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Donald North

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About Donald North

  • Rank
    Member of the Trade: Donald North Audio
  • Birthday 12/06/1972


  • Biography
    Life-long music and audio enthusiast. See http://www.dnaudio.com/About-DNA.html for more info.
  • Location
    Los Angeles
  • Interests
    Music, hi-fi, skiing, and Saabs
  • Occupation
    Audio design engineer
  • Hobbies
    Music, hi-fi, skiing, and Saabs
  • Headphones
    beyerdynamic DT990 (originals), DT931, IRS690, AKG K240, K240DF, K1000, JVC HP-DX1000
  • Headphone Amps
    Audio Note Kit One (for K1000s), and my own designs

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  1. Donald North

    Binaural Head

    The MKE 2002 was an affordable binaural microphone made by Sennheiser. It looked like a stethoscope which you could fit on the included head "Fritz"-I believe or wear yourself. Price was around $800 when I bought it new in 1991. I liked the formfactor, but sound quality was not nearly as good as my homemade using the Panasonic elements.
  2. Donald North

    Binaural Head

    This looks to be a fun project! Back in college in the early 90s I did a lot of binaural experimentation. For a dummy head I used a styrofoam head with silly putty pinnae and flushed Panasonic microphone capsules (purchased from Digi-Key) at what would be the entrance to the ear canals. No electronic EQ was applied. Replay was through beyer DT990 headphones. This combo sounded better and more realistic than the Sennheiser 2002 dummy head which I also owned at the time and later sold. With this kunstkopf, I made several recordings that were startlingly realistic to my friends/classmates. Listening through beyer DT990 yielded the best results, bettering the K240M, K240DF, K340, and Stax SR84 at the time. For best personal results, I made these hangers for the Panasonic elements that fit over my ears, again positioning the mic at the entrance to the ear canal.
  3. Donald North

    NorCal 8/8/2009 Meet Impressions

    I promise to bring some Senns to the next meet
  4. Donald North

    the NEW Zana Deux, ZDT and Balancing Act thread

    I'll take a GOOD transformer any day over a capacitor. As for transistors...
  5. Donald North

    DNA (Donald North Audio) Headphone Amp

    Talking with Kyle at RAM, they changed out the large JJ B+ cap for a Jensen (orange color) and some of the internal wiring to Audio Consulting silver/cotton wire.
  6. Donald North

    DNA (Donald North Audio) Headphone Amp

    USG: No, I've never met Oatmeal769. Doug: I too suspect we probably agree more than disagree
  7. Donald North

    DNA (Donald North Audio) Headphone Amp

    With my Amplitrex, for the 6H30 I measure a plate impedance around 1300 ohm at my operating point. For the IEC output, you are forgetting that I add a series resistor on the output to bring the output impedance up to 120 ohm. And yes, my minimum 3x plate impedance claim is based around 32 ohm Grados. However I suspect most people with Grados will probably use the Low setting with 28 ohm output impedance. In this situation, the plate load impedance is around 4.5x. On the IEC setting with 600 ohm headphones I do measure gain about 6dB. With low impedance headphones, the gain of course will be much less.
  8. Donald North

    DNA (Donald North Audio) Headphone Amp

    My choice of bias is based on sound quality. Yes, you can bias the tube with a battery or LED but it has not been my experience that these necessarily sound better, having their own non-linearities. Film caps sound different be also not necessarily better. The caps I use are selected as part to achieve the overall sonic synergy. As mentioned before, the output transformers are custom made to my specification. In my experience, Edcor makes very good sounding transformers independent of price. Transformer design is somewhat a "black art". I have heard transformers by some other well-regarded manufacturers which didn't catch my ear and sounded boring and uninvolving to me. Higher price does not guarantee better sound. I believe the Sonett is well balanced and value engineered to deliver the best sound possible for the price. In my opinion the next level up in output transformers are Audio Notes. To use their M4 EI core transformers will double the price of the amplifier. Regarding power supply sag and constant current sources, do remember a good output transformer does double duty approximating a CCS. Also note the high voltages are decoupled between the 2 channels. As I have mentioned before, in my design the tube is always presented with at least 3x the plate impedance as a load, even with low impedance headphones on the IEC setting. Desired damping factor is a function of the headphone design. Some are designed for low impedance sources; others are meant to see a higher impedance source. In the Low impedance setting the output impedance is 28 ohms, yielding a damping factor greater than 1 with Grados. As has been mentioned in other threads, some listeners find little to no sonic benefit with >1DF on headphones designed for low impedance drive. Of course to each his own and listen for yourself.
  9. Donald North

    DNA (Donald North Audio) Headphone Amp

    Hi Socrates, Glad your enjoying your high-z output. Regarding gain switch, to which amps are you referring? Can you list a couple examples?
  10. Donald North

    DNA (Donald North Audio) Headphone Amp

    I had those transformers designed and made for a phono preamp personal project. I was planning to use the 6AS7/6080 dual triode on the output. Recently I changed the design and will use different output tubes: 12B4. They require transformers of different specification, hence the sale listing of these.
  11. Donald North

    Linear tracking tone arms experience

    I think what is most important is to buy a turntable which sounds good to you. Have you considered by new from a local dealer? Elliot Midwood of Acoustic Image in Studio City is an expert on turntables and their setup.
  12. Donald North

    Linear tracking tone arms experience

    I wouldn't go so far as to say unprecedented For that you need a Forsell or Goldmund The Sowther wires were incredibly small and flexible. The first Clearaudio tonearms used the stiff Discovery wire. I'm glad to hear they've addressed this problem. Where do you live?
  13. Donald North

    Linear tracking tone arms experience

    It's been a long time since I set up a Sowther/Clearaudio tonearm. You need a lot of patience for it because it can get frustrating at times. The early Clearaudio TQ-1 arm uses thick Discovery wire which was much stiffer than the very fine wire originally used by Sowther. This thick wire resisted free movement of the cart along the track. You actually had to tilt it downwards a slight amount towards the spindle for it to track all the way across the record I hope they've improved this.
  14. Donald North

    Linear tracking tone arms experience

    The lateral mass of the ET2 is closer to 100 grams. I disassembled one several years ago and weighed the mass of each component. With eccentric records, the stylus has to move the entire moving mass back and forth, which modulates vertical tracking force and causes extra side wall wear. As to the VPI turntable, I'd avoid the 12.5 tonearm which is nothing special. If you want pivoted, go SME V.
  15. Donald North

    Linear tracking tone arms experience

    Inner groove distortion is a function of playback - it's not in the record itself because it was cut linearly. Play a record with a good linear tracking tonearm and cartridge with microline stylus and there is no audible inner groove distortion.