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Diagnostic Help Please: Audio is Weak and Scratchy

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Apr 10, 2013 3:42 pm Post subject: Diagnostic Help Please: Audio is Weak and Scratchy

At 05:02 PM 4/10/2013, you wrote:

 	  Quote: 	
		  



Thanks Bob, I'll check that and report back. It turns out the 

resistors were correct, but my EE friend thought at first that they weren't.


	


    Hmmm . . . the only other thing that

    could cause a hot-chip is to have it

    soldered in backwards.



    Bob . . .

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email(at)jaredyates.com
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Posted: Thu Apr 11, 2013 7:03 pm Post subject: Diagnostic Help Please: Audio is Weak and Scratchy

It looks like I have the audio troubleshooting solved. I replaced the amplifier chips because I had some extras locally and they are cheap. Then I tested the intercom input by connecting my mp3 player directly to the intercom, bypassing the 9009 all together. All was well. Next I removed all of the inputs to the 9009 except the music, and plugged it in. All was well. Next I connected the Dynon voice circuit. It was acceptable, but a little bit loud. I took out the 300 ohm resistor for that channel and tried a 500. The change was small, so I swapped a few more times, arriving eventually at 1.8k. This really surprised me, since I misunderstood and thought of 300 to be near the top end of the scale. Next I reconnected the 430 nav audio to the 9009 and it was way too loud.  I jumped right to the 1k, but it was still very loud. After several steps along the way, each astonishingly higher, I settled on 68k. Now everything works well and the chips aren't getting hot. I mention all of this for the benefit of anyone else who will be using the 9009 with these systems- start much higher than 150 ohms!  This whole process has given me much more understanding of my audio system, and also a real appreciation for the design of the 9009. Thanks Bob for making it available!  I don't know how other folks are getting by without it. 

On Apr 10, 2013, at 18:21, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	

 At 05:02 PM 4/10/2013, you wrote:

> 

> 

> Thanks Bob, I'll check that and report back. It turns out the resistors were correct, but my EE friend thought at first that they weren't.

   Hmmm . . . the only other thing that

   could cause a hot-chip is to have it

   soldered in backwards.

   Bob . . .

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sprocket(at)vx-aviation.c
Guest

Posted: Fri Apr 12, 2013 6:13 am Post subject: Diagnostic Help Please: Audio is Weak and Scratchy

Bob's design is the grandaddy of several commercial audio mixers, including 

at least one other open-source device.

It's probably a good idea to have variable inputs (see the AMX-2A or AMX-4B 

at http://store.makerplane.org/avionics/).



You haven't mentioned any objectional audio noise in the system, but in my 

experience the Dynon EFIS is a fairly noisy device.  There are a couple of 

easy fixes for this, so if you have this problem, let me know.



Thanks, Vern



--

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