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Thread: Problem simulating N3134

  1. #1
    Junior Member LocoDantes's Avatar
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    Oct 2010
    Woodland Hills, CA

    Problem simulating N3134

    Hi, all. I'm new here -- I've been lurking a while to get my bearings, and making my first post with some trepidation.

    I'm planning to build some 4430 clones (a thoroughly beaten dead horse, I know). I'm going to copy the N3134 crossover, so I built a simulation in SIMetrix (a fairly straightforward SPICE package), thinking I could use the simulation to predict the effects of Lpads that aren't exact matches for the factory version, varying coil resistances, and so on. I expected/hoped that my curves would resemble those posted here, but alas, they don't. I was hoping someone might be able to shed light on what I'm doing wrong.

    Here's the simulation schematic:

    Name:  N3134sim.jpg
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    Some explanation: SIMetrix allows multi-step analyses where component values are determined by expressions that include variables, said variables being stepped through specified intervals. R202 and R201 are swept with the varibles mid_sweep and high_sweep, respectively, and the expressions are given in the diagram. Those variables are in the range [0,1], corresponding to the control position (0 being full CCW and 1 being full CW). I used 6 ohms and 34 ohms as the values for the legs of R202 based on the measurements posted here, and the values for the series resistances of the inductors came from here. I used 8 ohm resistive loads as per the standard test fixture (did I do that right?). LF and HF are the probes for the voltages plotted below.

    Here's the output of the simulator with both controls wide open (full CW - mid_sweep=1, high_sweep=1):
    Name:  N3134vp1.jpg
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    It should (I think) look like the green curve in the top graph in Giskard's post I referenced earlier. Note the ~2 dB peak around 1.7kHz in Giskard's graph which is notably absent in my sim's output.

    Now, the output of my sim with R201 set to full CCW (high_sweep=0) and R202 swept from 50% to 100% (mid_sweep stepped from 0.5 to 1) which should correspond to 0 dB to +4 dB:
    Name:  N3134vp2.jpg
Views: 618
Size:  39.5 KB

    This should resemble the red curves in the second graph in Giskard's post, but it appears to be overdamped.

    I've stared at this trying to figure out what's wrong, and it's probably something really stupid that I've done. Please feel free to point it out.

  2. #2
    Senior Member grumpy's Avatar
    Join Date
    Oct 2003
    "As the first rheostat increases in resistance, the second rheostat decreases in resistance,
    keeping the load impedance (presented at the input of the L pad) constant.
    The second rheostat usually has a special taper (function of resistance versus rotation)
    to accommodate the need for constant input impedance." -Wikipedia

    Non-linear function for half of R202 is required. It appears you've assumed both to be linear
    vs rotation.

    Name:  Screen shot 2010-11-16 at 3.27.48 PM.png
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  3. #3
    Junior Member LocoDantes's Avatar
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    Oct 2010
    Woodland Hills, CA
    Yeah, it was something stupid that I had done. Thank you very much. That was precisely the problem.

  4. #4
    RIP 2011 Zilch's Avatar
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    Jun 2004
    Berkeley, CA
    [And Grumpy abides.... ]

  5. #5
    Senior Member 1audiohack's Avatar
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    Jul 2007
    Las Vegas Nevada
    Excelent avatar Herr Doctor.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  6. #6
    Junior Member LocoDantes's Avatar
    Join Date
    Oct 2010
    Woodland Hills, CA
    Thank you for the compliment, mein Fuhrer... I mean, Mr. President.

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