Vox AC4 based build

Discussion in 'Shock Brother's DIY Amps' started by tizianod, Jun 26, 2019.

  1. tizianod

    tizianod Tele-Meister Gold Supporter

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    Hi fellow tube amp tinkerers,

    I want to get to know English amps better from a technical point of view. I currently own a Vox AC30 handwired model and a couple of years ago I had a Vox AC4TV. I liked the amp, but it lacked some personality and the low end was too party… I know very subjective ;) I was getting into building my own amps, so I sold it to free up the budget. So what better than just building one instead! :)

    A while ago I bought "A Service Engineer's Guide to the Vox AC30 Valve Amplifier” by Stephen Grosvenor. It has listed all original schematics, resistor and capacitor values. I also did some research and found out that Andyfromdenver, a member of this forum, built one a couple of years ago. Here is the thread he started. I don’t know if he’s still active here? Anyhow, his findings and knowledge of fellow members is very useful for my build. So I want to give credit to them as well!

    Basically my initial thought is to start from the original schematic, but implement some modifications from the start such as a 10” speaker, a single input jack and a depth control. I want to keep the circuit as simple as possible, so I won’t go too wild with extra features. I also chose to remove the combined on/off tone pot and add a separate power switch.

    Besides the drawings from Andyfromdenver, I couldn’t find a layout for this amp. So I decided to draw one for myself. It’s the first time I draw a layout myself, so so keep in mind beginner's mistakes. The layout is far from perfect as well… I’ll upload a draft version of the layout with the original values for the components. Of course the values can still change, it’s just theoretical right now. Also I’m not sure if the depth pot is in the correct position like this. All insights and tips on this build are appreciated!

    At the moment I don’t know what the deadline will be for building this amp. I need to fine tune the layout and schematic, source parts for this project, I have no idea what type of chassis and cabinet I will use... So have some patience with me :)

    The hyperlink to the original schematic

    diagram.png
     
  2. tizianod

    tizianod Tele-Meister Gold Supporter

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    I was going through the layout yesterday and I noticed a couple of mistakes...
    C1 should be 0.1 µF and the numbering for the resistors isn't correct. Because I skipped the second input jack, I don't have R2 so I should update the numbering of all resistors in the layout as well. I'll upload an updated version soon.
     
  3. tizianod

    tizianod Tele-Meister Gold Supporter

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    Does somebody know a good schematic and layout builder? I know DIY Layout Creator, however the latest version doesn't seem to be compatible with the latest operating version of Apple.
     
  4. VintageSG

    VintageSG Friend of Leo's

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    Interesting looking project, should keep you busy for a while :)

    Tubeampdoctor, Musikding and Tubetown are a good source for parts, chassis etc if you can't find anything local.

    Keep us posted.
     
  5. Paul-T

    Paul-T Tele-Meister

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    I used Mouser and tube-town for a recent project, alongside local suppliers. But beware, Mouser add VAT to their UK prices after you've hit 'order' (which is essentially illegal), so factor that in.
     
  6. tvas22

    tvas22 TDPRI Member

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    You can run it on PlayOnMac (free software that lets you run windows programs) well enough - it's a little glitchy but it's not too bad
     
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  7. tizianod

    tizianod Tele-Meister Gold Supporter

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    thanks for the tip. I'm going to check that out. Meanwhile I had the chance to update the layout.
     

    Attached Files:

  8. tvas22

    tvas22 TDPRI Member

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    I’m going to be watching this closely, I have been hankering after something voxy for a while and was literally searching for an AC4 layout last week. Good luck with the build!
     
  9. tizianod

    tizianod Tele-Meister Gold Supporter

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    @tvas22 same here... I was doing some research, but couldn't find plenty of information online. Hopefully this thread will be qualitative enough for future builders! I know for sure I'm going to make lots of mistakes. But that's part of the process for me.
     
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  10. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Andyfromdenver had a falling out with some people here and is no longer active.

    Good luck with the build!
     
  11. tizianod

    tizianod Tele-Meister Gold Supporter

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    Oh that's sad to hear! Anyway his thread was a huge inspiration. I first need to service a Tremolux from '64 that I bought a couple of months ago. The previous tech didn't do a great job, so the amp is in need of new electrolytics and probably other components as well. I'll try to combine both project in one order.
     
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