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wgill10(at)comcast.net
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 Posted: Thu Dec 20, 2007 8:24 am Post subject: Alternator whine in audio |
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Hello All,<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
I have a PlanePower alternator and have noticed a whine noise in the David Clark headset audio. It is really noisy if the headset volume is high; however, if I turn the headset volume down low and turn the comm radio volume up to compensate, the whine is barely detectable. Can anyone explain this and/or provide possible solutions? I called PlanePower to inquire about filter and they informed me that their product has internal noise filtering and that I must have an audio ground problem. When the alternator is switched off-line, the audio is crystal clear. If there was an audio grounding issue I would expect to hear ignition noise too, but that’s not the case. Can additional filtering be installed external to the alternator? Suggestions please.
Happy holidays,
Bill Gill
RV-7 Lee's Summit, MO
[quote][b]
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frank.hinde(at)hp.com
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| Posted: Thu Dec 20, 2007 8:43 am Post subject: Alternator whine in audio |
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Have you got a good connection between the alternator case and the engine block?....I had kinds of noise issues before i realised that painting the alternator bracket is a very bad idea and is provides a hi resistance path...Ooops.
My plane power alt has been trouble free...no noise.
Frank
RV 7a IO360
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of wgill10(at)comcast.net
Sent: Thursday, December 20, 2007 8:21 AM
To: aeroelectric-list(at)matronics.com
Subject: Alternator whine in audio
Hello All,
I have a PlanePower alternator and have noticed a whine noise in the David Clark headset audio. It is really noisy if the headset volume is high; however, if I turn the headset volume down low and turn the comm radio volume up to compensate, the whine is barely detectable. Can anyone explain this and/or provide possible solutions? I called PlanePower to inquire about filter and they informed me that their product has internal noise filtering and that I must have an audio ground problem. When the alternator is switched off-line, the audio is crystal clear. If there was an audio grounding issue I would expect to hear ignition noise too, but that’s not the case. Can additional filtering be installed external to the alternator? Suggestions please.
Happy holidays,
Bill Gill
RV-7 Lee's Summit, MO
[quote]
.matronics.com/contribution
ist">http://www.matronics.com/Navigator?AeroElectric-List
ics.com
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rjquillin
Joined: 13 May 2007
Posts: 123
Location: KSEE
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| Posted: Thu Dec 20, 2007 9:52 am Post subject: Alternator whine in audio |
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At 08:20 12/20/2007, you wrote:
| Quote: | | I have a PlanePower alternator and have noticed a whine noise in the David Clark headset audio. It is really noisy if the headset volume is high; however, if I turn the headset volume down low and turn the comm radio volume up to compensate, the whine is barely detectable. Can anyone explain this and/or provide possible solutions? |
Is this something new, and if so, what has changed?
Only your headset, or also pax headsets?
You don't mention what you have for an audio/intercom system....
A question.
Is each and every headset audio and microphone jack ground bushing insulated from and do not rely on an airframe connection for the 'return' to the source equipment? That is, are there dedicated ground returns for the microphone and headset from each and every jack returning to the audio source, be it radio, audio panel or intercom?
Your audio source to the headset will amplify whatever signal it sees between its' input and input common, generally audio lo, chassis or some other airframe referenced ground connection. Likewise, what ever is connected to its' output will hear whatever voltage is seen between the hot or high connection and lo, return, chassis or whatever you wish to call it. Should some unwanted voltage also get stuck in there, it too will be heard. As you turn up the comm audio and the offending noise is not increased, it would be safe to assume the offending signal is after the volume control you are adjusting. In a similar manner, you adjust headset volume and the noise changes; the source is before the control.
Your headphones may well just be hearing some voltage drop caused by airframe currents between the jack where you connect them and the piece of gear at the other end of the wire to the jack.
| Quote: | | I called PlanePower to inquire about filter and they informed me that their product has internal noise filtering and that I must have an audio ground problem. When the alternator is switched off-line, the audio is crystal clear. |
So the offending source would seem to be the alternator; it's off, no noise. But how is the alternator noise getting into the headset? Even a good alternator is going to make some noise when under load. It's our duty to minimize how that noise can make it into unwanted places.
| Quote: | | If there was an audio grounding issue I would expect to hear ignition noise too, but that’s not the case. |
Generally ignition noise is radiated noise, not noise in the form of airframe current, so you could easily have (or not) ignition noise (generally) totally unrelated to stray currents causing unwanted voltage drops in audio circuits.
| Quote: | | Can additional filtering be installed external to the alternator? Suggestions please. |
Generally, additional filtering can be added and may help. But is that just a band aid covering up some other undiscovered issue that, if corrected, would yield an even better solution...
Ron Q.
[quote][b]
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wgill10(at)comcast.net
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| Posted: Thu Dec 20, 2007 10:42 am Post subject: Alternator whine in audio |
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Thanks Ron.
This is a new RV-7 aircraft and installation...been there since day one on both audio jacks . I have a Garmin 347 audio panel with an SL-40 comm...both prewired by Stark's. I do have the insulating washers on the jacks with a dedicated ground (unshielded) wired to a central ground. I also have a KX 155 navcomm w/glideslope -- the noise is there with either comm.
Bill
[quote]-------------- Original message --------------
From: Ron Quillin <rjquillin(at)gmail.com>
At 08:20 12/20/2007, you wrote:
| Quote: | | I have a PlanePower alternator and have noticed a whine noise in the David Clark headset audio. It is really noisy if the headset volume is high; however, if I turn the headset volume down low and turn the comm radio volume up to compensate, the whine is barely detectable. Can anyone explain this and/or provide possible solutions? |
Is this something new, and if so, what has changed?
Only your headset, or also pax headsets?
You don't mention what you have for an audio/intercom system....
A question.
Is each and every headset audio and microphone jack ground bushing insulated from and do not rely on an airframe connection for the 'return' to the source equipment? That is, are there dedicated ground returns for the microphone and headset from each and every jack returning to the audio source, be it radio, audio panel or intercom?
Your audio source to the headset will ampli fy whatever signal it sees between its' input and input common, generally audio lo, chassis or some other airframe referenced ground connection. Likewise, what ever is connected to its' output will hear whatever voltage is seen between the hot or high connection and lo, return, chassis or whatever you wish to call it. Should some unwanted voltage also get stuck in there, it too will be heard. As you turn up the comm audio and the offending noise is not increased, it would be safe to assume the offending signal is after the volume control you are adjusting. In a similar manner, you adjust headset volume and the noise changes; the source is before the control.
Your headphones may well just be hearing some voltage drop caused by airframe currents between the jack where you connect them and the piece of gear at the other end of the wire to the jack.
| Quote: | | I called PlanePower to inquire about filter and they informed me that their product has internal noise filtering and that I must have an audio ground problem. When the alternator is switched off-line, the audio is crystal clear. |
So the offending source would seem to be the alternator; it's off, no noise. But how is the alternator noise getting into the headset? Even a good alternator is going to make some noise when under load. It's our duty to minimize how that noise can make it into unwanted places.
| Quote: | | If there was an audio grounding issue I would expect to hear ignition noise too, but that’s not the case. |
Generally ignition noise is radiated noise, not noise in the form of airframe current, so you could easily have (or not) ignition noise (generally) totally unrelated to stray currents causing unwanted voltage drops in audio circuits.
| Quote: | | Can additional filtering be installed external to the alternator? Suggestions please. |
Generally, additional filtering can be added and may help. But is that just a band aid covering up some other undiscovered issue that, if corrected, would yield an even better solution...
Ron Q.
[b]
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nuckolls.bob(at)cox.net
Guest
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| Posted: Fri Dec 21, 2007 7:35 am Post subject: Alternator whine in audio |
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At 04:20 PM 12/20/2007 +0000, you wrote:
| Quote: | Hello All,<?xml:namespace prefix = o ns =
"urn:schemas-microsoft-com:office:office" />
I have a PlanePower alternator and have noticed a whine noise in the
David Clark headset audio. It is really noisy if the headset volume is
high; however, if I turn the headset volume down low and turn the comm
radio volume up to compensate, the whine is barely detectable. Can anyone
explain this and/or provide possible solutions?
|
Yes. The alternator is the noisiest device in the
airplane and there is no practical way to 'filter'
its worst noise component - AC 'ripple' voltage
left over after the 3-phase AC output of the stator
windings is rectified into DC.
The simple-ideas that support this assertion are
illustrated in an excerpted figure from the chapter
on noise in the 'Connection which you can see
here:
http://www.aeroelectric.com/Pictures/Misc/Figure_16p3.pdf
A rectified 3-phase AC voltage has a predictable
10% pk-pk ripple. I.e., your 14V alternator has
about 1.4 volts pk-pk AC signal at an audio rate
(you can hear it) riding on top of the DC power
output. Worse yet, the ENERGY in this 'noise'
is HUGE . . . let's say .5v RMS X alternator
output of up to say 60A makes this a 30 WATT
potential noise source.
The notion of adding a practical filter for this
condition is polluted by the knowledge that
many of the more useful filters for radio noise
are fairly easy pills to swallow (.5 lb, 10 square
inches footprint and perhaps 30 cubic inches
in volume). However, these are designed to work
at Megahertz frequencies and energy levels
perhaps 1 millionth as strong.
A filter capable of cleaning up the output
of an alternator is going to be more weight,
volume and loss of power than you're going
to want to put in your airplane.
This is why the graybeards in this technology
have provided guidance to designers in the form
of Mil-Std-704 and similar tomes that say, "Son,
that's one nasty noise generator out there on
the engine with no practical way to silence it.
Suggest you learn to live with it."
Indeed, DC power generation per Mil-Std-704
tells us to expect 3 volts pk-pk on 28v systems
as described in
http://www.aeroelectric.com/Pictures/Curves/MSTD704_28V_Noise.jpg
over the range of 1000 to 5000 Hz (you can HEAR
it) and tapering in intensity on either side.
Cut that value in half for a 14v system. Here's
a noise trace taken from my automobile's bus:
http://www.aeroelectric.com/Pictures/Curves/Safari_Bus_Noise_1.gif
| Quote: | I called PlanePower to inquire about filter and they informed me that
their product has internal noise filtering and that I must have an audio
ground problem.
|
But they didn't tell you everything. The only kind
of filter that can be physically installed in their
alternator goes to conducted RADIO FREQUENCY noise
from 150 KHz to 30 MHz in the form of a reasonably
sized capacitor. This filter cannot speak to the
AUDIO FREQUENCY noise described in the Mil-Std-704
excerpt cited above.
Their hypothesis about audio ground noise is a
strong one. The vast majority of audio system noise
problems I've encountered in the past had root
cause in poor ground architecture. This is why we
spend so much time exploring the potential for
grounding problems in chapter 16 and crafted the
ground architecture drawings in Figure Z-15.
| Quote: | When the alternator is switched off-line, the audio is crystal clear. If
there was an
audio grounding issue I would expect to hear ignition noise too, but
that's not
the case.
|
A faulty supposition. The propagation modes for
these two antagonists are entirely different from
each other. The presence of one does not automatically
include or exclude the presence of both.
| Quote: | Can additional filtering be installed external to the alternator?
|
No.
| Quote: | Suggestions please.
|
Suggest you first make sure that your headset
and microphone jacks DO NOT ground locally to
the airframe where they are mounted. This common
installation error probably accounts for 1/2 of
all the light aircraft alternator noise problems.
Understand too that you MIGHT have a propagation
mode that is difficult to find and/or fix. With
the advent of high quality, noise cancelling
headsets noises that used to be well below the
nuisance threshold for signal to noise are now
deemed undesirable. I'm not suggesting that your
problem is not fixable . . . just that the cost
in $time$ to fix it may not be very rewarding.
Is the noise you're hearing on the ground perceptible
and objectionable in flight? I've had MANY situations
where folks have chased over an airplane looking
for root cause and fix for noises that nobody
can hear while in flight.
If the mic/headset jacks ARE properly grounded
back at the intercom, then try running the noise
isolation traps described in Chapter 16. The noise
MIGHT be coming in through the +14v power leads
where its practical to add a filter like:
http://www.aeroelectric.com/articles/filter/RS_Noise_Filters.pdf
http://www.aeroelectric.com/articles/filter/filter.pdf
Unfortunately, all the components featured in
these two pieces are no longer offered by Radio
Shack since they got out of the automotive audio
products business. However, other companies
are very much IN that business. If your studies
determine that the noise IS coming in through the
+14v supply, perhaps a device like . . .
http://tinyurl.com/ynn7at
would do the job. There's no automatic recipe
for success here because the variables that set
levels of perception for the noise have a huge
range of cause/effect. Noise problems of this
nature are always plagued with a certain amount
of cut and try.
I've copied my friend Steven Klodd at Plane-Power
on this note. Steve, should you find it useful,
feel free to copy any or all of this stuff and
assemble it into a document for sharing with your
customers. A poor understanding of these simple-
ideas has cause our brothers to spend a lot of
$time$ chasing the elusive double-ugly, yellow-
beaked noise snipe!
Bob . . .
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bobf(at)feldtman.com
Guest
|
| Posted: Fri Dec 21, 2007 2:08 pm Post subject: Alternator whine in audio |
|
|
there are noise filters in the amateur radio realm that work reasonably well..... I am thinking about trying that in my audio ciruit to headphone to see if I could "tune out" the noise. Any pilots using those? You can see them advertised in QST, etc.
bobf
Glastar
W5RF
On 12/21/07, Robert L. Nuckolls, III <nuckolls.bob(at)cox.net (nuckolls.bob(at)cox.net)> wrote: [quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" < nuckolls.bob(at)cox.net (nuckolls.bob(at)cox.net)>
At 04:20 PM 12/20/2007 +0000, you wrote:
| Quote: | Hello All,<?xml:namespace prefix = o ns =
"urn:schemas-microsoft-com:office:office" />
I have a PlanePower alternator and have noticed a whine noise in the
David Clark headset audio. It is really noisy if the headset volume is
high; however, if I turn the headset volume down low and turn the comm
radio volume up to compensate, the whine is barely detectable. Can anyone
explain this and/or provide possible solutions?
|
Yes. The alternator is the noisiest device in the
airplane and there is no practical way to 'filter'
its worst noise component - AC 'ripple' voltage
left over after the 3-phase AC output of the stator
windings is rectified into DC.
The simple-ideas that support this assertion are
illustrated in an excerpted figure from the chapter
on noise in the 'Connection which you can see
here:
http://www.aeroelectric.com/Pictures/Misc/Figure_16p3.pdf
A rectified 3-phase AC voltage has a predictable
10% pk-pk ripple. I.e., your 14V alternator has
about 1.4 volts pk-pk AC signal at an audio rate
(you can hear it) riding on top of the DC power
output. Worse yet, the ENERGY in this 'noise'
is HUGE . . . let's say .5v RMS X alternator
output of up to say 60A makes this a 30 WATT
potential noise source.
The notion of adding a practical filter for this
condition is polluted by the knowledge that
many of the more useful filters for radio noise
are fairly easy pills to swallow (.5 lb, 10 square
inches footprint and perhaps 30 cubic inches
in volume). However, these are designed to work
at Megahertz frequencies and energy levels
perhaps 1 millionth as strong.
A filter capable of cleaning up the output
of an alternator is going to be more weight,
volume and loss of power than you're going
to want to put in your airplane.
This is why the graybeards in this technology
have provided guidance to designers in the form
of Mil-Std-704 and similar tomes that say, "Son,
that's one nasty noise generator out there on
the engine with no practical way to silence it.
Suggest you learn to live with it."
Indeed, DC power generation per Mil-Std-704
tells us to expect 3 volts pk-pk on 28v systems
as described in
http://www.aeroelectric.com/Pictures/Curves/MSTD704_28V_Noise.jpg
over the range of 1000 to 5000 Hz (you can HEAR
it) and tapering in intensity on either side.
Cut that value in half for a 14v system. Here's
a noise trace taken from my automobile's bus:
http://www.aeroelectric.com/Pictures/Curves/Safari_Bus_Noise_1.gif
| Quote: | I called PlanePower to inquire about filter and they informed me that
their product has internal noise filtering and that I must have an audio
ground problem.
|
But they didn't tell you everything. The only kind
of filter that can be physically installed in their
alternator goes to conducted RADIO FREQUENCY noise
from 150 KHz to 30 MHz in the form of a reasonably
sized capacitor. This filter cannot speak to the
AUDIO FREQUENCY noise described in the Mil-Std-704
excerpt cited above.
Their hypothesis about audio ground noise is a
strong one. The vast majority of audio system noise
problems I've encountered in the past had root
cause in poor ground architecture. This is why we
spend so much time exploring the potential for
grounding problems in chapter 16 and crafted the
ground architecture drawings in Figure Z-15.
| Quote: | When the alternator is switched off-line, the audio is crystal clear. If
there was an
audio grounding issue I would expect to hear ignition noise too, but
that's not
the case.
|
A faulty supposition. The propagation modes for
these two antagonists are entirely different from
each other. The presence of one does not automatically
include or exclude the presence of both.
| Quote: | Can additional filtering be installed external to the alternator?
|
No.
| Quote: | Suggestions please.
|
Suggest you first make sure that your headset
and microphone jacks DO NOT ground locally to
the airframe where they are mounted. This common
installation error probably accounts for 1/2 of
all the light aircraft alternator noise problems.
Understand too that you MIGHT have a propagation
mode that is difficult to find and/or fix. With
the advent of high quality, noise cancelling
headsets noises that used to be well below the
nuisance threshold for signal to noise are now
deemed undesirable. I'm not suggesting that your
problem is not fixable . . . just that the cost
in $time$ to fix it may not be very rewarding.
Is the noise you're hearing on the ground perceptible
and objectionable in flight? I've had MANY situations
where folks have chased over an airplane looking
for root cause and fix for noises that nobody
can hear while in flight.
If the mic/headset jacks ARE properly grounded
back at the intercom, then try running the noise
isolation traps described in Chapter 16. The noise
MIGHT be coming in through the +14v power leads
where its practical to add a filter like:
http://www.aeroelectric.com/articles/filter/RS_Noise_Filters.pdf
http://www.aeroelectric.com/articles/filter/filter.pdf
Unfortunately, all the components featured in
these two pieces are no longer offered by Radio
Shack since they got out of the automotive audio
products business. However, other companies
are very much IN that business. If your studies
determine that the noise IS coming in through the
+14v supply, perhaps a device like . . .
http://tinyurl.com/ynn7at
would do the job. There's no automatic recipe
for success here because the variables that set
levels of perception for the noise have a huge
range of cause/effect. Noise problems of this
nature are always plagued with a certain amount
of cut and try.
I've copied my friend Steven Klodd at Plane-Power
on this note. Steve, should you find it useful,
feel free to copy any or all of this stuff and
assemble it into a document for sharing with your
customers. A poor understanding of these simple-
ideas has cause our brothers to spend a lot of
$time$ chasing the elusive double-ugly, yellow-
[quote][b]
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wgill10(at)comcast.net
Guest
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| Posted: Sat Dec 22, 2007 2:38 am Post subject: Alternator whine in audio |
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|
Thanks for the information Bob.
With minimal load on the alternator, I see an output of 14.3 volts
during cruise flight. As I apply loads one by one (radios, landing
lights, strobes, pitot heat, etc.), the noise gets stronger and the bus
voltage drops to 14.0 volts. The loads total about 15 amps and I would
not expect to see the bus voltage drop -- does this seem normal? I am
going to return the 60-amp alternator to PlanePower for inspection. I
didn't notice this noise during the first 15 or 20 hours of flight
testing, so maybe I did lose an alternator phase as PlanePower
identified as a possible culprit.
Yes, I can hear the whine in flight. I have to turn the headset volume
down to its lowest level and crank the radio volume up max to obtain an
acceptable audio output (minimal noise).
Merry Christmas,
Bill
--
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nuckolls.bob(at)cox.net
Guest
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| Posted: Sat Dec 22, 2007 9:07 am Post subject: Alternator whine in audio |
|
|
At 04:36 AM 12/22/2007 -0600, you wrote:
| Quote: |
Thanks for the information Bob.
With minimal load on the alternator, I see an output of 14.3 volts
during cruise flight. As I apply loads one by one (radios, landing
lights, strobes, pitot heat, etc.), the noise gets stronger and the bus
voltage drops to 14.0 volts. The loads total about 15 amps and I would
not expect to see the bus voltage drop -- does this seem normal? I am
going to return the 60-amp alternator to PlanePower for inspection. I
didn't notice this noise during the first 15 or 20 hours of flight
testing, so maybe I did lose an alternator phase as PlanePower
identified as a possible culprit.
|
Internally regulated alternators can only sense alternator
output voltage at the alternator's b-lead terminal. One
of several advantages of external regulators is their local
or remote sense inputs that are closer to the bus. What
you may be experiencing is simple voltage drop along
your b-lead wiring. Make a temporary connection to the
alternator b-lead terminal and check for loss of regulation
under load. It may be that what you're observing is predictable
drop in ship's wiring and the alternator is holding the
b-lead terminal at regulator setpoint.
| Quote: | Yes, I can hear the whine in flight. I have to turn the headset volume
down to its lowest level and crank the radio volume up max to obtain an
acceptable audio output (minimal noise).
|
Okay, if this voltage drop thing and the whine thing
are NEW, then you may well have one of the three phases
missing in the alternator's output. loss of one winding
often manifests itself as poor regulation combined with
quantum jump in noise.
Take your alternator to an alternator overhaul shop before
sending it all the way to Texas. They should be able to
run it on a 5+ HP drive stand that will verify/deny the
open phase hypothesis. Automotive parts stores have table-
top alternator test stands but they may or may not be able
to spot the missing phase . . . and probably can't run
it under full load either.
Bob . . .
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klehman(at)albedo.net
Guest
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| Posted: Sat Dec 22, 2007 1:36 pm Post subject: Alternator whine in audio |
|
|
Even easier might be to find someone with an oscilloscope. It should be
obvious from looking at the AC ripple almost anywhere in the planes
electrical distribution. Every third peak will be missing. That
economical Owon scope that Bob mentioned a year or so ago runs very well
off a little inverter plugged into my cigarette lighter.
Ken
>snip
> Take your alternator to an alternator overhaul shop before
| Quote: | sending it all the way to Texas. They should be able to
run it on a 5+ HP drive stand that will verify/deny the
open phase hypothesis. Automotive parts stores have table-
top alternator test stands but they may or may not be able
to spot the missing phase . . . and probably can't run
it under full load either.
Bob . . .
|
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