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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 4th August 2012, 02:14 AM   #1
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Default Summing (2x) opposite-phase signals with Transformers

Hi, I've got a really neat old (40's? 50's?) passive (unpowered) EQ with balanced IO. It was originally either for vinyl mastering or maybe for some kind of recording pre-emphasis. It's basically an LPF in series with an HPF, and the controls allow you to scoop out varying amounts of bass and treble.

I bought it half-hoping that I could use it for the opposite purpose: to scoop out midrange in varying degrees. I looked into rewiring the EQ circuitry but it would be a crime, given how beautifully it's built.

Then I discovered that if I summed the EQed signal with the dry signal with the polarities reversed (not out-of-phase as the title says), it would behave in precisely the way I wanted it to.

I can accomplish this with active summing but I'd much rather do it passively, with a transformer(s). My sense is that I can do it with some combination of things similar to this: EDCOR - WSM6400

The confusion I'm having, though, is that the transformer above won't sum two balanced inputs (the dry signal and the wet signal), only two unbalanced inputs. It seems like there must be a way to accomplish it though, with this or something similar, as I have seen passive M/S encoding schemes that work with ordinary transformers.

Any hints in the right direction would be quite appreciated!

rs

ps - Makeup gain is not a concern here. I've got plenty to spare in this case.

Last edited by ryansupak; 4th August 2012 at 02:38 AM.
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