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John Warren

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John Warren last won the day on October 4 2014

John Warren had the most liked content!

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About John Warren

  • Rank
    "So much for the experts on this board"

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  • Interests
    Engineering-Audio, magnetics, materials for electronic and magnetic applications, engineering models and simulation, SPICE, MATLAB, FORTRAN, acoustics, complex algebra, physics of sound, microphones, vintage audio, loudspeaker design, amplifier design, McIntosh amplifiers, discrete semiconductor devices.....and movies including silents, foreign and indies.
  • My System
    12" Utah Tri-axial drivers mounted in LRE bass "reflex" enclosures.

    Sony Superscope FM only

    Lafayette Solid State Stereophonic Integrated Amp

    16 GA Lamp Wire

    Koss Pro 4AA

    Technics SL-QD33

    CD Player:
    NAD 325i (modified)

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  1. Crown XLI1500 a modern day staple?

    Getting a bit off topic. Simulated impedance magnitudes from the model show why the AK-4 was revised to the AK-5. The minimum is getting a bit too low. The AK-5 adds a little extra resistance to bring the level up to something closer to 4 Ohms over the range where the notch is dissipating.
  2. Crown XLI1500 a modern day staple?

    Doing a bandpass using a passive means large capacitances so electrolytics are a way to keep the cost reasonable. Some time back I put an electrical equivalent model together of the Klipschorn bass unit using the Beranek approach shown in Acoustics (http://www.northreadingeng.com/Klipschorn_model/basshorn_model.htm ). That model is useful as a simulated load for passive filter designs and it provides a way to predict a Klipschorn bass horn response for various filters. In the first plot the pink curve is the model output response (electrical equivalent) of the Klipschorn bass unit with no filter (raw). The peak in radiation resistance is ~100Hz and below that the horn output drops. The output below 70Hz (or so) is not due to horn loading but due to the woofer working is a sealed enclosure and firing into a folded labyrinth. That's shown in the dash line in the second plot, it's the seal woofer response. This provides the "salami whacking the sofa" sound characteristic of the Klipschorn. Combined is the measured Klipschorn response. It's the sealed woofer response that needs to go. Using the model as a simulated load, the blue plot is the model response with the AK4 network, the green is the AK3 and the light blue the AA. The AK4 is the notch filtered net with the dipsy-doo in the range above 150Hz, the idea to attenuate the peaks that occur over that range. The red plot is the model with a passive band-pass filter, it will attenuate the seal woofer response.
  3. Early Klipschorn Build

    The addition of the tabs provides considerable stiffening to that side of the horn. Too bad the factory decided to rev the design to eliminate them. Seems almost silly not to do it. But then again, the bulk of the horn today is MDF which is a real downgrade. The build above is 1/2 and 3/4" Birch ply, the real stuff, not the Home Depot stuff. I haven't built a pair of Klipsch clones in some time, the ones above were done two years ago.
  4. Early Klipschorn Build

  5. Early Klipschorn Build

    I was looking at the Klipsch Museum FB page and happened across this photo of a very early build that shows the reinforcement tabs that stiffen the horn side wall opposite the woofer access. What's interesting (to me) is that I was not aware that Klipsch ever made horns with the tabs. I have plans here that show the tabs and I've built set with them (second photo). Note that the tabs in the factory unit are formed with two vee-notches and with the plans I have, formed using three. The notches are necessary to allow the rear chamber volume to be added to the volume within the two ski slopes at the top and bottom panels. I was told they're factory plans but I was never really sure about that. This seems to suggest that they may actually be originals (they're D-sized blueprints, three sheets). The plans also show the 6" wide woofer opening and use a woofer mounting panel. In the builds I've done, I use the 3" wide opening and mount the woofer directly to the baffle board using tee-nuts.
  6. Crown XLI1500 a modern day staple?

    Yes. For subwoofer integration, I'd recommend the bass horn be bandpass filtered.
  7. Crown XLI1500 a modern day staple?

    I agree but must put the Klipschorn bass unit on a bandpass, all goodness then.
  8. Crown XLI1500 a modern day staple?

    Agreed, not critical but not trivial. Op-amp packages are Quads. The topology is cascaded Sallen-Key, four op-amps/ch.
  9. Crown XLI1500 a modern day staple?

    Yes, piece of cake.
  10. The Klipschorn Woofer Polarity Challenge

    The AK-4 and -5 nets implement the notch filter in the bass horn to reduce the peaking between 100-300Hz. It's a big change given 50 years of manufacture without it. Operating bass horns on band-pass filters is another improvement. They sound better operating where the horn acts as a horn. The low stuff should be handled by a sub.
  11. AA Crossover refresh?

    I've not measured but I think the physics is based on keeping the dielectric films in the capacitors charged to avoid soak back. I'm sure a SPICE geek could demonstrate that a bias voltage across the reactive elements of the standard capacitor model mitigates DA effects.
  12. Forte III

    "If I have seen further than others, it is by standing upon the shoulders of giants." Isaac Newton
  13. Crown XLI1500 a modern day staple?

    Distortion measurements across the pass-band of the filter with both the AD713 top and TLE2074CN bottom. Top curve in both plots is 400Hz then 300, 200, 100 and finally 50Hz. The AD713 is 3X the cost of the Texas Instruments package but distortion is about the same. Might have something to do with the fact that Analog Devices is headquartered in Norwood, Massachusetts and TI isn't! Distortion is very low up to about 300W(!). That's what happens when you filter out all the HF content from the amplifier. It's really shooting fish in a barrel.
  14. Crown XLI1500 a modern day staple?

    The installed 14 pin DIP sockets allows for device rolling. Analog Devices AD713 (red) and TI TLE2074 (green) packages compared. FFT is measured across 8Ohm power resistor. The low-pass section of a cascaded Sallen-Key band-pass filter is where different op-amps show measurable differences for a fixed circuit design as is shown in the plot below. Truth is instability in the stop-band can't be simulated in any of the SPICE engines I've used so it has to be determined experimentally, hence the sockets The AD713 is a "smidge" better than the TI device but both would work fine. The blue is the amplifier response with the filter defeated. What's interesting in this plot is the amplifier will produce output well below 20Hz which, without the high pass filter section, the K33E will respond to. It's useless mechanical garbage that does nothing but modulate the cone and contribute to resonance. So putting everything below 30Hz in the stop band it's goodness.
  15. Crown XLI1500 a modern day staple?

    After all this testing at full power, the unit has been on for about 3h. Now's a good time to measure the power transistors on the board to determine if I screwed something up with the temperatures. The max. junction temp for an MJE350 is 150C so we're looking good there and no need to add a sink.