Hacking Sena SMH10

[CHAOSHUMOUR]

Originally Posted by mwood7800

What happen to keep it simple(kiss) A year

ago I cut the wires going to the speakers and added a jack. If you wanted speakers or earbuds you just plug in what you want. Does not overdrive and works great with either or both.

Hey MWood

Can you post a pic of how you just did the straight wire cut and jack add?

What sort of Jack did you use?

I have been to my local "electronics" superstore, and all there jacks are shite!!!

If anyone knows a link to quality jacks (preferably waterproof) that would be awesome.

CHAOS!

[TXjames]

Excellent post genka!

I have the earbud baseplate. A buddy and I both broke ours on the same trip: where the flexible rubber mold meets the hard plastic body of the baseplate. So I foresee this eventually being a problem for most users with this type of baseplate.

Unfortunately, I don't have a pic prior to disassembly. Here, I dissected the soft rubber cover to see what I was dealing with.


My buddy approached it a bit differently by replacing the output and relocating it to the bottom of the baseplate. He did an excellent repair but I was stuck on the same idea that genka had.

I simply reused the broken wires


and jumpered the normal output to the appropriate sides on the fixed audio jack. However, I did replace the ground with a shielded wire.


Note that the right channel is not visible because it's under the ground wire. And I didn't have to add the 75 Ω resistors because they were already there.

Fortunately, I found this thread before attacking. Already knowing which traces to cut (to keep from shorting the aux in with the earbud out) saved me some time.


My observations of repurposing the aux in as the earbud output:
1. It's difficult to locate the new output in everyday use; with the baseplate mounted to the side of your head and motorcycle gloves on.
2. The microphone wire needs to be routed with attention so that it does not get in the way while plugging in the headphones.

[mwood7800]

I used a jack off an earbud extension and some heat shrink.

[genka]

StuartV pointed me on 2 problems with the mod. The first one is fairly trivial- I managed to switch L and R channels. The fix as as simple as wearing the earbuds appropriately. Also this problem is unnoticeable because of the second one.
The second problem is serious- the stereo signal separation is almost nonexistent. The reason for this is that Sena uses differential amplifiers for the helmet speakers, and both "+" and "-" terminals have signals on it. It works fine for the speakers, because they have independent wires. Earbuds have one of the wires joined together. Normally it wouldn't be a problem, but when this joined common wire is connected to joined "-" wires of the amplifier, the severe cross channel bleeding occurs. Let me make it clear- this is not a problem with my mod. Sena factory earbud clamp suffers from the same issue. This is a design flaw.
There is one way to work around the flaw- to connect the common earbud wire to the ground. It fixes the stereo problem, but introduces a new one- an interference from the digital section of the main unit can now be heard as a buzzing sound in the earbuds. It is very noticeable during quiet moments, but is completely masked by a loud music or wind noise while in motion. I'd say if you listen to a lot of music this fix pays off, but if you are more interested in intercom, phone, audio books or talk show podcasts, you'll be better of with the degraded stereo sound without the background noise. It is also possible that the noise level may very between the main units, maybe mine is particularly noisy.

To use the common ground for better stereo it is necessary to remove the jumper from the "L-" point and to resolder a trace which was cut. If you start with an unmolested clamp, you just cut 3 traces instead of 4.

The restored trace is on the left



The final layout for improved stereo





This is a track you can play on your smartphone to check stereo separation and alignment


What Sena did with their earbud clamp is such a glaring design error I am not sure how it could slipped past their QA. I urge everyone to contact Sena and request a fix.

[enduro0125]

Originally Posted by genka

What Sena did with their earbud clamp is such a glaring design error I am not sure how it could slipped past their QA. I urge everyone to contact Sena and request a fix.

The Sena earbud clamp also does the annoying buzzing noise as well.

Yup,it's not a very good product.

[genka]

My unmodified earbud clamp has no noise issues. Some older units suffered from bad connections between the main unit and the clamp. Mine were replaced under warranty long time ago and it fixed the problem for good.

[StuartV]

Originally Posted by enduro0125

The Sena earbud clamp also does the annoying buzzing noise as well.

My earbud clamp does not have a noise issue, either.

[enduro0125]

I have the first gen. They must have cleaned them up in later runs.

[genka]

I also modified the factory earbud clamp to use the audio input jack for the "full stereo" mode. I can still use the original output jack for the "no noise mono" mode. After riding for couple of weeks, I prefer good stereo even with the background buzz. The buzz is masked by the engine sound even on idle, but audio quality is considerably better. That mode is simple, just cut 3 traces and solder 2 jumpers.

[bluecrab]

I just modified my SENA baseplate today, turned out better than I had hoped.

I pretty much did the modification found here:

http://waggies.net/Ken/Sena/

The only difference is I mounted the 3.5mm jack INSIDE the SENA baseplate. I used a Radio Shack 274-246 stereo panel-mount phone jack ($2.69) and wired it to disconnect the internal speakers when the earbuds are plugged in. Everything else is untouched and fully functional (I did not cut any traces on the circuit board).

Sorry, I didn't take any interior photos. There's just enough room inside the SENA to mount the jack. I did have to cut out some of the plastic on the inside cover plate to get it to fit back together, but as you can see, it turned out great.

Steve

[TXjames]

Thanks for the part no. This is exactly how a friend did his. I think I will convert mine as well because I find it extremely difficult to locate the aux input jack with my helmet on. Try plugging in your earbuds with your helmet on and let us know how you like it.

[bluecrab]

Originally Posted by TXjames

Try plugging in your earbuds with your helmet on and let us know how you like it.

No problem at all. I just felt along the bottom edge and immediately felt the socket.

I also wanted to say that I didn't install resistors to bring down the sound volume. Everything was fine after a quick spin of the SENA's volume knob. Just need to remember that when using the internal speakers, I'll have to crank up the volume again.

I'm probably going to do my wife's headset next (I need to get her some earbuds first). If/when I customize her unit, I'll take some detailed photos and post them here.

[enduro0125]

Cool
I'm very interested in this mod.

I was going to buy a new earbud clamp(the buzzing is annoying)but will wait now