    The tubes have been replaced over the years (JJs), but everything else is stock. I've toyed with the idea of changing the speaker, but the greenback sounds just fine.

    I'm curious to hear what others have done (or not done) to get the most out of this amp.

    What has worked for you? Here are a few I've heard about:


    - Cut bright caps: the only mod I've done, and it made the amp much better. A few quick snips to remove three caps and it's done. This removed some unpleasant highs that made this amp hard to dial in. Now it sounds good almost all the time.


    - Add a bright switch: A mod I've thought about. Like on a BF Fender, it could be nice to have a switch to add the bright cap back in sometimes. This would only be for the normal channel, as the top boost doesn't need any more treble.


    - Replace reverb tank: I know that many have done this, but what's the difference? I find the stock reverb sounds ok, but I haven't compared it to anything else.


    - Change speaker: The famous and pricy Blue is a classic, but there are other nice alnico options by Celestion and other makers, as well as other ceramic options. I've found the old stock Greenback to work nicely, and also have a great clean tone, but again, I haven't tried anything else.


    - Different tubes: some have put in a lower gain tube for V1. I tried it once, but I don't remember a big difference.


    - Add a switch to jumper the channels internally. Do the same thing as you can do with a 4 input AC30 and a patch cable


    - New cab: find a plywood cab that can shave some weight off the obscenely heavy AC15 (that weight being the only real disadvantage)


    - Extra handles: two extra handles on either side (like an AC30) for the looks, and for carrying it two handed (that weight!).
     
  2. AJBaker

    AJBaker Friend of Leo's

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    Anyone try out any mods they're particularly fond of? Or something that's fine as is?
     
  3. maj34

    maj34 Tele-Holic

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    Reverb tank replacement was a great mod when I had mine. It wasn't perfect, but a lot better.

    I thought about adding the switch to merge the channels... That'd be cool I think. I used an aby though and that way it was foot switchable.

    I never clipped the bright caps. I tend to like bright.

    I did think about weight reduction. Building a new cab seemed to be the only option, but I ended up concluding that the effort was not worth the few pounds lost.

    Love that amp. Have an ac4hw1 now that scratches the itch, but I liked the ac15c1 more.

    I really liked EHX power tubes in it.
     
  4. maj34

    maj34 Tele-Holic

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    Switching the bright cap out for a same value silver mica cap might be worth a shot as well. Mica caps are often used for this application and I'm guessing stock might be ceramic.

    Usually I'm in the camp of "capacitor type doesn't matter, only value" and have tested this a lot in guitars... But I'm open to the idea that mica might make a difference in a treble bleed application.
     
  5. DADGAD

    DADGAD Friend of Leo's

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    My AC15C1 was made in 2013 and has an Accutronics/Belton reverb tank. The only mod I did to mine was to replace all the Chinese tubes with better tubes and replaced the Chinese Greenback Celestion with an alnico speaker. I did not cut any capacitors and it sounds... glorious.

    V1 - 5751
    V2 - 7025
    V3 - 12AT7
    V4, V5 - RCA 6BQ5A
    Spkr - 8 Ohm, Jensen P12R copy
     
  6. Marc Morfei

    Marc Morfei Friend of Leo's Silver Supporter

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    I had an AC15. Awesome mod: white knobs. What a difference. The black knobs on a black background were impossible to see. Made the whole amp sound better. ;)
     
  7. AJBaker

    AJBaker Friend of Leo's

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    I like the way you think! That mod had not crossed my mind!
     
  8. AJBaker

    AJBaker Friend of Leo's

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    Makes sense in theory. On a guitar, the frequencies that go through the cap go to ground and aren't heard. With a bright cap, the frequencies that go through the cap go into the signal chain (and louder than the other frequencies!)
     
  9. Marc Morfei

    Marc Morfei Friend of Leo's Silver Supporter

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    Here is the before and after. Best $10 I ever spent.

    IMG_6039.JPG IMG_6234.JPG
     
  10. maj34

    maj34 Tele-Holic

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    FYI The reverb tank I used was a MOD 8EB2C1B Medium decay.

    If the original tank was "way too much" the MOD tank was "a bit too little". It was still a good upgrade, but if I had an AC15C1 again I would think about modding the reverb driver circuit to increase the gain for the MOD tank.
     
  11. AJBaker

    AJBaker Friend of Leo's

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    Interesting. I never put much thought into reverb, despite always using it.
    I just add a bit to make it sound better, and turn it down if it feels like too much.

    Was the trouble with the stock reverb that it was too much? Too cavernous sounding?
     
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  12. KC

    KC Friend of Leo's

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    The only thing I ever did to mine was replace the tank with IIRC the MOD 8EB2C1B referenced above. Huge difference to my ear. That wide-open washy sound of the stock tank tended to get lost in the mix. New tank made it much more usable especially on stage.

    I did swap out the greenback for a Gold I had lying around. Then swapped it back. The Gold was louder and brighter and if I was only using it for a gig amp it would have stayed, probably (I found that I could push the amp all the way to the limits on a bigger show). But around the house it was too much.
     
  13. maj34

    maj34 Tele-Holic

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    It's been a few years since I had it, but yeah, I think cavernous... Dunno, there was just a quality to it I found overbearing or something. Notes would get lost in it. The only way I liked it was 9AM max.

    With the mod tank I found it to be a more usable range and the quality of it was also improved, but somehow the quality was now... Weaker, if that makes sense, but now I'm thinking if I went in and messed with the driver circuit I bet I could get it even closer. That said, for $40 or whatever I paid for the tank I'd do it again if I rebuy the amp.


    Washed out... Another term I'd use. And I found my notes would get lost in the mix of it's own reverb.
     
  14. Dismalhead

    Dismalhead Poster Extraordinaire

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    I put an Accutronics reverb tank from a dead 90's Fender solid state in mine. Much better reverb now than the stock unit IMO.
     
  15. maj34

    maj34 Tele-Holic

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    Digital reverb?
     
  16. Dismalhead

    Dismalhead Poster Extraordinaire

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    No, it's an old spring reverb tank.
     
  17. Sax-son

    Sax-son Tele-Afflicted

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    I replaced all the tubes with JJ's and I found that the Greenback Celestion was breaking up a little soon for me and I swapped that out for a Weber Blue Dog 50 watt ceramic. I wanted a little more head room from what I was getting and that speaker did the trick for me. I put the greenback in a solid state Hughes and Kettner and that was a good match for it.
     
  18. ozcal

    ozcal Tele-Afflicted

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    changed reverb tank in mine... play it into a 65amps 2x12 cab with a cel blue and a g12h30... love it
     
  19. AJBaker

    AJBaker Friend of Leo's

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    That's pretty much how I also use the reverb: somewhere around 9 o'clock sounds best.
    Didn't think of it as a problem, since that's also more or less how I use the reverb on my SF Vibrolux.
     
  20. simond

    simond Tele-Holic

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    I had a little money to spend and thought time to get a grown up tube amp and decided AC15 was way to go. In the shop they had a choice. AC15C1 vs AC15C1VB. The VB - Vintage Black - is a C1 with black grill cloth, JJ tubes and Celestion Creme back 65 watt speaker. It sounded a bit better a-b-ing in the shop with my guitar. Richer in harmonic content and worth the extra $$$$ to my ear, and I had the money to spend. (By the way not a particularly cheap item in this far flung corner of the world.) However I did find, as others have mentioned earlier, that the long delay stock reverb tank was too much too soon so I have swapped it out for what looked like an almost identical MOD tank (as recommended by the interwebs) with medium delay which improves the delay/mud ratio no end.
    I mainly go for clean. Sometimes I run it though my old Boss ME20 multieffects. This has two outputs so I can run two cords and get normal and top boost working together. Happy camper.
     
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