PNP positive ground fuzz circuits - do I need to isolate jacks from enclosure?

[luap77]

Hi,

I'm in the planning stage of building a typical PNP fuzz with a positive ground; hence the diecast enclosure which is usually 0V ground will be at +9V in this type of circuit.

My question is, do I have to isolate/insulate the 1/4" input and output jacks from the enclosure?

I'm aware of the dangers of powering the effect from the same powersupply as that used for a NPN negative ground pedal...i.e. shorting out, and so I intend on powering any NPN and PNP effects in the signal chain from separate power supplies. But, won't shorting also occur through the 1/4" input and output jacks if I plug a PNP positive ground effect into an NPN negative ground effect?

How do you all deal with this? Is it as simple as insulating the input and output jacks with plastic washers or using plastic jacks on the PNP effects?

Thank you

Paul E

[JimRayden]

Well no because 0 will stay at 0. You're merely changing the power supply to -9V.

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Jimbo

[petemoore]

   But, won't shorting also occur through the 1/4" input and output jacks if I plug a PNP positive ground effect into an NPN negative ground effect?
   the input and output caps will not pass DC voltage [DC Blocking Capacitors],  V+dc potential is contained within circuit DC blocking caps.

[markm]

I think this is one of the things that throws alot of guys with (+) ground circuits and makes them want to build them as (-) ground.

[luap77]

Sorry...I'm still struggling...a bit slow...please bear with me:

The 1/4" jack on my NPN effect is grounded to the enclosure as it is a metal switchcraft type. i.e. the thread/ring of the jack is actually connected to ground. Hence the ring is at 0V.

The 1/4" jack on my PNP effect is grounded to the enclosure as it is a metal switchcraft type. i.e. the thread/ring of the jack is actually connected to ground. Hence the ring is at +9V.

Could someone please explain to me why I won't be shorting +9v to ground when I connect the output of the NPN effect to the input of the PNP effect with a standard guitar cable? The input caps etc are not in this path.

Thanks again.

Paul E

[Stephen]

No worry because with the caps at the end of the circuits protect it to an AC current....NEG ground POSITIVE ground means nothing to the output of the pedal..DO as you may with both types!!

[Ardric]

The 1/4" jack on my NPN effect is grounded to the enclosure as it is a metal switchcraft type. i.e. the thread/ring of the jack is actually connected to ground. Hence the ring is at 0V.

The 1/4" jack on my PNP effect is grounded to the enclosure as it is a metal switchcraft type. i.e. the thread/ring of the jack is actually connected to ground. Hence the ring is at +9V.

That's the trick; it's not +9.  It's 0.  We call the + terminal of the battery/PS 0 VDC, and the - terminal is called -9 VDC.  The battery doesn't care.  Then it's ok to connect the signal grounds.  It becomes a problem when you also try to connect the power supplies together.  You need a second isolated supply, or a bipolar supply, or just run this effect from battery.

[markm]

Legend has it that positive ground circuits sound better with a battery.
Or, it could be that finding a positive ground wall wart is just difficult enough that a battery is an easy solution!

[luap77]

Thanks people!

It all makes sense now & the confusion cloud has evaporated.

Paul E