BM30 construction guide
barry (Administrator) 11-02-2011 at 04:51 AM.
Post: #1
1 - Kit contents

Your Box of Matches (BM30) contains the following:
* T1 - transformer
* S1 - SPST switch (Ground lift)
* VR1 - 4.7k or 10k Log pot (Line out level) with chickenhead knob
* R1 - 100r/1W resistor
* J1 - J7 - mono jack sockets
* two-part chassis

There's also a hardware pack:
* 8 M3.5 screws
* 4 M3.5 plain washers
* 8 M3.5 shakeproof washers
* 8 M3.5 nuts
* 4 self-tapping screws
* 4 rubber feet
* 1 large solder lug

There's also a wire pack:
* 50cm of each of green, grey, orange, violet and yellow wire
* 50cm of bare bus wire

Check your contents against this list and contact Amp Maker if there's any discrepancy.


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barry (Administrator) 11-02-2011 at 04:53 AM.
Post: #2
2 - Schematic
The BM30 circuit is very simple. There are two parts: speaker-level inputs and outputs on one winding of the transformer and line-level components on the transformer's other winding.

[Image: zk0100.JPG]
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barry (Administrator) 11-02-2011 at 04:55 AM.
Post: #3
3 - Getting started
The Box of Matches is very simple to build, with about 30 solder connections. Build time is about an hour.

First, use four sets of hardware to fit the grey rubber feet to the bottom of the chassis. Use an M3.5 screw with an M3.5 plain washer for the underside and an M3.5 shakeproof washer with M3.5 nut on the inside of the chassis. Tighten these fully, as they will be hard to access when the rest of the Box of Matches is assembled.
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barry (Administrator) 11-02-2011 at 05:06 AM.
Post: #4
4 - Fit the line-level components
Add VR1, S1 and J7 to the Box of Matches' front panel. VR1 is a general-purpose pot, and there are a couple of adjustments to make before fitting it. First, bend back the small forward-projecting tab (A) so that the pot can sit flush against the chassis. Then trim the soft nylon shaft of the pot to about 8mm (B), using a Dremel-type tool or junior hacksaw to cut it to size.

[Image: ak01cl2.jpg]

Fit S1 and VR1 and orientate them so that their solder lugs are towards the bottom of the chassis. Fit J7 so that its solder lugs face inwards to make for easy soldering. Add R1 and the wires as shown here:
* R1 directly linking lug 1 of J7 to lug 2 of VR1
* a wire link from lug 4 of J7 to lug 3 of VR1
* a violet wire to lug 1 of VR1
* an orange wire to one lug of S1
* a black wire and a violet wire to the other lug of S1, connecting the other end of this black wire to lug 4 of J7

[Image: zk0101.jpg]

Rotate the pot's shaft fully clockwise and then add the chickenhead knob. Point it to 10 on the dial and then tighten its set screw to hold the knob in place.
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barry (Administrator) 11-02-2011 at 05:13 AM.
Post: #5
5 - Add the speaker-level sockets
The six jack sockets for the speakers are identical and are wired in very similar ways. However, access to their solder lugs is easiest if you do them in pairs as shown here.

Add J1 and J2 as shown here, orientating their lugs to the insides of the chassis. Take two 6cm lengths of the solid bare wire and use a pair of pliers to make a small bent 'eyelet' in one end of each. Drop the other end of each link through lugs 1 and 4 of J1. Make sure that the links pass through to lugs 1 and 4 of J2.

[Image: zk0102.jpg]

With the 'eyelet' in line with the jack socket body solder the links in place on both sockets (at the points shown with the red stars below). This parallels lugs 1 and 4 on these sockets. You don't have to solder the others lugs (2 or 3) of the sockets, because those connections are not used for speaker sockets.

[Image: zk0102b.jpg]

Now repeat the process for J3 and J4. and then to the same for J5 and J6. You will now have three pairs of connected jack sockets, with 6 small wire 'eyelets' in two lines, ready for the next step.
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barry (Administrator) 11-02-2011 at 05:18 AM.
Post: #6
6 - Speaker-socket wiring
With the remaining length of unused bare bus wire, create another wire link and run it through the three eyelets that are closest to the chassis's rear panel. This creates a common ground and connects together lug 4 on all six sockets. Before soldering, add an orange wire to any one of these eyelets. Now solder all three eyelets.

For the three unused eyelets take three wires and solder them as follows:
* grey wire to the eyelet at J1
* green wire to the eyelet at J3
* yellow wire to the eyelet at J5

[Image: zk0103.jpg]
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barry (Administrator) 11-02-2011 at 05:23 AM.
Post: #7
7 - Mount the transformer
The transformer mounts with 4 sets of M3.5 hardware, and the grounding lug. It mounts slightly off-centre, and make sure you orientate it so that its solder lugs are between J5/J6 and S1 for easy wiring access. It can be rather fiddly to get the nuts and shakeproof washers installed so take your time.

[Image: zk0105.jpg]

Don't forget that grounding lug! It mounts closest to the 4-ohm lug on the bottom row (see below for close-up).

[Image: zk0106.jpg]
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barry (Administrator) 11-02-2011 at 05:27 AM.
Post: #8
8 - Final connections
First, twist together the two purple wires and run them over to the two lugs at the left of the top row of the transformer's solder lugs. Solder these wires, one to each lug (it does not matter which wire goes to which lug).

Now trim and connect three orange wires to the grounding lug:
* one wire from the S1 switch
* one wire from the J1-J6 sockets
* add one more wire from the '0' lug at the top right of the transformer's lugs

Finally, trim and solder the last three wires to the bottom row of solder lugs on the transformer:
* yellow wire to '4'
* green wire to '8'
* grey wire to '16'

The electronics for your Box of Matches circuit is now complete, and it should look like this (the photo shows a pre-production and unpainted chassis):

[Image: zk0107.jpg]
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barry (Administrator) 11-11-2011 at 01:26 AM.
Post: #9
9 - Checking your Box of Matches
There are very few electronic tests that you can carry out with a typical multimeter. All of the windings in the Box of Matches are have low DC resistance, which means that almost everything will appear to have continuity to almost everything else!

But the circuit is small enough that it doesn't take long to work through each and every connection to double-check that it's wired correctly. Use this version of the schematic - with wire colours shown - to check your Box of Matches.

[Image: zk0108.jpg]
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barry (Administrator) 11-11-2011 at 01:37 AM.
Post: #10
10 - Add the cover
All that remains is to add the top cover to the chassis and fix it in place with the four self-tapping screws. (Note that the first time you use these screws you are tapping the thread into the gold chassis bottom, so the first 2-3 turns are stiff. Then the thread is made and the screws turn more easily.)


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