DIY headset power supply?

[Chip Sylverne]

So, I got tired of pumping 9v batteries into my anr headset. So I go on the interwebs, and find a nice, simple design for a 9v supply using a 7810 regulator, a .33mfd 50v cap on the 12v in, and a .1mfd cap on the out. Solder it all together, connect 'er up to a 12v battery, check the output and get a nice, steady 9.4 volts. Perfect, or so I think.

Solder a plug on it and plug it into my aux 12v panel plug. Works great for a good 30 minutes until I reduce rpm for and approach and I get the screaming feedback banshee from hell in the headset. Seems to happen on throttle reduction, not sure if that's coincidence or not. The regulator didn't seem hot to the touch, and besides this regulator chip is supposed to have an automatic thermal shutdown.

I'm already a whole $4 into his thing, and was wondering if any of you IEEE guys have an answer as to why this is happening and a solution.

(other than spending $40 for one that has already been engineered )

 

[Fastglas]

Seems like ground loop issue. I'd keep feed it the the 9V batteries and be done with it.


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[Let'sgoflying!]

what are the specs on the headset? Many do well with 12v.

 

[Chip Sylverne]

Hmm, maybe it's not the power supply.

In my search for specs, Google found many complaints about high-pitch squealing from anr's on descent. That's when mine occurs. Funny thing it didn't happen in my old plane.

Flightcom II headset with gel seals.

 

[Chip Sylverne]

Maybe I'm just an idiot.

Shane has a post here in POA under a "headset feedback squeal" thread that says if this happens wit a fresh battery, the headset may be on backwards.
Or a cold solder joint, or other internal mic problem.

Time for further investigation.

Never mind.

 

[Dan Thomas]

.33uf on the input isn't much. I'd try to find an old car stereo power filter, with its choke and an electrolytic cap of 20uf or so. Stick that in the power feed, with the choke in series and the electrolytic between the choke's output and ground. Another electrolytic ahead of the choke would help, too. Ripple filter.

 

[Chip Sylverne]

.33uf on the input isn't much. I'd try to find an old car stereo power filter, with its choke and an electrolytic cap of 20uf or so. Stick that in the power feed, with the choke in series and the electrolytic between the choke's output and ground. Another electrolytic ahead of the choke would help, too. Ripple filter.

Thought about that, just getting a Buck converter, but was a little concerned about RF from the coil interfering with my stack. My aux power plug is real close to the comms.

 

[flyingron]

Why would there be any RF in that coil?

One thing I'd do is check the Voltage out when your aircraft is in the state you are experiencing the problem. Voltage drops below 11V on the input, that regulator is going to do odd things.

 

[Chip Sylverne]

Why would there be any RF in that coil?

One thing I'd do is check the Voltage out when your aircraft is in the state you are experiencing the problem. Voltage drops below 11V on the input, that regulator is going to do odd things.

Perhaps not RF, but coil + current could= EMI. Probably not to any real extent, I admit. A linear regulator seemed the easiest, since amp draw is probably in the milliamp range. The voltage dropout would be 11 volts, but if that happened I'd be getting a low voltage warning lamp from the avionics bus. Other stuff would be going wonky too.

No, actually now I'm thinking it could possibly be the headset itself. It would eat a 9v battery in about 8 hours use, so it's been a while since I used the anr. My Comanche has sound insulation out the wazoo, so It really wan't necessary and I had other fish to fry. Finally getting around to this.

Going to fly some tomorrow, so I'll try a few different things.

 

[MooneyDriver78]

I used rechargeable batteries, my are AA, but you can find 9v online and a charger, they pay for themselves

 

[Dan Thomas]

Perhaps not RF, but coil + current could= EMI. Probably not to any real extent, I admit.

A ripple filter isn't a tank circuit. It won't oscillate. Need a capacitor and a coil in parallel, and something to excite it.

 

[flyingron]

I used rechargeable batteries, my are AA, but you can find 9v online and a charger, they pay for themselves

Yeah, your headsets are must be power hogs if this is an issue. Either that or stop buying Lowe's Utilitech batteries. These are crap. I replaced a bunch in the smoke detectors in my house and found them beeping a month later. Testing the rest of them in the brick they sold me showed that half of them were already dead.

 

[MooneyDriver78]

Yeah, your headsets are must be power hogs if this is an issue. Either that or stop buying Lowe's Utilitech batteries. These are crap. I replaced a bunch in the smoke detectors in my house and found them beeping a month later. Testing the rest of them in the brick they sold me showed that half of them were already dead.

My 2 AA rechargeables last about 50 hrs, but they do lose their charge so if you don't fly much you may not want to use them. For that reason you may not want to use them in a flashlight.

 

[weirdjim]

.33uf on the input isn't much. I'd try to find an old car stereo power filter, with its choke and an electrolytic cap of 20uf or so. Stick that in the power feed, with the choke in series and the electrolytic between the choke's output and ground. Another electrolytic ahead of the choke would help, too. Ripple filter.

The only reason that 0.33 is in there is to tame HF instability. It has nothing to do with filtering, nor is filtering necessary. You've already got 3-4 volts of head room to get rid of ripple, so anything more is useless.

Now as to the banshee from hell effect ... let's ponder that.

Jim

 

[denverpilot]

I'd start with the basic test. Make sure ship's voltage is holding above 12 at idle on the ground.

If not, you have a problem to solve that isn't related to the headset at all.

 

[Chip Sylverne]

No problem with ships's voltage. Regulator output solid 9.4v in climb, straight and level and descent phases of flight over the course of an hour at different power settings. Regulator never gets excessively warm to the touch.

I'm thinking it's a bad solder joint or internal mic problem in the headset causing some sorta feedback loop. Strange that it only happens on descent.

 

[gismo]

The problem is likely the ground loop mentioned earlier in this thread. The headset was likely designed with the expectation that the power supply would be isolated.

 

[Chip Sylverne]

The problem is likely the ground loop mentioned earlier in this thread. The headset was likely designed with the expectation that the power supply would be isolated.

Don't think so because it's a) not constant and b) much higher pitch than any ground loop or I've heard before. Not whine, not a hum, but a screech.

 

[gismo]

Don't think so because it's a) not constant and b) much higher pitch than any ground loop or I've heard before. Not whine, not a hum, but a screech.

I'm assuming the headset is ANR given it needs batteries. The screech likely comes from the ANR electronics but it could also come from your intercom (crosstalk from the phone to mic circuit). Have you tried unplugging the mic or turning the intercom volume down?

 

[Chip Sylverne]

I'm assuming the headset is ANR given it needs batteries. The screech likely comes from the ANR electronics but it could also come from your intercom (crosstalk from the phone to mic circuit). Have you tried unplugging the mic or turning the intercom volume down?

The pnr headset I have for the right seater has no issues, so I don't think it's the intercom. I'm going to touch up the solder connections in the headset this week sometime. I'll let you know how it pans out.

 

[gismo]

The pnr headset I have for the right seater has no issues, so I don't think it's the intercom. I'm going to touch up the solder connections in the headset this week sometime. I'll let you know how it pans out.

I'd take a separate battery (one 9v should do) to power your regulator and see if that works OK. If it does, jumper from the battery minus to airframe ground and see if the squeal shows up.