load on pre amp

Discussion in 'Preamps / Channel Strips' started by Pre Amp, Aug 27, 2005.

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  1. Pre Amp

    Pre Amp Guest

    I was reading in another proaudio forum, that some guys use there API 512's for preamps (in a lunchbox). But what they do different is attach a bigger load (resistor) to the pre amp to make it sound smoother.
    For instance, they said that the API 512's were made to be installed into the slots on an API console. However, the circuit load on a board that size is signifigant, when campared with the circuit load contained in a lunchbox.
    Now one guy says that he read using a 600 ohm resistor was better than using it alone. His reasons were that, the load induced a more closely matched load from an API console, thus making the tails (peaks, ect.) have a different / better sound.
    And another guy says that a 1200 ohm resistor is better, because it is closer to an actual API console circuit design.
    Anybody else do something simular? I have an API3124+, and they are the same preamp as the 512's. Does this sound like it has any real truth to it?
  2. Kev

    Kev Well-Known Member

    Nov 13, 2001
    some truth to it

    the output has a transformer designed to carry some load ... certainly more than is typical these days when loaded into a modern bridging input.

    This load will get more energy running through the core .
    AND many people believe the sound comes from the iron.

    Additionally it may also need some attenuation post API. The API may have a max output of say 26 to 28dBu and the interface may be as low as -18dBu.

    SO by using a load resistor of 1.2 k ohms down to 600 ohms you can load the output trafo and stop ringing etc and get a little more 2nd Harm Dist
    then attenuate by 10 dB
    To allow the COOL sound and still keep things under the 0dBFS on the DAW ... give or take a couple of dB

    makes sense ?

    I could get deeper if you like but I think that covers the basics.
  3. therecordingart

    therecordingart Well-Known Member

    Jul 28, 2004
    This is good stuff, Kev. When I build my 312(s) do you know if Fabio pretty much cloned...or did he make improvements for the DAW fellas?
  4. Pre Amp

    Pre Amp Guest

    Please do.
    I went to school for 5 years for electrical school, so I should understand everything you throw at me.

    I would like to connect the load to my preamp and do some tracking to hear the results. I certainly can see where this all makes sense. It is somewhat along the same idea as the THD hotplate, or the Marshall Powerbrake.
  5. Kev

    Kev Well-Known Member

    Nov 13, 2001
    kind off
    but in the long run not as critical as a power amp.

    you are making Fabio's unit ?
    with what for an output trafo ?
  6. Pre Amp

    Pre Amp Guest

    No. I don't know Fabio

    I'm just looking to add a resistance to the load on the unit, that is closer to an API console. So that I can get that smoother sound out of my API 3124+.
  7. Kev

    Kev Well-Known Member

    Nov 13, 2001
    Just start with a 1.2 Kohm resistor across pins 2 and 3 on your destination XL3 or termination

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