After six months of ground loops, bad solder joints, and some bad ideas. My “Dog’s Breakfast” Series 2 Bose EQ is complete. No buzz, and hiss only when you crank the SGCD/Preamp and M700’s to 100 (no music). At normal listening levels, you only hear the music.
DHS who has an EBay service that will modify any Series Bose EQ was the “inspiration” for the mess I created. I took his Audiophile Modifications a few steps further adding a Toroidal Transformer (guess where I got that idea from - and it was a huge improvement in SQ over the crappy 50 year old one that was in there). After the transformer, I added an industrial grade full wave rectifier module followed by three KEMET super low ESR power supply capacitors for the 3 voltages that feed the Bose EQ circuits. All signal capacitors are SoniCraft ordered from their website (see DHS’s eBay Audiophile version). All other Aluminum Electrolytic’s are Made in the U.S.A. Vishay’s from Mouser. All resistors are Vishay 1% metal film 1W - 3W. For the transistor bypass caps, I removed the ceramics and installed WIMA’s. For the final wiring of the audio paths, I chopped up a 1.5m RCA cable and used it to interconnect between the Bose EQ and the Chinese “Black Bear” adapter boards. I replaced the cheap crap with OPA 2134’s, WIMA bypass caps and Vishay Aluminum Electrolytics. Left the “1% metal film” resistors intact cause that’s just too much work with little return. I’ll just assume they are what stated on their eBay website. The PCB quality is actually pretty good considering it’s Chinese.
Ordered some sample OPA627’s and Brown Dog adapters (work great) to try out some op amp “rolling”. No harm when the parts are free.
If ever put this awesome sounding mess into a chassis, I might actually finish designing and getting fabricated a full circuit board. That was my original intent before getting this Series 2 box from eBay and getting into some nasty Rabbit holes.