Blackboarcult
Active member
With 14 opamps per channel plus output transformer, this is unlikely to ever make it into a DIY PCB, but I'm still posting it for those who like to nerd out to EQ design 
The Urei 530 was allegedly one of producer Michael Wagener's favourite EQs for guitar. It was (again, allegedly) used on Dokken's "Under Lock And Key" and Metallica's "Master Of Puppets", among others, and probably in dozens, if not hundreds, of late 80's records.
It is reputed to be less aggressive than other gyrator EQs when dealing with guitar tracks, I suspect because of some of the original signal being mixed in via the R46 100k resistor, and the Q being fairly moderate.
I spiced the whole thing (and had to wait more than 2 minutes for Ltspice to come up with the freq plot) and the bands are actually on the frequency they claim to be on, and fairly regular at that. I really like the way the designer bypassed the interactiveness of frequencies when designing with gyrators: three consecutive stages, each with frequency bands as separated as they can be (50-400-3150; 100-800-6300; 200-1600-12500). 11dB up or down for each, consistent across the freq spectrum.
I'll definitely use this trick if I ever have to use gyrators for an EQ, and I don't rule out making a rack unit with one channel on vero, adapted for guitar (rather than line) further down the track
Schematic HERE
The Urei 530 was allegedly one of producer Michael Wagener's favourite EQs for guitar. It was (again, allegedly) used on Dokken's "Under Lock And Key" and Metallica's "Master Of Puppets", among others, and probably in dozens, if not hundreds, of late 80's records.
It is reputed to be less aggressive than other gyrator EQs when dealing with guitar tracks, I suspect because of some of the original signal being mixed in via the R46 100k resistor, and the Q being fairly moderate.
I spiced the whole thing (and had to wait more than 2 minutes for Ltspice to come up with the freq plot) and the bands are actually on the frequency they claim to be on, and fairly regular at that. I really like the way the designer bypassed the interactiveness of frequencies when designing with gyrators: three consecutive stages, each with frequency bands as separated as they can be (50-400-3150; 100-800-6300; 200-1600-12500). 11dB up or down for each, consistent across the freq spectrum.
I'll definitely use this trick if I ever have to use gyrators for an EQ, and I don't rule out making a rack unit with one channel on vero, adapted for guitar (rather than line) further down the track
Schematic HERE
