rzbill
Well Known Member
Gents,
I have been flying for 3 years and I have had a snag list that was down to a few items that were eluding my ability to solve despite a lot of effort. I got 'em a couple of weekends ago. Purpose of this post is to relate the story in the hopes of helping others.
The three problems (previously thought to be separate):
1) Low level alternator whine in headsets (not really noticeable in flight)
2) Low volume from both Coms. (Usable, but had to turn the radios way up)
3) No Nav audio but Nav indicator OK.
These were recognized right off in phase 1 so work began to correct them.
Here is a list of things I did.
ALTERNATOR WHINE: (none of these worked in my case)
Measured ripple on the 12v bus. OK
Replaced the regulator.
Put ferrites on the B lead.
Ferrites on the power lines to various audio system components.
Removed the cheezy 1/8" jack music input I had wired into the panel.
Installed a condenser on the alternator.
Built an LC noise filter and put it on the audio system power feed.
Refabricated my avionics ground D-Sub.
Replaced master switch
Wired in a relay to possibly give better bus 12V signal to regulator.
Checked grounds everywhere.
NO NAV AUDIO:
Pulled the 430W and put it in another craft to check it (OK)
Traced the wiring behind the panel. (Matched schematic)
Confirmed wiring with multimeter twice. (matched pinouts)
Checked wiring to Archer antenna.
Checked Nav ant SWR with signal producing SWR meter.
LOW VOLUME FROM COMs:
This needs a little explanation. I followed the Aeroelectric mantra of simplicity in the design of my audio system. In that vein, I decided to use his kit audio amp to join my 2 coms and nav signals and then feed that to a NAT AA-80 intercom.
PDF of Iso Amp here
This meant I had no audio panel, just a switch to flip transmission for com 1 to com 2. I could listen to one or both as I saw fit, just by altering their volume knobs. To alter the basic volume in the isolation amp, you change some resistors in the amp. I did that sooo many times, I could do it in my sleep.
I also checked my wiring against the provided schematic a number of times. The other confounding issue was my intercom was used. It was a question mark too.
THE RESOLUTION PATH
SO.... in another effort to attack the low com volume, I had the iso amp apart and was looking at it on the bench for the umpteenth time, trying to decide what to do with the volume resistors (I was at a dead end electrically) but this time I noticed that the circuit traces on the board itself did not match the external wiring diagram. Ummm !!!!!!!!!!!
I logged onto the net and re-downloaded the wiring diagrams from Aeroelectric only to find a revision note about the schematics. Argh.
The incorrect schematic caused the following:
1) +12v from the bus was going into an audio input.
2) Nav audio was dead ended going nowhere.
3) With no power to the audio amp, there was no amplification from the contained op amp.
It was a miracle I had any audio at all for the last 3 years. In hindsight, it would have been better if it did NOT work at all. I would have known to fix it.
I rewired my D-Sub connectors to match the actual traces on the board (and the new schematics). This immediately fixed the alternator whine problem (dead quiet now) and the missing Nav audio. However, the volumes were still not what they should be and were actually worse. I replaced the op amp (in case it was fried) and even raised the gains (wound up saturating the op amp but still really low volume)
While a 66% success rate was good, my plane was now unflyable because I could barely hear the coms. Monday morning I called Stein just to talk. I needed somebody to bounce this off of. As usual, he helped. Apparently, he has heard of impedance matching problems using an iso amp feeding an intercom. He suggested bypassing the iso amp with one radio to check the flow all the way from a radio - through the intercom to my headsets. I had done a bypass some time ago but I must have bypassed the intercom and not the iso amp and got poor results. Anyway, the conversation helped clear my head and set a path forward. (Thank you Stein) The following weekend I made a jumper D-Sub to bypass the iso amp and send the 430W com through to the intercom. BAM! killer volume! Now I knew.
Out came the Iso Amp. Even though I was peeved, I went back to the Aeroelectric book and looked up the resistor method to join audio signals. 3 resistors (150 Ohm) and a jumper D-sub later, I had the whole system working like gangbusters.
I finally get to scratch these three snags off the list. Yay!
Please understand, I am not trying to slam Aeroelectric. Not the purpose of the post and I am still using much of what I learned from his book.
I hope this post helps someone else in a similar pinch.
I have been flying for 3 years and I have had a snag list that was down to a few items that were eluding my ability to solve despite a lot of effort. I got 'em a couple of weekends ago. Purpose of this post is to relate the story in the hopes of helping others.
The three problems (previously thought to be separate):
1) Low level alternator whine in headsets (not really noticeable in flight)
2) Low volume from both Coms. (Usable, but had to turn the radios way up)
3) No Nav audio but Nav indicator OK.
These were recognized right off in phase 1 so work began to correct them.
Here is a list of things I did.
ALTERNATOR WHINE: (none of these worked in my case)
Measured ripple on the 12v bus. OK
Replaced the regulator.
Put ferrites on the B lead.
Ferrites on the power lines to various audio system components.
Removed the cheezy 1/8" jack music input I had wired into the panel.
Installed a condenser on the alternator.
Built an LC noise filter and put it on the audio system power feed.
Refabricated my avionics ground D-Sub.
Replaced master switch
Wired in a relay to possibly give better bus 12V signal to regulator.
Checked grounds everywhere.
NO NAV AUDIO:
Pulled the 430W and put it in another craft to check it (OK)
Traced the wiring behind the panel. (Matched schematic)
Confirmed wiring with multimeter twice. (matched pinouts)
Checked wiring to Archer antenna.
Checked Nav ant SWR with signal producing SWR meter.
LOW VOLUME FROM COMs:
This needs a little explanation. I followed the Aeroelectric mantra of simplicity in the design of my audio system. In that vein, I decided to use his kit audio amp to join my 2 coms and nav signals and then feed that to a NAT AA-80 intercom.
PDF of Iso Amp here
This meant I had no audio panel, just a switch to flip transmission for com 1 to com 2. I could listen to one or both as I saw fit, just by altering their volume knobs. To alter the basic volume in the isolation amp, you change some resistors in the amp. I did that sooo many times, I could do it in my sleep.
I also checked my wiring against the provided schematic a number of times. The other confounding issue was my intercom was used. It was a question mark too.
THE RESOLUTION PATH
SO.... in another effort to attack the low com volume, I had the iso amp apart and was looking at it on the bench for the umpteenth time, trying to decide what to do with the volume resistors (I was at a dead end electrically) but this time I noticed that the circuit traces on the board itself did not match the external wiring diagram. Ummm !!!!!!!!!!!
I logged onto the net and re-downloaded the wiring diagrams from Aeroelectric only to find a revision note about the schematics. Argh.
The incorrect schematic caused the following:
1) +12v from the bus was going into an audio input.
2) Nav audio was dead ended going nowhere.
3) With no power to the audio amp, there was no amplification from the contained op amp.
It was a miracle I had any audio at all for the last 3 years. In hindsight, it would have been better if it did NOT work at all. I would have known to fix it.
I rewired my D-Sub connectors to match the actual traces on the board (and the new schematics). This immediately fixed the alternator whine problem (dead quiet now) and the missing Nav audio. However, the volumes were still not what they should be and were actually worse. I replaced the op amp (in case it was fried) and even raised the gains (wound up saturating the op amp but still really low volume)
While a 66% success rate was good, my plane was now unflyable because I could barely hear the coms. Monday morning I called Stein just to talk. I needed somebody to bounce this off of. As usual, he helped. Apparently, he has heard of impedance matching problems using an iso amp feeding an intercom. He suggested bypassing the iso amp with one radio to check the flow all the way from a radio - through the intercom to my headsets. I had done a bypass some time ago but I must have bypassed the intercom and not the iso amp and got poor results. Anyway, the conversation helped clear my head and set a path forward. (Thank you Stein) The following weekend I made a jumper D-Sub to bypass the iso amp and send the 430W com through to the intercom. BAM! killer volume! Now I knew.
Out came the Iso Amp. Even though I was peeved, I went back to the Aeroelectric book and looked up the resistor method to join audio signals. 3 resistors (150 Ohm) and a jumper D-sub later, I had the whole system working like gangbusters.
I finally get to scratch these three snags off the list. Yay!
Please understand, I am not trying to slam Aeroelectric. Not the purpose of the post and I am still using much of what I learned from his book.
I hope this post helps someone else in a similar pinch.
