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joehpj

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Everything posted by joehpj

  1. I buy insulation ceramic kits, screws, nuts, or something like that from Taobao to cut the cost. I usually buy some samples first before I buy a lot. After I bought fake 10M90S, I've never bought high voltage silicons from China. It's indeed better not to buy form China when building high voltage amps. IMHO, it was like gambling. When you hit the jackpot, it explodes. LOL
  2. Buying from Chinese needs some more knowledge to know if the parts are genuine. I've bought from Taobao of 50 10M90S. Looked fine but turned out all fake. If you know which vender to buy from, of course you can save a lot of money.
  3. If I am going to drive high independence headphones with this, what should I do? 1) add triple darlington stage like tubehybrid/CFA did 2) add paralleled darlington stage like dynahi
  4. updated the BOM. 2K trimpot changed to 4pcs. 470R changed to 1/2w. 5W zener simply because it's slightly cheaper than 1/3w .
  5. Studied T2 schematic and found filament of EL34 was connected to -500V. Is there any benefit to separate -500V from AC in order to reduce AC noise? I was thinking floating the filaments just like GG and BH.
  6. 470R was connected direct to the tube structure so it will get hot easily. You can either lift the resistor or use higher power rating ones. I forgot why I used 5w. and the number of the trim pots. Please follow the silk screen. I will check the BOM later.
  7. Oh I was asking about the input attenuator. I used 10K for Carbon, GG which was JFET input. Should I increase to 25K or 50K for tube input? And thanks for the information! One more thing. Was the R65-R68 on the PS schematic used to keep the filaments grounded? I wanted to adopt the T8000 way of regulated input tubes filament power supply. So I will have to remove the two 47R of 6.3v and keep the rest two tied to 0V, right?
  8. What value of pot should be used? Kevin said he always use 10k but I wonder if it should be higher because of tube input?
  9. please use imgur and post the link.
  10. Was the trimmer in series of two 240R?
  11. When will you come to Taiwan? A HC Taiwan meet sounds interesting.
  12. I am at Taipei while ang is at the other side of Taiwan.
  13. What? Is mypasswordis also taiwanness?
  14. I was thinking if I should use regulated heater for the 6922. Those tubes amplify small signals and the amp itself has very high gain. And is there any problem to use same pair of leads for heating up the 4 front tubes?
  15. Yes. Chinese often call tubes as "gall bladder". It's just one word in Chinese. As an abbreviation.
  16. If low cost is the goal, JimL has a nice design SRX+. Simple and decent sound with fun of tubes.
  17. @kevin gilmore once mentioned JFET input. I have some J74 and K170. Any possibility to use them? Though I think I'll still stick to BJT anyway.
  18. Does this amp need extra standalone input stage? And can this amp ran single ended input?
  19. I believe SZ2 are 007A while SZ3 are 007mk2. (domestic / international version). All of my friends' 007A no matter manufacturing time are SZ2.
  20. Both. I didn't see any extra amp for headphone jack. See pic 3. The rear output and headphone jack was controlled with relays by the switch on the front panel. One will automatically mute when the other is on. It will be really sloppy for amp but I don't think people buying this kind of DA will not have their own amps. Yes digital volume control. I assume it was done by FPGA. I didn't take the picture of the 48 lead QFP so I don't know if that was the volume control. It could be bypassed so not really an issue (if it's really done by FPGA).
  21. This is not mine so I have to send it to the owner. I just got the chance of a brief listening. This DAC was really good for those have no skill/time to DIY. Compared with single 1021 w/ uber buffer fed into balanced CFA, uber has better sound stage and dynamics. 1541 has some more detail and sounded airy. The front panel is a convenient feature so changing digital filter and xfeed are much easier than DIY ones. The chassis however, was solid but compromised on finishing. It looked cheap. For a DAC now 1290 Euro, and made in Denmark, I can't expect it having a much better look though. The main issues here IMO, are 1) the performance of buck+LDO. I personally prefer some traditional way like transformer+ultra low noise linear PS. 2) the performance of the output buffer. It has only +-12V ps. But should be plenty for the output. It has different PS for digital and analog rail. The 1021 DIY module drive 5V digital parts form analog rail. Which was somehow compromised, too. So people have to choose form better buffer like Kevin's diamond buffer and some real ultra low noise LDO or isolated PS for digital/analog. PS. the OP based balanced buffer on 1021 is utterly shit. Use raw output and some better buffers.
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