Right, I get it. Yes, I think that copper foil EMI tape will help if used as you propose but if it only improves, rather than eradicates the symptom, then you could consider looking into and possibly replacing decoupling caps to take into account the altered nature of the EMI.
As luck would have it, there's a paper on that subject available as a PDF from HERE which proposes some capacitor-related ways to address this issue. It includes the calculations you'll need to establish any changes required in the values of caps that are already present in the vicinity of the added components.
And please forgive me if you're already au fait with this stuff too, but there's another potentially useful document - on EMI shielding theory - available to download HERE.
I guess you probably looked at the task from the capacitor angle already so apologies if this is something you've eliminated at an earlier stage in the process.
AWESOME!!!! ALL great info on this that I did not know already. I'm clueless as to proper ground shielding so any info is truly an asset for me.....Having said that, I can't use caps to filter or smooth the signal as that would defeat the strobing & flashing effect but the paper on EMI grounding should help me out heaps. You need pulse width modulation to control the LEDs like these controllers do & cap smoothing is a no-no on the LED circuits & the cards are silent, as far as EMI except the output voltages to the LEDs themselves since they are PWM driven, I'm pretty sure of, but not totally, of course.
Again, the only connection to the radio, for the controllers are the DC power input from the fused rail of the radio's power supply, whether AC, battery or 15v adapter fed. When the cards are inside the cabinet & ON, they introduce no noise that I can tell, even when the LEDs are hooked up & turned on. Even when I use the color white, solid 'on' they don't make noise in the circuit until I put the face back onto the front of the cabinet & the leds are closer to the internals, especially the volume & tone controls. The right side of the upper right LED strip is within a few mm of the preamp control board....I'll try to open it up tonight for a pic of the inside & where the LEDs go.
If I can lick this grounding/EMI problem, that would go a long way to making my future projects even better so I'm really hoping to find a solution for this particularly hard situation. The other boom-boxes, I could make adjustments, as far as cable routing & eradicate the issue almost completely, every time, until this project presented a different challenge...'