In 2015, I had already built a few custom Porter EQs, and I started rethinking parts of the original circuit, based on the experience gathered.

To be completely honest, the original idea was to put out a scaled back, "less controls",  but "easy-to-do" version, but rather than cutting corners, I got lost in the details at every step of the processs, refining the essentials, rather than drowning it in features.

So instead of dumbing the circuit dow, it turned into a three year development and listening project, with numerous hours spent on circuit design  and countless hours spent in front of speakers, with friends and colleagues to turn it into what it is today. 

What I have now feels like a very personal iteration of the circuit, with a new level of refinement. Still a Porter, because the parallel filter section is identical to the original design, but also, very much a Grinder, because everything else was changed.

Pictures shows the last batch of units manufactured, before I settled on the Q-on-top layout


To makes sure the tracking of the channels are identical, I match the filter caps to 1% (or better) relative tolerance.

If I matched for absolute values, I would have to go through batches of 1000s of capacitors without the certainty of finding a single, absolute match, so I match for relative tolerances and perfect stereo tracking.

That means I only have to go through about a hundred to find a matching set of caps (4).

Selection of caps for the 680nF value used in the low end of the Porter-Grinder Precision Mastering Equalizer



For the earlier prototypes, I tried various switches, ranging in price and quality from Uraltone to Elma, but I never really found anything I felt comfortable settling on. 

I almost decided to do two versions of the EQ - one on cheap switches, and one on expensive - without really loving either choice myself.

..but then Blore-Edwards restarted manufacturing of their old PZ line.

They offered me a sample, which turned into a small purchase to build a full unit, which turned into a perfect result, and a perfect match for GOLY.

Frequency selector for the PG EQ


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