Sunday, March 30, 2014

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 (, 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: 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:

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 your DC-in jack (the middle pin) 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.

Monday, March 17, 2014

Cleaning up a Strat after being in long-term (humid) storage

This very cool American Standard Stratocaster came in for a clean and a restring—normally a very straightforward job. However, it had been in storage for several years in a fairly humid environment and a lot of the metalwork, including the electrics, had become somewhat corroded.

It actually looks OK from that distance. Here are a few close-ups.

In addition to the dirt and grime, you can see that many of the screws have rusted quite badly. A quick test also revealed that the pots were scratchy, the switch was not working correctly and the output jack was making a lot of crackling noises.

A look down the neck shows corrosion on the frets, so these will need a bit of a clean and polish too.

Oh and... is that… blood?

The only way to deal with this is to dismantle it, but before I do that I’m going to take some measurements since it was actually playing pretty nice and I don’t want to change that if I can help it.

Measuring the saddle positions:

And the pickup heights:

First we remove the strings.

Let's deal with the tremolo next. First we remove the rear tremolo cover.

See the mould? Not the first time I've seen that on a guitar here in Taiwan.

We can lift out the tremolo springs by hand since the strings have already been removed (note the rust on the end of the spring).

And then we carefully lift up the guitar, leaving the tremolo unit sitting on the bench since there is no longer anything holding it in place.

Finally (as far as the tremolo goes), we remove the studs—these were just screwed all the way in so no need to take measurements in this case).

Now it’s time to remove the scratchplate/pickguard. 

Some of those screws were awfully rusty. We’ll deal with that later.

Now the neck. Four screws and off it comes:

Both the neck stamp and the body stamp confirm what the serial number suggests—that the guitar was made in 1989.

Check out the corrosion on those frets.

The jack socket plate needs removing too.

You can see above how tarnished the jack is., I’m going to try to clean this with contact cleaner, but experience tells me that it’s not going to be enough and that I’m going to end up replacing it anyway (and guess what, I did).

Let’s have a look under the scratchplate.

It looks OK till you have a closer look at the switch. As you can see, it’s also suffered from corrosion. No wonder it was cutting out.

Both the pots and the switch get some attention with the contact cleaner.

After applying that, I make sure to twist all three pots back and forth several times and move the switch between positions repeatedly in order to let the clearer do its work before it dries out too much.

Back to the body finish for a moment, I tried naptha first, but some of this grime is just too stubborn (most of it actually), so I switched to Pledge. Pledge did a great job. Just remember that this stuff leaves a wax residue, so never spray it directly onto strings, for example.

As for the scratchplate, let’s get those knobs and switch tip off first. I was able to pull these off by hand, though there are tricks for if these just won’t budge (such as wrapping a shoelace around the bottom of them and pulling up).

I don’t want to remove the switch if I can help it, so I take off one screw at a time to clean them.

While the screw's off, I take the opportunity to clean that area of the scratchplate.

These (and all of the other screws) are held in a vice and cleaned with a wire brush one by one.

The scratchplate itself is cleaned with Pledge. Most of it cleaned up pretty easily except a stubborn red mark (wait, was that blood too?), but that too came off eventually.

The scratchplate is screwed back on at this point.

The knobs and switch tip are cleaned in soapy water with a toothbrush.

And there they are back in place looking lovely, I’m sure you’ll agree. (I guess at some stage in this guitar’s life someone replaced the lower TONE knob.)

The jack plate is replaced after having been cleaned with Autosol metal polish.

Now we need to deal with the tremolo.

I don’t want to change the heights of the saddles, so I set them aside in order.

The screws and springs go in a dish of oil.

Meanwhile it’s a lot easier to tackle the tremolo base plate now that it's dismantled.



The saddles themselves are simply brushed with a soft brush. I don’t want to change the saddle heights if I can help it and the saddles are in pretty good condition anyway.

The screws and springs are given a quick scrub with a toothbrush.

And the tremolo unit is put back together with the saddles put in their original positions as measured at the beginning.

Before putting the tremolo studs back on the guitar, some petroleum jelly is placed on the threads and also on the little collar where the tremolo unit will lean against. This will act as a lubricant and help stop any undesirable creaking noises, etc when using the tremolo.

The studs and the tremolo are placed back into the guitar and it is carefully flipped over (remember there’s nothing holding the tremolo unit in place at this stage).

Before putting the tremolo springs back on, they get a quick clean and are then also given some petroleum jelly at both ends for the same reasons as outlined above.

Next, we clean up the neck.

After an initial clean with Pledge, each fret is cleaned with 0000 steel wool, using a fretboard protector to, well, protect the fretboard.

Polishing compound is then used on both the frets and the fretboard.

 The nut slots are cleaned out with a dental floss thing. I’m really not sure what they’re called.

The neck is placed back on the guitar (the neck plate was cleaned with Autosol and the screw heads were cleaned with a steel brush), and the guitar is strung up.

A tremolo arm is added since the old one was lost.

And we’re done.