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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. The Fifteen

    Perhaps they sounded too good?
  2. Crown D-45 schematic

    Above, decidedly, demonstrates that audio amplifiers are voltage sources and that all design considerations are to preserve accurate voltage transfer.
  3. Crown D-45 schematic

    Feedback is sourced to the INV pin which has same phase relationship as non-INV signal from the gain pot. The op-amp takes the difference (fractions of mV range) and amplifies the result (the error signal) and that's what drives the amplifier The open loop gain of the op-amp is large and applied to the differences (both AC and DC). SPICE simulation shows the difference signal (blue) and the output (red) of the second op-amp (in this case the MC33079) at 20kHz sine wave, 0.5VRMS balanced signal sourced from 660 Ohm source impedance, gain and CMR pots at nominal. The "glitches", when sent thru the amplifier, correct the signal to reduce distortion. The plot is taken a few milliseconds into the signal allowing caps to charge.
  4. Crown D-45 schematic

    Yes, Q107, my copy of the schematic isn't clear. I did explain the second op-amp. It provides the error signal and that's its only job.
  5. Crown D-45 schematic

    At max input (~0.7VRMS) the op-amp serves as a differential input amplifier capable of ~2Vp-p ground referenced error signal. Q102 is an emitter degenerated voltage-in, voltage-out amplifier with Q101 providing current limiting at clipping. At max input, the signal at the base of Q102 is about 50mVp-p referenced to the -30V rail and, by way of the effective load on its collector, produces ~40Vp-p ground referenced signal at the bases of Q110 and Q187.
  6. Crown D-45 schematic

    So where are you on this? Are you listening to your modified amps?
  7. Crown D-45 schematic

    I have a somewhat earlier D75 that I'll teardown here: http://www.northreadingeng.com/Audio/group/ Might give you some clues?
  8. Crown D-45 schematic

    On the ones I've seen, Pin 1 on both XLR input sockets are on dedicated trace to chassis ground which ties to Earth plug on 3-prong. P16 is circuit ground last time I looked. Curious to see what your seeing, can you post photo?
  9. Crown D-45 schematic

    I'm interested in changes, not absolute magnitudes. My anemic 3V/us is not a slew-rate, it's a compensated slew-rate, measured at 15kHz. I spooled-up the potentiometer to output a healthy voltage, in this case ~23Vp-p and then simply measure the time required to settle after responding to a 15kHz pulse. By comparing the time required to reach steady-state, an "apples to apples" comparison between op-amps, changes in compensation, output transistors and so on can be readily determined by storing the image before the change and then comparing after. An alternate approach would be to set the goal posts at 10 and 90% the vertical response and measure the time between. Plot below is example using the TLE2079 op-amp with compensated slew-rate of a bit over 3V/us loaded with 8 Ohm power resistor. Thought this thread had died, fancy that.
  10. Klipsch speaker Impedance curves

    Google "Impedometer" by Dick Pierce (of Usenet fame). It will gives basics to measure the magnitude only of the complex impedance. For complex impedance (R +jX) you need the phase angle and the piece part setups don't do it unless you get a phase meter or like struggling with X-Y plotting on an oscilloscope. Dayton Audio makes a thing called the DATS for $100 that you might considered. I don't have one but if it outputs the results of a sweep in a spreadsheet your good. If not then don't bother. Link below shows how to use Excel spreadsheet to acquire complex impedance from test signal frequency, impedance magnitude and phase angle. http://www.northreadingeng.com/Impedance/impedance.htm
  11. Tubes bad in 80 days on new Mc275? Are they BS'ing me?

    Although true, anyone that purchases a tube amp should go into it with the understanding that tubes are consumables and an escrow account for replacements a necessity.
  12. CL-D Bi and Tri-amping (lots of photos and plots)

    FFT between 500-20,000Hz. Nearly 100dB of distortion free dynamic range(!).
  13. CL-D Bi and Tri-amping (lots of photos and plots)

    FFT of CH1 buffer out with 560 Ohm load, +/-100VDC supply, 1VRMS balanced input at 1kHz.
  14. CL-D Bi and Tri-amping (lots of photos and plots)

    The Plitron, the capacitor board and the buffer waiting for CL-D amps.
  15. CL-D Bi and Tri-amping (lots of photos and plots)

    The R/W/B leads source +/-100VDC to the buffer. The Fastons source to the amplifier. The buffer current draw is negligible (about 40mA).