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TrueRTA SVT & Preamp analysis/results

Discussion in 'Amps and Cabs [BG]' started by johnk_10, May 3, 2010.


  1. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    i just ran some RTA tests today of my SVT using the TrueRTA program which allows up to 1/24th of an octave RTA testing of any preamp, amplifier or speaker cabinet. the results were kinda surprising.

    the amps/preamps that i tested in this run were my SVT-VR, my Universal Audio 6176, and my Avalon VT737SP preamp.

    the first graph is a test running pink noise into them and testing them directly from their preamp outputs. This first graph shows them at a 1/3rd octave so you can get an idea of how similar they actually are, with all of them set flat.
    (the SVT is the green line, the UA is the blue line, and the Avalon is the purple line):

    3rdoctave_SVT-Grn__UA-Blu__Ava-Purple.



    the next test was using the speaker output to see what happens when you place the SVT's power amp, and the Crown xti2000 (for the UA and Avalon) into the equation. This was done with a direct box with the 'speaker thru' patch and using the direct out, into the RTA program. (this time the SVT is Blue, the UA is green and the Avalon is turquoise):

    3rd_oct_SVT-Blu_UA-grn_Ava-Turq_with_load-1000.
    in this case, the SVT's results were, by far, the best, as you can see that the crown has as pronounced dip at around 80Hz, so after seeing that, i went into the crown's DSP software and gave the crown a 4.5 db bump at 80hz to try and flatten it out for the next test.


    The final test was to use a calibrated B&K 4006 with pink noise in front of my EL Whappo Jr. cabinet, running the TrueRTA at 1/24th of an octave. By looking at the graphs, although i love the sound of this cab, its obvious that it isn't anywhere near completely flat, but the SVT just sounds wonderful thru it (as do the others).

    here's the SVT (orange) as compared to the Avalon (green):

    cabinet_test_svt_orange_Avalon_green.
    as you can see, they are almost an exact match now!


    and here's the same test, only using the the UA 6176 instead of the Avalon. in this graph the SVT is orange and the UA 6176 is turquoise:

    cabinet_test_svt_orange_UA_blue-1000.

    keep in mind that these tests are just for frequency response only, and do not demonstrate the dynamics or 'feel' of playing thru the amps. even though the Avalon matches up a little better on the graph, the UA actually 'feels' more like the SVT with a bass plugged into it.

    what these tests also show is just how much a speaker cab (in this case, an Accugroove EL Whappo Jr-the newest version) 'color's your sound, with its largest dips being at 1Khz, 2Khz and 8Khz.

    i hope that some of you might find this info helpful. ;)
     
  2. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Thanks and great work.
    Will have to think about this one before posting; based on the sound clips I would have thought the UA to be more similar to the SVT.

    Who would have thought these old workhorses were this flat in freq response
     
  3. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    thanks Jim. yeah, i've always thought that SVT's were actually very hi-fi sounding. its just that you'd never know it once they're plugged into a bass cab. ;)
    and i had to actually eq the Avalon quite a bit to make it 'feel' like and SVT playing a bass thru it.
     
  4. Really nice work John! Thanks for all the efforts! :)
     
  5. anonymous02282011

    anonymous02282011 Guest

    Jun 27, 2007
    very cool. Thanks John:cool:
     
  6. Either those Crown XTI amps are junk or something is wrong with this test. No properly functioning power amp has a 10 dB swing in the space of less than an octave like the green line in the second graph.
     
  7. 12bass

    12bass

    Jan 2, 2003
    Victoria, Canada
    Yep... something sounds fishy.... Any chance you can run a response test on the power amp only?
     
  8. Mooblar

    Mooblar

    Jan 9, 2009
    Mid Michigan
    John, I always find your posts helpful and insightful. I made sure to snag a V4 4x12 cab because of you. Thank You!
     
  9. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    those xti readings (and the ampeg, for that matter) are with the power amp connected to the cab, so i'm suspecting that the uneven curve is due to it being a reactive load. i intend to run more tests on it , both with a non-reactive load, and without any load at all.

    oh, and i ran all of these tests mulitiple times to make sure that the results were repeatable and not just a fluke. (no pun intended).
     
  10. Interceptor

    Interceptor

    Mar 29, 2005
    Madison, WI
    Nice work!

    I'd be curious to see what the freq response is of your rig once you've eq'd for your stage tone.
     
  11. Rickett Customs

    Rickett Customs

    Jul 30, 2007
    Southern Maryland
    Luthier: Rickett Customs...........www.rickettcustomguitars.com
    Hey John, I got one for you: Vintage SVT vs SVT-VR....... ;)
     
  12. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    +1 on flat EQ graph vs. stage EQ
    Do you use similar EQ regardless of the cabinet?
     
  13. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    just ran the RTA with the Focusrite ISA 430 MKII, the Avalon VT737SP and the UA 6176. this time i used the quick sweep mode, which yields far more accurate results instead of the pink noise method.

    in the graph below, you can see that the Focusrite and Avalon are just about ruler flat from 10Hz to 20Khz, and the UA has a bump at both ends of the spectrum(hence it's 'color')
    Focusrite=Green, Avalon=Violet, UA=Blue:

    430MKII_Gr_Avalon_Viol_UA_Blue.

    i 'm going to run this quick sweep test with the SVT tomorrow, and then try all of them again, coming out of the power stage as well.
     
  14. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    i'll see if i can do that one too. ;)
    it should be interesting.
     
  15. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    my stage tone almost always varies depending on which cab i'm using, and what the room i'm playing in. i usually run it pretty flat, and cut or boost the low end according to the room's response.
     
  16. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    with my 1212/ and whappo jr, they are pretty close to the same settings, but with my 2x15, 4x12 or 810 it's quite a bit different.
     
  17. OldogNewTrick

    OldogNewTrick

    Dec 28, 2004
    Germany, EU
    John, very cool post - thanks :)

    I very much prefer the quick sweep method of TrueRTA, see my thread on the magic of VT Bass, interesting to compare those results to the real SVT.

    Could you please run some tests using a single frequency such as 100 Hz into the input of the SVT to see which harmonics are generated at various gain settings ?

    :cool:
     
  18. Rickett Customs

    Rickett Customs

    Jul 30, 2007
    Southern Maryland
    Luthier: Rickett Customs...........www.rickettcustomguitars.com
    Yeah, that would define just how close they really are (or not).......
     
  19. kringle77

    kringle77 Supporting Member

    Jul 30, 2004
    Massena NY
    I rta'd my 70's svt awhile ago and it was pretty flat. I never have agreed with many on here who have said that they have a mid dip. Even the bassgearmag review showed a very curved response. While I know that their testing gear is so far beyone mine, I never understood why we got such different results. Anyway, I love my old svt!
     
    f.c.geil likes this.

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