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John Warren

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Everything posted by John Warren

  1. I completed the preamp module some time ago, got involved in another project. Here's the module, based on a couple of 12AX7s. Requires a -45VDC supply for the tube heaters and a 250VDC supply for the anodes. Has treble and has contour pots located on the board. Caps are either NPO or film. The Fluke is showing anode voltage. Two channels on one board. Can be assembled in a morning. Sounds pretty good!
  2. One would also require a filament supply (VAC or VDC?), 350VDC supply that may also be on a PC board. There's also power transformer, OT transformer, chassis/cage. Are the tubes mounted to the PC board? or is the board for component and wire management only?
  3. LOUDSPEAKER ENCLOSURES (CONT.) The show was not crowded, and we spent well over 30 min in many of the rooms we visited, sitting in the "sweet spot". There were a number of 2-way systems based on the AMT which I found to be excellent reproducers. Incorporating the self-damping characteristics of composite enclosures, 8 and 10" woofers are capable of high volume, articulate bass output well down to the lows in a moderately large listening room. My favorite? The Fink Team "Borg". In the hotel room, with some drapes and bass traps here and there I found this system to be excellent sounding. They're in the mid $30k range. The enclosure is an engineered laminate. They also make a system based on a 15" woofer which is on display at the dealer here in Boston. Website for this system is interesting read with a few white papers that show what's going on inside the box. Borg – Fink Team
  4. Loudspeaker Enclosures MDF, Particle Board, Plywood enclosures are gone (thank goodness!). The top tier suppliers today have transitioned to composite structures including mineral casting, structural laminates and, of course, Aluminum plate. The enclosures materials are where the engineering is most intense and where the distinctions will be made. The small speaker below, made by Kroma (a German supplier) was an example of what a mineral cast enclosure provides. $16k/pr with stands, this little speaker was outstanding. The woofer surround is specifically designed to break-up standing waves that ripple along the cone. This wasn't my favorite at the show, it was the one I was most impressed with. Great reproduction at very high volumes. Upper mids and HF handled by the AMT. Many suppliers are transitioning to the AMT as well.
  5. The Doubletree by Hilton in SeaTac is adjacent to the SeaTac International airport, it's a large, somewhat dated hotel. There was a reduced rate for show attendees ($179/night + $22.38 room tax/night + $2 tourist assessment fee/night). Wife and I stayed four nights = $814 which, for a large city, isn't bad. SeaTac the city is the airport, airport support services, hotels and a few small businesses. There's nothing really to do there but public transport is available, light rail, and it's at the airport and it takes you directly into downtown Seattle. You can walk to the airport too (it's that close) from the hotel or you can ride the hotel shuttle to the airport. The light rail is not expensive either (compared to Boston's rail service into the city, the MBTA aka the "T") and it's clean and on time. It's a 45min ride into downtown. Along the way you're traveling thru a few sketchy parts and there's always addicts and homeless to keep you company.
  6. I was there for the entire event, Seattle WA and will report my observations and thoughts but... if you've never been to Seattle, don't bother. Seattle has a problem that is getting WAY out of control. It's a beautiful part of the US that has been overtaken by the homeless, many actually quite violent, bold. They toss excrement, confront poor folk just trying to go about their lives. They are EVERYWHERE. They're also where tourist congregate, the city does nothing to protect citizens, no cops anywhere. There was even an event in the lobby of the Doubletree at SeaTac, the hotel where the show took place. Then there's the addicts, young, male and female, mostly white. Strung out on either meth or heroin or glue. It will be a cold day in Hell before I go there again.
  7. I'd propose you ask for photos of the amplifiers, all of them in one pic. Good luck.
  8. Not modified but wasn't working when I got it, so fixed it.
  9. Have the original HP shipping carton, plastic wrapping and service manual too. It just didn't work. Does now. My ULD signal generator shown above developed a problem, sent it back to SRS for repair yesterday, it's still under warranty. I have another ULD unit but the SRS is insanely low distortion.
  10. Here's the Z of the Klipschorn bass unit (alone) measured by yours truly some years ago. The plot starts at 10Hz and ends at 1kHz. Below is Heyser's plot from the Audio magazine review article where he measured the 3-way system and plotted the result. The loop in the middle is the bass section, similar to what's shown above. Here's the alk plot using his Klipschorn "emulator". Here's the contraption.
  11. Both the 333A and the Krohn-Hite output the residuals of the signal being measured. The output of each is shown below taken between 500Hz to 60kHz, the bottom plot is the 333A. First thing to note is that they're similar, a good thing. The fundamental is 10kHz, attenuated to -60dBV by each instrument leaving the harmonics and whatever else is left to measure. At this testing extreme, the Crown D-75 exhibits some instabilities at 20kHz, the second harmonic. The amp gets hot as hell testing at high frequencies and it's not a mystery that thermal distress will show up in the residual spectrum.
  12. Here the analyzer is measuring a Crown D-75. Input is a balanced, 10kHz, 0.5Vrms sinewave from an ultra-low distortion source (<0.001%). Output from the amplifier is measured across an 8 Ohm power resistor. The gain is set to realize 10Vrms across the resistor. The amp stewed for about 30minutes before measurement. Testing at 10kHz will drive the amp to get very warm to the touch. The 333A is reporting 0.042% THD+N (0.1% FS, pointer a bit to the right of 0.04%). The signal is simultaneously fed to the Krohn-Hite 6900B analyzer that has a current calibration sticker (performed at Krohn-Hite, NIST traceable). The 6900B is reporting 0.046%THD+N indicating the 333A is a bit off from the actual magnitude.
  13. Did a complete overhaul on this 333A. New Al- and Ta-electrolytics, many new transistors. The goal was to achieve like new performance. I have many of the HP special BJTs including the Germaniums from this era. The 333A and 334A were popular distortion analyzers from 1968 to about 1980. They're actually very useful for measuring THD+N in tube amps but good luck trying to find one in good working order. They're straightforward to rework but getting the best out of them isn't so simple. The key to getting these units to operating "like new" is the voltmeter circuit, it must measure accurately to the micro-Volts level and that's not so straightforward. How does the analyzer work? A signal is applied to an amplifier to be tested for distortion, say a 1000Hz sine wave signal (the fundamental). The amplified signal is then sent to the analyzer where the operator "tunes" a Wien bridge to "notch out" the fundamental leaving the harmonics and noise for measurement by the meter circuit. The accuracy of the analyzer is governed by the accuracy of the voltmeter and the accuracy of the meter circuit over the bandwidth of the instrument (5Hz to 600kHz). Below is the signal source, a 100uV, 400Hz sinewave signal which requires specialized instruments to source. And the measurement of the 100uV sinewave at the 333A is below. The meter range knob (lower right) is set at .0003 which is 300uV or about 1/3 of a millivolt at full scale. The magnitude of the voltage is read at the 0-3 graduated scale. Note the pointer is at 1 (= 100uV). The 333A and 334A units are useful to about 0.03% THD+N which is about 30X higher than current state of the art units, like the Krohn-Hite shown above which is capable of 0.001% THD+N.
  14. The build "quality" on the Crimson-ring thing was absolutely, decided garbage. Why would anyone give these clowns a penny?
  15. That has virtually no impact to the layout.
  16. Here's a project I did a year ago. The measurements are the most basic, 1kHz THD and bandwidth. Without even listening to it, I'd state it will sound pretty good. But, do the measurements tell the whole story? No. Swapping the 5AR4 rectifier for a solid-state plug in improves the low end a bit which I don't need a plot to tell me, I can hear it. I can however measure the difference in 20Hz distortion and the temperature of two resistors. The hotter resistors mean output tube life will be lowered. A compromise I'm not willing to take. Why? Because the amp, as is, satisfies everything I look to a tube amp to satisfy.
  17. The tube crisis is manufactured. JJ can easily supply the current demand. For those that are in need, you're being played. JJ is shipping but $ are still x3 what they were this time last year. Wait.
  18. The PC board layout was done by newbie.
  19. Then there's the price point. How much would one be willing to spend on a match pair of, say 7591s? 80USD? My guess is the new WE will come in closer to 300USD. So 600USD for your Scott 299C. I was ready to pull the trigger on a new amp build based on the Citation II. That will not happen. Anyone interested in buying a tube amp should think long and hard about that purchase, you might be stuck waiting for 2 or 3 years before your EL34s or KT88s are readily available.
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