---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Thu 02/15/07: 11 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:16 AM - Re: Radio audio troubles (Hiflier68) 2. 09:23 AM - Re: Com audio issues (Jesse Kluijfhout, PE1RUI) 3. 12:06 PM - Re: Re: Com audio issues () 4. 12:11 PM - Re: AeroElectric-List: Radio audio troubles () 5. 12:26 PM - Re: Re: Com audio issues (Hopperdhh@AOL.COM) 6. 12:40 PM - Re: Re: Com audio issues (Hopperdhh@AOL.COM) 7. 01:56 PM - Re: Re: Com audio issues (Noel Loveys) 8. 03:49 PM - Re: Re: Com audio issues () 9. 03:49 PM - Re: Re: Com audio issues () 10. 04:01 PM - Re: Com audio issues () 11. 05:05 PM - Re: Re: Com audio issues (Doug McNutt) ________________________________ Message 1 _____________________________________ Time: 08:16:53 AM PST US From: Hiflier68 Subject: Re: Avionics-List: Radio audio troubles Hi James, Mitch Goodrich I have Gary Kirby's old varieze.. I am in Austin for the next few days. Wondering if we can meet up?? YI'd enjoy spending some time with you, Gary, and Hopper. Find me at 813-356-9758 Thanks, Mitchell --- berkut13@berkut13.com wrote: > > 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 understanding of the magic involved here. > > 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 > RST Marker Receiver - unknown > > I am still puzzled why Com1 has no issues with any number of other > inputs, > and > Com2 does....impedance differences and all. > > Any ideas? I have schematics for the KA-134 if you want to see it...but > for > this, it's just mechanical switches. > > Thanks for any help! > > James Redmon > Berkut13 N97TX > > > > > > ________________________________ Message 2 _____________________________________ Time: 09:23:30 AM PST US From: "Jesse Kluijfhout, PE1RUI" Subject: Avionics-List: Re: 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 > 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 > > ________________________________ Message 3 _____________________________________ Time: 12:06:36 PM PST US From: Subject: Re: Avionics-List: Re: 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 ----- Original Message ----- From: "Jesse Kluijfhout, PE1RUI" Sent: Thursday, February 15, 2007 11:22 AM Subject: Avionics-List: Re: 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 >> 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 ________________________________ Message 4 _____________________________________ Time: 12:11:37 PM PST US From: Subject: Avionics-List: Re: AeroElectric-List: Radio audio troubles > Actually, those "output impedance" values are completely > bogus. See: > > http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf > > The true output impedance of any of these devices > is considerably lower than the values stated. What > they really mean to say is, "This product will produce > rated output performance when presented with xxx ohms > of LOAD. I forwarded this to the office. It'll take a bit to read and absorb it. > If the mental image I have from reading your words is > coincident with your own, then it appears that something > may be amiss in the audio isolation amplifier. Amiss?...yup..there isn't one. So, that should be "amiss-ing" ;-) > Try swapping affected radios to different inputs to > the amplifier and see if the symptoms swap with the radios > or stay common to the switches on the amplifier. I sent an email with a link to the KA-134 schematic...it's just switches for these circuits to the "phones output". -James ________________________________ Message 5 _____________________________________ Time: 12:26:21 PM PST US From: Hopperdhh@AOL.COM Subject: Re: Avionics-List: Re: 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@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 ________________________________ Message 6 _____________________________________ Time: 12:40:01 PM PST US From: Hopperdhh@AOL.COM Subject: Re: Avionics-List: Re: 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@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@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 ________________________________ Message 7 _____________________________________ Time: 01:56:32 PM PST US From: "Noel Loveys" 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 > -----Original Message----- > From: owner-avionics-list-server@matronics.com > [mailto:owner-avionics-list-server@matronics.com] On Behalf > Of Jesse Kluijfhout, PE1RUI > Sent: Thursday, February 15, 2007 1:52 PM > To: avionics-list@matronics.com > Subject: Avionics-List: Re: Com audio issues > > > PE1RUI" > > 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 > > 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 > > > > > > > > ________________________________ Message 8 _____________________________________ Time: 03:49:41 PM PST US From: Subject: Re: Avionics-List: Re: Com audio issues > 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. ;-) > 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 ________________________________ Message 9 _____________________________________ Time: 03:49:41 PM PST US From: 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 ________________________________ Message 10 ____________________________________ Time: 04:01:40 PM PST US From: Subject: Avionics-List: Re: Com audio issues Referring to the schematic for the KA-134 in previous email: >>Are you sure that the switches connect the output of your problem >>audio source directly to another output? Maybe I have missed something. > 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!! ________________________________ Message 11 ____________________________________ Time: 05:05:07 PM PST US From: Doug McNutt Subject: Re: Avionics-List: Re: Com audio issues At 17:44 -0600 2/15/07, 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. <-- ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message avionics-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Avionics-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/avionics-list Browse Digests http://www.matronics.com/digest/avionics-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.