UNKNOWN: Parametric EQ / State-Variable Bandpass Filter

I found this schematic a little while ago and thought I might give it a try, as I've been looking to make a single band parametric equaliser, in this case, based on a State-Variable Bandpass Filter.   It's supposed to be from a Japanese textbook, but I'm not sure of its origin.  It looks remarkably similar to a schematic in an article published by John Roberts in Popular Electronics back in 1979.   

PARAMETRIC EQUALISER ORIGINAL - VERO LAYOUT

I've not built this yet, and I've only tested it on LTspice, so I can't vouch for how it sounds yet.  Could be a hot mess for all I know.  I'll update once I get around to testing this - fingers crossed...    

PARAMETRIC EQUALISER ORIGINAL SCHEMATIC

It has a broad frequency range of 70hz - 7khz, and approx 10db of boost and cut.  The Q also has a decent range, although I wouldn't mind making it a little tighter on the most extreme setting.

I added an extra opamp stage, as the stock version doesn't have a volume control, and it there would be a volume drop when cutting the signal.  I also like the idea of being able to hit whatever is following the EQ hard with a spike in the frequency range.

PARAMETRIC EQUALISER - MODDED SCHEMATIC