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RGB Buzzing in my PROSONIC! How do I sheild my LED strips with foil tape?


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#1 Cpl-Chronic

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Posted 15 July 2014 - 10:27 PM

I have RGB LEDs Buzzing in my PROSONIC!  Silent when LEDs are turned off & noise only enters the audio when the top LEDs are near the volume & bass/treble controls.........

 

 

How do I sheild my LED strips with foil tape so they don't bleed noise into the preamp stage & controls?

 

Thanx,

Cpl



#2 baddboybill

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Posted 19 July 2014 - 08:42 AM

I would think more than likely it's coming from your ground to LEDs. :hmmm:


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#3 Cpl-Chronic

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Posted 20 July 2014 - 12:00 PM

Ok, but can I use EMI tape & ground it?



#4 Beosystem10

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Posted 20 July 2014 - 12:51 PM

:hmmm: As long as you don't end up creating an involuntary earth loop and making the hum a thousand times worse then it's worth a try but I'm thinking that you've done this stuff many times before and had no similar issues, at least not that you've mentioned on the forum, so is some fundamental thing different in this installation?



#5 Cpl-Chronic

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Posted 20 July 2014 - 02:46 PM

:hmmm: As long as you don't end up creating an involuntary earth loop and making the hum a thousand times worse then it's worth a try but I'm thinking that you've done this stuff many times before and had no similar issues, at least not that you've mentioned on the forum, so is some fundamental thing different in this installation?

Good question.  Uh, yes some buzzing did enter some mods but moving connectors & LED wires away from pre-amp stages, did mitigate the issues somewhat to the point where it wasn't noticeable, even if you listened for it.  This one is different in that the LEDs are on the front face of the cabinet & very close to the pre-amp controls, volume, bass, treble, etc.  When I have the LEDs on WHITE, which is the noisiest, & the front removed from the cabinet, the buzzing goes away completely so I know it's coming from the LEDs themselves, not the controllers.  This also tells me, since the LED system is only connected to the blaster on the DC supply side, it's got to be magnetic inductance creeping into the low lever signal on the pre stage.....or at least I think so

 

I'm waiting on EMI shielding tape to be shipped so wanted to know if I could use a ground strap to drain EMI from the tape, covering the back side of the led strips, to ground & reduce the interference.  It's gotta be near field inductance causing the noise.  When the controllers are powered but turned off, & still inside the blaster cabinet, dead silence.

 

Would grounding the tape shield closest to the DC supply side negative, avoid such ground loop hum or do I gorund it on the mainboard itself?

 

Thanx,

Cpl



#6 Beosystem10

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Posted 20 July 2014 - 03:49 PM

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.



#7 Cpl-Chronic

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Posted 20 July 2014 - 04:22 PM

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...'

 

Thanx,

Cpl



#8 oldskool69

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Posted 20 July 2014 - 05:29 PM

Where are your LED drivers relative to the line source and power circuits? :hmmm:

 

And is the LED driver pack grounded? :hmmm:



#9 oldskool69

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Posted 20 July 2014 - 05:30 PM

Where are your LED drivers relative to the line source and power circuits? :hmmm:

 

And is the LED driver pack grounded? :hmmm:

 

Never mind, missed response above...



#10 Cpl-Chronic

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Posted 22 July 2014 - 05:53 PM

Well, I tried to read the EMI shielding guide that Beo10 posted but man, all went way over my head completely but still very much appreciated.  I pretty much got proof today that I am on the right track.  I was working on the Ghidorah project(2nd M90) & had installed a LED strip above the cassette bay & just below the main pre-amp/amp board.  Before the LED systems were almost dead silent when on FULL white & all LEDs are ON.  Once I installed the LED strip above the cassette bay & within mm's of the pre-amp/amp board, all kinds of buzzing was present when I did a test run.  I disconnected the newly installed strip, all other factors being identical, the buzzing was gone again.

 

So, this tells me that it isn't the controllers adding noise on the DC side of the connections but the PWM signals going to the LEDs getting too close to the low level signals of the preamp stage as I thought.  It has to be near-field EMI inductance, right?

 

any input on this would be much appreciated.

 

Thanx,

Cpl



#11 Cpl-Chronic

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Posted 28 July 2014 - 03:09 PM

The copper EMI tape I ordered from China just arrived today & have already installed & grounded the sections of the front face, closest to the LED strips.  It all went smooth & I tied the ground to the external ground screw for an external antenna, etc.  Luckily Prosonic provided a ground strap screw on the side of the blaster, next to the RCA Line-In & Out section which is located on the side of the blaster.  I used a fan connector to allow the disconnection of the ground when removing the face.  I'll install a temporary switch to do before & after comparisons & post a video, along with pics of the shielding....

 

So far, it looks promising.  I've already cut the buzzing down in volume by about 1/2 or more by my ear so that would translate into about a 10db drop in interference on line in....radio is good too so far....

 

stay tuned....

 

Cpl



#12 Cpl-Chronic

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Posted 28 July 2014 - 04:44 PM

This is what the tape looks like.  It's about 2" wide & five feet long per section.  I bought 4 sections & used up 4 feet of it to shield my Prosonic controls from the EMI inductance caused by the PWM controls of the LED controllers. 

 

2m6a73s.jpg

 

Below, you can see the foil applied to the front cabinet, around the pre-amp & function controls...the sections of foil accept solder quite well & I was able to solder connecting wires to the various sections & then ground it all to the chassis ground screw of the side input/output panel.  This drains EMI inductance & provides a path to ground that has almost no resistance & the magnetic lines of the interference shunt to ground...BAM!!!!

2dtdmpw.jpg

 

And, here, the new chrome knurled Fender knobs look sweet with the silver grills & silver/grey face.

rt0qye.jpg

 

 

Cpl :afro:

 

Video to follow shortly....



#13 Cpl-Chronic

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Posted 28 July 2014 - 08:44 PM

Hey modders & LED fans, what's crackin'?

I managed to reduce the noise of the LED strips to the point of inaudibility....very pleased!!!  :clap:  :clap:  :clap:

Watch the entire video as you can hear the difference between grounded & ungrounded shielding, throughout the track & especially near the end. 

 

 

There is a bit of transformer hum from the original power supply but that was always present since the Prosonic is a more budget oriented blaster..

Cpl



#14 Beosystem10

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Posted 29 July 2014 - 04:56 AM

Excellent stuff. The mains hum might be a result of the original smoothing caps needing to be reformed or replaced, but equally could be a result of the way the internal wiring was routed at the factory, in which case a slight increase in the value of the mains filter cap would take care of that, for example if the mains filter is a 0.1uF device, try another few pF in parallel with that and raise the value gradually until the hum is gone. Don't go beyond twice the original filter value though and make sure you only use X2 caps in applications where they go across the mains, I find that obsolete PC PSUs are an excellent source of X2s.

 

If the smoothing block is to blame, there are many diagrams out there in cyberspace for cap reformers and in cases where original caps have gone off form as a result of not being used, it's usually possible to bring them back rather than replacing with new.



#15 JT Techno

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Posted 05 August 2014 - 01:26 PM

Nice one Cpl - your dedication shines through here - loving this LED mod and your buz fix - sorted :-)

#16 Dancorp

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Posted 15 November 2017 - 03:27 PM

Very interresting topic. I have the same problem with my LED mod :)

http://boomboxery.co...for-m70-wip-90/

 

 

For now, i have to translate everything in french :)

 

Dan