DIY Stereo Microphones for my GoPro

A while back, I got a Sony ECM LV1 Lavalier Microphone, which is really two separate microphones in a common housing in a stereo configuration. On paper, at least, this is a good fit for my GoPro Hero 9 with a Media Mod, as it is capable of stereo recording. But every time I rode at highway speeds, the audio track would be full of pops and clicks, leaving the audio unusable. I made my own inline attenuator, which did drop the volume of the recording, but the audio still had pops and clicks at highway speeds. This had me blaming the mic, so I decided to build my own dual mic setup.

One goal was to have the ability to do stereo recording, like I could with the Sony mic. When recording inside a helmet, one could argue that the stereo effect will be minimal, but if GoPros and other action cameras can do stereo recording, why not do stereo recording? I wanted some distance between the microphones, with each on it's own side of the helmet to maximize the difference between what each mic records.

I also wanted a microphone that could handle a high volume of sound. It's difficult to find maximum SPL ratings for electret microphone capsules, but after some research, I found that the PUIAudio AOM-5035L-HD3-R is rated for a maximum SPL of 135 dB. This means that if what I'm hearing while riding isn't hurting my ears, the microphones should be ok. What I'm not sure of is whether that rating is how loud the sound can be before damage occurs to the mic, or if that's how loud a sound can be with good-enough audio quality. (See the datasheet for the AOM-5035L here.)

After ordering the microphone capsules, I wanted to house them in something that was long enough to make mounting the microphones easy. I also wanted to limit how much the wires could move near the solder joints to prevent cracking those joints. I decided to use a couple 1/4" copper plumbing fittings. The capsules did not fit initially, but were close. After a little bit of drilling, they fit well enough.

These capsules are the three-terminal variety with an internal JFET. This means the actual electret condenser element is internally connected between ground and the gate of the JFET. The external terminals are ground, the source of the JFET, and the drain of the JFET. You can find a good description of 2-terminal and 3-terminal electret capsules here. 

The data sheet recommends a source follower configuration, and so does the article linked in the previous paragraph. However, the GoPro Media Mod input circuitry seems to be setup for a common source configuration where the Media Mod provides the drain resistor and output capacitor for each audio channel, with the JFET being provided by each microphone capsule. In other words, the GoPro setup expects two-terminal electret microphones.

This means the recommended source follower setup is not an option. However connecting the source terminal directly to ground basically converts a three-terminal electret capsule into a 2-terminal one. This was my initial plan.

However, I didn't want to simply bridge the two terminals with solder. A common-source gain stage typically has much more than unity gain, and if that lead to clipping, I wanted to be able to add a resistor between source and ground to lower the gain. If the ratio of the drain resistor to the source resistor is one, unity gain can be achieved (or possibly less than unity gain.) More on this later. Also, having a wire for each terminal could mean wiring to source follower stages that I build myself in an external amplifier with output characteristics for using the line-in setting on the GoPro.

When wired together with the output jack, I wanted to be sure to be able to distinguish between the drain terminals of the left and right channels, so I chose yellow for left and red for right. Since I was starting off with the ground and source wires connected together, there was no need for color coding between the ground and source terminals of the two channels.  

After soldering, I added some hot clue for some mechanical support to the solder connections. I definitely want to avoid bending at those connections, which could lead to broken solder joints.

I then put each capsule into its "housing", filled the inside with more hot glue, soldered the wires to the output jack, and heat shrinking everything along the way.

I then positioned the bundled microphone setup along the inside of the front of my helmet with the left mic along side the front edge of the left cheek pad and the right microphone along side the front edge of the right cheek pad. I used the microphone from my communication system to hold it all in place.

When I first tested this setup, the audio was HORRIBLE - much worse than with the Sony Lavalier mic. The pops could be heard at anything above walking speed. I tried various things to make improvements - made shorter cable, closed vents on my helmet, etc. These helped a little bit, but still any audio I recorded was unusably bad at highway speeds.

I knew I had to reduce the gain to eliminate clipping. I knew that with a source-follower topology suggested by the data sheet, unity gain would probably be best. I tried various resistors between source and ground for each microphone, and using 5.1kΩ resistors worked well. 

When looking at the diagram below, keep in mind that the gain stage depicted is composed of elements within the microphone capsule, including the internal JFET, and components within the GoPro media mod. D, S, and G represent the labels on the solder pads on the microphone capsule. Rs is the 5.1kΩ soldered inline in the green wire for each mic. There's no way to know for sure what the circuit topology is in the GoPro media mod for its portion of each input gain stage.

If I were to build another one of these, I would connect the source pin and the ground pin with the 5.1kΩ source resistor as close to the capsule as possible for each mic, eliminating the need for a long green wire in the bundle. I might even use a chip resistor, soldering it directly to the source and ground pins. I would probably also shorten the wires a bit, with the output jack not sticking so far outside of the helmet.

I might would also consider doing just a single microphone supplying audio for both channels for mono recording. It seems that the stereo effect is minimal, and would be better with a separate audio recorder. With such a setup, one would probably only care about the GoPro audio for the voice of the rider, maybe even excluding that when the rider isn't speaking. 

I've since learned that GoPro 9's are notorious for having clicking/popping noises, and maybe the Sony mic was not at fault. Just adding an inline resistor for each microphone element might have solved the problems with the Sony Mic. But, of course, the very thin wires used for consumer audio products make such modifications very difficult. Building my own stereo microphone setup made me feel like I had more control over the end result.

Hopefully soon, I'll post a video demonstrating how well the microphones work. 

Here it is plugged into the GoPro with a short cable I made.

Shadow 500 - Weld repair complete!

I recently wrapped up my weld repairs on the project Shadow 500. Welding and shaping with my oxy-acetylene torch has been a pleasure. Here's a quick before-and-after comparison.

Here in this..... curved bolt-holey area (I have no idea if there's a technical term for this part of the frame), I welded a strip of steel at one bolt-hole curvy area two where it spanned straight across and somewhat past the other bolt-hole curvy area. I then heated the strip with my torch, and hammered it inwards to where it ran along the existing metal. As I went along, I hammered the edges over, and welded.

I then simply filled in the remaining open areas with welding rod. At this point, parts of the surface of the repair area looked like the surface of an iron meteorite. Hahah.

But it cleaned up nicely. Well, kinda nicely. I could clean it up a little more, but an angle grinder can remove metal very quickly. I'm worried that I'll grind the metal too thin. I'll finish this up with a little auto filler. After that, on to rust removal elsewhere and then painting.

Twisted Road Free Day

Back in September, the Re-cycle Garage in Santa Cruz, California announced a contest on their facebook page (See here.) To participate you had to go to twistedroad.com, find a listing for an electric motorcycle, email them with the city the bike was located in, and they would add your name to a drawing held while doing their Motorcycles and Misfits podcast. The prize for this contest was a free motorcycle rental day with Twisted Road. So I found a listing for an electric motorcycle, emailed the Misfits with the city, and the morning after their podcast, I got an email saying I won! WOOHOOO!

In case you don't know already, Twisted Road is an online business that allows people to rent out their own motorcycles to people who want to ride them. For those who own bikes, this might sound kinda scary, but the folks at Twisted Road go through a lot of effort to make sure the rental experience is excellent for both owners and riders. Their site explains this much better than I can, but they're definitely legit.

So last week, I decided to use my free rental day. I searched for bikes close to me, and saw a few good choices. My first choice was a Victory Octane. Before the Victory brand was killed off, I was strongly considering buying an Octane. Hell, one of these days, I might still. I made my selection and waited for confirmation.

Well, there was a complication with owner confirmation. I'm not sure if he simply rejected my rental. Owners get to do that if they aren't confident in a rider for whatever reason. This protects the owner. It's also possible the owner just simply didn't respond. I'm not sure why I would be rejected, but who knows.

But that's ok. Austin from Twisted Road contacted me to help me find a bike. He told me to give him my top three choices, and he'd talk to the owners to get me confirmation on a rental. I emailed him my three choices, and I was confirmed for a 2008 SV650.

After the confirmation, I contacted the owner. I noticed that I had setup the pickup time for 7:00 PM, but as I thought about how traffic can be in the Orlando area, I thought perhaps 8:00 PM would be better. I checked with him telling him I could still drop the bike off at 7:00 PM if he preferred that. He was cool with that arrangement.

When the time came, I met the owner at a location near his house. He described the bike, went over the controls, etc. He then told me about the existing blemishes, dents, etc. and uploaded photos of these to the Twisted Road site. The blemishes were very minor - just what you would typically expect from a bike that is actually ridden on a regular basis - minor scratch here, minor dent there. No biggie. The bike was very clean, and you could tell it was well maintained.

We talked for a few minutes, and he mentioned that he'd ridden the bike across the country a few times. It was clear from the conversation that he was a very experienced and knowledgeable rider. I asked him about his experience with Twisted Road, and he said that he had just listed the bike, and this was his first time renting the bike out. After the conversation, he walked back to his house. I went to start the bike and .... nothing!

I called him back and told him that I couldn't start the bike. He walked back to check out the situation. He told me I needed to pull in the clutch lever, and..... I felt like a huge idiot. Of course it has a clutch sensor - it's a modern motorcycle. But when you're used to riding old bikes with Harley technology, you forget that modern bikes actually have such things.

So I started the bike, and off I went. I originally planned to take a minor highway home to give me a little time to get used to the bike, but I was instantly comfortable riding it. SV650's really are easy to ride. I jumped on the interstate, and it felt like this was a bike I had been riding for years.

This is a very different bike than the ones I own. Comparisons with other bikes would be more appropriate, but I will compare this bike to what I know. And what I've got the most recent experience with are my current bikes - a 30 year old Sportster and a 20 year old Buell M2 Cyclone.

This bike did not feel as powerful as my Buell. It shouldn't - my Buell has a 1.2 liter engine which has almost twice the displacement of the SV650. But I can tell you this - the Buell definitely has less than twice the power of this bike. Also, I didn't come anywhere close to pushing the SV650 to it's limits. I was very mindful that this wasn't my bike and that it wasn't my place to flog it. The power delivery is very different between the two bikes, and had I pushed the SV close to it's max, I might have a different impression.

I can say the SV650 had all the power it needed. It didn't struggle to get to or maintain highway speed, and it felt like I could easily pass someone if needed. The throttle response was better than with the carbureted bikes I'm used to riding. The engine was smooth. I'm not sure it's the smoothest bike I've ridden, but it's much smoother than the paint can shakers I'm used to riding. 

The SV handled well. Now, I can't tell you that it's better than my Buell. I honestly dont' know. Like I said, it wasn't my place to flog the bike, but I sure didn't see any indication that it was any less nimble. And, of course it's more nimble than the Sportster, thought the Sportster isn't as bad as many may think.

It definitely had better brakes than either of my bikes. To be fair to my Buell, it is an old bike, but I think the breaks on the Buell are in good shape. I think the comparison is valid. But the SV has dual front disk brakes while my Buell has only a single rotor up front. My old Sportster also has dual front disk brakes, but .... well... should I bother describe it's braking? It's not bad, but of course it doesn't stop as well as the SV

The next morning, I got up and began my morning ride just as the sun was rising. I decided to take the Sugarloaf Mountain Ride described here. Sure, it's laughable that anything in Florida is called a mountain, but Sugarloaf Mountain is Florida's most prominent hill. At a whopping 312 feet (some moutain, huh), it's not much lower that the highest spot in Florida. It probably is the highest spot on the peninsula.

The route named for the mountain doesn't actually get to the tallest point, but it's still quite scenic. On the west side of Lake Apopka, it's a rural area with little traffic just outside the Metro Orlando area. While there's better twisties in other states, this route provides a nice break from the usual flat-n-straight roads typical in Florida. If you don't mind being slowed down by an occasional group of bicyclists, it's a fun ride.

At the end of the route, I turned around to go back North. I wanted to go to the actual "peak" of Sugarloaf Mountain or hill or whatever it is. I was actually surprised at how steep the road to the top was. It's not the steepest road I've ridden a bike on, but it's been a while since I've seen a road this steep. Of course, the SV didn't struggle at all on the way up. Once at the top, you could easily see across Lake Apopka. I've heard if the weather is right, you can even make out the space cost from there.

After that, I rode up North to highway 19 up through Eustis and then on to Ocala National Forrest. Ocala National Forest isn't quite as nice as the Sugar Loaf Mountain area, but it's still a nice enough place to ride. I've hiked out there just a little bit, and I get the idea that it's more scenic on foot. Part of the problem is that you've got tall trees right up to the side of the road. You can ride right past lakes and not know it.

Still, there were good things to see. I enjoyed riding through the small towns. I saw a dude on a tricycle dressed like a homeless version of Santa Claus. I'm not judging the dude - he seemed happy enough. 

It was while I was going through the forest that I started to needed to take occasional breaks. After a while, my left shoulder would hurt a bit for some reason. While the SV seat was very comfortable, I still needed to stretch my legs after a while. With each break, I'd get off the bike for about 10 minutes, walk around, maybe grab a snack if I was at a store, etc. Afterwards, I felt just fine, and could go for about another 45 min. to an hour before needing another break.

Somewhere around the North side of the forest, I rode over a tall bridge going over a barge canal. If there was a walk way, I might have stopped to take pictures. As I glanced down at the canal, I imagined being down there in a canoe. Maybe one day, I'll do that!

When I reached Palatka, I decided to make my way to highway 17 and then go south. As I got close to highway 17, I noticed the cooling tower of a nuclear plant in the distance. I didn't know we had one there. It was oddly scenic and beautiful in a way that I just could not capture when I pulled over to take a picture. So you might ask how the hell a nuclear plant's cooling tower might be scenic. Well, with the lighting, and the way it dominated the horizon and..... well, maybe you'd just have to have been there.

Going down 17 was actually nicer than going through the Forest, despite the fact that the area was more populated. Before actually turning south, I crossed a long bridge over the St. Johns River. Looking over the river was nice, and I regret not stopping to take my time seeing it. Maybe that's something else I can do on a future trip.

As I got to Crescent City, it was time for another break. I found a not-so-nice park, but it did have a cool pier going out over Crescent Lake. I walked out to the end of the pier and looked around. It was a nice relaxing place to rest. 

I noticed increasingly more motorcycles as I went farther south. Why not - it was a great day to ride! I was in such a great mood that I even waved to the guys on the Can Am Spyders. When I got to Highway 40, I turned back west towards the forest and started to see more folks on dirt bikes. One day, I should get a DR650 that I can ride to the forest and check out the fire roads.

Once I got back to Highway 19, I decided to turn East on Highway 42 and take the back roads back through Mount Plymouth and through the County Road 435 twisties just north of my house. I got home at about 1:30, so that was about 6 hours of riding with about 30 min. of breaks. I was drained but had a blast. The SV650 did very well.

So now for the not so great part of the day. At about 5:00 I decided I should ride round a bit before turning the bike in. My wife went to the store, and was going to meet me there to pick me up at 7:00. I started the bike, got to the intersection at the corner of my property, and waited for traffic to pass before turning right. When I got my chance, I started to leave when it felt like the bike was being yanked out from underneath me. At the same time, I was hearing what sounded like either gravel or dirt. I landed in a way that made a few of my ribs really hurt, but was otherwise ok.

Some guy in a van stopped to ask if I was ok as I picked myself up off the ground. I was dazed just a bit as I picked up the bike. The guy in the van kept asking me if I needed help, and I told him I was ok. If I wasn't still dazed a bit, I might have appreciated his offer to help more, but at the moment, I was just wanted him to move on. Then the "oh fucking hell, I dropped this dude's bike" feeling set in. I've made this same turn every work day with rare exception for the past three and a half years on either my Sportster or my Buell, but the one day I'm riding someone else's bike is the day the back tire slides out from under me thanks to some loose dirt and gravel at the corner of the turn.

So I decided to go directly to the drop off area near the owner's house in time for him to have daylight to see the damage. At that point, I really didn't feel like doing a whole lot more riding than that anyway. When I got there, the sun had just set, but there was still enough light to look the bike over. I called to see if he was home, and he walked over to survey the damage.

Luckily he had installed frame savers on the bike, and the right side frame saver took the brunt of the fall. It was easily scuffed up enough to justify replacing. There was also some scuffing on the muffler, the break lever was bent a bit, and there was some scuffing on the front. The function of the bike was definitely not impaired, but I clearly had some damages to pay for. We both talked to Austin at Twisted Road about how to deal with the damage. Austin asked if I was ok, and I told him I just had a couple ribs that could feel better, but was ok. The owner and I negotiated an amount, and arranged to have that paid out of the required credit card hold for the rental. During the negotiations, the owner was fair. And while I'm sure he wasn't thrilled to see that his bike was damaged, he didn't freak out about it. I think I was fair in the negotiations, too. At least I hope I was.

After I filled the bike up with gas and returned, we talked for a bit about motorcycles while I waited for my wife. Considering I scuffed up his bike, it was a friendly conversation. He seems to be a really good guy, and I feel so bad about dropping his bike. I know this was not a good rental experience for him, and I hope this doesn't deter him from continuing to rent out his bike through Twisted Road. I literally lost sleep that night thinking about it. Of course, the pain in my ribs didn't help with sleep either.

After my wife picked me up, I told her what happened and I told her how much the damage was going to cost us. She wasn't happy but she didn't freak out.  I thought she was going to give me a hard time over this, but she didn't. She was mostly just glad I was ok.

She did ask if I thought it was worth how much it cost me. This was supposed to be a free rental day, but through no fault the owner or Twisted Road, it ended up costing me more than it would to rent this bike for a few days. Obviously, if I could somehow know for a fact that this mishap would happen ahead of time, I wouldn't have gone through with the rental. If I could have known ahead of time that there would be no mishap, but it still would have cost me as much as it did, I probably wouldn't have rented the bike simply due to my tight budget. That's money that can go towards tools and parts for my own bikes. However, if I could know ahead of time that there would be no mishaps, no monetary cost, but I'd have to let someone punch me in the ribs really hard at the end of the ride, I'd go for it! 😝

The rental day may have cost me more than I anticipated, but a life without risks is a life without rewards. As motorcyclists, we take risks every time we get on a motorcycle. We are mostly rewarded for it, and on rare occasion, we're punished for it. Over all, the rewards outweigh the punishment. While I feel bad about the bike, I don't regret the rental day at all.

I don't know if I'll rent again with Twisted Road simply because it's not often that I need to rent a bike. But then again, I might! If I decide there's a bike I want to buy, Twisted Road offers an excellent opportunity to find a similar bike that I can test ride for a whole day. Had I done a test ride on an SV650 at a dealership, there's no way I would have gotten to know the bike like I did with the SV I rode yesterday. Also, I might see a bike that I'm simply curious about.

I might also rent out a bike through Twisted Road in the future. There's no way I'm renting out my old Sportster or Buell. They're a little too quirky, and need a little more maintenance than would be appropriate for something you let someone else pay you to ride. But if I buy a newer bike in the future, I could use Twisted Road as a way to help cover the costs of owning the bike. In fact, I could see myself buying a bike for the purpose of renting out through Twisted Road. An SV650 would be a great choice for this due to its flexibility, but the same could be said for many bikes.

In any case, whether you have a bike to rent or feel like renting a bike, I highly recommend using Twisted Road.

By the way, the owner said it was ok for me to put a link to his Twisted Road page here. So if you're going to be in the Orlando area and need a bike to ride, I recommend talking to this guy here: https://www.twistedroad.com/public-profile.php?user=21044

Buell Exhaust Repair

About two weeks ago, I thought I heard an exhaust leak around the lower front port side of my Buell Cyclone. (I'm using the navel term port here - in this case meaning the left side of the motorcycle from the perspective of a rider sitting normally on the bike.) I also noticed that the bike started to sound more like a Sportster. Heheh, go figure. When I investigated, I noticed what looked like a crack in my exhaust where a mounting bracket was attached to the exhaust pipe going into the muffler.

I think what happened was a stress fracture formed along the outer edge of one of the welds holding the bracket to the exhaust pipe. After that, the vibration of the engine simply caused the crack to spread. Then, at some point, the other weld was supporting more weight than it was originally and formed it's own stress fracture which grew in a similar manner. The edges of the weld are a natural place for this to happen, as the wall of the exhaust pipe is much thinner than the weld itself.

The weekend after discovering this, I pulled off the muffler to weld up the cracks. When I unbolted the front mounting bracket, it simply fell loose to the ground. The cracks had spread all the way around the original welds. Two holes were left on the pipe where the mount once was.

Fitting the bracket back in place was quite simple. When I put the bracket back in place, there were no large gaps, and gravity simply held it in place while I added a couple tack welds. I almost used no filler rod at all - I simply melted some of the excess metal from the weld beads and flowed it into the puddle I had formed along the crack.

Here, you can see where I stopped part way to show how I was using the existing weld material to fill in the crack.

Here's a pic from pretty much the same perspective after completing the welding on this side.

I also noticed a few stray cracks in the pipe leading away from the welds. I wonder if those were originally there, or if the thermal stress from welding caused them. I simply went over those with my torch to weld the cracks closed. After letting everything cool, I grabbed the bracket and tried to move it back and forth to see if there were any obvious weak points in my welds. Nothing broke apart, but I did see a very large crack in the bracket itself where it mounts to the frame. I simply went over that crack as well, welding on both sides of the crack.

Here's an example of where I welded up a stray crack.

Well, I think this should hold up. After riding around a bit to see that it stays together, I should probably paint it, since there's a lot of exposed ungalvanized steel there now. Below are some more pics at different stages of the repair process.

The weld repair from another perspective.

Weld repair of the crack in the bracket. Almost missed this crack.

The other side of the repaired bracket..

Here's the exhaust after reinstalling on the bike.

Shadow 500 Project

Back in April, I noticed an ad in Craigslist for a free Shadow 500. The ad described the bike as a scrap bike, and mentioned that the frame was badly rusted in one area and may need to be replaced. So after a few email exchanges, one of my sons and I went to pick the bike up.

We met at the owner's apartment complex, and the bike was in the parking lot next to his newer bike. He said he got the bike to fix it up, but didn't have the time or anywhere to work on it. He was moving, and really couldn't take the bike with him. Before I talked to him, he had called a metal scrap yard to see if they'd pick the bike up, but they would not. We loaded the bike in the back of the van, and he threw in some brand new carburetor parts. Originally, I wondered whether the van had enough room to hold the bike, but I probably could have fit three in the back.

The bike has definitely seen better times, but hey, it's a free bike! I think I can get it working after quite a bit of work. The plan, some of which I've done already, is to strip the bike down to the frame, assess whether the frame is salvageable, repair or replace the frame, paint the frame, get the engine running, and then reassemble, replacing parts as needed. I haven't checked but I bet the tires are old. Probably a good idea to replace the break lines.

One thing I get to look forward to is pulling the heads from the engine. The spark plugs were missing, and, of course, the bike had been sitting for who knows how long in a parking lot. When looking in the intake ports, one can see plenty of rust on the valves. An endoscope through the spark plug holes show crap on top of the pistons. Just to be safe, I think I should take the top end apart and clean things up.

The badly rusted part of the frame was fairly visible before disassembly. Where the rust holes are at, I think the frame is plenty strong enough to support the swing arm, but might be questionable for supporting the center stand.

So far, I've disassembled the bike to where essentially everything is stripped off the frame. I've also begun to repair the badly rusted portion of the frame. I've got some 1/8" (or close to that) steel from which I'm cutting small pieces and welding in place of sections of the rusted area.

 The rust repair has been a lot of fun! At first, I thought I'd be using my stick welder, but aside from a few initial welds, I'm doing a lot of work with my oxy-acetylene torch. I'm also getting some experience shaping the steel strips by heating with the torch and hammering into the shape I want. When the steel is hot, it almost seems like working with clay.

If I am able to successfully complete the frame repair (at this point, I'm pretty sure I will), the next step for the frame will be to remove any remaining fasteners, strip off the old paint, and then repaint with a good urethane paint. After that, I'll proceed with getting the engine going, and then decide what's next from there.

Here's some pics at various stages of the disassembly process:

The disassembly process has been started. You can see the green trunk I'm storing parts in at the top of the pic.

The engine had just been removed. The bike is almost stripped to the frame.

Here's pics of the rust damage:

Looks pretty bad doesn't it.

Here's some pics of the repair process (which has not yet been completed):

I'm holding a piece of flat steel that I've shaped to fit right about where I'm holding it.

As thick as this steel is, the repair should be plenty strong.

This is that same piece welded in place. You can see where I accidentally blew threw the edge.

Another patch in place!! I love welding!

I've welded over a couple bad places and filled in some rust holes using just a bit of welding rod.

Here, you can see where I've hammered the patch around the back.

I just didn't feel like cutting that tab off the patch before welding it on. This is on the other side.

I heated that tab and the edge of the patch on the other side and hammered them around. 

Here's the other side again. Basically, this is looking from inside the frame. You can see the tab hammered around.