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About steefdebruijn

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    The Netherlands
  1. 2018 PCB Group Buy with TKD pots

    The sws versions seem to have a tiny different mounting hole pattern. I see no other diffs but I could be missing something. I have the sws version.
  2. goldenreference low voltage power supply

    Sorry if I was not clear. I meant the rectifier boards.
  3. goldenreference low voltage power supply

    Is there a possibility to add them to the running group buy?
  4. 2018 PCB Group Buy with TKD pots

    Interested in boards for carbon (electrostatic) and balanced CFA (dynamic) builds. Already have GRHV so need several GRLV, carbon set and CFP2's. Could also use some attenuators for these.
  5. stax t8000 clone (well sorta)

    Hi how did you come to these values? As far as I understand the data sheet says typical 1.2Vf at 5mAf. With a 12V power supply (which I have on a megatron) running this through an online led resistance calculator gives a resistance of 2.2k can you enlighten me? tia steef
  6. Megatron Electrostatic Headphone Amplifier

    Ha! I knew that formula but didn't know if and how it could be put to use here :-) 3.9R gives me 166mA then. Should be enough for Megatron
  7. Megatron Electrostatic Headphone Amplifier

    Thanx @mypasswordis. I will use Kevin's suggested ones then. I have lowered the current limiter to 3.9R. Should that be enough? (how to calculate this value?) Steef
  8. Megatron Electrostatic Headphone Amplifier

    About load resistors to test the HV and LV sections of the PS. @kevin gilmore has stated somewhere in the Carbon thread 16K / 20W for the HV (per rail) 500R / 2W for the LV Can someone explain (or are these only valid for Carbon loads)? If I use 450V @ 150mA (to test with slightly higher load) I get values of 3K / 70W per rail (or two of 1.5K / 35W in series). If I use 12V @ 800mA (somewhat higher load) I get values of 15R / 10W per rail What am I missing? Tia Steef
  9. Closed - Megatron and GRHV PCB GB

    Package received. Thanks!
  10. Closed - Megatron and GRHV PCB GB

    Found another trafo manufacturer in Belgium (just around the corner so no excessive shipping fees I presume): http://www.monolithmagnetics.com/ asked a quote for one HV/LV and two filament trafos.
  11. Closed - Megatron and GRHV PCB GB

    Thanks for the follow up. Toroidy still a candidate then. Should I run for 13, 14 or 15 VAC secondaries for 12VDC regulated?
  12. Megatron Electrostatic Headphone Amplifier

    Thanks for your feedback. I agree to use a lot of trafo overhead but I just stated the trafo should be able to deliver 120mA @ 365VAC output (because higher current == lower voltage). If 20V drop is too low how much should we account for? I used the 10% variation twice because the land line (theoretically) can go as low as 10% below nominal and 10% above nominal. Maybe account for both 10% line overload AND 20% caps overhead is a bit over the top though. So, if we get a 350VAC trafo and use 25V dropout (for example) we can handle max 4% lower land line before PS falls out of regulation (350V ×,96 (4% lower land line) ×1,414 (rectifier) −25V (dropout) = 450VDC). Right? I reckon our land line is pretty stable so indeed should not be a problem. About the cap rating: with nominal output of 350V on trafo we have nominal unregulated 494VDC on first cap. That is at 89% of its max voltage rating of 550V. 'The internet' states larger margins - 20-30% - for this but the common sense here is that's overkill? With these numbers a 550V cap accounts for a max of 11% higher landline before it gets out of spec DC from the rectifiers. That indeed seems pretty unlikely. If we can feed the Megatron with +-400VDC without problems that indeed may be preferable. Are there other changes necessary besides the PS resistors and the 21k voltage drop resistor on the Megatron board to get 300VDC for the little tubes (should be lowered from 21k to about 14k i guess)? Steef
  13. Megatron Electrostatic Headphone Amplifier

    please bear with me but I try to understand the trafo/cap thing on the GRHV supplies. By reading this thread and the Carbon one from which the GR supplies emerged as far as I can tell we have to consider - 1.414 factor for rectified DC - minimum of 20V drop voltage across the regulator - 20% headroom on caps rating to assure long life - account for 10% max fluctuation of land line (230V here; governmental docs here confirm this) For 450V output I calculate 450(output) + 20(drop) = 470VDC prereg minimum / 1.414 = 332VAC minimum + 10%(max line flux) = 365VAC nominal output from trafo @ 120mA (which is the current the Megatron draws I read correctly). For the prereg cap we should use the max values. So 365VAC nominal + 10%(max line flux) = 402VAC max * 1.414 = 568VDC max prereg DC. Accounting for 20% overhead on caps to assure long life we come to 680V rating on the prereg cap. Am I way too conservative here, missing something or clearly not knowing what I am talking about? Steef
  14. Closed - Megatron and GRHV PCB GB

    I am very curious about your findings. Thanks in advance for any feedback on this.
  15. Closed - Megatron and GRHV PCB GB

    With these quotes and potential problems it is almost more beneficial to just get the Antek trafos and ship them to the Netherlands for the premium price. No fancy box to put on top of the case though... (and no 13/14VAC ones, just 15VAC so more heatsinking for the LV supply)