Summer Project Galore!

DIY fever!! Can't stop thinking about all these cool projects on diyaudio, diystompboxes, ax84, 18Watt, etc. I need to get better organized with multiple projects going on, let's see now:

Speaker Projects:
OB - prototype is done, sounds pretty good already with only may be 50 hours of play so far, will ask the carpenter to get the plywood and hardware ready for finished speaker
Frugel-Horn Mk3- the Mark Audio drivers are unfortunately in the States still, Edwin will bring them back after the summer, so on the back burner for now...
- Constant Directivity - again missing the horn, can't do much now...

Guitar Amp Projects:
- Finished Fender 5F2-A mod, need to put it in a decent head cabinet, will get the carpenter to do it at the same time as the OB speaker cabinet, need to order some grill and front face plate to dress it up.
- Test bed for tube amp, all the parts are here just need to spend sometime to put it all together, should be done by this weekend.
- Need to decide the next amp build for bread-boarding, probably still stay with SE design this time around, may be a higher gain model...

Pedals
- Putting together a parts list, most of the passive parts, switches, jacks are sourced and ready to be ordered.
- Need to decide which pedals to build, some candidates include: LPB2, Lovetone Brown Source, Mr. Skyripper, Shin-I Companion, OLCcircuit Eclipse Valve, Parallel Universe, BISAB, Cream Pie, DOD 250 (MXR Distortion+), Digitech Space Station. Some of the above are not beginner projects, so I will start with some real simple ones like the DOD 250.
Here is the basic steps that I am thinking of, to get myself organized:

1. Decide which pedals to build;
2. Setup test bench, basically just a pre-made bread-board, power supply, and some connectors to get started;
3. order the parts;
4. put the parts on the bread-board, wire and test, listen, tweak, listen, etc.
5. put the finalized design on pref-board, prepare the wires for final assembly;
6. use CAD to do parts layout, prepare template for drilling holes in the chassis (may be standardize the locations of the input, output and power jacks, so the layout could be re-used);
6. prepare the chassis for graphic transfer - sand, clean, fine sanding, make sure the surface is super smooth, so the graphic will stick properly;
7. find the right graphic for the box, transfer and glue the image onto the box, trim the edges off, paint with light varnish several times, let dry and finish up with heavy car wax, mount the hardware onto the box and go for a test drive!
8. future to do - etch the image directly onto the box (looks so cool), and make my own PCBs which is basically the same process as etching the box, not sure it is worth it at this point as the wiring is very easy with so few parts, but definitely try it with larger and more complicated designs.

That's about it. Lots to do, but it will be fun!!

Setting Up An Electronic Prototype Workbench

For DIY speaker projects, I'd love to set up a lab, stock it up with drivers, crossover parts and really experiment and build some of these projects instead of just reading them online. After all, nothing beats the real thing, and to hear them.

Well I quickly realize that I lack the skill or space to build speakers at home, so I will just ask the carpenters to build the cabinets based on my designs, it is not the quickest way and I have to explain to them on how to properly build the speaker as most of them have never build speakers before, but it will have to do for now.

But for my electronic projects, after months of thinking about it, I finally done it! The lab has been setup in Gaby's room, I stocked up on parts, test equipment, tools, etc. Now I can begin prototyping various guitar amp and stompbox designs, as there are so many to try. Since 80% of the work in building amps/pedals is actually the final assemby, i.e., putting all the parts into a nice-looking chassis, it is much better to quickly build a prototype on the bench, make sure the design is good before committing the time and energy to actually put the whole thing together.

The basic test mule chassis will have various connections made via EU-type terminal strips, with all the parts easily accessible from the top of the chassis. The chassis itself can accommodate upto 5 tubes simultaneously, the PT and OT will be mounted on separate sub-chassis to make the whole thing more modular.

I have also purchased some basic test gear for the lab bench - a digital multi-meter, a dual trace oscilloscope (20MHz), and soon a waveform generator. Since I will be working on high voltage, I also got a variac, so I can adjust the AC line voltage. On my shopping list at the moment are - heat shrink tubing, hot air gun, chassis punch, amp gauge (up to 5A), automatic wire stripper, alcohol for cleaning PCBs and solder...

A Simple Stompbox Build

After reading somewhere that using a buffer/booster could improve the sound for PC-based guitar sims - I suppose from proper impedance matching between the guitar and the soundcard, I decided to build one.

The design I chose was the Fat Booster, just a simple FET booster with some level and tone controls added, the schematic is shown below. The design is a derivative of Jack Orman's MOSFET Boost, a very popular design. The unit is very clean as expected, but you have to be careful with the level and gain settings as not to overdrive the other effects down the chain. The kit only costed RMB99 (Chinese red case included), what a bargain;-)

The kit came with 2 PCBs, one is the main board, the other is the footswitch board, which I screwed up big time by turning the switch 90 degrees and made a mess of things, it took a couple of days to discover the stupid mistake :-(

Here are the exterior, interior shots and the schematic:

Fender 5F2-A Build

Saw this cheap Fender 5F2-A (Princeton) kit on Taobao, the whole thing was only RMB345, even including the tubes and transformers! It came with a blue chassis, not bad since the amp is known for its bluesy tone. Here is a picture of the chassis (slightly damaged during shipping). Some of the holes were off, you can see the corrections the shop made... I suppose it is good enough for rock and roll?!

The kit has three PCBs - main board, input/tonestack, and effect loop - no PTP wiring here, stuffing the boards were pretty straight forward after I figured out the the kit was really a hybrid design based on the original Fender Princeton and the ProjectG5 modern day version, the main differences were power supply related - the choke was eliminated, and some of the bias resistor/capacitor values were changed. Here are the pictures of the stuffed main and input/tonestack boards. Notice that the pots have different length shafts, I will need to cut two of them shorter...

Here is a picture of the completed kit - under the chassis, it is really not much there since the components were mounted on the PCBs. I don't like the heater wires running across

the main board but with the input/tonestack board in the way, it did not make much sense to put the heater wires right up against the chassis, oh well...

Here is a shot of the completed kit, it's pretty plain looking, I plan to make some decals for the faceplate to dress it up a bit, what do you expect for RMB345!

I also changed some of the parts, nothing special - 1)

added two 100 ohm heater resistors to the output cathode pin to provide elevated heater in order to reduce hum (while the ProjectG5 design has the resistors, the kit did not come with them); 2) replaced the silly LED circuit on the input board with a single 6.3V lamp; 3) eliminated the NFB resistor and instead installed a "Fat" switch, which is just a 22uF cathode bypass cap for the 2nd pre-amp stage. 4) I also added a 10 Ohm/10W resistor as a dummy load, to prevent the output from arcing due to an open output, i.e., when no speaker is plugged in.

The sound from the amp is pretty clean, breaking into a mild distortion when volume is all the way up with a small Marshall 6.5". I am building a "proper cabinet" using an Eminence Raging Cajun 10" - I bet the combo will be louder and and meaner sounding... So stayed tuned!

Of course, the sound could be improved even more with better tubes, it currently runs with tubes that came with the kit, which are Chinese-made 6N4 and 6P6P. I plan to change them to 12AX7A and EL84 if I can find some cheap ones online.

The build is good for amp builders just starting out, like myself. The 5F2-A's design could not be simpler - 2 tube-Single End, while the non-original FMA tone stack give it a bit more knobs to fiddle with, really the amp could probably make do with just a simple tone knob like many of the minimalist boutique amps on the market.

Some lessons learned:

1. always double check the connections multiple times, it is simple errors and dumb assumptions that always get you!

2. always use good wires, connectors and the proper tools, otherwise, you either waste time or end up with a crappy looking kit.

Finally, the revised schematic of the build.