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  • Tape head pre amp

    Hi
    I am building a tape head amp from a Western electric circuit design using 417 A tubes, it is two mono circuits sharing the same cabinet. The power supply is a dual regulated shunt with a choke running a GZ 34 1950s Mullard It will have gain of 46 db. My question is this.

    The circuit that I have is for the Nab curve and I want to use a switch to change from Nab to IEC, I can not find any circuit schematics that show the IEC curve. I believe that I will have to change the resistance or capacitance or maybe both to change curves.

    Can anyone point me in the right direction ? Thanks

    Don

  • #2
    get your hands on the Bottlehead Eros schematic, they layout IEC (CCIR) and NAB curves.

    Comment


    • don
      don commented
      Editing a comment
      Thanks
      I have looked at the bottlehead and although I have and like some of their products I do not want a modified phono pre

  • #3
    I'm on my way to completing my DIY to compare to the deHavilland

    Try here I'm using ampex prints but this should work: http://www.nomanlab.com/sale/lim_docs/nab_to_ccir.pdf
    Phono: Aesthetix Io Eclipse with 2 Power Supplies and Volume controls
    Brinkmann Balance & RonT Tube Power supply with Kuzma 4-point ,FR64S, Brinkmann 12.1 , .Koetsu Jade Platinum,Koetsu Rosewood Signature Platinum, Lyra Atlas Lamda, Lyra Etna SL Goldfinger Statement, KLAUDIO RCM, HRSM3X
    Amps: Custom Direct Drive, Wyetech Topaz, Futterman H3 Quad II,Citation II, Marantz 8b, 5 ,2. Bedini 25/25
    Pre-Amps:Marantz 7, Marantz Model 1 Consolette Pair
    Speakers: Beveridge Model 3 Direct Drive amps, REL S/2 x 2, Quad ESL pair
    Otari 5050BXII, DeHavilland 222

    Comment


    • don
      don commented
      Editing a comment
      Thanks
      This is what I needed, I have searched for many hours and could find this, I guess that I will have to refine my search abilities. I do have one question, are you going to build as part of the circuit and use by a switch or as a separate device as it is designed to be.

    • kcin
      kcin commented
      Editing a comment
      I will be using a switching arrangement and will insert some trim pots to give me some further flexibility. Good luck with your project.

  • #4
    Hi Don
    ,
    If you compare the IEC and NAB curves after normalizing them both to 1Khz, you will see that up at the high frequencies the IEC is below the NAB by only a few dB. Practically, if you're using a series RC for the feedback network and you have it set pretty close for NAB and assuming that the R primarily effects the high frequencies (HF), try reducing it till you get the HF response above 1Khz "decently smooth" for IEC. Then put in a switch to select between values.

    The lows are another matter because you have the the response "bump" of the playback head "added to" the EQ curve applied to the tape, To mitigate this, I've found that either loading the head with a resistor (try starting with 10K), OR a much higher value (180K) across the C. This other R may have to be increased or switched out for IEC. I've found that the final low frequency response becomes a tradeoff between "taming" the main head bump (usually around 60hz) and rolling off ALL the lows (below 100hz) too much.

    Unfortunately, a test tape with tones may not have all you need in the low range. A sweep tape is more revealing but observing/measuring the results can be a real bi..h.

    Good Luck

    Charles

    Comment


    • #5
      Thanks Charles

      Comment


      • #6
        http://www.nomanlab.com/sale/lim_docs/nab_to_ccir.pdf
        Myles B. Astor, PhD, Administrator
        Senior Editor, Positive-Feedback.com
        ________________________________________

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