Headsets and the R22

[AdamSTL]

There are a few posts on headsets but most are more concerned with whether or not you've got two plugs or one.

 

So lets say you've got a headset with the U-174 - I take it GA is "High" impedance - Military is "Low." I'm getting the impression the R22 is odd (Only because this is what I keep hearing). One manufacturer told me they would have to put a "Bridge Rectifier" in because the R22 had "Old radio technology." I said sure but to my mind a Full wave rectifier would be better suited to a D/C power supply and I can't really imagine how one would be of any use at all in a headset. Obviously a low impedance headset could damage a high impedance radio. A High impedance headset may not work particularly well with a low impedance amplifier.

 

Do we have any numbers? This isn't voodoo. If nothing else - is the R22 High or low impedance? I take it the mic is not a concern. Any hard and fast rules for David Clark models? I'm looking to buy a used DC on ebay - most of them with a u174 appear to be military. I take it since most people appear to be successfully taking their GA headsets and using them in R22s and other helicopters the R22 actually isn't weird; that you can take your headset from the Cessna - plug it into the r22 with adapter (or vice-versa) and then into a 206 with no problems? In that case I would only want to beware of the headsets with u174s (Since theres a good chance they are miliary) and any GA two-plug headset will work with adapter or by soldering a u174 on?

[Gomer Pylot]

I don't fly Robbies, but I can't imagine that it's any different from any other modern aircraft. It should be 'high' impedance, about 300 ohms. Military systems are 8 ohms. Neither will harm the other, but the impedance difference is enough that military headsets don't work in civilian aircraft. You can hear ok, but the mike won't transmit well enough to be heard. You can use a military headset with a mike adapter, which plugs into the mike and increases the impedance, plus it probably has an amp in it also. Carter Engineering sells one, or used to. The last time I used on was in the early 80s. You can take your Cessna headset and plug it into an adapter and it will work fine. Or you can take the two plugs off and replace them with one U174.

 

I've built my own headsets for about 20 years, and it's not rocket science. I'm now using a Clarity Aloft headset, with an adapter, and I really like it. I could replace the GA plugs with a U174, but I just haven't gotten the ambition. DC headsets with a U174 are probably not military - they sell more headsets to helicopter pilots than just about anyone. If it has a model number beginning with H, such as H-13, then it's made for civilian helicopters, and should work in anything other than a military helicopter.

[PA Pilot]

I can only speak to the R22 Beta II. Every GA headset we've tried including the Bose X which I use has worked fine.

[delorean]

If you have a newer R22 with the intercom panel (with the volume & squelch control), it shouldn't be a problem.

 

But the older R22s that just had the Hot/PTT switch, there is an impedance problem with some headsets. You can take DC headset and some with work, so won't. I used to go up to the pilot shop, grab ten DC-13.4s, and then buy the ones that worked in our R22.

 

I believe RHC has instructions on how to put in a rectifier or something into their system. But it was just easier to try out different headsets until you found the one that worked.

[Goldy]

I honestly dont know what the differences, if any, are. I have never had a problem using standard David Clark headsets. I personally use a different brand, and once in a blue moon, I come across a situation where my mic doesnt work if one particular headset is being worn by my passenger...Impedance is a strange science, but the R22 uses a standard radio, same as any other GA aircraft I have flown.

[Witch]

There're no differences whatsoever. I have an old DC H10-30 with an adapter, and other than Nick setting the radio volume too low, they work fine.

 

You need no bridge rectifier. That's used to turn AC current to DC current. The manufacturer that told you your headset needed one is in error. Old radio technology in an R-22? I think not. These radios are the same as in all those old Schweitzers, Bells, and Hillers.

 

The U-174 is fine, and if you get a headset from Ebay, and it doesn't have the helicopter plug, then there're plenty of websites that sell the adapters-and they work fine.

 

But then again, I need to replace the straight cord on mine with a coiled cord...$80. Maybe next summer.

 

Later.

[zenmaster]

Hey Witch, I found a coiled cord on ebay with the helicopter plug for $13 with shipping. I have seen them for sale a couple times after I bought mine. Something to keep a look out for maybe.

[Witch]

Hey Witch, I found a coiled cord on ebay with the helicopter plug for $13 with shipping. I have seen them for sale a couple times after I bought mine. Something to keep a look out for maybe.

That's good, but I'd like to get another H10-30 to use for spare parts and modification into a helmet. I've looked at Ebay a few times but haven't seen anything suitable at the price I'm willing to pay. Ah capitalism.

 

Later.

[pa42]

Inside R22 headset incompatibility:

 

I have documentation from David Clark on the R22 hot-mic or simultaneous PTT conflict. It's a REAL PROBLEM if the two headsets in the aircraft do not have the same microphone impedance--and, worse yet, it's not a low-vs-high impedance problem, but an even closer match, so the year in which each microphone was manufactured strongly influences whether one mic defeats the other!

 

History: aviation microphones are wired to simulate the old carbon-cartridge mike of 60 years ago. So each microphone requires a "bias" current to pass through the circuit. David Clark adheres to the idea that the airframe manufacturer provides the standard method of having a Separate Bias Resistor for each microphone outlet, so that each mic can get the right current.

 

Robinson, for whatever reason, chose to imbed a Single Bias Resistor serving Both microphone leads--with the result that when you're on hot mic, or both IC switches are depressed, BOTH microphones use the SAME bias resistor--with the result that the microphone with the lower resistance of the two wins the battle, and takes all the current, and defeats the other microphone!!

 

I delivered the David Clark documentation to Pat Cox in about March of 2005, and he put this issue in the problems-to-be-solved hopper for me (what, they didn't notice the problem for 27 years after initial certification?!?), but there must be lots of other more important issues, nothing has happened on it since.

 

I have poked and probed and asked around, but there seems to be no simple rewiring fix short of installing a separate intercom electronics system interfaced to the factory wiring; on the R22 circuit diagram, the PTT relays connect to a single wire running to the radio audio, with no way to separate out the two microphones and install separate bias resistors for each. I still have $3.50 of Radio Shack resistor-capacitor combos if only I could figure out a way to wire them in!

 

Meanwhile, the solution is to keep trying headset combinations until you find two that work well together.

 

Happy to provide copies of the David Clark comments on wiring (a .pdf file, too) to techies more ingenious than I who want to figure out a fix.

 

Dave

W2DLS, Amateur Extra

Chief Flight Instructor, HelicopterAcademy.com

[Scarab]

I've had issues in the 22 as well. As long as I'm using matching headsets, 2 of whatever...no problem. As soon as I start mixing thats when the trouble starts. A lightspeed 30 G with a David Clark...nope. Sigtonics cheapy with a DC not so good. pair of lightspeeds great, pair of DC great, pair of sigtronics great, as long as they are the same no problem.

 

The real upshot, I bought a Lightspeed Mach1, thinking that would be ok, it won't cooperate with a Lightspeed 30G. Now I can only use the Mach 1 when I'm alone. Love it by the way, with the custom ear molds. With a pax I have to pull out the other 30G. Called Lightspeed and he said I should rewire the headset jacks. If anyone has the solution I'd love to hear it.

[aaron]

Electrical Engineer here. If someone could post some schematics, I'd be more than happy to take a look.

[pa42]

Preliminary try at microphone schematic--but wiring diagrams are deeply buried, so this is

a) from memory

using keyboard characters in lieu of graphics.

 

 

The international (?) standard for aviation microphones is based on ancient carbon-cartridge

circuitry--a small current has to pass though the cartridge so the audio (your voice) can

modulate the current; to prevent loss of power into the amplifier (and protect it) only the

audio frequency is passed through the .1 microfarad capacitor into the amp. Thus the AMOUNT of current is not critical--it's only the varying electric field which reaches the amp.

 

So what we'd like to have is:

 

12v .1mfd

D - - - - - - \-/relay - -}- -||- - - -\

{ -------- radio audio input jack (common OK)

47 ohms } /

gnd /

/

D - - - - - - /-\relay - -}- -||- - /

{ .1mfd

47 ohms }

gnd

 

An attempt to portray INDEPENDENT bias resistors, with either relay connecting its own microphone to bus voltage (sometimes 24v, I suppose, but still independent), so that any industry-standard microphone can get some current to modulate, without stealing current from the OTHER microphone in the circuit because they're isolated from each other by the capacitors.

 

Probably for convenience, and because the presumption in mid-1970's probably was that matching headsets would have nearly-identical microphones AND only one person would be talking at a time (shades of the WWII one-way rubber-tube gosport!) Robinson wired their microphones (in the absence of aftermarket electronic intercom systems) to use the bias provided by the radio itself--the audio intercom input on the VHF radio (or, at least, my 1991 R22's factory diagram shows it thus). Both of the mike relays connect to that one wire (relays being triggered by 1. PTT on the yoke or 2. left footswitch or 3. both relays simultaneously via hot-mike switch).

 

D - - - \-/relay - - - \ 12v .1mfd

mike ------------- single audio input to radio, internal bias circuit -{- -||-> amp

D - - - /-\relay - - - / }

bias resistor, 47 ohm .5w {

_ to

- ground

IF IF IF the internals of the microphones happen to match closely, each will take half

of the bias current and both pilots can talk simultaneously. If one mike has less resistance than the other, it will take most of the current, dropping the voltage on the common line so that the OTHER mike recives too little voltage (and therefore current) to produce a strong audio modulation. And thus becomes inaudible whenever both relays are activated.

 

THE PROBLEM is that one would have to hire an avionics tech (and get RHC approval, perhaps--or only a 337?) to dig into the panel or the overhead plug panel (I believe that's where the relays are housed), import 12 volts to the downstream side of the relay, and insert a 47-ohm resistor and a capacitor downstream from each relay. Trivial--absurdly trivial!--in amateur radio, but a dangerous FAA/RHC political mine field in a

helicopter! I haven't done it to my personal R22 because I'm worried about violating FAR's, the effect on resale value, AND the implied promise that the factory will come up with an official remedy. (And I have 11 school R22's that I can't really tear into because they belong to somebody else!)

 

Hello, RHC, how's that remedy coming?

 

Anybody got a wiring diagram for 2005/2006 R22's? Do they still leave out the separate bias resistors?

 

 

 

sorry, as expected the keyboard-character-schematic doesn't stay aligned all the way to the website, you'll have to use it as a base to draw your own, if that doesn't work I can draw one on paper and fax it. Then there's the stone tablet and chisel--please advance $200 cash for shipping costs . . .

[67november]

Hey sparky, I mean Aaron didgya get all that?

[pa42]

And for Brushfire21: good thinking, I tried to figure that out, perhaps one could add an in-line microbox to another (!) U174 plug with still ANOTHER relay inside it, and use the bias voltage from the radio to activate JUST that auxiliary relay. Inconsequential voltage drop, I hope. But I haven't gotten far enought to figure out how to pass raw bus voltage (12v for mine) through the U174 to the microphone-resistor-capacitor combo inside that auxiliary box--if I use the radio-supplied biased current, then the differential resistances would still defeat one of the mikes, no?

 

Haven't diagrammed this particular solution for 18 months, so I'm ill-prepared, but will hack at it some. Thanks for the idea.

[pa42]

Aha, stop the presses, I found the David Clark comments (.doc) and favored schematic (.pdf). Here's hoping the attachement is accessible for those interested. Initial tries at attaching both crashed; here's another try, hope not doubling the post!

 

dcmicph.PDF

dcmicph.DOC

[aaron]

Anyone able to provide the R22 schematic also? I'm not quite sure how the relays are wired up.