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About gepardcv

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  1. Spectacular. Starting to think about how small a Carbon can be realistically made. It still needs a big ol' transformer.
  2. 1 amp board and 1 set of split GRHV for me.
  3. Does this mean MrSpeakers gave up on the proprietary connector and went with Stax at 580V?
  4. Maybe a separate umbilical for the AC lines? Annoying to build, yes, but should help keep the EM noise away from everything else. I'm seriously thinking about joining this GB, if only to have the boards for the future. Which GRHV version do you plan to run? I suggest the split ones for layout flexibility, but could be convinced otherwise.
  5. Are you thinking a two-box build? The GRHV will need external heatsinks for the 10M90S and the SiC MOSFET parts, which complicates a single-chassis layout, given the size of the Megatron board, or calls for a huge box.
  6. @TMoney: What's your preferred setup these days, now that you ruled out both stats and the Utopia? Still have the HD800S?
  7. What headphone+gear and music combination do you think sounds great, relative to the Utopia? (Genuinely curious, I haven't listened to one yet.)
  8. AC buzz or hum sounds different from gain-related hiss, at least in my experience. What does your noise sound like? If it's more AC-like, then try to rearrange your wires, as Pars suggested. Sometimes trying to keep AC wires at right angles to all other wiring helps. Also, how did you connect the front panel switch? If you're running AC to the switch and back out into the transformers or PSUs, that might extend the resulting EM field. Shielded input cable might help reduce interference (not 100% sure about it). Sommer Galileo 238 cable, you can find it in 1m increments from various eBay sellers. Oh, and your heatsinks look fine! They also have rounded fin edges. Mine are sharp enough that I have to be extra careful picking this beast up. If you like my sinks, though, check out Fischer Elektronik.
  9. Are you trying to avoid the 750ohm and 500ohm parallel rig, or replacing the resistor with a single 300ohm part? I personally wouldn't short the R50/R51 because I'm not sure what might fry if the trimpot fails or if I slip while adjusting the bias and offset. Or are you trying to bias higher than 0.75V? I wouldn't do that, either. How hot does the amp run with the 0.75V you have now? My 0.40V passes the "can I hold my hand on it for a while" test, but runs way hotter than my Carbon, and I don't want it to run hotter than that.
  10. Yes, the Dynahi has a higher noise floor than the Dynalo. Not an unusual price for much higher gain. Just don't use the Dynahi with sensitive headphones, it's not meant to drive them and carelessness with the volume knob might damage the drivers (not to mention your hearing). It has a lower noise floor than a few much-less-powerful commercial amps I heard, which hiss like a snake with the HD600 and HD800.
  11. One day last year, while planning my Carbon build, I thought it would be neat to have a dynamic headphone amplifier in a matching case. The Dynahi suggested itself, though I wanted something a little less overkill. Then it occured to me that I might be able to stuff a Dynahi and a Dynalo into one case, and so make an amplifier capable of driving any headphone. So I made this, which I called the DDCA (Dynalo-Dynahi Combination Amplifier): one set of inputs feeding two amps, with separate output protection circuits, separate volume pots, three GRLV power supplies, and one transformer. It was a 3D puzzle to fit everything in (if I were to make another one, I'd position the Dynahi boards right-side up, turned out there is enough clearance that way and it would have simplified assembly) and the wiring took forever (plus keeping it perfectly tidy is beyond my skill). I lowered the gain on both the Dynalo and the Dynahi, since on most amps, I have the volume at 10 o'clock or less, and I wanted to use more of the volume control. Have to admit: the RK50 on the Carbon spoiled me, and the TKD 601 pots here don't live up to it. Not bad, though. Like I posted a couple of days ago, I couldn't bias the Dynahi section as high as I wanted, but even at 0.40V across the 20ohm output device resistors it runs fairly warm, so I decided to leave it alone for now. I also need to get the top anodized black. Maybe add some speaker binding posts... wonder how much of a speaker load I can drive from the Dynahi? Both sections sound great to me, though I don't have an HE-6 or K1000 to really put the Dynahi through its paces. As usual — many thanks to @kevin gilmore and @spritzer for all the designs and boards. This wouldn't exist without you guys. Thanks to @vilts for making matching titanium knobs, thanks to @Zashoomin for getting extra sand with me so we could make matched sets, and thanks to everyone here for group buys and all the help and support.
  12. I'm having trouble biasing a Dynahi. Board is from around a year ago, with the feedback resistors changed to 140k and the compensation caps to 3pF in an attempt to lower the gain. The highest bias I can manage is just around 0.42V. If I get it higher across one set of devices (the outer four on each side), it plummets to 0V on the other set (the inner eight). 0.42V is the best I managed so they're all the same (give or take a couple mV), with offset hovering at 30mV (I could probably get it lower, but it didn't seem worthwhile trying yet). Haven't tried my other board yet, but I imagine it'll be the same story, since I used the same batch of hFE matched transistors. I was thinking of replacing the 500ohm resistors next to the outer trimpots with 300ohm or 390ohm parts (I think they're R1 and R4 on the circuit diagram), since I have both values lying around, and try to get 0.75V bias. Is that a good idea?
  13. Yes, this was the problem. I drilled out the middle bridge holes to make the part fit and must have damaged the through-hole plating. A wire reinforcing the via fixed it, and all three power supplies work beautifully now. Thanks, guys!
  14. Interesting! I'm measuring no continuity between the collector of the MJW21193 and the bridge leg closest to the AC input. Would that explain it? In which case I guess I should just jumper those two points?