how do i use a positive ground pedal with a negative ground pedal??

[monkey2410]

I've recently just made a positive ground distortion pedal that i wanted to combine with a negative ground distortion pedal i have made but i realise this doesnt work because the positive ground pedal will short circuit the negative ground pedal and possibly cause damage. so how do change this so that i can use the 2 circuits with each other?

[thermionix]

Battery in the positive ground pedal.

[monkey2410]

how do you mean?

[thermionix]

If you use a single power supply for multiple pedals, a mix of positive ground and negative ground,  that will cause a power supply short.  If every pedal has an independent power supply, no problem.  Since you are likely to have more negative ground pedals than positive ground, seems the simple solution is to use batteries in the positive ground one(s).  If the current draw is large, that may not be such a good idea.  If batteries aren't practical, you will need multiple power supplies.

[monkey2410]

i tried independent batteries in both but it didn't work, it just clipped my interface so i had to disconnect them

[bloxstompboxes]

i tried independent batteries in both but it didn't work, it just clipped my interface so i had to disconnect them

There is something here we are missing. Separate batteries for both effects should allow operation of both but not add clipping. Though, two distortion pedals on at the same time certainly will. What are they and how do you have this setup connected?

[monkey2410]

Basically I have created a pnp fuzz circuit and a jfet overdrive. What i am trying to do is combine the 2 into one stompbox each with their own footswitch to work either independently whilst the other is bypassed OR to activate both together with the pnp fuzz being first in the signal chain. However once i had each circuit working as i wanted it (on breadboard) i connected the 2 together to test the sound (by 1/4" jack, even though that wouldn't be the case if they were in the same stompbox). I did wonder how the 2 would possibly work together if they have different polarity grounds but because i've not heard of this issue before i connected them up to see anyway, but obviously it wasn't a smart idea.

here is the schematics for each circuit, i'm hoping that theres some way to connect the 2 circuits together that will just solve this really simply??

PNP FUZZ


JFET OVERDRIVE

[Cozybuilder]

Try wiring your PNP Fuzz as shown below.
Notice that the circuit is DC isolated from the input and output with C3, C4, and C7, C8. Thus, C1 is able to be connected to 0V, as is RV3, giving the ability to use 0V ground on this circuit. Make sure the board is electrically isolated inside the box so that you don't inadvertently connect an emitter to 0V etc. I like wiring this type of thing on Plain Perf.
Comment- Q1 relies on leakage to bias- you might consider adding a high value resister between the base and collector of Q1, say 1M to 4.7M.

[monkey2410]

Thanks ill give that a try. Is the part at the bottom to be connected from the positive of the battery to the sleave of the jack? I can't quite make out what the writing says next to the +9v

[Cozybuilder]

The bottom is standard reverse polarity protection and low-pass filter to get rid of AC hum from your wall wart. Not needed if you use a battery, but why wouldn't you use a wall wart?

1N5817 Schottky diode will drop a couple of tenths of a volt, but gives real circuit protection. The 47R and 100.1uF LPF gives a knee at about 34 Hz.

[monkey2410]

Thanks i've tried it out and it works fine!:) only thing i'm unsure about is setting up an activation l.e.d connected to the 3rd pole of a 3pdt footswitch like i have in the jfet circuit, would i just switch it to the 0v line rather than ground? and in order to switch the power to the circuit by inserting the jack into a stereo socket would i need to connect the input ring to the +9v rather than the negative end of the battery??

[Cozybuilder]

The LED circuit is independent of the effect. To keep things in the box straight, think in terms of 0V and 9V, as labeling one as ground for one circuit and not for the other is really arbitrary. The power supply couldn't care less about the label, it just provides 0V and 9V potentials. The PNP Fuzz circuit I drew is DC isolated, so you can wire the box as usual. The main item you need to be sure to take care of is that the circuit card is not able to short out on anything in the box- thats easy to do with standoffs, or plenty of other methods.

Just think of the PNP Fuzz as a black box, it has 4 leads: Circuit IN, Circuit OUT, 0V, and 9V.

[monkey2410]

Can you tell me i've applied that correctly here?

[monkey2410]

Ignore the schematic I just sent, i forgot to make a couple of changes , its this one.

[monkey2410]

but with a full connection for the true bypass 

[Cozybuilder]

NO! You are connecting the power source / battery as a positive ground, this will screw up mounting a negative grounded effect in the pedal along with the positive.

Edit: sorry, yes you drew the power correctly, but don't need the 47uF cap now (C2). However, the jack sleeves are connected to +9V, they should be 0V.

Look at my last post- the circuit on its own card will have 4 connections. The rest of the pedal you do as any other negative grounded pedal.

Here is one way- this allows either effect on, or both with #1 feeding #2, and an indicator LED for the on effect:

Note that the jacks are grounded, connected to the power jack 0V (or battery (-) if battery only); if you use a battery then use a stereo input jack, the battery (-) is connected to the ring, and when a plug is inserted this will connect the battery (-) to the pedal.

The 9V jack has 3 lugs, the single at 90 degrees to the others is for the negative, the other two are for positive, and their normal condition is shorted. If a plug is not inserted the battery positive is connected in the circuit to the pedal +9V. If the power plug is inserted, the battery + is disconnected from the pedal.

[monkey2410]

Oh cool so I don't need to make any changes to that other than C2 and the jack sleeves??

And by that do you mean, remove the 9v connection to sleeve of input (pin3) and place the 9v supply directly to Q1 emitter?
If i do this the circuit the problem i suspect i will have is that the battery will constantly be draining power instead of completing the batteries connection within the circuit when a plug is inserted into the input?

[Cozybuilder]

Look closely at the drawing. 9V from the battery goes to only one place, the 9V power supply jack, on the leg that is disconnected when a plug is inserted. There are much better drawings on the internet, the principle is that when a power plug is inserted, the battery + is disconnected, so the power is drawn solely from the external supply. Inside the pedal, the 9V+ goes to the 2 current limiting resistors for the LEDs, and to the power filtering & reverse voltage protection I showed on the PNP Fuzz schematic. The filtered power goes to the 9V on each of the 2 circuit boards. C2 is not needed because it is replaced by the low-pass power filtering (47R and 100uF//100nF caps).

The sleeve of the input and output jacks are connected to 0V. Only the battery negative is connected to the ring, all other 0V are connected together.

I hope this clarifies.

[monkey2410]

Hopefully I have this right this time so I can stop bothering you 



As for powering the 2nd circuit I simply just need to take the +9v from this part of the circuit shown below (after powering the L.E.D's for both circuits) and the 2 caps that go to negative 0v on here wouldn't need to connect to 0v in the 2nd circuit as both the circuits 0v's will be joined up anyway, am i right?

[monkey2410]

i was meant to attach this