9 replies to this topic

[DDH69]

Seeking a bit of help here from the electrical / electronic experts.     I've finally decided to tackle a long standing problem in my cabinet of my RGB undercabinet lighting causing buzz in the audio.  For a long time I've just switched off the RGB strips and stayed busy with other things, but the time has come! 

 

I am unsure if the interference is direct electrical or induced.  I don't have the sorts of measurement tools that are likely to help.  Interestingly my flashers do not cause the same issue, they are driven from a second LEDWiz.  The buzz does change with the different colours set on the RGB lighting.

 

My setup is;

• 4 strips of RGB under the cabinet from the back to the front, entire length (4 x 1.5m) all connected to the same RGB booster circuit
• A switch on the +ve common line to manually turn off the RGB lighting
• A relay on the +ve common line to turn off the RGB lighting via an on screen menu
• RGB running from a LEDWiz
• Power is derived from a single 300VA toroidal transformer with a single 35A bridge and 10000uF main capacitor delivering raw DC into multiple power supplies set via 317's driving 2N3055 power transistors, so multiple 12VDC and 15VDC rails.
• The 12VDC amplifiers (two) are driven from a dedicated 12VDC rail
• Two amplifiers run main sound and table sounds, both buzz with RGB but the main sound is worse
• Main sound input comes from the PC via 1/8" stereo
• Secondary sound input comes from my playfield TV via 1/8" stereo

I was wondering about shielding the cabling from the booster circuit to the RGB (some serious cabinet surgery required, but worth it if it may resolve the issue).  Being negatively switched would the shield still go to ground? (am I over thinking this?)

 

Interested in any thoughts on how to narrow down this PITA issue.

 

[jeverds]

You can publish your connection scheme including the one of the supply source with its components.
Try to feed the 2 amplifiers with an external source to the equipment.
Verify that with the line out connectors unplugged from the PC and the TV you still have the problem.
Try isolating the masses of the line cable from the amplifiers with a mass isolator.
try to perform these tests and comment.
Sorry for my English.

Edited by jeverds, 01 June 2019 - 09:00 AM.

[zebulon]

Easiest way to eliminate shielding issues through audio ....

 

https://www.amazon.c...s/dp/B001EAQTRI

 

 

99.9999% effective back in my car audio days.

[DDH69]

Easiest way to eliminate shielding issues through audio ....

 

https://www.amazon.c...s/dp/B001EAQTRI

 

 

99.9999% effective back in my car audio days.

 

Thank you, on my list of possible things to try (in fact I ordered a couple of $6 versions to try).  This would give complete isolation of the source from the amplifier and resolve the issue if it is a ground loop, of course if its induced noise then that too will pass through an isolating transformer.

[MikePinball]

How about trying a separate 12V/24V power supply for the amplifiers and seeing if it is any better?

 

I have used a 19V 8A laptop power brick for my TPA3116 based-amp.

[JLPicard001]

I had audio buzz until I gave my mini amp it's own power supply.

[DDH69]

My first move was to install a separate LM317/2N3055 power circuit run from the same toroidal transformer with its own bridge.  Fairly separate, but not totally separate back to the mains.  I will try a completely separate PSU and see what happens.

[DDH69]

OK, today's test results .....

• A completely separate 12VDC PSU resolves the issue
• If I connect the separate PSU -ve as a common ground the issue returns
• My flashers do in fact cause the same issue, just far less noticeable - I'm thinking less current drawn
• I found two flashers that I forgot I had on the back of my back box - bonus!
• My beacon has stopped working - bummer
• The issue is more pronounced the more I force PWM on the RGB circuit, ie 255,255,255 is fine, but 100,100,100 is bad

 

So a separate mains supply and fully independent PSU hanging out the front of my cabinet would resolve this, some diagnostic progress but a very big ugly hammer as a solution.  Given that I don't really want another separate PSU in the cabinet (mains power and space would be a PITA), plus, it may not resolve the issue when mounted, and I'd be defeated, I'm still keen to try and resolve this.  My thoughts;

1. Connecting the common -ve from the separate PSU causing the issue to return shouldn't mean that a ground loop is the issue - is this a fair conclusion?
2. Most likely noise on the power rail - but how can this be when I have a separate PSU back as far as the transformer?
3. Am I inducing noise on the internal -ve common rail and the separate PSU only works because it avoids internal wring (my amplifiers are right up the front and I just connected the external PSU through the coin door)?

[jeverds]

The problem may be more complex than you think, although the source of power is separated, I imagine that some of the masses will be connected to the PC, this is enough to create electrical noise, I do not think it is solved with insulators in the input line because internally the amplifiers usually separate the mass of the input line from the mass of the set.
I'll show you my case.
Two equal power supplies, one for the PC (1) and one for the rest (2) with the mass of the two joined.
Two amplifiers connected to the source for the rest (2), in one of the amplifiers there is noise and in the other no, both are equal and connected to the same source, if we separate the mass of this source (2) from the source for the PC (1) the problem is solved but obviously some things do not work. Mass insulators were mounted and the problem continued. Solution mount another source that does not connect with the other sources and the problem solved.
If with this option your problem is solved you should not complicate yourself anymore, mount another source and you will not have any more sound problems.

 

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[DDH69]

As of today, the problem is now fixed.  What I've done to get zero noise is;

• Improve the input circuitry on the amplifier power module by adding a resistor / choke / capacitor filter circuit 
• Improve the output circuitry on the amplifier power supply by adding a noise shunt circuit to remove residual noise after the power regulator
• Add line isolation transformers to the input of both amplifiers (main back glass amplifier and base of cabinet amplifier

 

My sound is now pure and clean ... just what was required.