Jump to content

JimL

High Rollers
  • Content count

    568
  • Joined

  • Last visited

Community Reputation

251 Excellent

About JimL

  • Rank
    Limited Edition Bronze Participant

Recent Profile Visitors

2,299 profile views
  1. JimL

    CCS mod for 006t (t1 Variant )

    A few comments: 1) absolutely agree with KG and spritzer about ONLY using the ceramic insulators. This was explicitly stated in the parts list in my article. 2) the safety resistors are 5.1k, NOT 51k 3) for the T1, a 4.7 megohm resistor also needs to be added to the bias lines going to the output sockets - Mouser has a 1/2 watt 4.7 meg/1600 volt resistor that does the job. Don't know if the 006 already has this. 4) I recommend setting the CCS at low voltages before installing the circuit board - if you don't have a low voltage PS a 9 volt battery will do the job.
  2. JimL

    Megatron Electrostatic Headphone Amplifier

    No problem. Dropping R19 to around 19k should do the trick. Also, if R12 is increased to 11.8k, the gain structure will remain unchanged.
  3. JimL

    Megatron Electrostatic Headphone Amplifier

    !.5k for R11 is fine. R21 is the feedback resistor. If you want the front end voltage to be around 300 volts you should decrease R19, which is the drop resistor.
  4. JimL

    Megatron Electrostatic Headphone Amplifier

    I would start with changing R11, so that the plate voltage is around 240 volts. This will ensure that the driver stage does not clip. If you decrease R11 alone, that will increase the gain, as it is part of the feedback network. Increasing R12 to keep the sum of R11 and R12 the same will maintain the same closed loop gain, but it will only change the plate voltage by the amount of voltage change in that resistor alone. In other words, if you have 1 mA plate current, and you change R12 from 10k to 11.5k, that will only change the plate voltage by 1.5 volts.
  5. JimL

    Megatron Electrostatic Headphone Amplifier

    Jose, If you are using R11 of 2.0k, that is why your plate voltage is too high. I suggest dropping R11 to 1.5 or 1.6k. Then if you want, you can increase R12 so that the sum of the two is 13.3k. However, R12 shouldn't affect the plate voltage to any significant degree, it is R11 that is the prime determinant. You want to aim for a plate voltage around 240 volts.
  6. JimL

    Megatron Electrostatic Headphone Amplifier

    So, just a little technical explanation if anyone is interested. In the Megatron design, the driver 12AX7 and EL34 outputs operate within a global feedback loop with the gain set by the ratio of R21 (33) to R11+R12 (23+24). The operating conditions for the 12AX7 are set by the constant current loads Q1 and Q2 and the grid-to-cathode voltage which is set by R11. If you look at the tube characteristics, for a set grid-to-cathode voltage, as the plate current increases the plate voltage will also increase. However, because the plate current runs through R11, this makes the grid-to-cathode voltage more negative, which further increase the plate voltage. The result is that the plate voltage gets closer to B+, which can result in premature clipping of the driver stage. So in order to increase the plate current without increasing the plate voltage, we must decrease the grid-to-cathode voltage. This is done by decreasing R11. Note that this will also increase the overall gain and decrease the closed loop bandwidth, however, since R11 is only 1/3rd the value of R12, a 10% change in R11 will only result in a 2.5% change in gain and bandwidth. If we wish to maintain the overall gain and bandwidth, then we need to increase R12 so that the sum total of R11 and R12 are unchanged, .e.g if we decrease R11 to 2k, R12 should increase to ll.3k.
  7. JimL

    Egmont/Tubecad with CCS

    The CCS should definitely improve the Egmont as congo5 has reported previously, but you are still limited by the basic circuit - yes it's OK if you want to build the simplest, cheapest possible amp, but the basic SRX circuit is a significant step up and not that much more complex or expensive.
  8. JimL

    The Headcase Stax thread

    Weird. I was under the impression that they were assembled in a clean room, which means masks, gloves, etc. and so no finger marks. Or maybe that's just assembling the raw drivers?
  9. JimL

    The Headcase Stax thread

    Yeah, I think the Sonoma is more a "lifestyle" item than an audiophile thing. You know, young exec who owns a BMW, a full set of Danish modern furniture, and wants a stylish headphone set to display - sort of like a B&O system.
  10. JimL

    current feedback electrostatic amp

    Sounds like it's even less expensive than the SRX Plus! Which means there are now two good budget amps with different sonic "flavors."
  11. JimL

    The Headcase Stax thread

    BHSE/007 MkII w/ port mod is somewhat less of a financial jump, and some of us prefer it to the 009.
  12. JimL

    2SA1968 substitution

    The Single Power ES-1 for $23,000 USD cracked me up.😆
  13. JimL

    Constant pressure tube substitution

    As best I can tell, I believe you are referring to zener diodes Z3 and Z4, which are 47volt rated in the SMR600, and presumably the same in the SRM007. It would be less confusing if you didn't make up your own names for components.
  14. JimL

    Denafrips DACs

    FOTM = Flavor Of The Month, i.e. whatever is the latest internet favorite, generally replaced as soon as something new comes along.
  15. JimL

    Denafrips DACs

    In terms of price, yes. The Pontus (cheaper) and Venus (more expensive) bracket the Yggy in price. The Terminator is almost double the Yggy's price.
×