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Quadraphonic 90degree shifters (MC1312P)


Marek P.

Jan 1, 1970

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.


Jan 1, 1970
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