Aiken's Reactive Dummy Load.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by James Freeman, Apr 27, 2012.

  1. catalin gramada

    catalin gramada Member

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    you should try a Palmer:banana
     
  2. Blix

    Blix Supporting Member

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    Your point is?

    A Palmer Speaker simulator is meant to be used direct to a console, for FOH or recording.

    The Palmer PDI-03 popular in many rigs, have several line outs for slaving, feeding effects etc for a live rig, none of those have speaker simulation, only the filtered output.

    To make it clear, for slaving into a power amp and cab, you don't need or want speaker simulation.
     
  3. James Freeman

    James Freeman Member

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    [​IMG]

    Here is a taste from the pure Resistive dummy load with some nice IR.

    My clean channel never breaks up even on 10 Channel Volume, when master is on 1.
    Now the Master is on 10 and I play with the channel volumes on each channel from 0 to 10.
    So what you hear is pure power tube distortion when on clean channel.

    You can also hear what effect power tube distortion have on the gain channel, it makes it PHAT.
    This "Swishy" sound is only from the volume change and power tube distortion.

    When I say "Power Tube" it includes the Output transformer Phase Inverter and all the power amp chain.

    Enjoy.



    Don't forget its an Impulse Response so there is not Speaker breakup and no "Bouncy" properties of the Cabinet and room.

    P.S
    There is nothing Peavey nor Valveking about this amp (now).
    More like Fender with Marshall/Mesa/Bogner inside.
     
    Last edited: Apr 13, 2017
  4. catalin gramada

    catalin gramada Member

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  5. James Freeman

    James Freeman Member

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    Not the best demo but good enough to hear the power tubes and transformer melt into oblivion.

    Anyway catalin, if you build the attenuator include the Line-Out, its a great tool for Recording, Reamping, Monitoring.

    Also, from all the VST plugins I've tried nothing sounds as real as this.
     
  6. catalin gramada

    catalin gramada Member

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    I will do so, thanks for ideea.
     
  7. James Freeman

    James Freeman Member

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    They are big and they are HERE:

    [​IMG]


    The cap is Metal Film with endless ripple current (...well way above 5A).
    The 0.5mH inductor is an air core.
    The 20mH is a top notch laminated which behaves like an air core till 3kHz (exactly what we need for the resonance part).
    All of the above are High Quality Crossover parts from ERSE (or Parts-Express).

    Soon to come the complete build with actual impedance measurements of my 2x12 Vintage 30's cab and the reactive part of this dummy.

    I'm also going to post more info as to why tube amps behave differently into a reactive load compared to solid state.
    AND why attenuators on low settings make your amp sound "flat".

    Stay tuned....

    EDIT:
    And of course sound clips. :D
     
  8. TomOlsen1

    TomOlsen1 Member

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  9. James Freeman

    James Freeman Member

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    Framus 2x12 Vintage 30'S Impedance Curve:
    [​IMG]

    My Aikens Dummy Real Impeadance:
    [​IMG]

    Overlayed:
    [​IMG]

    Inside:
    [​IMG]

    Angled:
    [​IMG]


    First:
    It Sounds F*** AMAZING !!!

    Second:
    The inductors do not saturate (sine wave is perfectly shaped at full power).
    The Inductors and Capacitor do not get hot at all (They are rated for 300W+).
    The Resistive/Reactive switch is like Night/Day.

    The dummy resonance is a little lower (frequency and impedance) than the actual cab but the sound difference is minuscule to none.


    Third:
    Please read this great colorful article as to why SS sounds different than Tube and where the impedance of the speaker comes into the picture.
    http://www.lenardaudio.com/education/14_valve_amps_7.html

    In one picture this is the difference:
    [​IMG]

    In short: SS are Constant Voltage & Tubes are Constant Current.
    Tubes raise power with Impedance (speaker), SS is the other way around.
    So reamping with SS into a Guitar speaker will sound NOT FLAT... even worse, it will CUT frequencies the higher the impedance is.
    Now go read it, save me the wall of text and be smart.

    So for recording the Dummy is just PERFECT !
    but for reamping SS is close but no cigar.
    Unless you can find a Solid-State Constant Current Power Amplifier.
    They do exist but as kits.

    As for the conventional attenuator:
    The higher the attenuation is the less the amp sees the speaker and more the resistor.
    Higher attenuation = Flatter sound.


    Its late.
    Sound clips will appear tomorrow.
    :banana
     
  10. teemuk

    teemuk Member

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    Well... hate to break it to you but current feedback to acquire similar characteristics as a high output impedance tube amp was introduced already pretty much in the dawn of the transistor guitar amps. First amp I've seen using one dates back to 1966. Today current feedback is pretty much a standard in guitar amps.

    Read about it here (from the same site):
    http://www.lenardaudio.com/education/13_guitar_amps_3.html


    ...Anyway, it's all good. Congratulations for building a superb dummy load!
     
  11. catalin gramada

    catalin gramada Member

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    Nice build , congrats.
    Catalin
     
  12. James Freeman

    James Freeman Member

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    Few question:

    Is the typical Hi-Fi/PA SS Poweramp produces a flat line thanks to a very high Damping factor (even though its constant voltage driven)?
    Or does it produce these dips like in the small picture even though the high Damping?

    I wonder if the reactive dummy and the SS power amp cancel each other impedance curves leaving a flat line?
    Or the SS will actually amplify FLATLY what the reactive dummy puts out.

    I think I'm going to have to mod my Lepai 2020A+ SS Poweramp for constant current mode.

    Thanks for the support and interest.
     
  13. catalin gramada

    catalin gramada Member

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    one question please...
    which voltage you aplied into the load for your measurements ?
    Thanks
    Catalin
     
  14. James Freeman

    James Freeman Member

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    I used REW (Room EQ Wizard) with a test jig as suggested in the help file.
    I did NOT use a power amplifier.
    Headphones out to Dummy/2x12 (about 1VAC).

    EDIT:
    Sound clips soon to come.
    Also I can redo the impedance plots with higher output volume to see the difference.
     
    Last edited: May 24, 2012
  15. torquil

    torquil Member

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    Magnificent!! I will probably build one of those in the future, and your info will help a lot regarding parts selection.

    But I've long wanted to see also the full complex impedance vs frequency for that reactive load as well as for a real speaker. I.e. both real and imaginary parts. Or equivalently, the magnitude and phase angle. Do you also have such data, ilya-v?

    Correction: I have already simulated the complete impedance for such a dummy load, but would like to see the complete impedance for a guitar speaker. Here is the complex impedance for the Aiken dummy load:
    [​IMG]
     
  16. James Freeman

    James Freeman Member

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    The real deal:
    [​IMG]

    Also the real deal:
    [​IMG]


    You can see that the Real Cab is "pointier" and its Q factor is higher (thinner).
    Despite the Q, the sound (felling) of the dummy is 95% identical as to driving a real cab.

    Marshall did his homework with the Power Brake.
    The Power Brake has a higher resonant frequency around 120hz and a higher Q, just like in a real cab.
    You can play with the Inductors, Capacitor and Resistor values to mimic exactly the speaker impedance.

    Remember that aikens dummy emulates the speaker response in free air not in a cab.
    in free air the a typical Celestion speaker will look very close to what you see in the dummy curve about 35ohm at the resonance (8ohm speaker).
    I also don't know how volume affects the impedance curve (I have no intention to crank the Cab in the apartment for measurements).

    Here is what Redwirez Impedance Cureves IR's are doing to the sound:
    [​IMG]
    Pretty darn close to what we see with the Dummy.

    I would also love to see the impedance curve of the Aracom, Rock Crusher, Ultimate Attenuator, Power Brake etc... Reactive ones..
    Anyone up to it?


    Sound clips later today.
     
    Last edited: May 24, 2012
  17. reaiken

    reaiken Member

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    If you want higher Q and higher resonant peak closer to your V30 speaker, change the 33 ohm resistor to something around 50 ohms.

    If you want to move the resonant frequency closer to that of your speaker, change the inductor from 20mH to something around 8.2mH - 10mH.

    You could also lower the value of the 200uF capacitor to shift the frequency, but that will decrease the Q and widen the resonant peak. You can adjust the values of both L and C, along with the "de-Q-ing" parallel resistor to tailor the impedance curve to match any speaker you want.


    RA
     
  18. catalin gramada

    catalin gramada Member

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    Hi
    bassicaly the frequency of resonant peak will go up (depends of the volume) and also the impedance level will increase a little according with the Q of cabinet
    crank the cab man , it's in the name of science and how this stuff works...(joke)
    Thank man , many usefull infos here

    catalin

    question: which is the upper limit to rise the impedance , so safe to keep away from blowing up a standard cheap series OT transformer ?
     
    Last edited: May 24, 2012
  19. James Freeman

    James Freeman Member

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    EDIT:
    The firsts 2 clips didn't do it justice.

    Read next post.
     
    Last edited: May 25, 2012
  20. James Freeman

    James Freeman Member

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    This is a real & detailed comparison with audio notes.
    I have properly miked my amp with an SM57.



    You can definitely hear the difference between Reactive and Resistive.
    BUT the difference between Straight to Cab and Re-Amped (Reactive) is very small.

    Also the small Solid State Poweramp response is FLAT, so there is no contradictory effect of the SS on the Speaker (no cutting frequencies like I thought).
    Which means the reamped sound is Spot On.

    Ordered some resistors to closely match my cab and I'm done.


    Cranked amp in bedroom = SUCCESS !!!

    :banana
     
    Last edited: Apr 13, 2017
    Heph333 likes this.

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