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Thread: High quality 16ohm L-Pad

  1. #16
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    Thanks, now I understand how to use the R82b to operate at 16ohms!
    I expect the Fostex R82B to be of much better quality than the simple parts-express l-pads. But the way they work is the same, isnīt it?
    Whereas the Fostex R100T is different, they call it transformer type attentuator... but these are only 8ohms...

    Thanks for your offer of the Noble RPH25, but I would prefer new ones.
    But I suspect these arenīt available, are they?
    And again, are these functioning like the usual l-pads and just of better quality?
    Or are these something special like the Fostex R100T ?

  2. #17
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    Fostex r100 are autotransformer which is different from usual Lpads. Noble RPH25 is not available anymore, only on second hand market.

    https://m.review33.com/forum_msg.php...mber=11&sort=1

  3. #18
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    Ok, so R82b and Noble RPH25 are usual lpads.

    Are you aware of any other autotransformers on the market today?

  4. #19
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    Quote Originally Posted by Dr.db View Post
    Ok, so R82b and Noble RPH25 are usual lpads.

    Are you aware of any other autotransformers on the market today?
    There are nice autotransformers from Germany ;-) on eBay.
    I'll try to find the link. I had the opportunity to measure two of them, and they work well. You can use them directly with Compression driver/Horn (with a power resistor in parallel to the input) like in the TAD DN2404 crossover. Distorsion only rises below 600Hz.

    Note: it is there, with explanations in German special for yourself: https://www.ebay.fr/itm/Autotransfor...QAAOSwLjRa6v0N

  5. #20
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    Thanks a lot for providing this very useful link!

    I have to ask this silly question; do autoformers sound better than usual resistors e.g. l-pads?
    Some people dislike resistors/l-pads in crossovers... But than again, JBL got rid of these in their crossovers years ago. Especially Greg Timbers wasnīt a big fan of autoformers anymore...

    But Iīm still wondering why they used autoformers in the past rather than using resistors. Autoformers must have been of some advantage, if not why use these more expensive autoformers when you could use cheaper resistors instead?

  6. #21
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    Hi,

    the main advantages are that autoformers per se don't dissipate heat and that output impedance, as seen by the driver, won't increase when turning ccw. In contary it will decrease then. But there's also a big disadvantage: Input impedance, as seen by the filter, will increase when turning ccw. Xover designers have to cope with this, as otherwise the frequency reesponce depends on the attenuator setting.

    Best regards!

  7. #22
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    Input impedance variation is compensated by the resistor placed in parallel to the autotransformer input. With the apropriate resistor value, circuit input impedance will be the one of the resistor. For the model I provided the link I used a 8.2 ohm power resistor.

  8. #23
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    Just have to know where to look. I used these on the Ethyl Mermans for the 16 ohm 2251Js. You can also get them on ebay if you look for Fender L-pads. Ebay doesn't list the impediance, but uses the same part # and IIRC, that's where I got mine.

    https://www.guitarpartsfactory.us/in...roduct_id=5172

  9. #24
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    @Kay Pirinha & dn92:

    In laymans terms; what is the difference in sound?

    @Tod:

    I bet not many are aware of these, great

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