Here's the kick off for the Sparkling Orange (SO), Sparkling Yellow (SY) comparison from a bona fide treble junkie. Hope it helps!!
RIG: PRS Custom 22, treble p/u, into Tonefactor Eeyore A/B (with both participants) into THD Flexi 50(with 6v6?s) into THD 2X12 cab with Lead 80?s.
ERGONOMICS: Finished sparkly orange box (nice flavor) sized as per previous BJF products, AC tap and in/out access on the side, three "standard" BJFE "slender" knobs with index markings. From left to right, volume, treble, and drive. Nice Eva graphics on this one with no internal trimmers.
I tested both at home using moderately loud volume settings with amp just at breakup; enough for standard venues especially mic'd.
First, tested each with the drive totally counterclockwise. (11 / 12 / full CCW on both) I adjusted the volume to just above unity. The SO provides more bass response than the SY but at these settings, its subtle. Both add some thickness and sustain.
Settings changesd to: 11 / 12 / 12 on both - definite differences are noted. Both have good sustain. The SY "barks", the SO is more even tempered and not nearly as trebly. High single string response of the SY can give you that ice pick sensation that you don't get with the SO which makes it better for leads on the higher ledger lines. The overdrive is similar in both with more perceived girth of the SO when chording. Strike an open chord hard and it fades very smoothly with an even texture; the bass and low mid response is preserved. As you increase the drive to full, the SO maintains the low end and the harmonic differences become more noticeable.
Settings to: 11 / full CCW / full CW: again the SO has more low end and low mids. The tone knob in this position on the SY tames the treble. The SY is still more "in your face" if that's what you are looking for..
Adjusting the tone from full CCW to full CW while striking a hard chord yields a linear response on both with the treble on the SY becoming noticeably more harsh at the higher settings.
Overall, both provide more than ample levels of overdrive. Both are effective with varying guitar volume and/or pick dynamics. The SO is more useful along a broader range of tone settings. If you try the SY and find yourself continually using the tone at 10 and below, the SO is probably more suited to your taste. Since I own the SY, I'll keep it. But, I'd give serious consideration to making these changes permanent on the "Sparkling" line up. I am not opposed to owning another "color" in the CS line up either....but, sometimes, I just gotta have my treble!!
Play on...and thanks again for allowing me to participate...
cork