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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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  • Gender
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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. https://www.mcmaster.com/adjustable-feet
  2. Recently swapped the OEM power supply transformer in an LK72A with a Heyboer replacement. The Heyboer is a well made component. Removing the bell is a bit tricky but it can be done without causing mechanical strain in the lead wires. The leads are tinned, multi-strand and the insulating jacket material very tough. Excellent results are achievable. This is a great little amp, very quiet! http://www.northreadingeng.com/Audio/group/viewtopic.php?f=4&t=8&p=29#p29
  3. I use a Staco Energy product. Current and voltage monitored using DVMs that can also be used for other things. 1.4kVA. ~$550 on Mouser. 100% = 140VAC. Limit current by swapping in a 0.5A fuse. Wall voltage in my house ranges from peak of 126 to low of 115VAC. Ripple voltage on the B+ changes too from 12Vp-p to 5Vp-p and can be audible buzz in mid and HF drivers. Also wears out electrolytics in the supply.
  4. The plans for the Electro-Voice Georgian would be a good place to start. I've pointed a few builders in that direction with good results. FWIW, having perfectly cut panels isn't the only hurdle, the assembly is another potential pot-hole that can leave you in wishing you just bought a used pair for $1200 USD. http://www.northreadingeng.com/Klipschorn_build/Klipschorn_build.html
  5. Don't go to college and major in anything that ends in "studies".
  6. John Warren


    Playing with video on my site and would like to get some feedback on this. Particularly interested in how it plays on various browsers and hand held devices. Seems to work ok on Android. A customer suggested I do this, says no one reads anymore. http://northreadingeng.com/Video_Library/R4_buffer_video.htm
  7. Does your Hershey's Kiss have a broken-off tip?
  8. Hence the reason personal observations regarding the sound "quality" of just about anything are of no value.
  9. The transformer couples to the chassis and the chassis covers act as sound boards. On the bench, the amplifier is quieter with the covers removed. I suspect you'd prefer not to use the amp with the internals exposed. There are wooden enclosures for the D-series amps but they're hard to find. Alternative is to make a wooden enclosure. On the Chinese amps I've wrapped the coils with Mu-metal and poly over-wrap but that makes for a tight squeeze but there's some attenuation of the buzz. I've also removed transformers from donor units and swapped them into the Chinese versions. The older transformers were impregnated with varnish and then paper wrapped (right photo).
  10. The speaker behind Armstrong does have a badge at the lower right, the amp sits on top and the pre-amp just behind his left ear at arms length. Can we identify them?
  11. Yes, DCM50, Tweeter is STH100 Tractrix w/HF10AK compression driver.
  12. I've used the Selenium HM3950. On a passive bandpass type net and with a decent tweeter the horn can sound quite good. I fabricated an new baffle to replace the factory baffle. I then tri-amped it for a wee time using active, analog filters that I shoe-horned into the old Crown D45s. It was a great little setup. I did sell it however and I regret that on occasion. Parts Express sells the HM3950 for $200/pr. That includes the support bracket that is required for big drivers like the BMS unit shown below. Making the baffle insert isn't that straightforward because it requires routing which is a hassle. I'll post the plans for the insert.
  13. Yes, guilty as charged. Note the plot is a simulation result using a SPICE package, it's not a measured response.
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