Need help wiring up a transformer

Discussion in 'The Projects Forum' started by Sho Bud, May 28, 2010.

  1. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    Not sure where to connect the 4 wires to the pcb.

    any help would be great.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    The 180v trace is practically touching the 0v/ground pad on the left end of the board. This is not good.

    Here is a datasheet for the LL1530: http://www.lundahl.se/pdfs/datash/1530.pdf
    The LL1530 is a 1+1:3.5+3.5 transformer.
    The datasheet for the transformer does not agree with the board layout.

    Here is the datasheet for the CM-2461NiCo transformer: http://www.cinemag.biz/mic_output/CM-2461NiCo.pdf
    See page 4 for the transformer diagram.
    It is a 6.5:1 ratio transformer.
    Red and brown are the 6.5: ratio side (high impedance)
    Yellow and orange are the :1 ratio side (low impedance).
    The red and the yellow are the dotted windings. This indicates the winding polarity.

    This is my best guess:

    [​IMG]
     
  3. Sho Bud

    Thread Starter New Member

    May 28, 2010
    11
    0
    Is red "ground"?

    thanks for the help!
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Red is connected to F-, whatever that might be.

    I basically don't have a lot of faith in the circuit.

    Perhaps AudioGuru will give you a hand with it.
     
  5. 311499

    New Member

    Apr 29, 2010
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    0
    [edit 05/31/2010]
    The 1G resistors are actually 1G; you can see it in the documentation.
    [/edit]
    [edit]
    The transformer is an LL1538, not LL1530. Datasheet for LL1538: http://www.lundahl.se/pdfs/datash/1538_8xl.pdf

    A larger schematic for the amplifier can be found at http://www.gyraf.dk/gy_pd/g7/gic_s.gif. The resistor I assumed was 33k is actually 33M. The two resistors in the grid circuit are marked 1G in the original schematic. It must be an error. Probably 1M is close to what they're intended to be.

    The "pattern" voltage (0...160V) appears to control the directional pattern of the microphone.

    More information about this amplifier can be found at http://www.gyraf.dk/gy_pd/g7/gic.htm.
    [/edit]
    "F-" and "F+" connect to the filament (heater) of the tube. "F-" is also connected to ground. This is not shown very clearly in the schematic.

    Here is a schematic with the connections shown better. I also tried to guess some resistor values:
     
    Last edited: May 31, 2010
  6. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    AudioGuru..... are you out there?
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    I studied vacuum tube preamps in University 45 years ago. I never used one and never saw one. Why do you have one?
     
  8. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    this is a vacuum tube mic.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    AudioGuru can't seem to figure it out, therefore he's pretty useless.

    I still stand by my initial recommendation.

    You can try it out, or not.
     
  10. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Sho Bud ... which transformer are you replacing? The LL1538??
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    GYRAF make only tube preamps and amplifiers. They are in Denmark.
    I don't like the distortion of tube amplifiers and I have never been to Denmark.

    The "tube" microphone is actually an old design "condenser" microphone.
    A modern electret microphone has the high polarizing voltage built into the electret material. A Jfet is used inside the electret mic to reduce its output impedance instead of an external vaccum tube. A very low distortion opamp is usually used as a preamp.
     
  12. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    Joe, yes, i'm replacing the LL1538.

    SgtWookie, i think you're right, but i just want to be certain.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Well, you might write a note to the person who drew the original schematic, and ask them what they think.

    I've already made my best guess.
     
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