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Com audio issues

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berkut13(at)berkut13.com
Guest

Posted: Tue Feb 13, 2007 9:47 pm Post subject: Com audio issues

Hi Gurus,



It's been awhile, but I hope all is well with you all.



I'm having audio issues with my new Becker 4201 #2 com and was wondering if

you could help.



The issue is the output audio from the radio whenever there is another radio

switched into the same output.  As soon as any other input is selected on

the audio panel at the same time, the com#2 volume goes very very low and is

overpowered. Sidetone during transmit seems un-affected as does the audio of

the other sources selected - only the Com2 audio drops down.  By

itself...the radio sounds fine, and operates properly.



The #1 com (iCom A200) works fine and is nice and loud with any number of

inputs selected on the audio panel (KA-134).  Adding additional inputs has

little to no affect on com1 volume.  It works great - as it should.



According to the KA-134 schematics, the only thing it's doing with the phone

outputs from the radios is mechanically switching them (no electronics)

together to a single output line to the intercom.  Because of this, I was

wondering if the impedance differences of the radios are a problem.

However, I have no real understand of the magic involved.



They are as follows according to the respective docs:

Com1 iCom - 500 ohms

Com2 Becker - 600 ohms

Eng mon - 560 ohms

Nav KN-53 - 500 ohms



I still puzzled why Com1 has no issues with any number of other inputs, and

Com2 does.



Any ideas?  I have schematics for the KA-134 if you want to see it...but for

this, it's just switches.



Thanks for any help!



James Redmon

Berkut13 N97TX

j.rippengal(at)cytanet.co
Guest

Posted: Wed Feb 14, 2007 12:45 am Post subject: Com audio issues

It could be an impedance problem. But before doing anything else it would be 

as well to check that there is nothing peculiar about the com2 input. Change 

the Becker and Icom inputs round to make sure the problem either stays with 

com2 (in which case the problems is with the audio panel) or changes over to 

com1 (in which case the problem is with the Becker)



It is rather poor practice to just mechanically parallel the outputs. 

Normally the audio panel would provide a simple op amp circuit which would 

enable the outputs to be combined without affecting each other at all. Are 

you sure it does just parallel them all up? If it does then I would expect 

any output to be attenuated noticeably when paralleling multiple others.

John



Subject: Com audio issues

 	  Quote: 	
		   



 Hi Gurus,



 It's been awhile, but I hope all is well with you all.



 I'm having audio issues with my new Becker 4201 #2 com and was wondering 

 if

 you could help.



 The issue is the output audio from the radio whenever there is another 

 radio

 switched into the same output.  As soon as any other input is selected on

 the audio panel at the same time, the com#2 volume goes very very low and 

 is

 overpowered. Sidetone during transmit seems un-affected as does the audio 

 of

 the other sources selected - only the Com2 audio drops down.  By

 itself...the radio sounds fine, and operates properly.



 The #1 com (iCom A200) works fine and is nice and loud with any number of

 inputs selected on the audio panel (KA-134).  Adding additional inputs has

 little to no affect on com1 volume.  It works great - as it should.



 According to the KA-134 schematics, the only thing it's doing with the 

 phone

 outputs from the radios is mechanically switching them (no electronics)

 together to a single output line to the intercom.  Because of this, I was

 wondering if the impedance differences of the radios are a problem.

 However, I have no real understand of the magic involved.



 They are as follows according to the respective docs:

 Com1 iCom - 500 ohms

 Com2 Becker - 600 ohms

 Eng mon - 560 ohms

 Nav KN-53 - 500 ohms



 I still puzzled why Com1 has no issues with any number of other inputs, 

 and

 Com2 does.



 Any ideas?  I have schematics for the KA-134 if you want to see it...but 

 for

 this, it's just switches.



 Thanks for any help!



 James Redmon

 Berkut13 N97TX

Hopperdhh(at)aol.com
Guest

Posted: Wed Feb 14, 2007 6:53 am Post subject: Com audio issues

In a message dated 2/14/2007 3:51:25 AM Eastern Standard Time, j.rippengal(at)cytanet.com.cy writes:

  	  Quote: 	
		  It is rather poor practice to just mechanically parallel the outputs. 

Normally the audio panel would provide a simple op amp circuit which would 

enable the outputs to be combined without affecting each other at all. Are 

you sure it does just parallel them all up? If it does then I would expect 

any output to be attenuated noticeably when paralleling multiple others.

John 	


 James,

  

 I agree with John.  Actually the output impedance of each unit is probably not 500 or 600 ohms.  It could be as small as 1 ohm or as large as 600 ohms, but designed to drive a 500 or 600 ohm load.  If you put a resistor of about 200 ohms in series with each unit, then you give each one a chance to compete with the others.

  

 Dan Hopper

 RV-7A

 Retired EE

  

  [quote][b]

jessevli(at)zeelandnet.nl
Guest

Posted: Thu Feb 15, 2007 9:23 am Post subject: Com audio issues

Suspect the Icom for low impedance as Dan descriped. I did had the same 

problem with a no audio panel (just switches) aircraft. When the Icom audio 

output was turned on, the audio of the other radio would be very low as 

well. The resistor as Dan descriped solved this issue.



Best regards,



Jesse

 	  Quote: 	
		   It is rather poor practice to just mechanically parallel the outputs.

 Normally the audio panel would provide a simple op amp circuit which would

 enable the outputs to be combined without affecting each other at all. Are

 you sure it does just parallel them all up? If it does then I would expect

 any output to be attenuated noticeably when paralleling multiple others.

 John

 James,



 I agree with John.  Actually the output impedance of each unit is probably

 not 500 or 600 ohms.  It could be as small as 1 ohm or as large as 600 

 ohms, but



 designed to drive a 500 or 600 ohm load.  If you put a resistor of about 

 200

 ohms in series with each unit, then you give each one a chance to compete 

 with



 the others.



 Dan Hopper

 RV-7A

 Retired EE

berkut13(at)berkut13.com
Guest

Posted: Thu Feb 15, 2007 12:06 pm Post subject: Com audio issues

Yup...switches with "ganged" inputs.  See below link for the schematic. 

(300K .jpg)



http://www.berkut13.com/dloads/ka-134.jpg



I'm glad you attached Dan's reply, I never received it.  I guess I can 

perform surgery on the input lines and install a 220-ohm resistor on each.



Yeah, it's a hunk of junk King!  I wish I had never installed it...but it's 

far worse to try to extract it and start over now.  Anyone know if the VAL 

(same size) has a isolation circuit built in?  It might become a "throw 

money at it" solution if the resistors don't help.



What I don't understand is why Com1 (iCom) can be "switched" in with all the 

other inputs with no adverse affects.  But, the com2 (Becker) can't - ANY 

input source that's switches in takes the Becker to almost zero and, of 

course, when the volume is turned all the way up it's all distorted.  Add 

all you want to the iCom and the blend in just fine.  Is that what John is 

suggesting might be cause by the iCom possibly having a significantly lower 

impedance than the other radios?



I can also tell you that the iCom's output is very robust compared to the 

other radios.  It's quite loud, deep and clear with very little turn of the 

volume knob - very sensitive.  Not sure that says anything other that it's 

got a good amp on it, but I'll put that out there too.



Again, thanks for all the help!



James

---

Hopperdhh(at)AOL.COM
Guest

Posted: Thu Feb 15, 2007 12:26 pm Post subject: Com audio issues

James,



In looking at the schematic, I see the isolating resistors in the resistor 

pack with 11 resistors in dashed lines.  I can't make out the value, but I'd bet 

that they are 600 ohms or possibly 1K ohm.  Are you sure that the switches 

connect the output of your problem audio source directly to another output?  

Maybe I have missed something.



Dan Hopper

RV-7A

Retired EE



In a message dated 2/15/2007 3:09:39 PM Eastern Standard Time, 

berkut13(at)berkut13.com writes:




Yup...switches with "ganged" inputs.  See below link for the schematic. 

(300K .jpg)



http://www.berkut13.com/dloads/ka-134.jpg



I'm glad you attached Dan's reply, I never received it.  I guess I can 

perform surgery on the input lines and install a 220-ohm resistor on each.



Yeah, it's a hunk of junk King!  I wish I had never installed it...but it's 

far worse to try to extract it and start over now.  Anyone know if the VAL 

(same size) has a isolation circuit built in?  It might become a "throw 

money at it" solution if the resistors don't help.



What I don't understand is why Com1 (iCom) can be "switched" in with all the 

other inputs with no adverse affects.  But, the com2 (Becker) can't - ANY 

input source that's switches in takes the Becker to almost zero and, of 

course, when the volume is turned all the way up it's all distorted.  Add 

all you want to the iCom and the blend in just fine.  Is that what John is 

suggesting might be cause by the iCom possibly having a significantly lower 

impedance than the other radios?



I can also tell you that the iCom's output is very robust compared to the 

other radios.  It's quite loud, deep and clear with very little turn of the 

volume knob - very sensitive.  Not sure that says anything other that it's 

got a good amp on it, but I'll put that out there too.



Again, thanks for all the help!



James

Hopperdhh(at)AOL.COM
Guest

Posted: Thu Feb 15, 2007 12:40 pm Post subject: Com audio issues

James,



I see what I was missing!  I didn't see the "headphone out" at the top right.



My suggestion would be to use the speaker output to drive your headphones.  

Then all the audio inputs go through the isolation resistor pack.  The only 

difference is that you leave the "SPKR" button pushed in all the time.  You won't 

have a cabin speaker anyway, will you?



You may have to use a pad (or resistor to each headset jack) to lower the 

level if the output is too much -- that is the volume control too sensitive.



Does this solve the problem?



Dan Hopper

In a message dated 2/15/2007 3:29:11 PM Eastern Standard Time, 

Hopperdhh(at)aol.com writes:


James,



In looking at the schematic, I see the isolating resistors in the resistor 

pack with 11 resistors in dashed lines.  I can't make out the value, but I'd 

bet 

that they are 600 ohms or possibly 1K ohm.  Are you sure that the switches 

connect the output of your problem audio source directly to another output?  

Maybe I have missed something.



Dan Hopper

RV-7A

Retired EE



In a message dated 2/15/2007 3:09:39 PM Eastern Standard Time, 

berkut13(at)berkut13.com writes:




Yup...switches with "ganged" inputs.  See below link for the schematic. 

(300K .jpg)



http://www.berkut13.com/dloads/ka-134.jpg



I'm glad you attached Dan's reply, I never received it.  I guess I can 

perform surgery on the input lines and install a 220-ohm resistor on each.



Yeah, it's a hunk of junk King!  I wish I had never installed it...but it's 

far worse to try to extract it and start over now.  Anyone know if the VAL 

(same size) has a isolation circuit built in?  It might become a "throw 

money at it" solution if the resistors don't help.



What I don't understand is why Com1 (iCom) can be "switched" in with all the 

other inputs with no adverse affects.  But, the com2 (Becker) can't - ANY 

input source that's switches in takes the Becker to almost zero and, of 

course, when the volume is turned all the way up it's all distorted.  Add 

all you want to the iCom and the blend in just fine.  Is that what John is 

suggesting might be cause by the iCom possibly having a significantly lower 

impedance than the other radios?



I can also tell you that the iCom's output is very robust compared to the 

other radios.  It's quite loud, deep and clear with very little turn of the 

volume knob - very sensitive.  Not sure that says anything other that it's 

got a good amp on it, but I'll put that out there too.



Again, thanks for all the help!



James

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Feb 15, 2007 1:56 pm Post subject: 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



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

berkut13(at)berkut13.com
Guest

Posted: Thu Feb 15, 2007 3:49 pm Post subject: Com audio issues

 	  Quote: 	
		   I see what I was missing!  I didn't see the "headphone out" at the top 

 right.



 My suggestion would be to use the speaker output to drive your headphones.

 Then all the audio inputs go through the isolation resistor pack.  The 

 only

 difference is that you leave the "SPKR" button pushed in all the time. 

 You won't

 have a cabin speaker anyway, will you?


	


Actually, I do have a cabin speaker.  



 	  Quote: 	
		   You may have to use a pad (or resistor to each headset jack) to lower the

 level if the output is too much -- that is the volume control too 

 sensitive.


	


Oh, the volume on the iCom is not "too much" as much as it is just much 

louder than the other radios.  It can all be adjusted with the various 

volume controls but I just wanted to make it known that I barely turn the 

iCom volume up as compared to the others.



-James

berkut13(at)berkut13.com
Guest

Posted: Thu Feb 15, 2007 3:49 pm Post subject: Com audio issues

 	  Quote: 	
		   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

berkut13(at)berkut13.com
Guest

Posted: Thu Feb 15, 2007 4:01 pm Post subject: Com audio issues

Referring to the schematic for the KA-134 in previous email:



 	  Quote: 	
		  >Are you sure that the switches connect the output of your problem

>audio source directly to another output?  Maybe I have missed something.


	


 	  Quote: 	
		   I see what I was missing!  I didn't see the "headphone out" at the top 

 right.


	




Yeah...and the bloody thing is marketed as having an isolation amp built in. 

That's true...but what they don't tell you is that it's for the cabin 

speaker and ramp hail ONLY!  Grrrrr!!

douglist(at)macnauchtan.c
Guest

Posted: Thu Feb 15, 2007 5:05 pm Post subject: Com audio issues

At 17:44 -0600 2/15/07, <berkut13(at)berkut13.com> wrote:

 	  Quote: 	
		  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. <--

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Feb 16, 2007 9:01 am Post subject: Com audio issues

 	  Quote: 	
		  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



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Feb 16, 2007 1:51 pm Post subject: 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



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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