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Showing content with the highest reputation on 01/07/2021 in all areas

  1. RTJ hands fixed Honestly, I'm pretty psyched with how these came out and they were a great test bed for figuring out how to accurately combine/sequence engraving and cutting. Now for a light sanding and finishing and then delivery to their owner.
    8 points
  2. For reasons unknown Sam likes to go head first and squish his head against the wall in this particular cat tree
    5 points
  3. Ramon Allones Specially Selected
    4 points
  4. Now if you could just change the one on the left to fold in the index finger, and then point it toward the Whitehouse. Seriously though, nice work!
    2 points
  5. A documentary about what became the cornerstone of Eva Cassidy's discography: Live at the Blues Alley. The musicians that were backing her up talk about her and the music those nights
    2 points
  6. I don't know the preferred delivery device, but I believe the kids refer to the product as "whacky tabacky"?
    2 points
  7. I'm surprised someone hasn't posted about lighting up the bong tonight. This would be the day for it. Pardon me if the bong is not still in fashion. I haven't kept up with these things.
    2 points
  8. To see what and how to improve, let's have a look at the original schematic. KSA-5 is designed along the lines of "moderate feedback", that is, it uses very little to no global feedback but lots of local feedback a.k.a degeneration. The pair of input JFET buffers (Q1, red box on the schematic above) run independently of each other and outside of the global feedback loop. With low loop gain, they see very different signal levels, so the differential stage downstream doesn't cancel their distortion. (BTW, because of this JFETs need not be matched. Also, the expensive and hard-to-find JFETs can be easily replaced here with BJTs.) Still, a JFET follower loaded by a current source has 100% degeneration and relatively low distortion, at least at low signal levels, so the buffers are not the biggest problem. The pair of differential stages (Q2+Q3, Q7+Q8, orange box) is heavily degenerated by 680ohm emitter resistors and produce R10/(R1+R2) = 2 = 6dB of gain. The pair of common emitter stages (Q12, Q13, purple box) is also heavily generated by 402ohm emitter resistors and, with the low load of R23 and R24, provides R23/R16 = 9 = 19dB of gain. Since the output stage (blue box) is a double emitter follower with approximately unity gain, the total open loop gain of KSA-5 is 2x9 = 18 = 25dB. The feedback divider (R45-R47) attenuates the output signal by a factor of 9 (19dB), which leaves 18/9 =2 (6dB) of global feedback. That is, the global feedback loop attenuates the distortion of the output stage by a small factor of 1+2 = 3. The output stage, meanwhile, is a large source of distortion. Although Krell claimed that KSA-5 runs in "pure Class A", in reality it can easily slide into Class AB. The output pairs run at only 50mA of quiescent current each and leave Class A (that is, one half of the output stage stops conducting current) when the output current reaches 200mA. The driver quads (Q15-Q22) also run in Class AB (R37 and R38 are connected to the output), which means they stop conducting at that point, too. With a 100ohm load, it would happen at 20V peak output voltage, so the amp never leaves Class A with such a load. However, with 32ohm, KSA-5 leaves Class A at 6.4V peak; with 8ohm, at 1.6V. Even within Class A region, the output stage is not very linear, especially with low impedance loads. It uses paralleled transistors with relatively large emitter resistors to ensure current sharing. The dark side of large emitter resistors is that they make the output impedance of the emitter follower large and nonlinear in the crossover region (see e.g. Douglas Self and his "wingspread" diagrams). Since the output impedance forms a voltage divider with the load, its nonlinearity makes the gain of the emitter follower nonlinear, adding crossover distortion and negating the benefit of the large bias current. Overall, KSA-5 has a nice and linear front end followed by a not-so-linear output stage, with little feedback to let the former help the latter stay linear. The game plan, then, is to improve the output stage and add more feedback.
    2 points
  9. Let me first modify the output stage. The mod affects only the performance with lower impedance loads, and even there it can take us only so far, but it is a start. The front end modification that increases the feedback loop gain will be posted separately. The changes are simple. Here is the schematic: R33-R36 are replaced with 0.22ohm 3W resistors, R19 is reduced to 470..560ohm to allow proper biasing, and R37-R38 are replaced by a single 47..51ohm resistor. The bias will need to be re-adjusted. Note that 50mA per transistor that resulted in 100mV between the test points in the original will now give 11mV - still easy to measure with a DVM. The performance improvements are as follows. With 1W and 5W into an 8ohm load: With 4Vpeak (2.8Vrms) into a 33ohm load the effect is much smaller: Distortion into 100ohm does not change appreciably, so I don't show it here.
    1 point
  10. Was the first album I bought with my own money as a kid (quickly followed by Weird Al's In 3D).
    1 point
  11. hmmm... interested.... I will have a look at the build thread, gerbers etc...
    1 point
  12. Oh! https://www.waxingmoonhumidors.com/
    1 point
  13. Thank you, I’m kind of also coming to the conclusion I need to learn Illistrator or Inkscape for vector creation. Like guitar, wish I would have picked some of these things up years ago.
    1 point
  14. I’ve already purchase VCarve Pro and have been learning to use it, seems pretty easy for most tasks. There is a post processor for my machine so it all should (hopefully) work well. I’m also working through Fusion and putting my head into the parametric modeling mindset since I know it’s probably the best thing for long term 3D design. So much to learn, so little time.
    1 point
  15. Tab "Hunter." I brought him to the vet because he had a nasty cough, almost like whooping cough. We got the devastating news that he has lung cancer, and it could be as little as one week left. Four months later (!) still has the cough, and spits up sometimes because of it. But he loves being with me, purrs up a storm when being pet or brushed, eats and drinks regularly, etc. Is definitely breathing shallower and faster, and pretty much sleeps a lot when not hanging with me. But still great company, and he hasn't told us it's time yet.
    1 point
  16. Sam, Mr I Need to be on a Diet and Jax, the old man resting comfortably.
    1 point
  17. Artemis, tree climber and destroyer of wrapping paper, wishes everyone Happy Holidays.
    1 point
  18. Finally got a new humidor that I can use to transport today’s selections out to the patio. Today’s choice
    1 point
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