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Ruby Amp from


Since this is the Project Log forum I'll post a short description of the project I am working on here.  I am going to document it on my blog as well, but as I am going to use dirtypcbs to make the board I thought it would be useful to mention it here too.  That way, other people can see my mistakes, errors and incompetence and hopefully avoid it.

The project is based on this design:

It's quite a popular design and you can find lots of builds on the internet, in blogs, instructables, and YouTube.  I used it as the base for a pocket amp in an Altoids tin, and I build them as gifts for friends who take up the guitar.  I have built around four or five so far.

I generally build the circuit on perfboard, but I find it tedious to wire up the off-board components, viz. the pots, the battery, the input socket, and the speaker.  I have also added a power-on LED, but that makes one more thing to hook up.  So, this project is to make a board to hold everything, with flying leads for the battery and speaker only.

The cross-section of the inside of an Altoids tin, perpendicular to the long axis, measures about 56 x 20 mm.  So, it's a perfect candidate for a board limited to 5 x 5 cm.

This socket:

is a PJ-804A 6.35mm stereo jack with switch.  It's easy to get here in Korea, but I don't know about elsewhere.  It's neat because the integrated switch can be used to turn the amplifier on when the guitar is plugged in.  That uses up about half of the board area.  The components are fitted into the other half.

The board is designed to sit vertically inside the Altoids tin.  On the top edge of the board are two groups of three pads, sliced in half by the board router going along the long edge.  The two potentiometers for the amplifier will be mounted in the short end of the tin, upside-down, with the solder tags at the top.  These will be bent back and short wires used to connect them to the pads on the top edge of the PCB.  I expect this to be easier than connecting 5 wires between the board and the potentiometers as I used to do.

The input jack will protrude through the front of the tin, with a 2mm thick M12 nylon washer behind it to spread the mechanical load over a larger area and strengthen the tin a little.  This also allows the PCB to clear the rolled edge at the top of the walls of the tin.

The potentiometers will have a smaller PCB with 7mm holes cut out to align them horizontally and vertically, and 3mm holes for the anti-rotation tab which stops the body of the potentiometers from turning.  This smaller PCB is a mechanical shim only, to strengthen the tin and align the potentiometers, but without it I'd have to cut off the anti-rotation tabs or use another spacer about 2mm thick.  In the past I used the plastic from a candy box which happened to be 2mm thick and was easy to cut.  The small PCB will be attached to the amplifier PCB with mouse bites during manufacture.

I am using my old Linux laptop for design, with a version of KiCAD almost three years old.  The board is pretty simple, and I think I understand all of the requirements and limitations of dirtypcbs, so I'm going to try submitting my gerbers and see what happens.

So far I am doing what is suggested in this blog post: ... ypcbs-com/

I have also changed my PCB outline to 0.05mm and drawn my own mouse bites, with a long slot between them.  The slot and the potentiometer mounting holes are all drawn on the edge layer.

KiCAD produces two drill files ending in .drl.  One contains plated holes, the other contains non-plated holes.  dirtypcbs ask for a single drill file ending in .txt, but I have read of cases where this was not necessary, so I am awaiting confirmation of that.

If all of this is ok then it means that KiCAD can be used with dirtypcbs with no post-processing, other than to zip up the gerbers.  If it's not ok then I will document here what I had to do to make it work.


Re: Ruby Amp from

Reply #1
Today I managed to get PayPal to send some money to dirtypcbs.  It was not easy as I work abroad, but that's sorted out now.

Yesterday I printed a copy of the artwork and glued it to some card to make a mock-up of the assembly.  I discovered that the whole thing (including the protrusion of the socket entry) might be too long to install into the Altoids tin.  I modified the layout slightly by putting a notch in the top-right corner of the board, which will allow the edge of the PCB to fit under the lip on the edge of the tin.  I am hoping that when I drill a hole in the tin for the socket it will push through far enough to allow the board to slide into position.  If not, I will have to make a new layout.

Anyway, artwork is submitted, payment is made.  Now we wait.

Re: Ruby Amp from

Reply #2
The boards are in the post!  I got a message on Monday morning to say the design had been submitted to the factory.  Then I got a message on Thursday morning to say they had been posted to me.

I am using the standard shipping (Hong Kong airmail), so I will get them in 1 to 8 weeks.  Naturally I am hoping for 1 week, not 8.

I will post pictures here when they arrive.  So far my experience with dirtypcbs has been straightforward.

Re: Ruby Amp from

Reply #3
Boards arrived today!  Very happy with how they look.  Now to assemble one and see if it works.