Negative ground vs Positive ground wiring - here we go again.

[MikeH]

I did a search on this topic, and quite frankly I was left a little more confused than enlightened.  I'm working on a Ge Fuzz Face (with transistors from small bear).  Here's what I think I've figured out so far:

1.  DC jack is bad?  I read someone saying they wouldn't use a DC jack because it can fry the transistors if the voltage is incorrect/inconsistent.

Here's what I'm confused about:

1.  If you know your power supply is a reliable, steady 9 volts, and you want to use one, the circuit has to be positive ground for it to work?  Is this right?  It seems to be the opposite of what I'd expect.

2.  How do you ground the jacks in a positive ground circuit?

[ildar]

No help here, but I'm wondering if you could use a tip positive adapter.
That, or reverse the wires coming from the jack using a tip negative adapter, maybe? As long as positive voltage goes where it's supposed to, in this case to ground, shouldn't it work?

Nothing like answering a question with more questions.   

[Ronsonic]

Here are the issues:

Most pedals follow the Boss standard, Ground negative and the tip of the jack negative. This means the jack body/barrel must be isolated from the enclosure. It also means that if you have a pedal with a positive ground you cannot run it from the same supply as your other pedals.

You can use a seperate supply for your positive ground pedal and all will be well.

There are debates about the sonic quality of running a classic fuzz from a supply, but that's another can of worms I'll ignore here.

Ron

[MikeH]

Here are the issues:

Most pedals follow the Boss standard, Ground negative and the tip of the jack negative. This means the jack body/barrel must be isolated from the enclosure. It also means that if you have a pedal with a positive ground you cannot run it from the same supply as your other pedals.

You can use a seperate supply for your positive ground pedal and all will be well.

There are debates about the sonic quality of running a classic fuzz from a supply, but that's another can of worms I'll ignore here.

Ron

I'm sorry, but when we say jack (in terms of isolating it), we're talking about a DC jack, not the in and out jacks, right?

I think I'm going to go the purist route and just go with the positive ground and use battery power.  For a positive ground circuit do the in and out jacks still get grounded to the batt(-) terminal?  You definately wouldn't want to connect them to the ground on the circuit board because that would send 9V to the ground on your in and out jacks. 

[Ronsonic]

Here are the issues:

Most pedals follow the Boss standard, Ground negative and the tip of the jack negative. This means the jack body/barrel must be isolated from the enclosure. It also means that if you have a pedal with a positive ground you cannot run it from the same supply as your other pedals.

You can use a seperate supply for your positive ground pedal and all will be well.

There are debates about the sonic quality of running a classic fuzz from a supply, but that's another can of worms I'll ignore here.

Ron

I'm sorry, but when we say jack (in terms of isolating it), we're talking about a DC jack, not the in and out jacks, right?

I think I'm going to go the purist route and just go with the positive ground and use battery power.  For a positive ground circuit do the in and out jacks still get grounded to the batt(-) terminal?  You definately wouldn't want to connect them to the ground on the circuit board because that would send 9V to the ground on your in and out jacks. 

Yes, I meant the DC power jack. The usual arrangement is to connect the ring terminal on the signal input jack to the Positive terminal of the battery. Then when the guitar is plugged in the positive is connected to ground. All grounds are then positive and connected. GGG has some very clear drawings of just about every variation of PNP positive or negative ground and NPN negative ground. Those three pictures are better than all my words.

Ron

[brett]

In simple terms, and as I understand it, the choice to go negative ground with a circuit designed for postive gound circuit such as the FF carries a couple of risks. 
The main one is: IF there isn't a low-resistance path for any signal on the circuit's power supply line to flow to ground, that signal might show up where you don't want it.  Like back into the input.  Because low frequencies have the highest resistance to earth through capacitors, the resulting oscialltions will probably be at low frequency, and will be a form of "motorboating".
However, even really low frequencies can be beaten.  Big or many caps on the power supply help (try 4 x 1000uF or 2 x 4700uF).  Also, a smaller cap on the input will help (0.47uF instead of 2.2uF for a Fuzzface).

Batteries are a poor choice environmentally, though NiMH rechargeables are better that throw-away types.
cheers

[Meanderthal]

 Here's another can of worms- I built the ggg neg ground pnp fuzz face, and for some reason have no complaints...

[brett]

ditto
neg ground PNP FF working fine for 1 year with me.  (with big cap power supply)

[Ronsonic]

Here's another can of worms- I built the ggg neg ground pnp fuzz face, and for some reason have no complaints...

That's what you get for using a proven design in a good layout and decent construction practices. I hope you've learned your lesson.

Ron

[choklitlove]

just wondering, can someone explain to me the point of positive ground circuits?  it just messes with everything i have learned so far.  what are the differences with the circuits that need it?  they can easily be converted to negative ground, right?

i guess what i'm asking is: why does positive ground exist?

[puretube]

PNP...

[choklitlove]

pnp as opposed to npn: i guess, why would they make pnp in the first place?  or, they make equivalents in both styles, right?  then why would someone design a circuit with pnp?

i know it's obvious i don't know much about it...

[Seljer]

a large amount of old germanium transistors are PNP, its harder to find NPN ones

[MartyMart]

All my PNP positive ground FF's work great, tried a neg ground and had all the detailed problems !
I've made a few NPN Ge neg grounds and that's all good too, got a handfull of AC127's that are useable
but the OC140's (CV7112)  that aron/steve stock are just fantastic !
Battery powering a FF should last a VERY long time, so long as you remember to unplug it !

MM.

[choklitlove]

a large amount of old germanium transistors are PNP, its harder to find NPN ones

so the main reason for positive ground (in our area) is germanium transistors which are mostly PNP.  and fuzz faces like these.  am i understanding this correctly?

what about the original purpose of these germaniums?  why would they be made to operate like that?  it had to be abnormal, even back then, right?

[MartyMart]

Someone with more "tech spec" needs to chip in, but from what I remember
making PNP Germanium devices is easier and more reliable than NPN Germanium.
Has to do with the substrate / Layers and how they are formed in manufacture.

... so there's more "good" PNP Germaniums around in general.

MM

[R.G.]

MartyMart is correct about germanium and PNP.

Germanium has the quirk that it's more suited to a PNP type bipolar transistor than NPN. So most germaniums were PNP, and the best germaniums were PNP. It was only late in the germanium life cycle that NPN germanium was made and sold as commercial products.

As a sidelight, the inherent PNP-ness of germanium was one thing responsible for the loss of a generation of EEs who never made the leap over from tubes to transistors. The difficulties in making PNP devices work properly with a negative ground like tubes always used, and the idea that power supplies even could be positive ground, as well as just the idea of how they worked literally put many EEs out of a job back in the time.

Silicon is more inherently NPN. That's why the first commercial bipolars in silicon were NPN, and why PNP silicon was rare, expensive, and poor performance for many years. It was not until silicon devices got about 15 years of experience on them that really complementary power devices were feasible for audio power output devices. That's the reason that the quasi-complementary output stage even existed - it was the solution to the lack of good, reasonably priced PNP silicon outputs.

[MartyMart]

 

.... Torchy told me about this some time ago BTW !

MM.

[R.G.]

There are two kinds of people in this world.
(a) people who have had circuits not work properly because of reversed-ground wiring

and

(b) people who have not yet run into this situation.

I tell you three times - there are situations where you can get uncontrollable oscillation from reversed-ground wiring that cannot be cured by anything except putting the wiring back to the correct ground. Enjoy playing with this if you like, but be aware that if it works you got away with something.

[Ronsonic]

a large amount of old germanium transistors are PNP, its harder to find NPN ones

so the main reason for positive ground (in our area) is germanium transistors which are mostly PNP.  and fuzz faces like these.  am i understanding this correctly?

what about the original purpose of these germaniums?  why would they be made to operate like that?  it had to be abnormal, even back then, right?

It's all they freeking had. There were no silicon transistors, or they were rare and expensive and NPN germanium were also more expensive and frequency limited. It seems hard to believe but back in the sixties even the full audio range was difficult with transistors.

The funny thing is the sound of that clanky old technology for amplifying and distorting a guitar sorta stuck and it's considered part of the instrument now.

Ron