Sunday, 23 March 2014

Building a Wooden Ghettoblaster: the enclosure (part 2)

The wooden ghettoblaster case ready to
receive its audio equipment
Here are some news of my wooden Ghettoblaster project...
In case you missed it, you can find here the first steps. I used marquetry techniques to give this ghettoblaster a retro look. I did not want to build yet another box with an amp and speakers (where would be the fun in that?).

I had old 3 way car speakers lying around. These are meant to be flush mounted. If you're familiar with building speakers, reading on might make you scream (you've been warned).

Googling around, I discovered a little of the science behind building speakers and lots of people arguing about technicalities (as always). I'm therefore not going to start a debate here...
here is an interesting source of information if you want to push your education about this topic a little further...

Speakers are now ready to be
flush mounted
Using a router to flush mount the car speakers

Here is (in very short) what I discovered about speakers: home audio is usually made of ported speakers where the driver (the thing producing sounds) is mounted in a box with a hole in it. If done right, it will sound great and will make your speaker much more efficient. It also requires more room (which is not a problem at home). Car audio speakers are however meant to be flush mounted either on the parcel shelf (large to infinite space called infinite baffle) or in very tight spaces such as car doors. These speakers ('drivers') are much more forgiving and should accept most box designs. I'm happy this is my case (car audio speakers) as I won't have (and don't want to) make all the calculations. This is as far as I'll go in this post and will go over audio in another one later.

Speakers can now be flush mounted
Where I left it, my front panel wasn't ready to be assembled in a box just yet. I still had to add VU meters (real ones), make the grooves to flush mount the speakers (using a router, see pictures above) and add an rusted handle.

Adding VU meters

VU meters - Woodwork

We're not going to talk about electronics here, we will focus on the physical integration of the VU meters I purchased from eBay.

This is what I'm going to add to the front panel
These VU meters are cheap plastic Chinese meters I got are supposed to be flush mounted and need to be attached from underneath the wood. The result above is the trickiest part of this project (see how thin the wooden edges are?). To give you an idea, the whole thing is 4cm high (about 1.5 inch).

To build this I needed a thin board of oak (5mm). Since I had none, I used a thick one (14mm) and used my router to make it thinner once both holes for the VU meters were drilled. If you ever need to do that, you should stick your plank between two other pieces of wood in a vice before using your router to remove a layer of wood that way you can avoid touching your vice with the router. I then glued a lath of darker wood all around it and let it dry in the vice:

VU meters front panel
drying in the vice
Once ready, I had to select and mark where to place my VU meters:

VU meters selecting and marking
the right spot
Remember: better make a smaller opening and enlarge it with a file than having to fill large gaps with little pieces of wood (or wood filler):

Cutting the opening with a jigsaw

If you're like me ... it never fits the first time you try:

The opening is a little too small,
I'll have to enlarge it with a file

Filing is always a little tricky: Remember to make an angle (front face needs to be the largest) so it is easy to insert your piece of wood. Depending on your needs, you can file the insert, the opening or both:

Filing the (VU) insert with an angle
to be easy to insert it in the opening
The insert is glued and drying inside the opening of the front face:

Rear view


Front view after adding a little wood filler and
sanding off the excess filler and wood to make it perfectly flat

Et voilà !
Front face finished and ready to add the VU meters and
power light (where does that hole on the right come from? ;-)
Glueing VU meters: to do this I used only a little (hot) little glue so the VU meters can be removed if needed and leds can be added for backlight. Remember to put it on an even surface to have your meters at the same level as the front panel:


VU meters glued to the panel
Original idea as backlight
for the VU meters

VU meters - Lights

I want my wooden ghettoblaster to look good even at night and to be able to see the needles dancing as I'm blasting music around.

My first idea was to use bright white leds (in series with a resistor). Out of the three I had only two worked, they were cool white (therefore not so cool ;-) and they were a little bulky so I decided to use SMD leds from a broken (warm white) led bulb. I strongly recommend always keeping a broken led bulb handy, they're a gold mine for leds.

Unsoldering leds from a broken bulb
I unsoldered 8 of them in total to put two on each side of each meter. Since I had only a few resistors left I used only one and wired my leds in parallel ... which is not a good practice (no guarantee you get the same current in all leds) but does the job just fine when they're all the same model and only requires one resistor. Note that I rated my resistor for only one led so all led were underpowered but at least I'm not risking to have to replace them after they're (hot) glued to the VU meters :-)

4 warm white SMD leds wired in parallel
with only one resistor for a 12V supply
And voilà, we've got two nice VU meters with a warm white backlight.

VU meters with a warm white backlight
on my Wooden Ghettoblaster

Adding controls

I'll have a limited number of controls:
  • A volume control, connected with a shaft to the volume potentiometer of the amplifier
  • A USB charging port
  • Two line-in/line-out/headphone 3.5 jacks wired in parallel
  • A power switch (230V) for the power supply
Since the volume control is the only one coming with a real challenge, we'll focus on that one. 

I started by inserting my 'The Crunch' amplifier (from 1992 !) in the box to find the precise place where I'll have to drill the hole for the volume control shaft.


The amplifier in the casing
(to align the volume buttons)
I then made a shaft extension for the volume potentiometer by cutting a wall plug and a threadbar:
My DIY volume control extension
I then cut it to the appropriate length and added a couple of bolts to prevent it from sliding out:

The wooden ghettoblaster (box) with its volume control (I added the speakers for the photo):

The wooden ghettoblaster
with its volume control

The handle

Adding a handle is not as easy as it seems... you need to combine both metal and woodworking techniques and need to be precise with both.

Building the handle

I chose a 16mm square iron tube. I wanted it square and wanted iron because I wanted to solder it (with my soldering machine) and wanted it to rust.

This part is straightforward but needs precision. You need to cut your tube at a perfect 45° angle... and I always manage to screw that up but eventually always file my way through it (this is annoying to get the correct length). The pictures below are before and after:


I then clamped the tubes to a set of (white) bars I had lying around to make sure my angles were square and I had the exact same length as my boombox.


Taking pictures while soldering is difficult so I didn't do it: you'll have to believe me when I say I did it myself ;-) I however managed to make holes in my handle  by accident. This happens when you're terrible at soldering (which is my case). Anyway it does not matter since I want it to be imperfect and rusted.

To let it rust, I had to remove all the coating it with a metallic brush

Removing the coating with a metallic
brush
And sprayed it with water during a couple of days to make it rust (note that you can use hydrogen peroxide to make it rust faster. I felt it was cheating).

My handle rusting on the
kitchen sink

Adding a groove to the sides to insert the handle

I'm taking a shortcut here and skip the part where I build the box, there's nothing special there. We're going to add the handle and to do that I'll make 10m long grooves on each side with my router to slide the handle in.
The mark where the handle will come
And made the groove:

The freshly cut groove in the boombox
A couple of chisel strokes, a little filing and sanding later and voilà:

My wooden ghettoblaster box with
the rusted handle on 
The handle is secured with two stainless steel (hum...) screws on each side.

You can read my following posts where I take care of the audio and electric parts as well as paint these speakers (fake rust, ongoing).

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