Friday, 26 September 2014

The Noisy Cricket Guitar Amp

The Les Paul DIY guitar project is nearing completion. Only a few more coats of Tru-Oil, and then assembly, wiring, stringing, tuning and intonation are necessary. Oh, wait...

What I really meant to say is that I want a small guitar amp that I can take anywhere. When googling "simple diy guitar amp" you'll quickly come across the Noisy Cricket Guitar Amp, the latest of a series of LM386-based mini amplifiers like the Ruby amp, Little Gem and Smokey Amp. It is a simple amplifier running off of a 9V supply (wall wart or battery) and consisting of a handful of components around a LM386 audio amplifier chip.

You can find various veroboard designs for a Noisy Cricket on the intertubes, but I chose a small protoboard to build mine. Here's a picture of the component layout. I usually do small layouts in Microsoft PowerPoint. No, I'm fine.

Veroboard panel. Note pinout difference between MPF102 and 2N5951.

I ordered all the components at Futurlec, especially the LM386 that I don't have at hand. It's one of the cheapest supplier, but they ship from Hong Kong which takes at least three weeks. The speaker is a small 10cm Visaton full range speaker (FR 10 HM) from Conrad at less than CHF 15, including shipping.

The build follows closely the guide on DIY Strat with the following exceptions: instead of a separate power switch I'm using a potentiometer with switch for the volume control. I also had to use a 2N5951 JFET instead of the original MPF102, and finally, I'm going for an integrated amp and speaker design.

Noisy Cricket parts

I soldered the board according to the layout above. The picture below shows the result (LM386 not in place yet). Note that the board is not a stripboard. Therefore the connections have to be made by bending and soldering the component leads appropriately. Apart from the two gain connections on pins 1 and 8 of the LM386, no additional wires were necessary to complete the circuit.


The leads that stick out on either side indicate the connection points for the potentiometers, switches, and power as indicated on the layout above.

Panel wiring in progress.

In the meantime I brought my (limited) wood working skills to fruition and built a wooden cabinet for the amplifier. As usual, the corners are nearly but not completely at right angles, but thanks to modern photography it can all be blamed on visual perspective.

Raw amplifier cabinet, sanded and ready for staining.

I then stained the box using a water based mahogany stain, and after it had dried completely, I applied 3 layers of Tru-Oil, giving it a nice vintage look that goes very well with my shoddy wood work.

Stained and oil-finished cabinet, surrounded by a glow of contentment.

I also finished the panel wiring, and the amplifier is now more or less ready for final assembly. The following picture shows the completed panel. From left to right we have volume control with power switch, tone control, grit, gain control, and bass switch. The protoboard is attached to the back of the panel using an aluminium carrier that is held in place by the grit switch. I soldered a 4 pin connector (Vcc, Ground, Input, Output) to the board to allow for easy assembly/disassembly.


The connector plugs into a 4 pin header that is part of the back panel, where the input, headphones, and power jacks are located (see last picture). There's also a 2 pin header there for the actual speaker.

After having fixed a small problem with the protoboard (I had forgotten the connection between pins 3 and 4 of the LM386; see design above), the amp worked! YES!!! It won't fill a concert hall, but as an exercise amp for the living room, it'll do just fine.

The controls have less effect than I expected, something I have to check, but at least I get some sound through the speaker. The connectors have already paid off, because now I can disassemble, check, fix, and then reassemble everything. For now, I have assembled everything and made a few pictures.

Finished guitar amp. I'll look for a speaker grille later.
Back of amp with power, headphones, and input jacks.
This more or less completes the construction of the Noisy Cricket Guitar Amp. I'll check the tone, grit and tone controls to see, if I did everything right, but for now I'm quite satisfied.

I'm aware that you can get a Marshall Micro Amp for around 50 Dollars, but to be honest, building the Noisy Cricket was way more fun than making an online order.

5 comments:

  1. Mine did. Until I plugged in the wrong power supply. Now it's dead. Lesson: always add a protection diode to the power connector.

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  2. Hi Ralph, congratulations on this project; the cab looks amazing. How does the amp sound like?

    also, where did you get the metal plates for the front board? I've just started to build the amp and I'm out of ideas. I think it's better to have a metal plate rather than mounting the pots on the wood (more work); any ideias?

    Thanks

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    Replies
    1. You should get alumin(i)um sheets at your DIY store. Saw them to size and keep all left-over/scrap pieces. They make great noisy cricket panels. Or cut a piece out of a food can (preferably empty). Fold it for extra strength.

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  3. mine worked on the breadboard but not on PC board. trying to figure it out

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