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Homebrew attenuator?

Discussion in 'Shock Brother's DIY Amps' started by TelZilla, Mar 16, 2017.

  1. TelZilla

    TelZilla Friend of Leo's

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    So I've been looking at the Dr. Z Airbrake attenuators, and I find them intriguing, but really pricey.

    It's a tiny little thing, and I'm wondering what's going on inside there. Any schematics for that or other attenuators? Has anyone built one?
     
  2. Rambs83

    Rambs83 TDPRI Member

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  3. AAA71

    AAA71 Tele-Meister

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    I used a 100 watt L pad in a box. But truthfully I've given up on attenuators.
     
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  4. TelZilla

    TelZilla Friend of Leo's

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    Not sure I really need one, either, and I def don't need another project.

    Why have you given up on them?
     
  5. kleydejong

    kleydejong Tele-Holic

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    You didn't ask me, but I'll weigh in on my theory as to why attenuators can produce less than desirable results.

    When you crank up a tube amp into glorious distortion there is a series of things that happens. With most of the vintage style non-master volume amps the glorious distortion is produced by collectively pushing every stage in the signal path beyond its limits. To spell it out that means some combination of:

    1. Preamp distortion
    2. Phase inverter distortion
    3. Power amp distortion
    4. Output Transformer sag
    5. Speaker distortion
    6. Human ear compression
    7. Interaction of those sound waves bouncing around in the room and perhaps with the guitar / strings / pickups itself

    When you insert an attenuator you enter at about step 5. So while you get that tubes pushing, you can't capture the impact those remaining elements have on the experience of a cranked amp.

    Also, attenuators tend to come with changes to EQ. Combine that with fletcher munson (the reality that humans don't hear all frequencies evenly at all volume levels) and it is likely that your perfect cranked tone will become dark or brittle or just different.
     
  6. TelZilla

    TelZilla Friend of Leo's

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    All are welcome!

    I have to say, I've never used them much, except for one on a Toneking Royalist 45 at Chicago music Exchange- Glorious amp, but real spendy. My solution is usually just lower wattage. A cranked 5F1 never killed anybody.
     
  7. Tony Done

    Tony Done Friend of Leo's

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    You can make an L-pad attenuators from two resistors, there are plenty of resources, as noted by Rambs83. However, mine, designed for 12dB attenuation, turned out to be a tone killer, so I never use it. A bit more research suggested that putting a 0.1 to 0.5 microF cap across R1 might fix it, but I haven't tried it yet.
     
  8. kleydejong

    kleydejong Tele-Holic

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    Sure. And to be clear, I don't think attenuators are entirely worthless though. I have a Weber Mass that I actually is great for using as a DI for silent recording.



    One more thing to think about is the type of load you're using. Resistive loads use resistors and tend to be a little more flat. This is because a real speaker has a dynamic impedance - as I understand an interaction with the output transformer. So a reactive load is a more realistic way to mimic this.

    https://www.thegearpage.net/board/index.php?threads/aikens-reactive-dummy-load.1072793/
     
  9. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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  10. telemnemonics

    telemnemonics Telefied Ad Free Member

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    Wait for a cheap 4x12 to come up on CL for maybe $50, wrap it in heavy plastic, bury it in the back yard, run the cable into the house, and plug it in along with your regular cab.
    Mind your impedance.
    You'll only hear 1/5 of the watts, or 10w instead of 50w/ 4w instead of 20.
    Around 25% lower volume.
    Or just put a 4x12 in the basement under a pile of blankets.
    Think of all the 4x12 cabs saved from the landfill...

    Attenuate more than that and it sounds like crap.
     
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  11. ndcaster

    ndcaster Poster Extraordinaire

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    "homebrew attenuator"

    i.e. a wife
     
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  12. mRtINY

    mRtINY Friend of Leo's

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    Sometimes (like when you have a 5E3 and a semi-quiet gig) you need an attenuator so a NMV amp breaks up at the right loudness...
     
  13. mRtINY

    mRtINY Friend of Leo's

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  14. Guitarzan

    Guitarzan Poster Extraordinaire

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  15. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    Sometimes homebrewed attenuators accidentally produce very cool guitar tones. The tone on the first two Boston albums is a perfect example. Note that I said "cool", not "good". It's a groovy sound, and the Rockman (based on that tone) is also pretty groovy, but I think we can all agree that you wouldn't want to hear that sound for more than about 5 songs in a 24-hour period or you'd end up with PTSD.
     
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  16. telemnemonics

    telemnemonics Telefied Ad Free Member

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    If you look at some speaker response charts like Eminence publishes for every speaker model, you'll see interesting stuff like the fact that speaker impedance (measured as resistance, but not actually the same) changes with input frequency.
    For example an 8 ohm speaker offers the amp around 8 ohms of impedance in the frequency range between 200 and 500 hz, but pushes back with increasing impedance above and below that frequency range.
    It may go up to 100 ohms impedance at 100hz, and 16-20 ohms in the harmonics range.
    Additionally the changing speaker load (AKA impedance) sends signal back to the output transformer in varying ways depending on frequency, power level, and transients.

    The point being that a resistive load box will not interact with the amp the way a speaker does, and some amount of dynamics will be lost.
    More expensive ones might genuinely "sound" better though.
    Attenuators work best if you don't ask too much of them, as in don't try to get a cranked 12w 5e3 down to bedroom volume.
    Many prefer a good MV to a load box.
    And many also prefer an iso cab because it preserves the interaction between tubes, OT and speaker.
    Lugging an iso cab might not be attractive though, but choosing to use an amp at a volume range where it does not sound good is going to be some sort of compromise.
     
  17. M Fowler

    M Fowler TDPRI Member

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    I built my Trainwreck Airbrake years ago and it is a cheap and simple project. Marks Airbrake front.JPG Marks Airbrake inside.JPG
     
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