LAL GMR Gomorrah (Lastgasp Art Laboratories)

karul · Post by **karul** » 02 May 2022, 15:15

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 · Post by **ppluis0** » 02 May 2022, 15:39

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 · Post by **krystal** » 03 May 2022, 13:11

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 · Post by **Manfred** » 07 May 2022, 03:30

Ready-to-print PDF-files:

LAL GMR Gomorrah Componets Side.pdf: (14.91 KiB) Downloaded 40 times

LAL GMR Gomorrah Solder Side.pdf: (4.58 KiB) Downloaded 35 times

SprintLayout6.0 file:

LAL GMR Gomorrah Layout.zip: (18.95 KiB) Downloaded 31 times

Manfred · Post by **Manfred** » 07 May 2022, 08:39

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 43 times

SprintLayout6.0 file:

LAL GMR Gomorrah Layout corrected.zip: (18.54 KiB) Downloaded 32 times

karul · Post by **karul** » 07 May 2022, 11:12

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

Manfred · Post by **Manfred** » 08 May 2022, 00:55

karul wrote: ↑07 May 2022, 11:12 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 51 times

SprintLayout6.0 file:

LAL GMR Gomorrah Layout corrected 2.zip: (18.55 KiB) Downloaded 34 times

Gila_Crisis · Post by **Gila_Crisis** » 15 May 2022, 17:21

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 · Post by **Manfred** » 15 May 2022, 17:51

Gila_Crisis wrote: ↑15 May 2022, 17:21 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 · Post by **karul** » 15 May 2022, 18:32

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 · Post by **Gila_Crisis** » 15 May 2022, 20:31

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 · Post by **karul** » 15 May 2022, 21:32

Gila_Crisis wrote: ↑15 May 2022, 20:31 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

Post by **digi2t** » 16 May 2022, 02:41

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 · Post by **krystal** » 16 May 2022, 05:36

karul wrote: ↑15 May 2022, 21:32
Gila_Crisis wrote: ↑15 May 2022, 20:31 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 · Post by **Manfred** » 16 May 2022, 10:03

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