Author Topic: building the Obsidian (again)  (Read 1432 times)

Marcos - Munky

building the Obsidian (again)
« on: April 05, 2017, 11:08:34 AM »
Back in 2002, when I built my first pedal (a Bazz Fuss), one of my main goals was to build a high gain overdrive/distortion. After a few Bazz Fusses and a 386-based amp, I jumped right into Joe Davisson's Obsidian (transistor version). It was a big jump, from about 8 parts to about 40, and it worked at first try. Until I decided to do a mod, and it never worked again... A few years later, I built it again twice, and it didn't worked. So, it's time to build it again!

This is the schematic I used. Hope Joe don't mind I post it, because there's only the MOSFET version in his page.

I drew the layout using Eagle.

The board was made using iron tone transfer, with the layout printed in a piece of glossy paper. I mirrored the layout, just because of the pots positions.

After all the drilling, I put some solder flux and, with a little bit of solder, I do a solder layer. This protects the traces from oxidation and makes the solderings easier. Then I wash the board with water and detergent.

All the parts soldered at their places. I do resistors and jumpers first, then IC sockets, caps, diodes, transistors, then offboard wiring, always folowing this order. I didn't took pictures of the whole process, but you can get the idea.

This is what I've done so far. Hope to finish it today.
« Last Edit: April 05, 2017, 11:17:29 AM by Marcos - Munky »


Re: building the Obsidian (again)
« Reply #1 on: April 05, 2017, 09:55:52 PM »
On the schematic you posted, the 3rd transistor emitter resistor looks wrong. Its shown as 100K, I think 1K is more reasonable.
Some people drink from the fountain of knowledge, others just gargle.

Marcos - Munky

Re: building the Obsidian (again)
« Reply #2 on: April 06, 2017, 11:26:16 AM »
Hey Russ. I didn't noticed that. Compared to all the other schematics I have (transistor and mosfet versions), all of them have 1K resistors emitter resistor, just this one have a 100K. I tested it yesterday with a 386 amp and a small speaker and it worked, I wonder how this resistor affects the sound, since the speaker I used is crappy enough just to use as a "it's working or not" test, and I can't get an idea of the real sound of the pedal.

More building photos to come later today.

Edit: I've checked again and, since the 1st stage is exactly the same as the 2nd, I just duplicated it when I was drawing the schematic on Eagle, so I've actually used a 1K emitter resistor. This is the correct value.
« Last Edit: April 06, 2017, 02:20:30 PM by Marcos - Munky »

Marcos - Munky

Re: building the Obsidian (again)
« Reply #3 on: April 06, 2017, 07:22:53 PM »
Here are the last photos of the process:

The offboard wiring:

For the enclosure, I used another sardines can. I drilled the led hole a little bigger, but got to fix the led anyway (super glue :icon_cool:). There's enough space to fit the 3 pots, but they are too close to use the knobs I originally planned to use. Not a big problem.

Here's where the problems started to happen. After I finished all the wirings and tested it, I noticed I need to set volume to full to get something near unity when the Obsidian is on. Then I remembered the first time I built it I had to skip that 470K to get more volume. I just cut the wire that cames from the tone pot and soldered it directly to the wire that goes to the volume pot. But the main problem is I couldn't get the led to light up! I changed leds, resistors, soldered the positive wire again and, about 2 hours later I found the problem was a dry joint at the negative wire :icon_mad:. Problem solved.

The rats nest:

And here's the outside. I was planning on using black knobs and a blue led, like my Vulcan, but the black knobs I have here didn't fit, so I had to use these white ones. And I burnt my last 3 blue leds (don't ask) while I was trying to figure out the led problem, so I decided to go with a red one.

Was it worth all this work? Yeah! It sound amazing for heavy rhythm guitar playing, and have lots of gain for solos. Actually, the gain pot is useless to me, if I build another I will put a fixed resistor to set it to almost full :icon_twisted:. I wish I had built it again sooner, but now that I did it'll be my main heavy distortion.


Re: building the Obsidian (again)
« Reply #4 on: April 07, 2017, 11:05:40 AM »
.... I burnt my last 3 blue leds (don't ask) ....

was it the sardines? very nice end result, and some less for the landfill.
winter. booo.
"Surely, it's only a matter of time before that quote makes it into someone's signature line?" - anotherjim

Marcos - Munky

Re: building the Obsidian (again)
« Reply #5 on: April 07, 2017, 07:14:09 PM »
Yeah, let's say it was the sardines' fault :icon_lol:. I don't like them, so let's blame on them.

I still have a few of those cans. I think they look cool for pedal building.