The 32 OD Pure Germanium Overdrive pedal - design and build in words and pictures

[laurie]

This is the loading of the board. You start with the lowest height components and work your way out to the highest components.
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32OD_build2.jpg (115.52 KiB) Viewed 5371 times

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32OD_build3.jpg (123.44 KiB) Viewed 5371 times

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32OD_build4.jpg (107.69 KiB) Viewed 5371 times

[laurie]

The Zener diode legs are bent to ensure the diode stands well clear of the PCB. If the wrong power supply is used the zener will get VERY hot and leaving it close to the PCB will burn the PCB.
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32OD_build6.jpg (43.96 KiB) Viewed 5368 times

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32OD_build7.jpg (73.68 KiB) Viewed 5368 times

[laurie]

The potentiometers are soldered in one place only, then aligned by eye before soldering the rest of the legs.
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32OD_build8.jpg (68.75 KiB) Viewed 5367 times

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32OD_build9.jpg (142.07 KiB) Viewed 5367 times

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32OD_build10.jpg (68.42 KiB) Viewed 5367 times

[laurie]

Load is complete apart from the Germanium transistors.

Because the Germaniums are comparatively fragile, they are soldered in last.
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32OD_build11.jpg (153.32 KiB) Viewed 5362 times

[laurie]

The metallized polyester capacitors are Kemet box style. I've been using them for years and they are reasonably priced, are easy to load, and they sound good.

[laurie]

Main board complete. Awaiting switch board (the jacks are connected through the switch board).

Powered it up and tested the bias points - Q11 bias is +3.7V which is just fine. The bias point for the Q21/Q22 Darlington pair was easy to set to +4.5V with the trim pot and the meter touching the "TP" test point.

As soon as the switch board comes I'll connect the jacks and fire it up to make sure it sounds the same as the prototype... After that is confirmed I'll load the rest of the PCBs.
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32OD_build1.jpg (105.7 KiB) Viewed 5353 times

[laurie]

Nice! Sometimes I have to wait for specific parts and then a project is delayed for weeks.

Surprisingly, the thing that will delay these will be the ribbon cable that joins the main PCB to the switch PCB. It should have been here by now, but it seems to be stuck in the Canada Post black-hole.

[BearBoy]

Exciting stuff. Looks great, Laurie.

Can’t really comment on the technical side of things but it’s a very neat design

[laurie]

I just spent about 3 hours sorting through the heap of transistors to find the best ones for this pedal and the 32 TB2.
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Bags-o-transistors.jpg (164.92 KiB) Viewed 5334 times

[laurie]

I connected some input and output sockets to the PCB temporarily to try it out.

Everything works perfectly... sounds just like the prototype.

I did decide to make one change. The "CLEAN" potentiometer was originally a logarithmic/audio taper which meant that the clean was added "all at the end" ... very little clean from about "1" to "7" on the dial, then everything added from "7" to "10".

It worked perfectly, but after playing with it for a while it has become clear how critical the control over the added clean signal will be (it is a GOOD thing...).

Changing the "CLEAN" potentiometer to a linear one brings the clean signal in earlier and makes it more intuitive.

New schematic below. I'll provide a clean print of the schematic with every pedal so you don't have to rely on the dodgy one I had to reduce in size and quality so that I could upload it here. The best way to view the schematic below is on a computer (not phone), and right click on the image and select "open in new tab" on your browser.

If you are on the pre-order list and would like an electronic copy, PM me here with your email address and I'll email you a copy.
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32 OD full schematicV1_1.jpg (196.13 KiB) Viewed 5320 times