John Warren

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John Warren last won the day on October 4 2014

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About John Warren

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    "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. 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.
  2. 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.
  3. "If I have seen further than others, it is by standing upon the shoulders of giants." Isaac Newton
  4. 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.
  5. 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.
  6. 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.
  7. Distortion, each channel at 300Hz (green, purple) and 50Hz (gold, blue) up to about 200W or so. Very low. Op-amp is TLE2074.
  8. Stability check at various power levels. Amplifier output into 4 ohm, 1/2kW resistor. No oscillations. Both channels shown, some differences but nothing that would cause any eyebrows to get raised. Op-amp is TLE2074, 14 DIP. Not bad for a $240 amplifier!
  9. Some responses with the amplifier connected to a Klipschorn bass unit. First plot is the horn measured with and without the filter operating. Second plot shows the response with different front panel pot settings. Nothing fancy with the measurements. The mic is laying on the floor facing the front of the horn and located at the centerline. Although simple it reproduces a similar response plot to the anechoic chamber response. The filter is a bandpass and you can see there's a tad of attenuation at the low end. That can be increased by lowering the cap values on the high pass section of the filter and would be the way to go about incorporating a sub-woofer into the system. It would take a wheel-barrow of parts to make this in a passive, no thank you.
  10. Placed the amplifier board back into the chassis and made the small signal connections to the filter. For the Crown XLi, the connections are very simple and requires only one pair of wires to be connected to each channel of the board. The black and white leads are the taps off the lower rail voltage that drive the op amp powers supplies on the filter board. The entire board draws about 25mA of current which the SPICE model predicted exactly, btw. FWIW, I've treated this amp like a "rented mule". I had a few screw-ups with it and had to repair it a couple of times. While inside I changed things too but more for my own interests.
  11. Dielectric material used to make the capacitor is important for low distortion and noise levels. High-K dielectric materials allow large capacitor sizes in small packages which is a good thing for PC board layout but not so great for distortion and noise. The capacitance of high-K materials will vary as a function of both signal voltage and temperature causing distortion. Low-K materials are less sensitive to these effects but physically much larger for a given capacitance and voltage rating. In an existing design, changing from a high-K to low-K is usually not possible because of space and mounting constraints. This is the case for all small signal circuits, not just active filters. .
  12. Finished a couple of the filter boards. When I was testing them I took a few pics. The first set of tests are to drive the board off the lower rail taps and measure the heat dissipation in the power supply transistors. I pulled the amplifier board out to avoid damaging it with an unexpected pop or blowout. Good news was nothing happened. The current regulating transistors on the board are MJE350/340. No over temps, no oscillations. The FFT plot shows the filter response of the two channels driven by the XLi power supply after about two hours of operation. The small signals were applied directly to the input pins of the board. This would be the response for a Klipschorn bass unit. The big caps on the board are Panasonic polyesters which is over-kill but easy enough to install.
  13. Is area highlighted indicative of something?
  14. Here's what we're going after (in theory!). For the Klipschorn will run something like the red response and for the Jubilee the blue. I don't have a Jubilee here to measure however so will need some guidance from those that have them. I could also look at what Delgado has posted for a design and use that to derive an upper corner frequency. This is small signal simulation mind you, what's fed to the front panel gain potentiometer. The low end corner is -3dB at 28Hz. I have found that placing a low end filter on bass horns cleans them up a bit. Note the response is +6dB in the passband because the model considers balanced inputs. And yes, the output at that the Speakons is in-phase with the input!
  15. Yes, but not difficult to install. The two leads from the lower PS rails are soldered to the +/-V solder pads on the board. J1, J2, J3 and J4 will be used to connect the filter to the amplifier and front panel potentiometers. Those connections will be made using the terminals show in the photo (the white part with pins will be soldered to the filter board at J1, J3, etc). The "finesse" part is stripping the 26AWG wire leads that feed the potentiometer and then connecting the small signal cabling into that. That's where the right wire stripping tool comes in. A Stripmaster or other tool is a must. The splice is then covered with adhesive shrink tubing and shrunk tight. So not too difficult if the tools and hardware are on hand.