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woodear

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  1. this one is the first revision shown here on headcase: the one using Lundahl LL1690 and Jantzen Superior Z-CAP
  2. Does anyone want the PCB files? I've just made some changes for the older version PCB. coupling transformers are removed to give place to coupling capacitors(ideally Mundorf Supreme EVO or EVO gold-silver, other axial caps are OK if the size fits the position). By using coupling caps, the amp is cheaper and easier fur DIYers. filament power supplies are no longer constant current source, as the actual working current of filaments of different tubes may differ greatly, making it possible for the voltage across the filamanet to exceed 6.3V±0.3V limit, so I swithced to a pair of
  3. This is the new version of this ES. amp using a pair of Mundorf Supreme EVO instead of input transformers. When using coupling capacitors, the ground is not isolated anymore like a line input transformer with Faraday shield, and <1M grid risistors should be connected to the grids of ECC88 to establish a -420V DC bias voltage, which is the same bias voltage as transformer input version. This capacitor coupled version sounds more straightforward, more transparent, but with less "transformer distortion" which is a fraction of traditional "tuby sound". An
  4. This is a detailed(relatively) schematic of the latest version. The transformer should be a 1:1 input transformer with proper insulation(1000V or more), and a Faraday shield which is connected to ground plane. the plate load resistors are 2 or 3 watt 62k resistors. The power supply ripple rejection(PSRR) of resistor load is low compared to a constant current source load, so I added an active de-coupling circuit using only one enhancement MOSFET, and a few resistors and a capacitor, which significantly reduce power supply noise seen by the 4 62k resistors. -360V and -420V vol
  5. Sure, but I cannot upload pictures anymore, 500kB is all I can upload to this forum... Does anyone here know how to upload more stuff?
  6. The high voltage power supply is regulated, using a HV reg derived from John Broskie's idea of using high voltage depletion mode MOSFET, together with a 3-terminal voltage regulator IC, to form a simple but high-performance HV regulator. I did some modification on John Broskie's original design I use AMS1117adj instead of LT1085. AMS117adj has lower drop-out voltage than LT1085, and the 3A output current of LT1085 is basically unnecessary.(and AMS1117adj is cheaper) The large 120uf capacitor connected to the ADJ pin of AMS1117 lowers output noise, and also act as
  7. a 74kHz -3dB bandwidth is far more reasonable, the Cin of MOSFET buffer is certainly lower than 100pf.
  8. Hi JimL, 1, the input capacitance of MOSFET follower is not simply the input C shown in data sheet, when functioning as a follower, the AC voltage difference between MOSFET's gate and source is quite small(Vgs of the follower is roughly a constant DC voltage, the AC component is tiny), so the equivalent Cgs will not be as large as when S is grounded. the drain of the MOSFET follower is connected to power supply, so the capacitance between gate and the drain is only 1 x Cdg, therefore the Cin=Cgd+Cgs(1-gain of the follower), the gain is very cloase to 1, as a result, the Cin is quite clos
  9. I've built 6 versions, and this is the latest one(PSU board not finished in this photo, and there is only one pair of 500V 180uf filter cap in side the main chassis, but the amp does have another pair of 180uf cap, and rectifiers and a 250W transformer in a separate PSU chassis, so altogether,360uf x2 for the HV power supply, which is perfectly enough capacitance). It sounds quite fast and transparent due to a single voltage gain stage design, when compared to other tube ES amps. And due to the low output impedance, the sound is relatively powerful sounding and the bass is tight, although it's
  10. Hi guys,here is my hybrid e-stat amp design using only ONE cascoded voltage gain stage and a solidstate buffer which translate the high output impedance of the voltage gain stage into low impedance. The cascode voltage gain stage uses an ECC88 as input tube, for its low noise and high transconductance, and a 6SN7GTA/GTB to bear the high voltage(anode voltage is around 350V to get reasonable voltage swing). This stage will get approximately 200x, or 46dB gain. And please note that, the grids of ECC88 is biased at around -420V, so you can't really go DC-coupled, coupling capacitors or trans
  11. Enterprise is similar to T1 or KGDT, but the input stage is BJTs, not JFETs. Its high voltage power supply is classical Zener diodes plus MOSFET follower--nothing special, but the 580 bias voltage is supplied from a separate transformer winding and an independent voltage regulator while bias voltage of most electrostatic headphone amps are generated from positive HV power supply winding. Finally, Enterprise has a little OP AMP pre-amplification board, which amplifies the input signal before it goes into potentiometer. PS: I'm not the one who made Enterprise, but I know
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