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About zeta4

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    Oxford, , United Kin

Wigwam Info

  • Turn Table
    Rock 7
  • Tone Arm & Cartridge
    excalibur benz micro
  • SUT / Phono Stage
    own design with SUT
  • Digital Source 1
    Tom Browne Starlight
  • Digital Source 2
    Mirand usb Dac
  • DAC
    Discrete r2r
  • Pre-Amp
  • Power Amp/s
    300B SE/Ucd400
  • My Speakers
    own design
  • Headphones

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  1. The implementation that rabski mentioned turns out to be expensive, basically trimming the R and 2R values to less than 0.01% and making sure they stay that way. This was too expensive for chip manufacturers hence use of noise shaping technology to avoid having to do this. This brings its own set of subtle problems. A lecture given by the designer of the ESS Sabre line of dac chips went into this in some detail and showed it required some unusual measurement techniques to highlight and then solve these problems if they ever did. Personally I prefer the sound of an R2R dac with its set of problems over the noise shaping S-D ones like ESS or AKM with theirs so I made one, the Starlight 18 bit dac designed by Tom Browne of Sonic Illusions. I would love to demonstrate it sometime to see what others think perhaps at a bake off.
  2. Last week Boris Johnson visited an Institution for the Seriously Mentally Disturbed (no it wasnt because they voted for him) to see for himself the state of our mental health services. He inspected all the treatment and facilities available for the inmates. One area that stood out was the lovely kept garden so he struck up a conversation with the man tending it. It soon became clear that this man knew everything about gardening and a lot else besides, which really impressed Boris. Boris said "Well my man you sound perfectly sane to me and not the kind of person who should be in here " "That,s what I keep telling them but they wont listen " said the man. "When I get back to no10 Im going to get the Home office to review your case and get you out of here " "Thank you sir thats very kind " So Boris continued his visit but just when he was leaving a half brick flew out of the crowd and hit him in the back of the head. Dazed and bleeding he got up to hear a cheery voice say "You wont forget now will you ". .
  3. zeta4

    Time for another preamp

    Yes thats right about LA its all to do with the internal construction. I found that the ones made by Haze were good. which you used to be able to get them from Rapid. Even these do get noisier as they age but they are still quieter than most regulators. Sorry that doesnt help with small batteries but I thought I should just mention it.
  4. Yes thats right, both use the GAU-8 Avenger gun.
  5. zeta4

    Time for another preamp

    Depends on were you want to put the cut off point to minimise phase shift in the audio band . I think Morgan explains it in his book ( like everything else ! ). However like you said its worth giving it a try. I think you have a good point about the distortion reduction properties of cathode degeneration.
  6. These kind of guns are based on the ancient gatling principle with multiple rotating barrels. This gives the time to load fire and eject a shell in each barrel, andhelps cooling as well. Aircraft cannon like the Aden/Mauser use a revolving breech block to achieve a similar effect but with only one barrel they have a slower rate of fire.
  7. zeta4

    Time for another preamp

    An un bypassed cathode resistor will increase the valves Ra over a bypassed one which is probably only ok if the valve has a low Ra to begin with. I also think 100uf is a bit low. If you want a rule of thumb 1hz cut off, something like 330uf would do it though this doesnt take into account the valves parallel resistance. 1hz is a bit extreme though so a slightly higher cut off would compensate for the lower effective Rk. Something like 220uf might be a good compromise. All this is a good reason for other kinds of biasing like battery. Im using a string of 9 SIC diodes to provide - 7V bias for my HA/pre. Its very simple and effective. I dont know if something like this is practical in your case. If you have time a schematic would help.
  8. zeta4

    Time for another preamp

    Now back on line, electric keeps going off ! I think that bias scheme would be sonically better than a bypassed Rk but it wont do anything for your gain problem. Just how much gain do you need to loose ? Im sure the pot location is to do with the bias scheme. Come to think of it you could always use a step down transformer on the i/p which would provide a means for battery bias and give you a bit of gain reduction.
  9. zeta4

    Time for another preamp

    What about parafeed connection for the transformers ? You would be able to use a much smaller one. Im using some 4:1 step downs which measure 30mm x 25 x 25. However Im using a hybrid mu follower load with low o/p impedance. You would have to use a bigger one with a higher o/p impedance though but still much smaller than the Sowter. How much room do you have ?,
  10. Im sure its already been said before elsewhere but the usb signal shouldnt need reclocking , thats the job of the DAC. A decent DAC will generate its own clock. A usb DAC could be affected by a noisy power supply and ground connection but again a good DAC will be self powered with ground isolation. So in my experience if this device is an apparent improvement then the downstream device is suboptimal . Anyway Ill be interested in what you think when you try it. If I read the spec correctly thers is one reclocked usb o/p and one non reclocked ? If so Im sure you will try both.
  11. Good advice. I made the mistake of buying a Revell kit of a Spitfire Mk9 but didnt realise it was a level 5 for very experienced builders. Beautiful model but the painting particularly is beyond me. I should have started with that one.
  12. I think credit,s ok as long as your able to pay it back eventually . Our counrty works on credit (quaintly called borrowing) but look at the ratio of national debt to cdp. Im not sure of the exact figures but I think its now over 80% and going to get bigger. That,s apparently what austerity was all about. How can a government lecture people on credit when they are so deep in debt themselves.
  13. A friend who is a retired BA 747 captain told me that he was once reprimanded for over enthusiastic use of the rudder on the simulator. Apparently you can bend it easily (the real one). Is this true ?
  14. In PWM the pulse width is modulated by the analogue signal. It can be continuous or in discrete steps. Perhaps your thinking of Pulse Density Modulation where the analogue signal value is represented by the number of digital pulses per sample.
  15. Just as there many different ways of implementing a Class B or Class A amplifier there many ways of implementing Class D. So one Class D amp could and probably will sound different to another design. Each one should be judged independantly rather than as a class.