Building a Ruby


I own Park G10 practice amp, but it broke down. I had no luck trying to fix it, so I built a Ruby amp in the case, instead. (And now for the real story: my girlfriend and I are moving to Berlin next week and we're taking the minimum amount of stuff with us. A broken practice amp was not considered minimum, so I had to do something.)
Here's a picture of the G10. It has a pretty weak 8" speaker and puts out about 10 watts. (Click any picture to enlarge.)

The circuit

My first step was to get the parts and create the circuit. The schematic came from the fabulous Run Off Groove. It may not be clear from the picture, but I used a LM 386N-1 and a J201. The IC, the transistor and the cap from FET source to volume are socketed. A good thing, because I decided the amp sounds a lot better with a 0,1uF instead of the .047nF. The bassman mod! I ended up using a 50K volume pot, as suggested by RDV. I'm running it at 12 volts, the 386 won't take any higher than that.
The sound is good, especially clean. The overdrive isn't very natural, a little too flabby. There is not a lot of highs in the sound, and the cap over the volume pot added loads of hiss. This is all nitpicking, because the amp sounds great for what it is! So few parts, such a great sound!


I'm very happy about the wiring, I think this is my first neat soldering job. For this project I had the use of a Weller soldering station. What an advantage over my own Weller low-watter! It's so much easier to solder and de-solder. This is ofcourse without all the wires to the pots and such, so I'm cheating a little here... Nonetheless, I'm proud.

Next up: the cabinet

In the mean time, I needed to 'upgrade' the cabinet so it would fit the new amp and would be eligible for a ride to Berlin.
Here's when I stripped the insides out of the enclosure. Dusty, huh?

Are you sure? (y/n): _

Now for an 'Are you sure?'-moment... I though 'what the heck' and stripped the tolex off! No turning back now...
The tolex left behind some dried-up glue which came right off after a good sanding. The enclosure turned out to be made of MDF.


A friend who happens to be an art painter told me to make the box white, so the colour would be brighter afterwards. I did this with cheap house-paint, the stuff called 'Latex' in Holland. It's just the most basic indoor white.


The whiter, the brighter, so here's for another layer of white.


... and another.
It's nice and white, with no streaks anymore.

First layer of yellow

Finally! Yellow! This is after the first layer of 'Flexa Zonnegeel Hoogglanslak', or sun-yellow high-shine lacquer. (Aren't word-for-word translations great?)

And it's done!

Three layers of white, three layers of yellow, and a whole lot of sanding in between. The faceplate is brushed aluminium, which is a fancy way of saying 'I didn't know how to fill the holes, so I just sanded that, too'. There was this sturdy sticker with control names on there. Taking it off was easy, but the glue that was left behind was a real pain. I ended up buying this really chemical smelling sticker remover. Nasty stuff, but it did the job. The headphone jack moved to the bottom of the amp-casing and acts as a speaker jack now. This way, I can plug in some other speakers and see what the Ruby sounds like. I'll try to find some time to put up a couple of sound samples soon.


I'm really happy with the way the black and the yellow contrast. I think the amp came out very nicely and I can take it with us when we move! Hurray! Now for a way to fill those holes... Perhaps a sticker?
When I hooked up the circuit out of the box, it fired right up, but when I put it in, the sound was really weak and power was low. Turns out I can't connect the speaker's ground to the star ground on the back of the volume pot. When I connected it to the casing, it was fine. Still, the resistance between case and star ground is zero... Anyway, I'm glad it works. Great value, works better with effects than my Smokey!
I'm thinking of putting the cap over the volume pot, another suggestion by RDV, and making it switchable. A 'bright' switch.
Thanks to all the people who helped me build this amp and to the guys at ROG for the schematic and layout and clear explanations!