Help me get rid of Audio Whine

[Gomer Pound]

When I purchased my plane recently, I immediately notice a medium to high-pitch whine in the headset. The prior owner was not aware. The PA 30B has the InterAv alternator conversion. As far as I have been able to find out, the InterAv conversion does not use a noise reducing condensor on the alternator. It seems the huge capacitors have some function in reducing whine. I read on another forum about someone concerned about the longevity of those condensers, especially on a firewall. Mine are not on the firewall, but are pretty old.
Does anyone else have a "whine" problem with their PA-30 / InterAv setup? The whine is heard mostly at lower RPM's. I don't hear it after takeoff, but maybe other noise is drowning it out. While on the ground, if I use the intercom or transmit using the PTT, the noise goes away. After the audio panel turns the mic back off, the noise returns in the headset.
Gomer

[Warren Janzen]

I had a little whine on my 180. I added an additional grounding wire from the magnetos to the engine. It helped some. Maybe that will help you.

[Gomer Pound]

Quality Parts no longer carries the InterAv voltage regulators or overvoltage relays. They do have the large Mallory capacitors in stock. Victor at QP recommended Plane Power voltage regulators as a substitute for both the regulator and overvoltage relay. The PA30 is on the Plane Power approved plane list. I happened to call John at AeroTech of Louisville when trying to decide if the Plane Power voltage regulator was the best regulator for the InterAv system.He is an AeroStar driver and is quite knowledgeable as well as personable. The Plane Power R1224 seems to be a reliable unit. I plan to have the right and left Plane Power R1224's communicate with each other by a simple paralleling wire. The present InterAv systems is non-paralleling.
He recommended I have the bearings and brushes changed in the alternators about every 300 hrs. He said the alternators should last a long time with that maintenance. I ended up buying two Plane Power voltage regulators to have installed at annual in November. If the whine disappears after the Plane Power voltage regulators are installed, I will not know exactly what part of the system was contributing to the hum. My feeling was it might be the Mallory capacitors. I was considering replacing the Mallory capacitors to see if that made the whine go away, but at a cost of $65 each, I felt the new regulators which no longer require the capacitors and are a newer, more modern design, were a better option.

[Gomer Pound]

Update on the alternator whine. whine. I don't know why I didn't think of it before, but by turning the gain down on my headset and turning the COM1 volume up, the noise is much less annoying. The plane is now in annual at Heritage. Both alternators are being sent to AeroTech of Louisville where the alteranators will have new brushes and bearings. AeroTech will also check the diodes. Avionics Place will test with an oscilloscope to see where the noise is being picked up after they are remounted and run.
Gomer

[William Hughes]

I would bet you a dollar there is a loose ground somewhere. Every time I've chased one of these down it was some version of a loose ground.

[N3322G]

Ditto on William's post.

[Gomer Pound]

Hi William & Pat, I spoke with John Evans at AeroTech of Louisville yesterday. He inspected the alternators and put them on the oscilloscope. The diodes are fine, so they are not the source of the noise per say. John recommended using the Lone star alternator filters by cutting the alternator battery cable where it goes through the firewall and inserting the Lone Star there. He said the problem is the alternator wire and the main bus wire are supposed to be 15" apart or shielded. I emailed Geoff @ Avionics Place to let him know. Geoff emailed me back and said he found a ground bus that was not properly wired. I will have to find out more next week. My plane has the "Approach Fast Stack" which uses a method so there are no stray grounds as all harnesses and grounds are all grounded at the hub. I don't know at this point if Geoff is referring to a ground bus unrelated to the avionics or not.
Gomer

[Gomer Pound]

I was told by Geoff @ Avionics Place that there was an improper termination to a common ground bus. I won't know any more info until I pick up the plane in 2-3 wks. I will let you know which bus he is referring to. Sounds like you might be correct, William & Pat ~
Gomer

[William Hughes]

Would be interested in that for sure!