Positive and negative ground in one enclosure

[Timebutt]

I should have thought about this before I started doing this but anyhow here's my current problem: a friend of mine asked me if I could upgrade his Green Russian Muff by installing a clean blend and a booster into it along with making it true bypass. All of that works great (I used buff 'n blend and millenium bypass) when the enclosure is not assembled, but from the moment I assemble the enclosure I get no sound anymore.
It took me a very long while to finally find out what was going wrong (very frustrating to see your pedal work completely but seeing it shut off when you assemble it): the enclosure part where the Muff circuit is mounted on is positive ground and the other half of the box where I mounted the blend and booster is normal ground, so when the two contact -> problems ...

Now my question is: is there any way at all to still fix this problem and have those circuits reside in the Muff enclosure? I'm out of ideas myself on how to solve this and I don't want to dissapoint my friend so I was hoping somebody could help me out?
FIY: I did use the search but not much helpful came up ...

Thanks

[jlullo]

at the very least, without messing with the muff, couldn't you just make booster/blend PNP?

[Auke Haarsma]

Maybe you find some uses in this article:

http://geofex.com/circuits/+9_to_-9.htm

[Ben N]

unless you change either the booster to PNP or the Muff to NPN, you have two problems: power supply (You need two of them, or a +/- supply, which is basically the same thing) and ground. The bigger problem, I would think, is ground, since both power supplies have to reference it, and typically both circuit grounds should be tied to the chassis, not to mention biasing headaches. More trouble than it's worth--do what Jon said.

[tranceracer]

You may want to try to isolate your jacks, power plug and anything that may be using the chassis as a ground.   using the plastic marshall style (Neutrik) female jacks, and floating all components from "touching" anyting worked for me when I had a similar problem.

-tR

[Timebutt]

Jlullo, I'm not quite sure how I am to change the booster and blend circuit to PNP? Does this involve a lot of work or can this be achieved by simply using other but similar transistors?
In the meanwhile I'll try what tranceracer said and hope that works out.
Thanks for all the help.

[Paul Perry (Frostwave)]

I would go for the tranceracer approach, but I wonder whether it would be even safer to have a 100uF cap in series with each of the input and output ground connections on the isolated jacks?
I say that, because I can imagine one day a lead from the + ground part and a lead from the - ground part being plugged into the same bit of gear - that could cause tears..

If you draw out block diagrams of the whole scheme, including the two grounds (one going to the + of the battery and one to the -) you will see what I mean.

[petemoore]

Jlullo, I'm not quite sure how I am to change the booster and blend circuit to PNP?
 not sure, I see 3 options, and assume this is a PNP BMP?...
1 use two separate PS's, DC floating outputs, or batteries.
2 Find Buff 'n 'Blend transistors which are of opposite polarity to the ones shown in the schematic, *reverse all Polar components.
3 make a Green Pi compatible with the BnB circuit supply.
----
1rst option: messy or bulky or time consuming, may have it's own complications.
2nd: not bad if you can find the 'mirror compliment' active [what'd be in a +gnd Cct. I assume].
3 with lots of trouble you can come very close to the original copy.
 *reverse anything with a polarity mark like '+' [on DC supply and capacitor], a line on a diode, a diode arrow inside a transistor.
 I guess the boost is a GE RM, IWCase reversing polarizations on that [including use of NPN transistor]..
 Starting with an NPN schematic for the booster..getting that working is an option.
 Simply using a battery for the PNP Pos Gnd. Cct. is another.
 Spyder PS is another.

[shredgd]

One of my diy pedals is a "triple pedal" containing a Mosfet booster, a PNP Treble Booster and a Si Fuzz Face.

It works perfectly with a standard negative ground, being the PNP Treble Booster schematic a little adapted in order to avoid problems (i.e. shorts): I "grounded" (read this "connected") to +9v everything the schematic said, except for the level pot which I connected to normal negative ground to give it a "0" reference. So, you might consider converting the pedal enclosure to negative ground and do those little adaptations as above, by looking at the Big Muff schematic for a reference.

On the other hand, my successful experience with a PNP project inside a normal negative ground pedal leads me to think you might follow an easier approach, which simply is the contrary: you should be able to successfully put an NPN circuit into a PNP positive ground pedal by doing small adaptations to the NPN circuit. In practice, you should connect all the ground points of the NPN circuit to the (-) side of the battery, avoiding any contact to the enclosure or whatever. Seen in another way, your NPN circuits "won't be grounded", just consider all the ground points of their schematic as a point of junction with no other meaning.

The fact your mods work outside of the enclosure is great, and it means you basically have to lift the ground of the "added" circuits you just built from that half of the enclosure. That is where your problem lies, at the moment.

[SonicVI]

I wasn't aware that the green Big Muffs ever came with PNP transistors. 

[Ben N]

I wasn't aware that the green Big Muffs ever came with PNP transistors. 

Me either; I thought PNP was an artifact of the misty, uncharted prehistory of BMP-dom, i.e. the early '70s.

[Timebutt]

Well I found that out today as well: the Muff is negative grounded and not positive as I thought.
Still: the grounding was causing all of these problems. I think you all know the feeling when you are debugging a pedal but just can't find out what's wrong with it? Well I've had that feeling since last saturday and I simply couldn't find out what was causing this problem and now it's finally finished thanks to this forum! I finally got to box it up correctly and get everything to work a few minutes ago and I'm very happy now

[Ben N]

So, out of curiosity--what did you do differently? Isolate the PS+grounds? If so, I wonder why... 

[Timebutt]

Well basically, I disconnected all of the grounds (the green muff enclosure is connected to ground through two screws) from the enclosure and that seemed to solve everything. Very odd: when they were connected everything stopped working once I put the enclosure together. It also makes me wonder why all of a sudden things are fixed through doing this: perhaps the real problem was something else touching another component but got fixed through moving some wires? Who knows ... all I know is that it's fixed now