LAL GMR Gomorrah (Lastgasp Art Laboratories)

[Gila_Crisis]

Here the gut pictures for the Lastgasp GMR Gomorrah, which is a very cool input sensitive subharmonic fuzz.

Enjoy tracing!

[Manfred]

Can you take a snapshot of the solder side that is more or less rectangular, with that I can then make PCB layout clones for tracking.
What are the dimensions of the PCB?
What types are the transistors?

[krystal]

They're all C1815GR, NPN.
It says so in the last picture (+ pic number 5).
Thanks for the pics, interesting device !

[Gila_Crisis]

Transistors are classic Japanese C1815 (se my last noted picture).
PCB is 22x39mm
This is the best straight shot I was able to take.

[krystal]

I gave it a go, and interesting it was.

Common base transistors almost threw me off. I've got no experience whatsoever with this configuration and haven't breadboarded the circuit yet. Could these actually be EBCs disguised as ECBs? Lastgasp Labs have been known to troll tracers by painting resistors before, so i guess anything goes, right?

This is my first trace so a good check is in order.

Thanks for the pics Gila_Crisis!

Edit: Flipping the pictures did my head in. Sorry about that, should be in order now. Thanks Manfred & Gila_Crisis

[Manfred]

Thanks for the traced schematic.
The transistors pins are not in the right order.

[krystal]

Ah, of course, because i flipped the pictures to match the trace side! i should have flipped the trace side instead. So i guess E is B and vice versa. Will correct immediately.

[Gila_Crisis]

You're welcome Kristal, and thank you for the schematic!

Note that 2SC1815 transistors have a flipped pin layout than most transistors (like BC153 or 2N5088), which is ECB instead of EBC.
The markings on the Gomorrah transistors are genuine and don't look faked or modified!

[krystal]

Yeah i saw that as i was tracing, but i flipped your picture component side and superimposed it on the picture of the trace side, making E-B and B-E. It's corrected now. Next time i trace a circuit i'll flip the trace side.
Also c1815 isn't flipped in regards to 2n5088, it's a different order altogether (ECB vs EBC)

Edit: I've updated the schematic (again), the input wasn't quite right. I'm also wondering about the values of some resistors. That 22M seems huge doesn't it?

[Gila_Crisis]

Red-Red-Green-Gold = 2.2M Ohms 5%

I suggest to recheck your resistors values:
https://www.digikey.com/en/resources/co ... color-code

[krystal]

Damn, i didn't realise 4 band resistors aren't read the same as 5 bands. Just divided everything by 10.
Sorry about these silly mistakes. I'm learning stuff at least !

Updated the schematic.

[Manfred]

I have the PCB clone so far.
Can you make me a bigger photo of the component side with a better resolution so I can see the position of the components.

[Nocentelli]

Edit: I've updated the schematic (again)....

Thanks for all your work on this. I am still curious about R7: It would make much more sense to have this vref resistor connected to Q1's base rather than the emitter (as with Q5).

[Manfred]

Here the corrected PCB clone, it was still missing a few traces some soldering eyes were too large.
I tried to place the components which I did not succeed because of the small and blurred photo and gave up.

[karul]

I am still curious about R7: It would make much more sense to have this vref resistor connected to Q1's base rather than the emitter (as with Q5).

True. I find another minor error in krystal's schematic. Capacitor C7 is connected to Q4's collector, not to Q4's base.

Here the corrected PCB clone, it was still missing a few traces some soldering eyes were too large.
I tried to place the components which I did not succeed because of the small and blurred photo and gave up.
gomorrah PCB layout bottom.JPG

I've done it. But let me double check everything before I post the drawing.

Here's the corrected schematic.

[karul]

Manfred, the layout should look something like this. C11, Tone pot pins 2 & 3, and Q5 can be rearranged. Yellow wire is connected to Level pot pin 1, purple wire (output) connected to pin2. One hole (for R20) under Level pot pin3 is missing. One avoidable hole between Q5 collector and C11 positive lead can be removed. Enumeration was done according krystal's schematic.

I can't confirm all the components values - they are simply not visible from those photos. I don't know how @krystal detected their values. Second drawing is the same - some traces are colorized for easier troubleshooting.

[krystal]

I got the values from the last picture Gila_Crisis posted, going by what they wrote in pencil.
I can't seem to edit my post with the schematic, i would have liked to update it with the corrections. Thanks by the way !

[karul]

For some reason I thought that you made those writings. I didn't saw that Gila posted that one. It was late night when I started lurking though the tread. Maybe that's why xD.

[Manfred]

Manfred, the layout should look something like this. C11, Tone pot pins 2 & 3, and Q5 can be rearranged. Yellow wire is connected to Level pot pin 1, purple wire (output) connected to pin2. One hole (for R20) under Level pot pin3 is missing. One avoidable hole between Q5 collector and C11 positive lead can be removed. Enumeration was done according krystal's schematic.

I can't confirm all the components values - they are simply not visible from those photos. I don't know how @krystal detected their values. Second drawing is the same - some traces are colorized for easier troubleshooting.

Hello Karul,
thank you very much for the great work!
You had more patience than me and quite probably the younger eyes.
I will change the PCB layout according to your found differences.

[karul]

Diode D2 orientation in the schematic should be corrected too. Visible markings suggests that it is not 1n4148 or 1n914. Is it a zener ?