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Everything posted by joehpj

  1. I tried to take every detail. I still have some photos if someone need more details. Overall sound is good. This dac runs warm. Quiet curious about the buffer design. comments plz @kevin gilmore
  2. Nice build! Quite interested about how will RK50 affects the sound. Never heard one before.
  3. What's the current of -15V? I was thinking of using some ultra low noise LDO instead of GRLV to shrink the footprint. If I have to compromise one lead of the umbilical because of not enough lead for the TS. Should I use one 1085 for the front end tubes or tie F- to GND? I have 10 leads in total. +-400/+100/-15/GND/bias/6.3VAC are 8 already. For the tubes, I think 6922 will be a better choice because of higher max voltage for longer life. 6DJ8 is pretty limited. I was thinking using some 6H23p though.
  4. What's the PS plan for front end tubes now? Separated GRLV for both positive and negative rail or use voltage dropper on negative rail?
  5. A few noob questions. There are some more parts after voltage dropper to get +100V. Is that because the B+ in T8K is unregulated? It seems stax use regulated PS for the tubes. What's the function of Q19, Q21, Q27, Q30? These seems to first appear in T8K. Stax used some low-noise parts like KSA992 and KSC1845. And stacked KSA1156. Any chance to adopt them in Tube-carbon/Sandwich or even Carbon? Feedback is 200K in Carbon and 300K in T8K. So maybe there chance to lower the feedback in Carbon? Most important is how do you think about the front half of T8K comparing to your design? For the negative supply for the tubes, I like the way tube-carbon does which doesn't need -15V supply. But I don't know the noise level difference between GRHV and 7915/GRLV. Thanks.
  6. Whoa! Looked much more complicated than previous Stax amps. Looked like regulated heater. Zener string for front end tubes?
  7. sounded promising is tempting! detail please.
  8. Did you use regulated supply for front end tube heater?
  9. Connecting G3 to anode is theoretically better. But EL34 is a pentode so it has a real suppressor grid so tying G3 to anode should be fine. 6CA7 is a beam tetrode, so the G3 is actually a beam forming plate. By connecting G3 to plate will make it unable to form electron beams. I don't know if this will make the tube kinks or acts strangely as the plate was originally trying to avoid secondary emission. KT77 has G3 internally connected to cathode and pin 6 jumped. So far as I know EL34, 6ca7, KT77 worked fine in GG. I wonder if it will be the same under T2 configuration.
  10. I am thinking of building a Uber power amp. Can I just add a pot in front of the driver board to make a single ended amp? So I will just need 1*40V GRLV and 2 sets of driver/amp. Or should I use a dynalo as input buffer since I have one? What does the + reg drive on the uber2 stands for? And I plan to lower the bias to cool down the amp a little bit. Which resistor(s) should I change? Thanks!
  11. Really? I don't even know RK50 will fit
  12. I use 325V/250mA secondary for [email protected]*4 for carbon. Megatron should be almost the same.
  13. The voltage there was 10.xv as I recall. Change to 18v will avoid clipping but 12v should be plenty during normal usage. Congrats on the successful build!
  14. Please call an ambulance. 1021's dead. BTW, the noise should be out of 20kHz so it shouldn't matter?
  15. How would these compare with LDO+IXTP01N. I assume noise will improve a little bit by using using LT3042. I like the simplicity of the LDO and modern parts are easier to source.
  16. Yeah... So, I will do it with separated winding with LT1083 regulator. All floated. I do it mainly because I plan to use separated ps box. Running AC with DC in a same umbilical cord seems somehow compromised for me.
  17. Is there actual benefit to have both 6922 and EL34 filament regulated or only 6922 is required?
  18. I was thinking to build one adjustable DC supply to use some P88CC or 6N23P. Those have much more reasonable prices. Filament will sit a little bit at negative. So negative LDO is preferred?
  19. I always wanted something that can beat T2 output power. 2SC4686 has been obsoleted and need 3/ch to do 500V/20ma. I check the datasheet, c4686 has 2.2pf output capacitance so it will be 6.6pf in total. Fairchild announced SiC BJT but was never available on the market. GeneSiC has some available on the market with some silly price. Among those, this has the lowest Coss. http://www.genesicsemi.com/images/products_sic/sjt/GA04JT17-247.pdf 16pf Coss about 2.5 times than c4686. But I don't know why this thing should be BJT(alike?) but those pin out are labeled as DGS. BTW. series caps are need for 600V and means we'll need 4x caps than 450V to get the same capacitance. Much more expensive to build. I don't know if this has that much difference on the sound. Normally no one will and should drive it to clipping.
  20. I googled for some substitute for c4686 which has been obsolete. And found MJW18020 seems to be a nice current production one. 1kv Vceo with much higher Pd makes it easier to do 500V 25mA. Any thoughts? Edit:No. output capacitance way too high.
  21. I wonder if it's possible to add a voltage dropper like megatron did to lower 1156 and 5026 Pc and push the output voltage a little bit further? Say 475V~? ( I assume 10M90S+DN2540 can take 950V in total to be safe.) Or even -500V since EL34 output will need approx 35V across the tube.
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