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.
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:
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:
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.