Troubleshooting

Hi- I am a amp builder in the USA that normally builds my own boards, etc when building my amps. I build amps under the Frugal Amps name. At any rate, I recently completed a 100 watt version 102 using the AA Elec board and wanted to post some of my build experience.

First- I used a chassis that I source from Amplified Nation. Its a classic Dumble clone style chassis of very high quality. I have used this chassis to build several dozen ODS amps over the years. So, the first thing I observe is that the ODS board from AA is a tight fit in the Dumble Reproduction style chassis. The board is pretty wide and it spans the entire open area of the chassis and was difficult to avoid having the input jacks on the front panel hit the board. I had to use very low standoffs to make the close quarters work. Those using wider chassis will have an easier fit.

Pay close attention for various small jumper wires that need to be used on the board. Depending on the circuit you build, the jumper requirements change. The printing is small and easy to miss. The layouts help in doing this correctly for your circuit variation.

Because I needed to set the board so close to the chassis, I note that you will want to secure front panel to rear panel and various other long wiring runs under the board with some sort of adhesive (I use a hot glue gun) to keep the wires away from the underside of the PCB thru wire leads. This applied to the transformer output leads as well.

Use your board as a template to locate the attachment spots for standoffs and mounting screws. Mark your holes and drill them before you do much else. The raw board is perfect for this but a populated board will make it harder.

I noted that my amp was noisy when I fired it up. By this I mean Hum. Years of building amps have educated me to suspect filter caps. In checking voltages, I found that the two power filter caps in the B+2 and B+3 positions when checked at the positive cap ends where they are supposed to be soldered were receiving no B+ voltages. The dropping resistors located just in front of these two caps were getting voltage but the caps themselves were not. I found that there is NO connection from the dropping resistor pads to the filter cap pads. This means there is no power filtering going on and hence the HUM. You will note tiny lettering saying for a #183 build, add a jumper. This is also needed for any of the variations using the old style filtering setup. So 102 and others need these jumpers.

Now that I got it all straightened out, its sounding very nice. I am next going to build my pedal for PAB and OD/Clean switching. I will be posting my build pictures on the Frugal Amps Facebook page for those wanting to see the journey. Hope this helps folks out.