Boss SG-1 project

[Zero the hero]

Hi everyone!
How many of us have succesfully built the Boss SG-1 using the layout from my site or from GGG?
I received some mails from unsuccesfully builders, so I would like to know the impressions from anyone experienced by this project.

I have to say that I've built it three times and they all worked instantly BUT I reported that they doesn't work with some guitars, for example with my Ibanez Artcore (hollow-body with two humbuckers). I still have not fully understood why it happens.
I used (layout / FET):
1: GGG layout, 2SK30A
2: GGG layout with true bypass, 2SK30A
3: Topopiccione layout, BC264

Thanks to anyone who replies!

[Mark Hammer]

The SG-1 is a sidechain/envelope-controlled device, and like many of this category of circuit, it is designed around an anticipated input signal.  The SG-1 uses a full-wave rectifier circuit almost identical to the Dynacomp, and precedes it with a fixed gain stage with a gain of x257.  In principle, that is enough gain to suit all expected input signals, which is why the gain stage is preceded by a Sensitivity control that attenuates the input, as opposed to increasing gain.

I tried one out once, but I have no idea why or how an Artcore might not be successful in these circumstances.  I'm assuming that the trimpot is adjusted properly on all the copies of the SG-1?  Perhaps the bass content of a semi-acoustic is playing havoc with the recitifier.  Try reducing the 1uf cap before the sensitivity control for, say, .047 or something like that. Or maybe reduce the 1uf cap in the ground leg of the rectifier gain stage after the 3k9 resistor (C17, I think) to .22uf so that it is less sensitive to bass content.

[jmasciswannabe]

I built this from your site and it worked just fine. I combined it in a box with a rebote 2 to get a very interesting slow attack delay. Kinda like a reverse delay sound, only not reversed....if that makes much sense. Alone it worked fine too, put i Prefer using a volume pedal because I have more control.

[RickL]

I've built it successfully. Can't remember off hand exactly what layout I used (it was a fairly big one) but it works exactly the same as my original one.

[Zero the hero]

Thanks Mark for your suggestions! It really puzzles me, and if I remember well it doesn't work properly with my Yamaha Silent Guitar SG-100, too!
Thanks for your build reports, now I know that everything is working fine!!!!

[MR COFFEE]

Hi ZTH,
I haven't built one using your layout, but a quick view of it makes me wonder about the possibility that some of the traces might not be reliable since there is no "teardrop" connection in several places, just a pad butted up against the trace with no overlap. Connections like that can look connected when they're not, because sometimes enough echant lodges in narrow places like that (where a trace is run tangent to the pad) and eats through the foil leaving a nearly invisible gap that *looks" like it's OK. So it could be a working layout but an occasional bad board.

Coupla other things that might explain the "works with some guitars, not others..."

If the diodes are in backwards, the FWR doesn't work very well, but it still works "sort of", only the transistor gain clamping the capacitor to ground is greatly reduced, like "piggybacking" transistors. It's not a precision FWR design to start with, and even without diode problems, that could make it sorta work and be more waveform sensitive.

Sometimes folks get confused about which end of a zener is which, and put them in backwards, too.

There is also a Slow Gear "MODIFIED" schematic floating around by Mr. Huge dated 2/08/00 which has errors on it - the op amp is not properly biased due to the omission of the coupling cap after the Sensitivity pot and the bias resistor from the non-inverting input to Vcc/2. Might also explain some of the complaints about it not working.

Hope this helps some of those folks.