Building a Noisy Cricket Mk II Amp and Mini Speaker Cabinet

I quite like the look of the Noisy Cricket Mk II amp from Beavis Audio (http://www.beavisaudio.com/projects/NoisyCricket/), and I happened to have a wooden box lying around that looked like it would work great as a 6” speaker cabinet, hence today’s project. (EDIT: Actually it turns out the Mk I and the MK II are the same. The only difference is the PCB design, and since I'm using veroboard, that's irrelevant.)

The Noisy Cricket is a little 1/2 Watt guitar amplifier that fits into a standard Hammond-like enclosure (such as the one I used here: http://diystrat.blogspot.com/2013/04/building-modified-ea-tremolo-pedal-on.html). It uses a MPF102 or a 2N5951 transistor as a preamp channel and an LM386 as the power amp. It’s also powered from a standard 9v guitar pedal power supply (or even a battery). What’s not to like?

As I usually do, I’m going to use Veroboard for this. A few people have already done layouts for it, and I decided to go with this one:

Which can be found here: http://tagboardeffects.blogspot.tw/2012/04/noisy-cricket-mkii.html

In addition to the Veroboard layout, this one has an additional tone switch, which lets you choose between the original 47nF tone capacitor, or the “improved bass” 100nF capacitor. In the end, I didn’t use a switch, electing instead to try both caps and choose whichever one I thought sounded best (in my case the 100nF).

Anyway, let’s get started. First we cut the veroboard to size:

You can see above that I have drilled a hole in the bottom right corner to match the one in the top left. That’s because I’m going to secure it inside the box (more on that later).

Now I cut the tracks in the appropriate locations:

And then give the copper a clean with a wire brush. This is to remove any tarnish from the copper, making it easier to solder.

Meanwhile, I’m also working on the box. First I work out where all of the controls/jacks will go:

Then I drill them out using a stepping drill bit:

After that I do a quick layout check to make sure everything is going to fit like I’d hoped:

I also glue in a couple of clips to hold the board in place once it’s done.

OK, let’s get soldering:

Here are all of the components in place (except for the chip itself, which I'll do as a last step):

Then the wires:

And then finally wired up to the pots, switches and jacks:

EDIT: I'm adding some extra information below about wiring up the box, since a couple of commenters so far have asked if I could share more details.

First, let’s look at the power switch. You need to connect the positive wire coming from your DC-in jack to one leg of the power switch (let’s go with the middle pin). The bottom leg of the switch connects to the 9V wire on the board. Make sure the negative pin of the DC-in jack connects to “ground”.

Here's a close-up of the power switch:

Actually, a point about “ground”. What I usually end up doing is choosing a fairly solid patch of metal to connect all the grounds to. In this case, I used one of the ground tabs on one of the ¼” jacks (doesn’t matter which jack since they’re connected electrically through the metal enclosure [this approach won’t work if it’s not in a metal enclosure, but simply hooking up the other 1/4" jack's ground to this same point too will keep you right]).

You can see that there are a few ground wires all connecting the right-hand jack in the image below.
 

The wire labeled “LED+” goes to the long leg of the power LED (the other leg should then also be connected to ground.

“Grit 1” and “Grit 2” connect to the middle leg and bottom leg of the grit switch (doesn’t matter which way around). If you buy a DPDT switch (six legs), then you can use the other column of pins to give power to an LED that will indicate when the grit switch is turned on. To do so, connect the middle leg in the other column of that switch to ground. Connect the end leg of the switch in that column to a 1k resistor and connect the other end of the resistor to the short leg of the grit LED. Finally connect the long leg of the LED to 9V ON THE BOARD (not straight to the DC-in jack).

Here's how my switch looks:

OK, that’s the switches and LEDs. Now let's look at the pots.

I’ve attached a photo that sort of shows the pot wiring. Basically as you look at that picture, the pin on the right of each pot is pin one, middle is pin two, and the left one is pin 3. Same for all three pots. If you mix up pins one and three, it’ll still work, but everything will work in reverse (turning up will actually reduce the volume, for example).
 

So, for example, “Vol 3” refers to pin 3 on the volume pot.


Some more points:

• Gain pins 1 and 2 are connected together. You can’t really see it in the photo, unfortunately.
• Tone pins 2 and 3 are connected together too.
• “Output” goes to the tip pin of the output/speaker jack (the other pin goes to ground of course). 
• Many speakers will be marked + and -. Theoretically, “-“ should go to ground, but it doesn’t really matter that much.

Here’s how it looks all closed up:

Now remember I mentioned that box? Well here it is beside a lovely 6” speaker I picked up:

We’ll need to cut a big circular hole, so let’s make sure we get the centre in the right place:

Then we measure the diameter of the speaker:

I’m using this adjustable spinning blade of death to cut the hole. Believe me when I tell you that this particular tool deserves all of your respect and then some. It will happily remove some of your body parts if you are not careful.

But for all of its scariness, it does do a great job:

A few more small holes for the securing screws and here’s the speaker attached (I'll add a grill to this later):

Now we need to wire up a jack. Unfortunately the thickness of the wood is more than the length of the thread on the jack, so I’m having to get a little creative with the solution.

I use another boring bit to scribe a line a few mm down into the wood. This will act as a guide for the next step, both for the depth and the outer diameter.

I then use a flat-bottomed drill bit (really, it’s a routing bit) and very carefully lower the depth of the wood within the confines of the outer circle I’ve just cut:

I also cut a little lip in there to match the lip that’s on the jack itself:

Here’s the jack in place:

I wanted to make some sort of handle, but also use the handle to hold the amp in place. However, I’d like to be able to remove the amp at any stage to use with a different speaker, or even use a different amp with THIS speaker.

So I attached a piece of leather like so:

Now the jack gets wired up to the speaker:

And I used a couple of metal fasteners to hold the back cover on:

After a bit of a search, I found a suitably-sized grill to protect the speaker:

And here it is holding the Noisy Cricket in place:

Finally here is a quick, dirty and extremely amateur demo of the amp. I probably should have planned what I was going to play before I started the camera rolling, but hopefully it will at the very least give you an idea what the amp sounds like.