LAL GMR Gomorrah (Lastgasp Art Laboratories)

[karul]

I could be wrong but my guess is that diode is zener. Small signal diodes won't work, they will block the current flow from the LED. I don't know what kind of LED they have used but that 4.7k is bit to high for regular red LED. For current around 5mA min for LED to emit light that resistor should be lower e.g. 1k will do with zener cca 3-4V. I'm not sure why they used that arrangement.

[ppluis0]

Hi pals,

After take a look at the schematic of a Boss SD-1 found that pedal (and almost all Boss series) employs zener of 5.1V and 3.9K in series with the indicator led.
This way the led does not light when the battery needed to be replaced.
Ibanez place 4.3V zener and 3.6K in series with the led to achieve the same effect.

Cheers,
Jose

[krystal]

From what i can make out the bottom line says "n523", so it could be a a1n5230 4.7V, or a 1n5231 5.1V, probably doesn't matter which really. Well spotted!
Edit: just took a look at the green monster thread, it's a 5.1V there.

[Manfred]

Ready-to-print PDF-files:

LAL GMR Gomorrah Componets Side.pdf

(14.91 KiB) Downloaded 79 times

LAL GMR Gomorrah Solder Side.pdf

(4.58 KiB) Downloaded 69 times

SprintLayout6.0 file:

LAL GMR Gomorrah Layout.zip

(18.95 KiB) Downloaded 66 times

[Manfred]

I am sorry, I had faults in the designators of the potentiometers.
Here are the corrected documents.
The PDF file for the solder side in the previous post was not affected.

Ready-to-print PDF file:

LAL GMR Gomorrah Componets Side corrected.pdf

(15.23 KiB) Downloaded 76 times

SprintLayout6.0 file:

LAL GMR Gomorrah Layout corrected.zip

(18.54 KiB) Downloaded 64 times

[karul]

And L3 & T2 should be swapped. It will work either way.

[Manfred]

And L3 & T2 should be swapped. It will work either way.

Thank you Karul, I have swapped.

Ready-to-print file:

LAL GMR Gomorrah Componets Side corrected 2.pdf

(15.25 KiB) Downloaded 85 times

SprintLayout6.0 file:

LAL GMR Gomorrah Layout corrected 2.zip

(18.55 KiB) Downloaded 72 times

[Gila_Crisis]

Note that Deadend FX released a PCB for the Gomorrah, called Deuteronomy!
Their schematic is 100% proof. Krystal schem has few mistakes.
https://www.deadendfx.com/product/deuteronomy

[Manfred]

Note that Deadend FX released a PCB for the Gomorrah, called Deuteronomy!
Their schematic is 100% proof. Krystal schem has few mistakes.
https://www.deadendfx.com/product/deuteronomy

I checked the circuit of Krystal by tracing the PCB.
and found it to be correct.
Maybe Deadend FX has modified the circuit.
I will trace again to be sure

[karul]

Schematic is the same, only difference I've noticed so far is the C5 cap on Krystal's schematic. Their value is the correct one, 22n as is on the photos. On Krystal's is 10n.

[Gila_Crisis]

Check the 1M resistor going to Vr... the one on Q1 is connected to the Emitter, not the Base. Also the switch with the 2 condensators is different.
Did anybody test Krystal schematic and successfully built the pedal based on that?

[karul]

Check the 1M resistor going to Vr... the one on Q1 is connected to the Emitter, not the Base. Also the switch with the 2 condensators is different.
Did anybody test Krystal schematic and successfully built the pedal based on that?

There is a corrected schematic already, maybe you've missed it:
viewtopic.php?p=290683#p290683

[digi2t]

While all the transistors are the same, I did some experimentation with different transistors when doing the validation build. I found that Q2 can really define the sub octave performance. In the end, I found that using a lower gain transistor in Q2 gave better performance in tracking and sound. I used PN2222A for all except Q2, where I used a 2N2219. YMMV.

[krystal]

Check the 1M resistor going to Vr... the one on Q1 is connected to the Emitter, not the Base. Also the switch with the 2 condensators is different.
Did anybody test Krystal schematic and successfully built the pedal based on that?

There is a corrected schematic already, maybe you've missed it:
viewtopic.php?p=290683#p290683

Yeah I'd love to remove or replace that first schematic as it does contain mistakes, unfortunately i can't edit the post.
Great stuff Digi2t

[Manfred]

The retracing of PCB layout gave me the same circuit structure as shown in the schematic, maybe anthing went wrong with the circuit design.

[krystal]

I've been breadboarding Fuzzrite variations and found myself with Gomorrah's Q3/Q4 but with the octave cap coming from Q3's collector and blended in with a pot. Sounded pretty cool, no octave, but like a super heavy, loud and nasty Fuzzrite. I got mad oscillations by taking the cap from Q3's base, nothing to write home about though. One could test different values and configurations for the pot, the one shown on the left is just the basic Fuzzrite, you get a pretty nice array of textures along the sweep, on the right, the cap is bigger and you get some timid octave action on the low E.
I've not really refined the idea or anything, just thought it was kinda fun.
You could also easily mod a Gomorrah to have that as an option although you would get a volume loss and it would probably sound super tame in comparison.

[Gila_Crisis]

Finally I've built the Gomorrah clone using the Deadend FX board: sounds 1:1 as I remember my original Gomorrah used to sound!