You don't need the Garmin 340 Audio panel mod!

Guest Discussion
1

If you’re having trouble hearing your CD player/MP 3 player etc. through the audio panel, you may be contemplating having your avionics shop do the procedure outlined in http://www.cirruspilots.org/members/adsb/cd/SA-01-12.pdf>Garmin*. Don’t.
I was considering this, because the volume from my wonderful, all-singing, all-dancing, expensive Archos Jukebox was too low to hear in flight. I was even prepared to pay the two-to-??? hundred dollars for the mod. But I know what’s involved, and I wan’t convinced that a typical avionics shop would be able to deal with the tiny surface-mounted components; they don’t usually do repairs at this level. Plus, Garmin warns that “Removing these four resistors may increase unwanted noise levels”.
After a little digging, I found that what the mod did was to match the input impedance of the Garmin 340 to the output impedance of most consumer electronics audio devices. That made it easy to fix, without increasing any noise levels, without paying for any up(down?)grade of my audio panel, and completely external (so no regulatory concerns). (It also explains why some devices work OK - they have non-standard output impedances).

I used two audio matching transformers (Radio Shack catalog number 273-1380), and a couple of stereo mini-plugs. I housed the parts in a 35mm film canister. Parts cost ~$5. It took less than an hour to build. Not something to try if you’ve never played with electronics, but easy if you have. Now I have to take care not to turn the volume up too high – and I have no “unwanted noise levels”.

  • Mike.
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Great Job. Could you please provide a little more detail on the assembly and tuning required?
thanks, Jim

3

I just build one last nite with the help from Michael Glazer from the UK. It worked awesome!! Michael provided some basic drawings. I will enhance these with the specifics of the assembly and post them up here.
Be careful when plugging it into the plane, it most certainly will require volume management!
cheers, jb

4

Mike, Can you build me one and I will pay for this device?
Thanks, billw

5

> Could you please provide a little more detail on the assembly and tuning required?

Jim,

Would be happy to – as soon as I return from AOPA Expo in Ft. Lauderdale. I leave today; back in about 10 days. There is no “tuning”, though. This is an easy, slam-dunk circuit; no more than 10 or so soldered connections and some shrink wrap.

  • Mike.
6

I’d be interested to learn more of the details, also. Heck, with all of the SR2x’s out there, maybe you’ve got a head start on a nice aftermarket product, but it would probably kill your weekends!

7

Bill (or is it Dennis? [;)]),
Still digging out from the fiasco of a corrupt email file; and as I do so, I’m finding a number of emails similar to yours - many asking for details of the design (which could hardly be simpler), and some asking whether I would consider building one.
The truth is that I’m not very keen to get into the electronics manufacturing business (I thought I got away from that when I retired!); but I figure that (a) there seems to be a need here, and (b) I see an opportunity to get my son Max (15) exposed to the life of an entrepreneur. So… here’s the deal.
Again, if you’d rather build your own, I’d be happy to help by providing a schematic and/or emailing photos of my unit - no charge. If you have the skill and knowledge to do this, I can assure you that it’s really quite easy.
If you’d really prefer to just buy one, we will build these units to order for a limited time, and strictly to our schedule (which includes school!), for $25, including shipping in the continental USA. The units will not be fancy - we’ll probably house them in 35mm film containers, just like mine. Although we expect these units to be utterly reliable (they contain only an audio transformer), we will not be responsible for any damage they may cause to your CD player, Jukebox, Airplane, or anything else. We’ll provide a money-back satisfaction guarantee, valid for 30 days. After that, you’re on your own.
Still interested? Drop me an email and give me your mailing address.
-------------->This ends the serious part of this email.<---------------

Now, if we get overwhelmed by the response to this offer, we will get out of the kit-building business completely, have our units certified by Underwriters Laboratories, and start selling positions in your very own Impedance Matching Transformer (Model 20). A mere $2 will secure your position, but it will be non-refundable, and you should be aware that it will not be put in escrow; instead we will use these funds to further our internal R&D and fuel the growth of Surplus Designs.

A day or two before your IMT ships, we’ll contact for final details (choice of color, etc). At that time, you will provide a further payment of $10. The balance will be due upon delivery.

There is one important option we wish to emphasize. For a modest $200,000 or so, we’ll complete the IMT by attaching a brand new SR20 to the “Airplane” connector. Or, for around $300,000 (give or take, depending on some minor details), we’ll attach an SR22. [;)].

Mike and Max

8

New product suggestion for Mike and Max Inc.:
Ship’s power adapter for the Bose X headset. (Product # 679-22-021MM)
This would consist of a 9V battery “shell” that would be inserted into the Bose in place of a normal 9V battery. A wire would lead from the shell to a plug suitable for the headset power jack in the console. Inside the shell is a regulator as necessary to step the 12V ship’s power (or is it 24V there?) down to 9V. Only mod necessary on the Bose would be to file a little notch in the battery cover to allow the pigtail to emerge. Pigtail length should match distance from Bose battery box to existing phone connectors.
(Mike already has a very similar setup up and running, so the technology already exists.)
This is particularly nice because you don’t have to pay for an expensive mod from the radio shop to put Bose connectors in and pay for your existing battery-powered Bose headsets to be converted. Plus you can still use the Bose with a regular 9V battery for emergency use or if you are flying another aircraft.

9

Will there be the customary CPI adjustment on the positions?

10

Inside the shell is a regulator as necessary to step the 12V ship’s power (or is it 24V there?) down to 9V.
Gordon,
Even easier, my friend… it just so happens that the voltage that is provided as “Ship’s Power” is already 9 volts! There are actually jumper options to change that to 12, 24 and maybe a few others on a board somewhere… but 9 is the default. Unfortunately, 3 volts is what the Lightspeeds need, and that is NOT an option, which is why I built the little regulator-in-a-AA-battery-thingy that you saw.
Surplus Design (a.k.a Mike and Max Inc. ) would be pleased to build a prototype of a suitable connector+wire+9v Battery Shell and send it to you for testing. Early bidders will be guaranteed a preferential delivery date. [;)]
Mike and Max
Note: We’re NOT about to build the 9v-3v thingy for the Lightspeeds… it’s WAAAY too much of a pain! This Bose one, on the other hand, sounds like it could be another suitable candidate for a relatively low-cost offering.

11

allow me to place the 1st order and thanks
Don Rennie

12

By chance does Mike&Max Inc want to license Dave’s and my cold-weather refrigerator modification / hangar heater design? We’re auctioning it to the highest bidder!!

Andy

13

I would gladly act as beta tester for the Bose thingy, except I don’t have my Cirrus yet. So please ship an SR20 or SR22 in the box with the beta test unit so I can properly test and evaluate it. [H]

I’ll send you an email with a recommended length for the pigtail. I can send you a Bose at some point for a quick test and/or you can get one from Bose for a free 30 day trial.

Question for you. You mentioned that you can select the “ship’s power” voltage with a jumper. Does that also affect the “cigarette lighter” adapters in the console? I’m looking for 12v there for an MP3 player. I don’t know if it would be satisfied with 9v.

14

allow me to place the 1st order and thanks

Don,

You’re among those who asked quite a while ago, so yours may in fact be the first order; although they’ve been streaming in!

Please email me with your mailing address.

Mike.

15

By chance does Mike&Max Inc want to license Dave’s and my cold-weather refrigerator modification / hangar heater design?

Andy,

Wonderful - we’re very interested, although I finally reached Rube; he’s a bit down on the whole idea… something about this not being imaginative enough. For example, how does the cat light the candle? If there’s no candle, what will burn through the string?

I went to bat for you and Dave, telling him that I can probably pull some unburned strings and get a spreadsheet that proves the viability of the whole thing. But that just got Rube started on a whole series of tangents about spreading eiderdowns, blanketing the market, and a whole slew of stuff that seemed unrelated to me - but what do I know? [;)]

  • Mike.
16

Gordon,
I would gladly act as beta tester for the Bose thingy, except I don’t have my Cirrus yet.
Oops - 'mI bad! I knew that. I’ll get someone who already has a Cirrus attached to their Bose to test.
I’ll send you an email with a recommended length for the pigtail.
Thanks - will still be appreciated.
Question for you. You mentioned that you can select the “ship’s power” voltage with a jumper. Does that also affect the “cigarette lighter” adapters in the console? I’m looking for 12v there for an MP3 player. I don’t know if it would be satisfied with 9v.

No, to the best of my knowledge, the jumper sets the voltage to the little jacks meant for powering noise-canceling headsets, but the Cigarette Lighter adapter (one only) stays at 12 Volts.

Mike.

17

Hi Michael,

Any chance you still have the schematic laying around? I’d like to build one.

Thanks

Oliver

18

Uh, you replied to a 15-year-old post!

Schematic attached.
IMD-stereo.pdf (11.9 KB)

19

Proof positive that it doesn’t matter how old a post. If you need an answer, just ask the question! [;)]

20

What’s this “35mm film canister” of which you speak?

Amazing how much can change in 15 years.

(and boy those little devils were handy—esp. the older metal ones)