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About j4cbo

  • Birthday 10/14/1988


  • Hobbies
    Urbex, photography
  • Headphones
  • Headphone Amps
    Dynahi; DynaFET in progress
  • Sources
    Slim Devices Transporter

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  1. I use the DAC in my Transporter. Which option?
  2. If you plug it back in soon enough, it won't even stop.
  3. It was oscillating at very low bias, about 25mA with no heatsinks. Now that I've got the larger heatsinks it's still running cool at 75mA; I guess I'll recheck the stability with the higher current. R19-R20 are 2k, the series closed-loop feedback resistor is 1k, and the shunt resistor is 220R, so gain is 5.5 with either feedback point.
  4. I don't have my laptop with the final schematic/board with me at the moment, but this: http://b.j4cbo.com/temp/gbf2.0rc1-sch.png is very close. I'll upload the one that matches the boards that were ordered when I get home. I have two boards up and running now, with a single set of output devices each attached to s22-style heatsinks. Bringup was painful. When I first powered it up I got several volts of oscillation at 10 MHz - yikes! This happened on two different boards and with either feedback point, so I figured it wasn't just a build error. There seemed to be a lot of noise/hash/oscillation/something coming from the VAS stage, so I tried putting a 22pf ceramic between base and collector of one of the transistors on each side; that didn't fix things either. Colin suggested removing one of the paralleled transistors. After doing that it was entirely well-behaved. Later this weekend I'll take it in to a lab on campus with good function generators and get some measurements. After some tweaking (and using the values I have around) I've settled on 2k ohm R17-R18 and 1k in series with the pot. I'm using a 20k pot but the usable range wouldn't be much less with 5k. The oscillation is worrying me a bit. Did anyone else have trouble with using two non-compensated transistors per side in the VAS stage? The only difference I can think of is that I'm using a different version of the PCB layout, but my SMT-only one should have far fewer parasitics, and the circuit itself is identical. I really want to figure out what the most appropriate value for VAS compensation is, but 22pF was the only low-value C0G chip cap I had on hand; I'll poke around and try to find some other values to test with. But even now it's hard to tear myself away from listening... Vortex: are you using the through-hole group buy PCBs, my SMT version, or something else?
  5. I'm not sure. The PMD200 is a Blackfin, but I suspect the PMD100 may be hardwired silicon.
  6. You bet. The Touch just runs Linux with Logitech's UI and playback software. It requires a bit of configuration tweaking to get the player to use a different audio device than the built-in DAC and S/PDIF, but some of the other beta testers have managed to get it working, including with a Wavelength async USB DAC.
  7. No, just stereo, quint-amplified.
  8. That's a stupid amount of money for something that can't possibly cost more than $100 to build - it looks to be one board in a Hammond case with some ultra-simple milled front panels. An utter ripoff. I'm working (slowly) on my own asynchronous USB implementation and may just open source it once it's done.
  9. About $350 worth of parts from Digi-Key. D:
  10. Looks like a bog-standard Sabre32 implementation with some fancy marketing terms to describe the Sabre chip.
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