LumberJocks

Small Projects #42: Indoor Car Stereos (two)

  • Advertise with us
Blog entry by Madmark2 posted 03-14-2021 03:22 AM 1360 reads 0 times favorited 3 comments Add to Favorites Watch
« Part 41: Crosses -- More Easter Gifts -- Rosewood, Zebrawood, Cherry, Yellowheart, Purpleheart Part 42 of Small Projects series Part 43: Kitchen drawer replacement »

Have had this idea about building a home stereo (glorified AM/FM) out of a “one DIN” car stereo. Saw someone make a beautiful zebrawood case for an old Marantz receiver and got the bug to make a wooden stereo of my own.


Continue reading for build details …


2nd set for SWMBO

I’ve got a beautiful piece of wenge that I’m going to use for the front and top. The plan was to use cherry for the ends but things change. The wenge is very dark and the cherry was to be a light contrast. This will help show off the fancy Fast-Joint Mini jig joints.


The hearts really contrast nicely in pink & red. It looks like another fine MOM CORP. product.

The wenge top will be glued on flush with the four sides. The back needs to be removable for fuse and connection access.

I started by looking for an inexpensive yet functional car radio. I found a nice one in my budget ($25) that had 4×50w outputs and usb, Bluetooth, etc features. Its also controllable by smartphone. This means I can use it like a stereo even when offline.

I settled on the Dual XDM17BT single DIN (50mm x 180mm, 2-1/8” x 7-3/16”) unit. This is a very shallow (under 1-3/4”) box so it will fit in a 1×4 sized box.


Full featured car stereo.

Being a car stereo it is expected to be hard wired into the vehicle chassis but for this app the speaker and antenna wires need to be externalized to standard connectors.


Radio and harness stub.

Electrical Selection:
Had to bring the antenna connector stub to the rear panel and then to an external screw block for connection to a standard FM dipole antenna.

Home stereos normally use a folded dipole (T shaped & a yard wide) antenna while the radio has a coaxial plug. The dipole antenna connects to the screw terminal block. Its a lot of nonsense but you have to have all the bits and bobs to make it work.

For power I’m using a 12vdc @ 10A “brick” power supply. This seems simpler and easier than wiring and mounting a internal power supply. I wanted to keep all the voltages in the box “hand safe”.

Because the relatively high peak current demand—10A, good high current connections are needed. Cars have lighter outlets that support high currents. It seemed like a fun and appropriate idea to use a car lighter connector pair.

By using the lighter plug you could lug it to the car and plug it in there. I don’t know why you would want to, but I digress.

I found a home audio surface mount four speaker terminal panel. Cars have four, corner speakers that need a pair of terminals each for a total of eight.

This has screw terminal on both sides so connecting to the harness pigtails is a no brainer. Since it is designed to surface mount with screws no special wiring box or mounting issues should occur.

This should mount to the left rear for easy connection to the harness stub. Likewise the antenna terminal block should be on the right rear. The power plug cord can go anywhere convenient since that line has plenty of slack.


Brick, antenna stub, lighter set, speaker terminals, and radio with harness.

Project Dimensioning:

Can’t really begin the actual detail dimensioning until all parts are specified with known dimensions. This is why we discussed all the part selection crap before getting here.

The Fast-Joint Mini uses 3/4” materials for the ends and since the stereo is about 7-1/2” the box plus an inch on each side for clearance means the stock for the sides (front) should be 7-1/2” + 3/4” x 2 + 1” + 1” = 11”. In reality the end stock is 7/8” and the overall final size is 11-1/8”.

The front panel will fit four reps of the CROWN patten in a 4-3/4” width. The plan is for square 3/4” cherry ends (sides). Plans change. The ends are African Padauk now.

The 2nd unit has three reps of the 1-3/16” HEART pattern for a sleeker look. The rstereo was centered in the front as well. Otherwise the secondary woods are the same.

The front and top will be 1/4” resawn wenge, hopefully bookmatched. Its an odd bookmatch, wrapping around the top front edge, but a bookmatch nonetheless.

The back is screwed on for access to the wiring and will fit into a 3/8” W x 1/4” D rabbet on either side. The top will fit edge to edge and cover to top of the side rabbits and the top edge of the back. The bottom will be glued in place and will be made from a secondary wood. I’ve got a nice thin (1/8”) piece of purpleheart that will look weird but otherwise perfect for the back.

I’ve got plenty of speakers here so I decided not to build any in.

Mat’l:
  • stereo — $25
  • wenge — 2/3 bf @ $25.00 = $16.66
  • African Padauk — 1/3 bf @ $27.00 = $9.00
  • purpleheart — 1/8×5x12 — salvage
  • variegated jatoba —1/4×5x9 — salvage
  • power supply, 12vdc @ 10A w/NEMA 5 cordset — $25.00
  • connector pair, 12vdc @ 10A, car lighter type — $8.00
  • terminal block, 2P, solder tail — $6.00
  • antenna pigtail — $7.00
  • FM dipole antenna — $6.00

Close to a c-note and no sawdust yet!

Mat’l Prep:
After evaluating stock on hand I decided that the cherry was “Meh.” when set against the almost black wenge. Rummaging around I came up with a nice African Padauk board that was variegated and just a perfect contrast to the wenge.

The max height for the front is four 1-3/16” reps of the Fast-Joint Mini template or 4-3/4”. The wenge is almost 6” but I can’t resaw quite that much. So I ripped it to 5-3/8”. The wenge is 13/16” thick less a 3/32” kerf so I then resawed it at 11/32”. The thickness difference was easily sandable and no planing was needed.

The top is the full 5-3/8” depth and will be flush on the front and sides. This will put the book matched edges of wenge on the top front of the case.


Bookmatched wenge top and front.

Looking at the end grain of the wenge I’m reminded of phenol or that stuff they make knife handles. It looks ... man-made.


Kinda looks like a carbon fiber layup.

The padauk sides were rabbeted 1/4” x 3/8” for the purpleheart back. Got a nice sized thin (1/8”) slice of purpleheart that might work as a back mounting plate.


African Padauk smells sweet and delicious when cut.

Scrap piece of variegated jatoba is the right size for the bottom. Color will clash, but who cares, it’s the bottom!

Decorative Joinery:
Its time to cut the corners. I’m using the CROWN pattern on the Fast-Joint Mini cutting jig. On the second unit we’ll cut the HEART pattern.

Setup only takes a few minutes. Pull the router, change to the PC guide plate, insert the bit & collet and tighten. Set the clamps and stops on the jig, mark the edge and you’re ready to cut.

One tip. When cutting the pins, a thru cut, set the bit 1/16” or so proud. This will give a cleaner cut than the cutter being dead flush. If you do this you must remember to reset the height to flush before cutting the tails!

Like a dumbass I got twisted around and cut two lefts instead of a right and a left. But as luck would have it one of them had a bit of chipout on the pins. So I used the spare left to replace the chipped out tail board.

The second unit was cut correctly on the first try. Again everything is an easy hand fit — no “gentle persuasion” needed.


Both ends slip together by hand.

Both units have a very slight gap in the upper corner where the pattern didn’t quite match. No biggie, but a spot for more sanding.


Slight width offset by changing ends on jig. Alignment not quite perfect.

This thing is LOUD even without the electronics. I used what I had on hand and, er, the back and bottom … contrast the rest.


Rear view shows 1/8” resaw scrap purpleheart panel.

Total of four species:
  • wenge — top & front
  • padauk — sides
  • variegated jatoba — bottom
  • purpleheart — back

Its the most gawd awful color clash but the bottom and back won’t show — much.


Bottom is 1/4” resaw scrap variegated jatoba.

Preliminary Layout:
The remaining electrical parts are trickling in, enough have arrived to begin the layout process. The DIN mount cage and the antenna terminal block are in. Still waiting on the power chain, speaker terminal block and antenna stub.

Initially I was going to perfectly center the radio on the panel but the layout looked “Meh.” My plan is to add a “power present” green LED somewhere just as a decoration. Putting it to the side seemed to throw it off balance. I thought centering it above the radio would look cool and I moved the radio down so the lower edge of the opening was at 1”. This will give it a lower look with the idiot light up top as an accent.

  • Well, idiot light concept didn’t work out so 2nd unit is slimmer without provision for it.

One aspect of the Fast-Joint Mini that I’m still having issues with is trying to predict the exact final dimensions both inside and overall based on the material sizes. While the side dimension is consistent relative to the end, the tail spacing references the inside face. The overlap between the pins and tails isn’t specified and the answer isn’t simple to compute and, I suspect, varies with pattern.

Did the layout prelims with the Incra rules. Marks light up at the correct angle but are close to invisible otherwise.

Mounting the Antenna Block:
The antenna block is used to connect the FM T-dipole antenna to the rear of the stereo. The block has two screw terminal tabs and two mounting holes all 1/4” apart. The tabs are 1/8” down from the mounting holes centerline. 3/16” bit should work for all four holes.

On 2nd unit the terminal holes remained at 3/16” but the mounting holes were drilled and 6-32 tapped.

The terminal block is positioned on the rear aligned with the antenna jack on the radio. This is to maximize cable slack.

The 1/8” dia mounting holes call for 4-40 hardware but 6-32 fit when driven in.

Power Inlet Notch:
The 12VDC power cord will be fed thru a 1/4” rounded notch on the lower right aligned with the radio power connector. A simple knot in the cord will act as a strain relief. Drill the rounded top and then zip-zip on the bandsaw to cut the notch. Easy-peasey.


Antenna block & power inlet.

Drilling the DIN Mount:
Gave a lot of thought to how to cut the 2X7 DIN opening. Router? Scroll saw? Jig saw?

At first I had planned on using the router, nice clean cut, fairly simple to layout— or so I thought. Cutting the long sides would be no problem but the narrow ends are more of an issue. To avoid a trapped cut I’d have to rout the far end using the CROWN pins against the fence. Errr, no.

Scrollsaw seemed too slow, especially with a really hard hardwood (1630 Janka) like wenge, plus I’m not a super scroll sawer.

Finally I settled on the jig saw. Easy to use, faster cutting than the scroll saw, and I figure I can clean up the cut with my new detail sander. We’ll see.

… goes into shop & returns …

Well, just got done with cutting the DIN hole with the jigsaw.

When cutting the DIN hole with the jigsaw I clamped the workpiece to the saw fence rail. I used a shop rag between the fence rail and the workpiece to absorb the jigsaw vibrations. Three small clamps held it firmly in place.

I got to within 1/8” to 1/16” with the jigsaw and started sanding from there.

The advantage to sanding to final dimensions is that the process is s-l-o-w. Being slow makes it forgiving, easy to sneak up on the fit without going too far.

Went thru half a dozen nose sanding pads but got the hole sized just right.


Used drill, jig saw, magnetic base light, three sanders, shop knife and file to cut DIN opening.

The key to the final fit was getting the corners right. Sanding tends to leave the inside corners proud. The sanders just can’t square the corners properly. A little judicious paring with the shop knife followed by a small bastard file readily cleaned up and squared the inside corners.


DIN cutout progression: 1/2” pilot hole, rough cut, final fit, radio installed.

2nd Unit Scrollsaw works bettah!
1st unit was a lot of effort to get right. 2nd unit I used the scrollsaw and got better results faster and easier. Lesson learned.

Speaker Terminal Block:
Speaker plate came in. It has screw terminals on both sides. Since the harness stub was prestripped hookup was simple.

It took a little time to layout the hole. The spacing was such that if I centered on one of the terminals and drilled with a 3/4” forstner bit the fit would be perfect.

After drilling I used the scrollsaw to cut the rest of the opening. There was a lot more clearance than with the DIN hole and I used the scroll saw to good effect.

Since purpleheart is so hard it will thread easily and hold even at 1/8” thickness. I drilled and tapped four 6-32 holes in the corners for the terminal plate mount plus two centerline screws..


Rear panel dry fit.

Final Assembly, Wiring, Finish, and Test:


Finishing samples.


Pre-assembly finishing.

Gluing up required some thinking. The front has a ton of glue surfaces but there is a little flex in the sides so it was important to glue the bottom in at the same time to hold the sides square.


Four part glue up.

Glued the face to the sides first. The joints just fell into place. Once the sides were glued the bottom was glued on three sides and everything was clamped.

While waiting on the main glue up I finished up the back mounting. I’d predrilled the mounting holes with a #8 pilot. This gives a nice tight clearance for a #6. Setting the back in place I drilled and tapped one hole for 6-32. Placing the first screw in held the back in place while I drilled and tapped the remaining three 6-32 holes.

I put screws in finger tight to make sure the holes all aligned. The 6-32 1/2” SS cap screws were lubed with paste wax and snugged finger tight.


Top glue up.

After the main glue up the box was sanded with 120 to knock off any imperfections. And there are always “imperfections”. The top was intentionally cut 1/16” long so there was 1/32” overhang on either side to be sanded out.

Now we use the 240 to give a good clean base for the finish. I do “ten out and back reps” at each grit. I can usually feel the paper stop cutting at about rep #8.

Finish schedule is two coats of 50%-50% poly / MS mix. The thinned poly penetrates better than full strength.


Finishing.

At this moment the box is drying the 100% poly final coat.

I used a 6” lazy Susan bearing as a paint stand. I finished the inside first and flipped it onto its back on the bearing plate. This allows me to finish the outside and rotate without any additional contact with the wet surfaces.

Now if the last few parts would get here I’d be able to hear if it sounds as good as it looks …

A day has passed and the poly is nice and hard. Time for the final connections.

First I soldered the antenna stub to the teminal block lugs. No polarity needed.

Next came the power lead. The plug has two wires one black and one black with a white runner. There is no standard for these types of markings and in this case the stripe was the +12V and not ground as many others mark it so.


Only one gnd contact is wired.

Additionally I experienced a moment of panic when the gnd side wouldn’t buzz. Turns out that of the two gnd contacts on the plug only one side is connected. Damn cheap China crap. The wire gauge looked a little small for 10A but we’ll find out.

All of the wiring was soldered and covered with heat shrink tubing.


Soldering and heat shrink prevent loose connections.

I had worried about how to reach in from the inside to bend the DIN frame tabs to hold it in the box. When I put the cage in without the radio I had a Homer Simpson “Doh!” moment when I saw how easy it was to bend the tabs from the outside!

The radio clicked into the frame and the cables all plugged in without issue. There wasn’t a lot of slack, but there was enough.


Final touches include felt feet.

2nd unit got 1/2” rubber feet 6-32 threaded into the end pieces on the bottom. This raises the unit up and adds a bit of lightness.


Ready to rock!

Final Wiring and Power Up:
I bought a pair of small home theater speakers, each about 7” tall. I’m not going for ear splitters, just some gentle background noise.

I spliced the 12VDC lighter socket onto the tail of the 12V power supply being sure to verify polarity and voltage with my DVM. The soldered wires were individually insulated with heat shrink tubing and then the pair were over-wrapped with another layer of HS tubing to form a clean “running splice”.

The 2nd unit I found a power supply with the lighter socket standard so that was cleaner and easier — no splice needed.

Since this is destined to be a table radio, miles of speaker wire isn’t needed. I cut, stripped and tinned two, 3’ lengths of 16/2 zip cord as speaker wire. As a matter of habit I color tag each cable with a short length of colored HS tubing. Finding the far end isn’t much of an issue on a short cable, but the HS banding also serves to limit how far the zip cord unzips.

I made a temporary antenna out of about a 2’ length of 20ga solid wire and attached it to the antenna terminal.

Everything is tagged, labeled and ready to go.


Final wiring.

  • Drum roll please …
    .
    .
    .

IT WORKS!


Ta da!


Two for two!

Not only does it pass manual functionality but the Bluetooth wireless let’s me completely control it from anywhere in the house.


Radio screen snapshot.

We installed the Dual iPlug P2 app and were able to pair and immediately operate on both my Samsung Galaxy Tab A and SWMBO’s cellie.

Unlike a Bluetooth speaker this stereo continues to play even when the tablet controller is out of range or off. A nice feature for ambient music.

Again, unlike a Bluetooth speaker it can be operated from the front panel. Not bad for an el cheapo box.

  • Mat’l: ~$100 <== My out of pocket—true cost
  • Total Labor: 8 hrs @ $20 / hr = $160
  • COGS: ~$260
  • MSRP: ~$520

PS:
After playing with it for a while I gotta admit its a cool toy. Its just enough noise in my ear without taking over the room. The Bluetooth control is fun to play with and works flawlessly everywhere in the house.

PPS:
After finding out she could use it as a Bluetooth stereo speaker, SWMBO ordered one for her office. She really likes pink. Now to see if my supplier has any pink lumber …

-- The hump with the stump and the pump!



3 comments so far

View go4tech's profile

go4tech

37 posts in 2109 days


#1 posted 03-15-2021 11:26 PM

Would be concerned about the power supply. The radio is rated at 4×50W. That is 200W total plus whatever the radio uses and heat.

Not too sure of A) Current capacity of the power supply, and B) Noise rejection / filtering.

While the supply says 10A on a 12V DC rail, not so sure that it can really supply that much current and maintain the 12V rail…

Second, not so sure how well it is noise filtered. The Radio should have some filtering to assist. Then do not know how big / good are the capacitors are inside to supply the current when driving large current (ie: low frequency and reasonable volume) loads.

Worse case, you can always use an old computer power supply. If needed, add some capacitors to keep it stable for high current conditions.

Hope this is seen as helpful.

View Madmark2's profile

Madmark2

2660 posts in 1672 days


#2 posted 03-16-2021 12:11 AM

Fuse is 10a, everything was sized based on that.

Automotive 12vdc is very noisy with ignition noise. Voltage wanders all over from 14v+ down to 9v when cranking. Lights on, engine off 11-12v. Radio is designed to work under wide range of voltages from a noisy line. So holding a hard 12v rail shouldn’t be critical.

PS selected also is UL approved (means higher quality), it should push its rated output w/o much effort.

That power is peak and I don’t intend to rattle the walls with it so I should keep it in the SOA envelope.

I test powered the radio with an old 12vdc 2.5A wall wart. It came right up and I connected to it on Bluetooth with my Samsung Galaxy Tab A. Pretty cool.

Old computer PS has lots of +5vdc, +12vdc not so much, 150W PC PS may only push ~4A on the +12. PC PS form factor (with fan & fan noise) won’t mount in 4-3/4” x 5-1/2” space. Cost is 2x the selected “brick”.

Good idea considered and rejected along with open frame and caged power supplies.

Stated design goal is everything in box is to be low voltage, intrinsically safe, 12vdc. No 110vac cord or terminals anywhere in the box.

-- The hump with the stump and the pump!

View Craftsman on the lake's profile

Craftsman on the lake

3861 posts in 4521 days


#3 posted 03-17-2021 01:44 PM

When I built my boat I purchased a $29 automotive radio. When I went to install it, parts of it broke in my hands. I picked up one of these. It’s a class D amplifier. Radio on a chip. Very low power requirements. AM/FM, USB, SD card. etc. etc. I had a couple of new pioneer auto speakers I had from years go that I never used. It’s still running today and is great. They cost about $30. on Amazon. Many different makes/models. This one comes with a remote and works with your phone too. Built in antenna is as good as a portable radio. Works fine.

-- The smell of wood, coffee in the cup, the wife let's me do my thing, the lake is peaceful.

Have your say...

You must be signed in to post the comments.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com