Today's Message Index:
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1. 09:01 AM - Re: Re: Com audio issues (Noel Loveys)
2. 01:51 PM - Re: Re: Com audio issues (Noel Loveys)
3. 08:54 PM - Com issues - resolved ()
Message 1
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| Subject: | Re: Com audio issues |
>From what you say the problem is definitely inside the audio panel. I say
this because of the fact that the com2 is good when selected alone.
If you get time I recommend drawing up an interconnect diagram yourself.
(Rainy day activity) It makes change outs much faster and there will be less
chance of confusion if you ever want to add say an Ipod.
Also if you ever sell the plane, right after cows learn to fly, the next
person will be able to see exactly how the avionics were installed.
Noel
> -----Original Message-----
> From: owner-avionics-list-server@matronics.com
> [mailto:owner-avionics-list-server@matronics.com] On Behalf
> Of berkut13@berkut13.com
> Sent: Thursday, February 15, 2007 8:14 PM
> To: avionics-list@matronics.com
> Subject: Re: Avionics-List: Re: Com audio issues
>
>
>
> > As with all things... check the Installation manual for
> both the radio and
> > the audio panel. Those manuals should give you not only
> the pin outs for
> > the interconnects but also the levels for those
> interconnects. The other
> > thing you will want to have a look at is the interconnect
> diagram that
> > should have been drawn up at the time the equipment was
> installed. Some
> > will keep this in the aircraft technical logs, others will
> have separate
> > files. Any way check the interconnect diagram to make sure
> that there
> > hasn't been a mistake made in wiring up the various
> connectors. As a hint
> > you already know the problem is in the input to the audio
> panel or the out
> > put of the Icom.
> >
> > Noel
>
>
> Oh boy...did I forget to say that this is an Experimental and
> I outsourced
> the panel integration to a local shop...PRIOR to installation
> into the
> aircraft. There are no "integration manuals" or even "levels
> for those
> interconnects". I do have the pin-outs for the panel and radios
> individually and have double and triple checked those.
>
> Remember, the Becker works and sounds great when it's the only thing
> selected on the audio panel - aka the hook-ups should be OK.
> Com1 (iCom)
> works great with any of the other radio sources mixed in.
> Only the comm2
> (Becker) drops it's audio when any other source is switched in.
>
> Confusing, huh.
>
> -James
>
>
>
>
>
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Message 2
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| Subject: | Re: Com audio issues |
Terrible to live in a country where the main consideration is how, not if,
you will be sued. Unfortunately there are a lot of low life lawyers and
politicians who are dragging this country in that direction too. Generally
what I did on the few, emphasis on few, installs I did was put the
interconnect diagram in the technical log. Most pilots never look there.
The corollary of what the FAA inspectors said was also true. If you have an
interconnect as to how the radio was installed you have evidence that you
didn't mess up (PG) and the owner, if he ever looks at it will realize if he
makes changes his possible claims to warrantee will also be out the window.
When I was in school and afterwards I even photographed installations so I
could tell if anyone fooled with them.
Copy what you are saying about the Op Amps. Best thing since sliced bread
.... BUT!!!!
Noel
> -----Original Message-----
> From: owner-avionics-list-server@matronics.com
> [mailto:owner-avionics-list-server@matronics.com] On Behalf
> Of Doug McNutt
> Sent: Thursday, February 15, 2007 9:34 PM
> To: avionics-list@matronics.com
> Subject: Re: Avionics-List: Re: Com audio issues
>
>
> <douglist@macnauchtan.com>
>
> At 17:44 -0600 2/15/07, <berkut13@berkut13.com> wrote:
> >Oh boy...did I forget to say that this is an Experimental
> and I outsourced the panel integration to a local
> shop...PRIOR to installation into the aircraft. There are no
> "integration manuals" or even "levels for those interconnects".
>
> When I last was chief guru of a radio shop (circa 1982) the
> FAA would come by and inspect the paperwork. We were told
> NEVER to include a detailed installation schematic. Their
> idea was that it was "safer" for the shop to simply say
> "installed in accordance with manufacturer's instructions".
> Safer to them meant "less likely to be sued." I made up the
> drawings anyway but aircraft owners never kept them.
>
> Adding audio with resistors is an old technique that made
> sense when vacuum tube amplifiers were the only thing around.
> The idea is that every audio source has the same output
> resistance, usually 600 ohms. The headphones also had a
> standardized resistance, 600 ohms. That way each audio output
> connected to the phone jack drove a load that was the
> headphones in parallel with all of the other inputs which
> were being driven backwards. It is wasteful of audio power
> but cheap and reliable.
>
> With transistor op-amps it is easy to create an audio drive
> that has nearly zero output resistance. If you do that it's
> easy to drive that 600 ohm, or lower, load and manufacturers
> will tell you that the output is suitable for a 600 ohm load
> while being silent about the output resistance of the device.
> If it is actually zero and you hook it up the old way
> everything else is trying to drive a zero ohm load backwards.
> It won't work. You need to 1) use a mixing amplifier or 2)
> add a series resistor to provide the missing output resistance.
>
> Speaker drives are typically arranged to drive 4 or 8 ohm
> loads and may also have that zero resistance output when
> transistorized. Using a speaker output for the old style
> resistive mixing will short circuit the 600 ohm impedance of
> the headphone line either way. Don't do that.
>
> --
>
> --> Life begins at ovulation. Ladies should endeavor to get
> every young life fertilized. <--
>
>
>
>
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Message 3
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| Subject: | Com issues - resolved |
Well gang...it's fixed.
I added 150ohm resistors to all input audio leads into the panel.
Everything is living together quite nicely now. I guess something in the
combination was not playing well with the new radio.
However, there was one wild card that might also have something to do with
it. While I was removing, moving, installing, and re-installing the pins in
the 134's connector, one of the ground leads (mic I think) broke off a pin.
I was forced to strip and crimp a new molex pin on there and re-secure.
This was done in the same operation as the resistors. After all that, the
audio was loud and clear with all radios mixed in, regardless of the
combination. I'm not convinced this was the issue, since the radio did work
correctly by itself.
So...was it the resistors?...was it a bad ground?...was it a gremlin?
Personally, I don't care anymore...it's fixed!
Thanks for all the help, everyone. Nothing like beating your head against
the wall in a cold hangar.
James Redmon
Berkut #013 N97TX
http://www.berkut13.com
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