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ceengland7(at)gmail.com
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 Posted: Fri Apr 05, 2013 4:47 pm Post subject: Diagnostic Help Please: Audio is Weak and Scratchy |
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On 04/05/2013 03:40 PM, Jared Yates wrote:
| Quote: |
I've been testing my audio system and have encountered poor
performance. Does anyone have any suggestions for what to check?
Here is the problem:
All audio through the headsets is too quiet, and pretty scratchy. This
applies to radio reception, intercom audio, Dynon voice out, and music
input. With the intercom volume, headset volume, and individual device
volume all the way up, the total volume is about where I would want to
have it with 25% volume selected instead. The issue seems to afflict
each of the various inputs to a similar degree.
Here is the setup:
New construction, wired by me (a non-professional, so anything is possible)
The airframe is a steel tube 4-place fuselage with the mic and audio
headset jacks isolated from ground, as verified by voltmeter
continuity checks.
I used shielded cables to connect the intercom and the mic and stereo
phone jacks, with the shields connected at intercom end to each other
and not connected to anything at the jacks.
I have a self-assembled AEC 9009 Audio Iso Amp handling VHF nav audio
on one channel, dynon warnings on one channel, left music in on one
channel, and right music in on one channel, with the 9009's output
going into the intercom aux input
The intercom is a Flightcom 403, with the pilot wires going to the
left front seat, copilot wires to the right front seat, and passenger
jacks to the back two seats.
The GNS430 is the only radio, with com audio routed directly to the
intercom per the intercom directions.
I'm testing with two known-good David Clark headsets (one stereo, one
mono) and one brand new Lightspeed headset, all with freshly buffed,
shiny connectors.
I'm using battery power only, since the engine is not installed
presently. I've tried the battery by itself and the battery with the
charger connected. The voltage range is about 13v to 14v for those
two cases, but I can't see that changing from one to the other makes
any difference in the audio system issues.
Here is what I have tried so far with no improvements:
First, I unplugged aec9009. I lost the channels that run through it,
but the remaining intercom and VHF com audio were still the same.
Then I swapped intercom for the bypass plug that I built per the
intercom manual. this plug is designed to connect the pilot seat
jacks directly to the radio, so that the airplane can still function
as a single-place if the intercom is removed entirely. As with the
9009, I lose intercom function in this configuration (as I should),
but the vhf com audio is still weak and scratchy.
I tried changing the Headsets around in various combinations to
various seats with no appreciable change.
I changed out the volume resistors in the AEC9009 to increase the
volume of those channels, and the volume did go up on the channel in
question, but the quality really suffered.
I'm not really sure what to try next. Does anyone have any
suggestions for what to check?
The fuzzy part sounds like some segment in the audio chain is being
|
overdriven by a source, or is being asked to supply more than it's
capable of giving. The low level could be too much of a load on the
output (load impedance too low). A partial short to ground (from an
audio 'hi' to an audio 'Lo', or to the chassis) is the 1st thing that
comes to mind. Having both fuzzy & low volume from multiple sources
*might* mean that you have two or more outputs trying to feed into each
other, with no isolation resistors between them. (This will make all
affected outputs 'think' that they are effectively shorted to ground
because each is trying to drive a very low impedance load.)
So to proceed, 'Divide & conquer.'
It's extremely unlikely that you have the same problem with every
source, so job one is eliminating the known-good items. I'd get a set of
clip leads, and extra phone jack, & start testing each source by itself,
without it connected to any other component. Isolate the output line
(typically 'audio hi' on the hookup diagram) from the rest of the plane.
Hook a clip lead from that wire to the tip terminal of your spare jack.
Hook another clip lead from the ground ('audio Lo') to the shield
(ground) terminal of the jack. Plug in a known-good headset & listen to
that source. Sound ok? If not troubleshoot settings, ground paths, etc.
If good, move to the next source & repeat. Annddd repeat, until you've
checked all or until you find a bad component.
If all is good, hook one (and only one) source to the iso amp & move
your test jack to the iso amp's output (with it hooked to nothing else).
If bad, there's your problem. All good? that means the iso amp is almost
certainly good, too.
Hook the iso amp to the intercom's input again (with nothing else hooked
to the input). Move the test jack to the intercom's output (with nothing
else hooked up to the output lead). Listen again. If bad, check intercom
settings (especially if there is an internal gain setting or aux input
volume control in the intercom).
All good? Without hooking up the 430, add one component to the iso amp &
check for level/quality at the intercom output. (We've actually skipped
a few steps by doing this, but if one iso input is good, odds are high
that all will be good.)
All sources (except 430) good? Use your test jack to check the 430, with
its output connected to nothing but the test jack. Bad? There's your
problem. Good? Proceed.
Now look at how the 430 ties to the intercom. In your message, you say
that the iso amp is hooked direct to the intercom. Is this a separate
input on the intercom? It probably is, but if it's tied to the same
input with the iso amp, that might well be your problem. Different
input? Move your test jack to the intercom output & listen to the 430
through the intercom. Bad? Re-check wiring & intercom settings, then
check the intercom itself, if possible. Still good? Re-check your
headphone wiring harness in the plane.
Having said all that, I'll say this: I've worked on a couple of 430
installations for friends, & they can be real snakes to troubleshoot.
The most common issue is ground pins on the d-Sub connectors. There are
quite a few, & if you miss one, stuff isn't going to work (not every
ground terminal is common to every other ground terminal in those d-Sub
connectors). On one system, I spoke with directly to a Garmin factory
tech while holding the installation manual in my hand, and read off the
pins that were connected. Even the Garmin tech failed to mention a
(ground) pin that needed to be connected.
Charlie
(pro audio tech, consumer electronics tech and industrial electronics
tech in various former lives)
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email(at)jaredyates.com
Guest
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| Posted: Sat Apr 06, 2013 3:51 am Post subject: Diagnostic Help Please: Audio is Weak and Scratchy |
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Thank you very much Charlie, I'll try those procedures and report back when complete.
On Apr 5, 2013, at 20:46, Charlie England <ceengland7(at)gmail.com> wrote:
| Quote: |
On 04/05/2013 03:40 PM, Jared Yates wrote:
>
>
> I've been testing my audio system and have encountered poor
> performance. Does anyone have any suggestions for what to check?
> Here is the problem:
>
> All audio through the headsets is too quiet, and pretty scratchy. This
> applies to radio reception, intercom audio, Dynon voice out, and music
> input. With the intercom volume, headset volume, and individual device
> volume all the way up, the total volume is about where I would want to
> have it with 25% volume selected instead. The issue seems to afflict
> each of the various inputs to a similar degree.
>
> Here is the setup:
> New construction, wired by me (a non-professional, so anything is possible)
> The airframe is a steel tube 4-place fuselage with the mic and audio
> headset jacks isolated from ground, as verified by voltmeter
> continuity checks.
> I used shielded cables to connect the intercom and the mic and stereo
> phone jacks, with the shields connected at intercom end to each other
> and not connected to anything at the jacks.
> I have a self-assembled AEC 9009 Audio Iso Amp handling VHF nav audio
> on one channel, dynon warnings on one channel, left music in on one
> channel, and right music in on one channel, with the 9009's output
> going into the intercom aux input
> The intercom is a Flightcom 403, with the pilot wires going to the
> left front seat, copilot wires to the right front seat, and passenger
> jacks to the back two seats.
> The GNS430 is the only radio, with com audio routed directly to the
> intercom per the intercom directions.
> I'm testing with two known-good David Clark headsets (one stereo, one
> mono) and one brand new Lightspeed headset, all with freshly buffed,
> shiny connectors.
> I'm using battery power only, since the engine is not installed
> presently. I've tried the battery by itself and the battery with the
> charger connected. The voltage range is about 13v to 14v for those
> two cases, but I can't see that changing from one to the other makes
> any difference in the audio system issues.
>
> Here is what I have tried so far with no improvements:
> First, I unplugged aec9009. I lost the channels that run through it,
> but the remaining intercom and VHF com audio were still the same.
> Then I swapped intercom for the bypass plug that I built per the
> intercom manual. this plug is designed to connect the pilot seat
> jacks directly to the radio, so that the airplane can still function
> as a single-place if the intercom is removed entirely. As with the
> 9009, I lose intercom function in this configuration (as I should),
> but the vhf com audio is still weak and scratchy.
> I tried changing the Headsets around in various combinations to
> various seats with no appreciable change.
> I changed out the volume resistors in the AEC9009 to increase the
> volume of those channels, and the volume did go up on the channel in
> question, but the quality really suffered.
> I'm not really sure what to try next. Does anyone have any
> suggestions for what to check?
The fuzzy part sounds like some segment in the audio chain is being overdriven by a source, or is being asked to supply more than it's capable of giving. The low level could be too much of a load on the output (load impedance too low). A partial short to ground (from an audio 'hi' to an audio 'Lo', or to the chassis) is the 1st thing that comes to mind. Having both fuzzy & low volume from multiple sources *might* mean that you have two or more outputs trying to feed into each other, with no isolation resistors between them. (This will make all affected outputs 'think' that they are effectively shorted to ground because each is trying to drive a very low impedance load.)
So to proceed, 'Divide & conquer.'
It's extremely unlikely that you have the same problem with every source, so job one is eliminating the known-good items. I'd get a set of clip leads, and extra phone jack, & start testing each source by itself, without it connected to any other component. Isolate the output line (typically 'audio hi' on the hookup diagram) from the rest of the plane. Hook a clip lead from that wire to the tip terminal of your spare jack. Hook another clip lead from the ground ('audio Lo') to the shield (ground) terminal of the jack. Plug in a known-good headset & listen to that source. Sound ok? If not troubleshoot settings, ground paths, etc. If good, move to the next source & repeat. Annddd repeat, until you've checked all or until you find a bad component.
If all is good, hook one (and only one) source to the iso amp & move your test jack to the iso amp's output (with it hooked to nothing else). If bad, there's your problem. All good? that means the iso amp is almost certainly good, too.
Hook the iso amp to the intercom's input again (with nothing else hooked to the input). Move the test jack to the intercom's output (with nothing else hooked up to the output lead). Listen again. If bad, check intercom settings (especially if there is an internal gain setting or aux input volume control in the intercom).
All good? Without hooking up the 430, add one component to the iso amp & check for level/quality at the intercom output. (We've actually skipped a few steps by doing this, but if one iso input is good, odds are high that all will be good.)
All sources (except 430) good? Use your test jack to check the 430, with its output connected to nothing but the test jack. Bad? There's your problem. Good? Proceed.
Now look at how the 430 ties to the intercom. In your message, you say that the iso amp is hooked direct to the intercom. Is this a separate input on the intercom? It probably is, but if it's tied to the same input with the iso amp, that might well be your problem. Different input? Move your test jack to the intercom output & listen to the 430 through the intercom. Bad? Re-check wiring & intercom settings, then check the intercom itself, if possible. Still good? Re-check your headphone wiring harness in the plane.
Having said all that, I'll say this: I've worked on a couple of 430 installations for friends, & they can be real snakes to troubleshoot. The most common issue is ground pins on the d-Sub connectors. There are quite a few, & if you miss one, stuff isn't going to work (not every ground terminal is common to every other ground terminal in those d-Sub connectors). On one system, I spoke with directly to a Garmin factory tech while holding the installation manual in my hand, and read off the pins that were connected. Even the Garmin tech failed to mention a (ground) pin that needed to be connected.
Charlie
(pro audio tech, consumer electronics tech and industrial electronics tech in various former lives)
|
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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