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Quadraphonic 90degree shifters (MC1312P)

Discussion in 'General Electronics' started by Marek P., Jun 10, 2004.

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  1. Marek P.

    Marek P. Guest


    I'm interrested years in classical gramophone quadraphonie and also
    studied some (in Czech republic often used in 70's) schematics with
    MC1312P and also with "logical circuits" MC1314 & 15.

    Now I'm going to write some pages and make epxerimental circuits for
    this SQ quadraphonie. I've only schematics, where the MC1312P is used
    with two Wien-like RC nets. I computed some frequency and phase
    responses and now I have some oppinion, which the internal structure
    of MC1312P is.

    From my computations it seems to me, that external RC Wien nets, when
    signals from their input is amplified and subtracted, gives signal
    with phase shift 90deg. at 0Hz and it's linearly increasing (a group
    delay [or is it call transport delay?]). So I think, that inside
    MC1312P there should be sth like "delay line", to do that linear
    phase shift with 0deg at 0Hz. Is is true? Or is the point of the joke
    somewhere else?

    I'd like a much to know, how this really works. Do you have any (MC1312P)
    **datasheet**s, descriptions or other (discrete) circuits? I know allpass
    filters built with opamps, but in configuration known to me they
    doesn't use Wien nets, only derivative RC and feedbacked opamp.

    Thank you for your help,
    Marek Peca.
  2. WDino

    WDino Guest

    The RC networks are basically delay lines. The DIFFERENCE between the
    two networks gives a 90 degree phase difference over the frequency range
    of interest.
    The MC1312 is a very old IC and as I recall just provided inputs and
    outputs to these networks. All of that can be achieved with opamps these
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