Hello, that is a fantastic coincidence, I too have just built Harald Sabro's Decimator with the G-string add on. Mine does not make a sound. It is my first build, and I have no idea how to troubleshoot, so this could be fun.
Although I think I can in principle explain how to add the daughterboard, if I have done that bit correctly:
You need to remove C3 from the main board and replace it with two wires, which attach to two of the connections on the daughterboard. You then run another wire from row i between column 16 and 26, and connect that to the VR1 connection on the daughterboard. Then you add the ground and power wires, connect up the pots, and hope that it works.
From reading other posts about this build, the advice is to ignore the U7.1 label as Harald Sabro reorganised the ICs in the build, so they do not necessarily match the numbering on the schematic. Every other component should still match though. So it is probably easier to think of the C5/U7.1 wire as just the C5 wire.
So the C5 connection on the daughterboard is wired to the lower rail where C3 was on the main board (n16), as that is right next to the connection for C5. The R3 connection from the daughterboard is wired to the higher rail where C3 was on the main board (m16), as this is connected by row m to the bottom of R3 at m21. So the R3 wire can go anywhere on row m between columns 15 and 20.
I think I am reading that correctly, that is my understanding it. But that is the way I have done it, and mine does not work. So I will be interested to hear if yours does, and eager to understand where I have made errors.
Referring to what Motterpaul has said on this thread and the other Decimator one here, have you noticed your standard Decimator sucking tone?
I have connected g-string addon and it does not work...for some reason pot just acts as volume...messing with trimmer does nothing.
Also for what I have red online U7.1 connection is just missed what does not means that it is not needed...if sabro is reading this please tell us how to properly connect this addon...
When it is disconnected and C3 back in place it works like a charm.
If someone knows why please share your knowledge....
When g string is added and other pedals are in send->return loop pot just works on 1/3 of turn.
also guys what is connection scheme with guitar, amp(without send return jacks) and pedals? what jack is for what because some schemes that are around are just false...
If someone is questioning why am I trying to build g string if basic decimator is working - answer is that I need to switch from distortion to clean and then I don't have a sound since threshold is little past half of turn....
A new layout with the add-on included would be fantastic. The Sabro layout is good but I have been debugging it for a week and have still not got even a sound out of it. I suspect I may have fried a component, as I have resoldered every joint and made no progress.
There is an extra op-amp in the top left corner, DA1.1, which I thought might be a buffer for the loop of some kind. The power setup with all the parallel 100n capacitors is slightly different, and the Russian schematic has an extra power assembly coming down from pin 4 of the THAT chip. The final thing is the presence of a 100p capacitor to VR before op-amp DA4.1 at the top in the middle. I am wondering if that capacitor is key to generating the correct trigger voltage from VR, and if its absence would explain my own build not working.
The main problem I am having is that the existing layout is from several years ago, and the main board and daughter boards were drawn by different people, and the threads discussing it are now mostly quiet. This has made debugging more awkward, for things such as posting voltages. So a new layout would be exactly the solution for me; I may be able to verify it myself.
Never seen that schematic.
Can you try the different add-on part on breadboard or vero to see if it works?
It goes instead of C3 on Sabro's layout.
Send and Return need to be connected when there is nothing plugged.
I have ordered the additional new 100p capacitor from Farnell, but as it is a UK bank holiday tomorrow it may not arrive until mid-week. Once it does, I will attempt the new G-string layout and hopefully verify that it works. I must caution that my Decimator has yet to be tested as a standalone, non-G-string unit, so the fault may lie in my main board, and therefore I would be of little use as a tester for the new G-string layout (I loathe that name, it is the oldest guitar-based joke there is). I will try when the new capacitor arrives and report back. Thank you very much for the new daughterboard layout, it is much appreciated.
I have reworked my Decimator circuit with the new G-string board and double checked all the offboard connections, and for me it is still not working. The trimpot correctly functions for raising and lowering the signal level, although the only thing heard is static. This greatly increases when a distortion unit is in the send and return loop, as is to be expected. Turning the threshold pot clockwise reduces the noise, creating near-silence by the time it is 1/3 of the way through. However I cannot hear guitar signal through it, not with the pedal on or off, or even when just going through the first part of the unit (guitar connected to input, amp connected to send). Which suggests that the problem is near the beginning of the effect circuit.
I cannot get this to work properly, it may be that one of my components has been damaged during construction.
I am wondering about buying a second set of components and trying to build the effect on PCB, but I fear my PCB soldering is not good. Would anybody else be able to try this effect out on breadboard please?
I can post voltages, if that would help narrow down the problem with mine. All the power and ground connections are correct, but I do not know how to check if the ICs are working correctly.
I built this and cant get it going. What kind of trimmer did you use? Should i be using a 30 turn trimmer it goes from quiet to extreme noise when adjusting just wondering of saller increments matter . This has been a head scratcher im wondering of the current layout was rewqorked and not verified or something. I rarely have this much trouble in favt never. Even ifr its a brand new bad part I figure it out usually
I am going to have another attempt at debugging my Decimator and G-String tomorrow evening, hopefully with an audio probe. I may also replace C3 and remove the daughterboard, and see if it works as the standard Decimator, in an effort to isolate the problem.
I've done one but the only schematic available is the same that Sabro used.
The layout came out bigger (no standing resistors).
I didn't include the G-String part because at this point I'm not sure they do work.
I'll add it in Contributions for now.
i made one using the layout on sabro's site a few years ago and it worked for the most part. i had to have the trimmer almost maxed out. maxing it out cut the signal completely. it seems to work well - i always have it on in front of my amp. i haven't tried the g-string mod on it.
the only thin i've noticed is that it seems to be a bit above unity gain.