My version of the AC15

Discussion in 'Shock Brother's DIY Amps' started by voskarp, Nov 21, 2021.

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  1. voskarp

    voskarp Tele-Holic

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    •VOP.AC15.png

    I'm about to build an AC15, and this is the schematic I've come up with.

    My sources has mainly been the original 60's VOX AC15 and the later hand wired reissue.


    •AC15.jpg



    •VOXAC15HW.png



    My version is closest to the HW one, but I have thrown in a AC30/6 normal-channel, a channel jumper switch, a high gain switch cascading the "normal"-channel into the EF86; and my modification of the "Brilliance" switch to a potentiometer (which I call the Bass Cut).

    The Top Boost channel is purposely made to be out of phase with the "normal"-channel, so that you can combine them to get a blackfaceish sound that the original AC30 with Top Boost could get.



    I am now working on a layout, incorporating the latest research into parts placement and grounding! ;)

    It will be in a combo cabinet with one 12" speaker; so I've done some research on how to keep the EF86 from getting too microphonic, and I've also got the Tung Sol reissue EF86 (which should be better than the Electro Harmonix I used in my AC4).



    I'm also not quite sure what speaker to use, the AlNiCo Blue is of course the best, but a bit too pricy in my opinion (if you not just have to get the right sound).

    The Celestion V-type and the G12H Anniversary are the ones that I've thought about to get reasonably close to a vintage sound. Any suggestions?
     
  2. kLyon

    kLyon Tele-Holic Platinum Supporter

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    My only suggestion: make it out of lighter wood than Vox does.
    (And then make me one:))
     
  3. 2L man

    2L man Tele-Holic

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    I would use a Star grounding when there are that many parallel pre amp stages.

    Blackbird 40 is very good sounding speaker when amp has max 20W. It is cheaper, lighter bit sweeter than Blue and sound close to Gold but without schrilling sounds Gold sometimes produce.

    I follow your build journey with high intrest because I have not built true AC yet. I had AC30 already 40 years ago and I miss its sound but not its weight and loudness :)
     
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  4. 2L man

    2L man Tele-Holic

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    That third schematic has a "ground loop breaker circuit" drawn below power transformer.
     
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  5. voskarp

    voskarp Tele-Holic

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    I think the newer cabinets are made of MDF, it is heavy...
     
  6. voskarp

    voskarp Tele-Holic

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    Speaker-wise I'm now thinking about the Celestion G12H 70th Anniversary Special Edition or Vintage 30 (at about half the price of an AlNiCo Blue). Any thoughts on that?

    I thought that the Blackbird really was a good sounding speaker, but better suited for a Fender style amp.

    The Weber ceramic Blue Dog is hard to come by here, and it's almost at €200, so two thirds to the price of an AlNiCo Blue... So if you've gone that distance, better go all the way.
     
    Last edited: Nov 23, 2021
  7. Dacious

    Dacious Doctor of Teleocity

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    The G12H is a good choice. It's open and quite efficient. A bit smoother than a Greenback. I wouldnt go V30. Bit spikey for a treblish Topboost circuit. A Greenback actually works quite well.
     
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  8. voskarp

    voskarp Tele-Holic

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    I find that the G12H Anniversary Special Edition frequency response curve (dark gray) is quite similar to the AlNiCo Blue (red). The V30 (white) is more different in the high mids and treble.

    CelestionB.A.V..jpg
     
    Last edited: Nov 23, 2021
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  9. 2L man

    2L man Tele-Holic

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    BB40 does B May kind sound at least as well as Blue and sound great with EL84 tubes. For vintage Fender sound I like Jensen Vintages more but BB is great with 6L6 amps too. There are four Blackbird 40 youtubes worth searching but to find one you need to use also word Toob and there it is against Tornado 100. I think BB40 has potential to become a classico and it could have been painted using sexier color and there Italians failed now :)
     
  10. Orpheum

    Orpheum TDPRI Member

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    I might as well get started in the making of a guitar, acoustic or electric, as the realization of an amp paralyzes me ...
     
  11. voskarp

    voskarp Tele-Holic

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    Went with the AlNiCo Blue anyway... I don't know if it sounds twice as good, and I'm quite sure I would have been satisfied with the G12H 70thA.S.E., but what the heck... The Blue sounds sooooo sweet!

    All parts are now ordered...

    Now back to get the layout finished! (Any day now...:rolleyes:)
     
    Last edited: Nov 24, 2021
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  12. andrewRneumann

    andrewRneumann Tele-Afflicted

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    I think you will need a 100n (if blocking distortion is a problem, might have to be reduced) cap here between V4B grid and ground.

    0E4A43C8-E7E5-4091-B203-58EFF772AB1F.jpeg
     
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  13. voskarp

    voskarp Tele-Holic

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    I see now that it's in the HW schematic (R14), but it goes to the ch1 volume wiper.

    Namnlöst.png

    I thought it just had something to do with the "brilliance" switch thing, as it is not in the original schematic.

    What is the sign of blocking distortion (more than distortion in general)?
     
    Last edited: Nov 24, 2021
  14. voskarp

    voskarp Tele-Holic

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    OK, now I see it in the original schematic, but it goes to the wiper of the trem./vibrato channel.

    Looking at some Fender schematics I see its everywhere where there's a long tailed pair P. I.
     
  15. andrewRneumann

    andrewRneumann Tele-Afflicted

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    I suppose you could couple the J3 valves to that grid via a coupling cap. That would be similar to how the originals mixed the two signals.

    But if you aren’t mixing two signals with the LTP, then the non-inverting side (right side) needs to have steady DC bias voltage on its grid. It should have 0 AC voltage—thus the need for a coupling cap to ground.
     
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  16. voskarp

    voskarp Tele-Holic

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    It's in the Tweed Bassman and the Deluxe Reverb

    TweedBassman.png

    DeluxeReverb.png
     
    Last edited: Nov 24, 2021
  17. voskarp

    voskarp Tele-Holic

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    OK, that sounds right.

    Now I have read a bit about it, of course it's right! :)

    http://www.valvewizard.co.uk/acltp.html
     
    Last edited: Nov 24, 2021
  18. voskarp

    voskarp Tele-Holic

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    .1µF cap added from V4b grid to ground. Thanks for the help with that!

    Also added a 8,2Ohm 25W resistor from the speaker jack switch to ground.


    •VOP.AC15.png
     
    Last edited: Nov 24, 2021
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  19. David Barnett

    David Barnett Doctor of Teleocity Ad Free Member

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    Can I suggest that if you put the EF86 and the Normal channel on one side of the phase splitter, and the Top Boost channel on the other, you'll be able to combine any of them without cancellation.
     
  20. 2L man

    2L man Tele-Holic

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    Quite often on Vox type amps both phase inverter anode resistors are 100k but on majotity guitar amps other is 82k (R27 on yours) Obviously using different values power tubes drive signals come better balanced. Can anyone tell if slight unbalance is substantial for Voxy sound?
     
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