a question on inputting -9v

[funkamunk]

i have a schematic that shows -9v being inputted, what ive done is just reverse the battery. i was wonderning what i do with the earth connections from the guitar inputs, do they still go on the negative end or do they now swap to the positive end of the battery?
kevin

[smoguzbenjamin]

Is there a positive battery input, because it could want a bipolar PS.

[funkamunk]

whats a bipolar ps?
im just using a regular 9v battery there is a symbol for ground but i just assumed that would be positive

[funkamunk]

whats a bipolar ps?
im just using a regular 9v battery there is a symbol for ground but i just assumed that would be positive

[smoguzbenjamin]

A bipolar power supply is a PS that gives ground, +9v and -9v. If there's a symbol for ground, +9 and -9 then you need a bipolar PS. Could you maybe post the schematic or point me to it so I could check it out?

[funkamunk]

thats what my other post is on about, trying to find the schematic! i have got a very messy pritned version but i need to have it electronically. its from joefus.com (which is currently down) it only has a -9v and a ground symbol but itdoes have some transistors i think are mosfets (bs250)

[smoguzbenjamin]

Are you referring to the obsidian overdrive? Maybe I've got that somewhere. Hold on a sec and I'll have a look.

[funkamunk]

yeh i am

[smoguzbenjamin]

No sorry I don't have it. If there's no +9v reference in the schemtic, then it's a positive ground. Mind you that using a positive ground circuit will mean that you can't use it in a daisy chain with most effects. You'll need to have seperate wallwarts for positive an dnegative ground pedals, or just use batteries

[funkamunk]

oh rite ok, thanks for your help

[smoguzbenjamin]

You're welcome!

[Samuel]

I'm like 95% sure that all versions of the Obsidian and Blackfire are negative ground. And then I'm like 40-50% sure that they were all single supply (is that the right term? I mean not bipolar) I'd be surprised if there was a version of the Obsid. that wanted -9V....

[funkamunk]

it definately says -9v

what do you reccomend for a second pedal? ive already made the easy drive. i thought this was going to be quite simple but its turning out to be more complicated than i thought

[smoguzbenjamin]

If you like tremolo the EA tremolo is a nice circuit to play with. Check out www.runoffgroove.com and build the version there. It works great for me!

[petemoore]

If you can see what kind of transistors there are in it, you can probably de-mystify the PS connections.
 Once you find out where say an emitter or source is, it should be easy to find which way is to ground, then once you find that, it's a matter of which battery terminal + or - makes the DMM Beep.
 If it's transistor, have I seena bipolar Transistor schematic>? I know I've seen OA bipolar supplies

[petemoore]

See if you can identify a part # on one of the active components...[more than two legs and not a pot]..more specific de-bugging techniques can probably be rendered to help resolve the this problem.

[smoguzbenjamin]

Hey pete aren't most SS amplifiers fed with bipolar power supplies? Anyway If you're gonna find groung, what are gonna reference the measurements against? The whole problem is that we don't know how to put the battery. You could try the easy approach and see which way round it makes noise

[Gringo]

The last versions of the obsidian released by joe where:

- A transistorized one (2n5089) -> negative ground

- A mosfet one (bs250) -> positive ground

(Untested) layouts are available at munky's site. I'll be checking them shortly, as i got some mosfets