j4cbo
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About j4cbo
- Birthday 10/14/1988
Converted
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Hobbies
Urbex, photography
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Headphones
HD650
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Headphone Amps
Dynahi; DynaFET in progress
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Sources
Slim Devices Transporter
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I use the DAC in my Transporter. Which option?
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If you plug it back in soon enough, it won't even stop.
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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.
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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?
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Gettin' there.
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I'm not sure. The PMD200 is a Blackfin, but I suspect the PMD100 may be hardwired silicon.
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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.
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No, just stereo, quint-amplified.
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It's coming along...
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Wavelength WaveLink Asynchronous USB to S/PDIF converter.
j4cbo replied to Hopstretch's topic in Home Source Components
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. -
About $350 worth of parts from Digi-Key. D:
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That's exactly what I said.
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Same here
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Fuck Photomatix.
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Looks like a bog-standard Sabre32 implementation with some fancy marketing terms to describe the Sabre chip.