Oops, sorry Harpo. I'm using a Toroid-brand transformer, model #602.152. It's 0-15V, dual secondary, rated for .80A per secondary. Right now, I have it wired with BROWN and ORANGE together to the GROUND of the PSU (as a pseudo center tap)(with a third wire which goes to star ground), while the RED and YELLOW secondaries each attached to a respective AC input on the PSU. Previously, I had RED and ORANGE twisted together and attached to the GROUND input on the PSU (also with a third wire to star ground) and YELLOW and BROWN each separately attached to one of the AC inputs on the PSU.
Both configurations had a high level of stray field buzz injected into the EQ boards. To confirm this, I unbolted the transformer and lifted it out of the chassis (as far as it could go with the wires still attached). As I moved it around, I could find areas and positions where the buzz diminished considerably. However, none of those positions lent itself to convenient mounting. Furthermore, no position was able to diminish the buzz to a level at which the EQ could be usable.
As an aside (due to other posts mentioning this), I've measured the resistance of each of the chassis panels to star ground and none measures more than 1 Ohm (most, if not all, were below 0.5 Ohms). Accordingly, I'm doubtful that the Faraday-cage-like effect of the chassis is compromised in any way.
To further muddy the waters, another pair of Night EQs I am building at the same time used a different brand/model of toroidal transformer. That transformer is an AMVECO 62063-P2S02 (25 VA, dual 15V secondaries). This transformer has much less buzz induced in the EQ boards, but is still not quiet enough for use.
Anyway, I hope this makes my problem a little clearer. Thanks for the attempts to troubleshoot this one.
Dan