Switchable passive audio D.I box

Discussion in 'The Projects Forum' started by passive, Apr 18, 2012.

  1. passive

    Thread Starter New Member

    Apr 18, 2012
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    0
    Hi this is my first post and I could do with some help.

    I fancied making a passive D.I box, D.I box as in turning an unbalanced line level into a balanced mic level for use in studio recording.

    I think I have attached the circuit diagram but wanted to have two transformers in the enclosure and had a switch to choose between the two and have the switch for the transformers after the switch for the pad in the chain.

    I hope I'v made sense and hope to hearing back with some help.

    Ta.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    I see your diagram just fine, but I don't really see a question. When you say multiple transformers, are you really wanting different turns ratios? There are impedance matching transformers that provide many options, maybe 5 or 6 different ratios from the same transformer.
     
  3. #12

    Expert

    Nov 30, 2010
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    That's a top quality schematic. I don't know why you'd risk gumming that up to add an unknown transformer level. You need to get clear about WHY you need something different or we won't know how to guide you.
     
  4. passive

    Thread Starter New Member

    Apr 18, 2012
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    0
    Well I mainly wanted it as a comparison, so one transformer gives the certain "sound" of a console that use's it against another. With the other transformer being an 11.5:1 transformer. Sorry if I sound like I don't know what I'm on about, but I don't.
     
  5. #12

    Expert

    Nov 30, 2010
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    You're barking up the wrong tree. 10 to one compared to 11.5 to one, in a pair of transformers that do everything they can to NOT cause any changes, is a fools errand. The only thing that will change is the amplitude, and the PAD does what you have ASKED FOR, already.

    To get what you WANT, you should be looking in a very different place.
    Please resume thinking about what you want. With a better definition, I might be able to steer you where you should be looking.
     
  6. passive

    Thread Starter New Member

    Apr 18, 2012
    3
    0
    Thanks for your input. If you could be so kind as to help me with what would I need to introduce an active buffer in the circuit, as described in the attachment?
     
  7. #12

    Expert

    Nov 30, 2010
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    OK. "Passive high impedance instruments" means things like guitars. Single ended, fairly high voltage, sometimes greater than 6 volts peak to peak, impedance as high as 250k ohms.

    An ideal buffer would be a TL071 op amp with at least dual 9 volt supplies, configured as a gain of 1 positive amplifier. Figure one on the datasheet.

    I could do a pretty good compromise with a single jfet and a 9V battery, but it takes skill to bias one of those.
     
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