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Helium

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About Helium

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  1. Blue Hawaii BJT Build thread

    What are the consequences if you just wire jumper 5R1?
  2. goldenreference low voltage power supply

    Is OPA134 or LME49710 good for +/-30VDC output? Supply voltage is ±2.5V to ±18V, so I guess not. Only choice is OPA445 then. Could you elaborate more on zener please? Is 9.1V 1W 1N4739A from the BOM good for +/-30VDC output?
  3. and now for something completely different part 3

    Kevin, still I have a question about input impedance. Maybe I don't get it right. There is a diffrence between schematic and PCB silkscreen. Schematic says R17 is 10K (=input impedance). Board silkscreen says R17 is 1K + 20K. Does it mean that actual input impedance is 21K? Or is it 1K? I'm trying to figure it out to build relay attentuator. 10K vs 21K is huge difference for proper potentiometer selection.
  4. KG Balanced Dynahi build discussion thread

    I may be missing something, what is GRLV plus? Edit: I mean GRLV vs GRLV plus.
  5. and now for something completely different part 3

    Yes, but it's better to know voltage first. If it's close to 30V, I personally wouldn't use tantalum cap rated 35V. They will be at boarderline of specified voltage and tend to explode, unlike MLCC.
  6. and now for something completely different part 3

    @Pars, What p/n you used for 47uF cap? Can you please measure voltage across it (at 30VDC power supply)? I have difficulties in finding that rated over 25V.
  7. and now for something completely different part 3

    Well, maybe Kevin knows something I don't know) Anyway, I would use metal-oxide or metal film insted. To be specific, I'm ordering 71-CPF3-D-1. Also I remember AMB clearly discouraged against using wirewound in similar locations in his beta.
  8. and now for something completely different part 3

    Are you using 1 Ohm wirewound type resistor? I would stay away from wirewound type in sigal path due to their high capacitance and inductance.
  9. and now for something completely different part 3

    What's the input impedance of cfa3? And same question for krell ksa5 klone please. My guess is 10K and 50K respectively, but want to reconfirm.
  10. and now for something completely different part 3

    While thinking over building this amp, I'm considering to replace 546B/556B with 550C/560C. I've got a lot of them matched for B22 projects. Could anyone advise if any problems with them (Vceo lower 45V vs 65V, but typ. hfe is higher)? PS will be 30VDC.
  11. and now for something completely different part 3

    Kevin, so is matching them at Ib=1mA OK? (provided that hfe is ~200) Why? They are basically identical, except that MJE can sustain more power (=better), but doesn't have isolated tab.
  12. and now for something completely different part 3

    Yeah, English is not my native language I'm going to use Toshiba 2SC5171/2SA1930 as output BJT. Pinout is same to MJE/MJF. Regarding matching, I'm trying to figure out what Ic or Ib or Ie I should aim at while matching them for CFA circuit. I've got different devices for measuring hfe. One of them declares measuring hfe @ Ic=5mA, others do this @ Ib=10uA, 1mA, 10mA. So I'm a little bit stuck here (Ic vs Ib, and appropriate range). mwl168 mentioned he's running 220mA bias current. Can it be asumed that 220mA is Ie? Maybe Kevin could chime in?
  13. and now for something completely different part 3

    After mwl168 wrote his impressions on the sound, this amp looks very temptating. Ordered 20pcs PCB (SE version, so 4 needed for balanced bridged amp). Plan to use Toshiba BJT as output transistors, as I was unlucky with matching MJE15030 and 15031. Never tried to match MJF though, but I think they are hardly different from MJE.
  14. The Multi Amp aka Dynalo Mk2

    It might be transistors are heating THAT340 thru copper layers. Are they soldered directy to board, or plugged in sockets?
  15. grounded grid

    @Laowei: Just curious, what GG board file are you using? What I'm looking at has slightly different traces layout (was posted 20160224). Can you check yours if its newer?
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