Turn Coordinator noise in Audio

[Gary0747]

I have the original Brittain turn coordinator and seem to be picking up some low level noise in parts of my audio system. Does anybody have experience solving this? 
Ferrite Beads?  Capacitors?  Improved Grounding?

[0TreeLemur]

Yes, recently did that.   Moving the ground can make a big difference.   There is a thread discussing this topic, helpful input that I gleaned from @takair and @Baker Avionics. 

[Gary0747]

How does the ground get from the engine/generator to the instrument panel?  I see the big ground strap to the firewall but is there a strap from the firewall to the instrument panel some where?

[takair]

2 hours ago, Gary0747 said:

How does the ground get from the engine/generator to the instrument panel?  I see the big ground strap to the firewall but is there a strap from the firewall to the instrument panel some where?

It’s through the airframe.  Many junctions, so many opportunities for degradation.  In your case, the noise is likely induced by the relatively common ground point between the audio panel and the TC.  Move the TC ground to a more remote location and your noise will likely be reduced.

[0TreeLemur]

41 minutes ago, takair said:

It’s through the airframe.  Many junctions, so many opportunities for degradation.  In your case, the noise is likely induced by the relatively common ground point between the audio panel and the TC.  Move the TC ground to a more remote location and your noise will likely be reduced.

Following this advice from @takair made a huge difference.  That 400 Hz whine is gone from my intercom.  I don't miss it a bit.    I moved the TC100 ground point from a screw just above my knees to one over between the co-pilot's knees- on the tubular steel frame at the bottom of the panel.   Noise gone.

[Gary0747]

Would it also make sense to add a braded ground strap from the firewall to at least the left panel which is floating on the rubber shock mounts that probably do not conduct? 

[takair]

1 hour ago, Gary0747 said:

Would it also make sense to add a braded ground strap from the firewall to at least the left panel which is floating on the rubber shock mounts that probably do not conduct? 

Oh, yes, if you don’t have a jumper.  As I recall, there should be a sheet metal “U” tab that bridges one of the shock mounts.  Would certainly not hurt to add one....even if one already exists.

[Gary0747]

Thanks,  The TC inverter ground was found to be on just the aluminum skin of the airplane.  Moving it to the right side panel near the TC circuit breaker made a big improvement. 

[carusoam]

Proof that more grounds are better than less...

A small amount of dirt and corrosion can affect the quality of the ground...

Instrument panels supported by rubber vibration absorbers can make mediocre grounds....

The more modern the electronics, the more sensitive they are to crummy grounds...

Rubber Engine mounts also make crummy grounds....

Be on the lookout for good grounding wires that are supposed to connect engine to airframe, and airframe to instrument panel...

PP thoughts only...

Best regards,

-a-

[tmo]

10 hours ago, carusoam said:

Proof that more grounds are better than less...

Until you end up with a ground loop and the resulting whine, squeal and hum. For example, shield is only to be grounded on one end.

[0TreeLemur]

On 2/24/2021 at 12:10 PM, takair said:

Oh, yes, if you don’t have a jumper.  As I recall, there should be a sheet metal “U” tab that bridges one of the shock mounts.  Would certainly not hurt to add one....even if one already exists.

When we updated our panel a few years ago, we discovered that the metal U tab had long-since failed from fatigue.  I added a grounded wire connection.  There doesn't seem to be much current flowing through the left-hand panel though- just the post lights and they are LED.  All electrical instruments include a (-) lead on my a/c.