Hello, 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.