Demeter Fat Control Installation

[spaceace76]

This isn't exactly a stompbox question but here goes:

I'm installing the onboard version of the Demeter Midboost/Fat control into a project guitar, and as far as I can tell it's wired correctly, but it's not working.
It didn't come with any specific instructions, and I'd like to get it working tonight, but they didn't pick up when I called. Hopefully you guys can help me figure out what I'm missing.

A quick google search turned up this:
http://www.thegearpage.net/board/archive/index.php/t-174955.html

Now, as of yet, this guitar doesn't have a common ground. I didn't bother to make one yet since I was waiting to get everything working (pickups, coil taps, midboost) before doing any full-on wiring, since I'd just have to tear it up later anyway. Would not having the common ground disable the unit? Right now (with black ground wire soldered to nowhere) it is wired in the method mentioned in the link, and the signal does go through. I even pulled some of the insulation off and tested to see if the battery was providing juice, and it is.

So do I need the common ground in place for it to work? What can I do right now to send it to a makeshift common ground? I still don't want to make one since I won't be wiring up everything till sometime next week.

Heh, I was thinking maybe I should register over at TGP, but it doesn't seem worth it for one question...

Thanks for any help you can provide.

[frequencycentral]

I would ground it if I were you......

[spaceace76]

Well I did ground it. I sent it to the tone pot's ground, but that didn't work. As the link suggested, you have to send it to common ground, not a ground that goes to the output jack. I  don't currently have a way to do this, so I can't tell if the thing works without doing my full wiring bit. I've got a lot of things to cover and I'd rather be sure that the unit works before this last phase starts, otherwise it'll probably add another delay that I honestly don't feel like going through. What can I do that will simulate a common ground without actually making one?

[DavidRavenMoon]

Well I did ground it. I sent it to the tone pot's ground, but that didn't work. As the link suggested, you have to send it to common ground, not a ground that goes to the output jack. I  don't currently have a way to do this, so I can't tell if the thing works without doing my full wiring bit. I've got a lot of things to cover and I'd rather be sure that the unit works before this last phase starts, otherwise it'll probably add another delay that I honestly don't feel like going through. What can I do that will simulate a common ground without actually making one?

The only ground a guitar has is to the output jack... it's grounded to the amp. There are no other ground points. I make all my ground connection on the back of the pots.  I put lots of active circuits in guitars and basses this way. They all work.

[GibsonGM]

+1 David...the only exception to that I can see is grounding shielding back to the output jack at times.  The more junk you throw into that path, the more noise you get...the jack should be your star ground point (IMHO).

[slacker]

From reading the TGP thread it sounds like it is supposed to use a stereo output jack on the guitar to switch on the power only when a lead is inserted.
The black wire from the circuit board goes to ground (common ground in the thread), like David said the ground in a guitar is always attached to the sleeve of the output jack. The black wire from the battery snap then goes to the ring of the output jack, just like in standard stompbox wiring.
To test it just connect both of the black wires to ground, if you only connect one of them to ground it won't work.

[spaceace76]

The black wire from the circuit board goes to ground (common ground in the thread), like David said the ground in a guitar is always attached to the sleeve of the output jack. The black wire from the battery snap then goes to the ring of the output jack, just like in standard stompbox wiring.
To test it just connect both of the black wires to ground, if you only connect one of them to ground it won't work.

That's is exactly what I thought, and I had it in this configuration at one point. I feel kinda bad for not noticing it before, but I probably had the unit working when in that configuration but didn't notice. I later had it attached to the tone pot ground, but that wasn't working. I think that connection was just a bad solder joint, so I soldered it to the output jack sleeve again as you guys mentioned. The boost is less pronounced with my method of testing it, so I turned my amp up to give it a good listen and it does work fine.

Since I've got the electronics out of the body, the pickups don't "pickup" very well. I had them mounted up and functional a few days ago, and they were much louder since they had a whole guitar body and neck resonating along with the strings. Right now I'm just holding an extra string above the pickup and plucking it to see if everything works. Thanks for your help everybody! This turned out to be a really dumb question...

[DavidRavenMoon]

+1 David...the only exception to that I can see is grounding shielding back to the output jack at times.  The more junk you throw into that path, the more noise you get...the jack should be your star ground point (IMHO).

I don't do star grounding. I see no point in it. The usual reason stated for doing star grounding is to prevent ground loops.  I don't believe you can get a ground loop in a guitar anyway, since at no point is the ground potential any higher or lower, as there is only one ground to contend with, and any path to that ground is pretty short and of low resistance.

A real ground loop happens when you have two pieces of AC powered gear, each plugged into a different mains circuit, and then plugged together with a patch cord.  One piece of gear's ground might be at a different potential, and you get a current flowing across the grounds of the two devices. That's a ground loop. The easiest way to fix that is either lift the ground from one piece's AC plug, or the better way is to use a shielded cable with the ground only attached to one side, to patch them together.  This is why DI outputs have ground lift switches.

It doesn't hurt to do start grounding, as long as it helps keep things neat and tidy.  But I wouldn't go out of my way to do it thinking it will prevent ground loops, or is intrinsically quieter than the way guitars have been wired up for the last 50 years.
If you have to run your wires all over the place to get to the common ground point, then you are better off grounding to the back of a pot, as the path to ground is shorter. Neatness counts more than anything.

I do keep my pickup shields separate from the pickup's ground connection, but at some point before they leave the instrument, they are all going to get connected together!  Think of a shielded control cavity as a metal box you build an effect in.  Everything touching that box is grounded.. that's your ground plane.  I use foil under the pots, but I make my real connections to the pots themselves. The metal can of the pot is just part of the overall shield.  That shield connects to the output jack's ground, and ultimately to your amp.  So it's all connected to the jack anyway.  Take your VOM and read between the metal baseplate on a pickup, and the jack.  Should be zero ohms.  Then from a pot to the jack. Same thing.  It's all the same ground.

That's my 2 cents on the subject.   

[spaceace76]

I've actually shielded every cavity with copper tape, and the shield will be connected to ground via a ring terminal on my tone pot. The shield works extremely well. I had the pickups mounted along with my barely functioning bridge, and the guitar didn't seem to add to the preexisting noise in my practice area, even when in single coil mode. My current Strat has a dummy coil to cancel hum in every pickup position, but it doesn't help when I've got florescent lighting, and the t.v. is usually on while I'm practicing and/or tweaking. The shielded guitar (or maybe the pickups? it looks like DiMarzio potted them) didn't appear to be affected by these.

Also, I won't really have a common ground per se, its more of a wire nut with all the grounds joined there. I guess it's about the same thing, I just didn't want to drill. Drilling would just add more time, and I just got hit with another little delay today, so anything I can do to save time will really help. Luckily I got the Midbooster working within a short period of time.

Is there a section in this forum for DIY guitar build reports? I feel like I should do one since this is taking so long. I'm even doing a time lapse video of the build set to the theme from Rocky.