Dear Amimbari, Duffy49, Modern Growl, M0ses and Toastfuzz; thank you so much for your informative, honest and thought-provoking feedback. It is deeply appreciated, believe me.
The Phat II EQ unit is now in the innards of my bass player's
Washburn XB125. After several rehearsal sessions and live gigs, it continues to function as it should, i.e. boosting the volume/highs/lows; sans noise. Case closed.
Amimbari, that's a nice preamp you have in your GSR200. Neat layout and soldering. Perhaps you could share the circuit diagram with us? Just a suggestion

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Toastfuzz, I will definitely check out the SR400's active circuitry if they have one on display at Kuantan Music (the only guitar store here). Thanks for the info.