I think I'm making things a lot harder than they need to be. (Polarity, etc.)

[pinkphiloyd]

I want to try to build some things.  I'm gonna start with a simple A/B/Y box so I can switch between channels on my DC-30 or run them both at once.  Okay, that's pretty simple.  I've got a handle on that.  Eventually though, I want to move on to more and more complex things.  I need a new hobby and something else to eat my money.  But I don't want to just throw stuff together blindly, I want to know how and why.  So, I've been scouring the net for a couple of days now.  Reading tutorials, FAQ's, basic electronics stuff, etc.  As of this moment, there are a couple of things that are bugging me more than others.  These will probably seem asinine to most of you.  Forgive me.  I'm a biologist, not an electrician.  Also, I apologize in advance if there's some resource I've missed somewhere that explains these things, but I assure you I've looked.  Okay, that said...

Okay, my first question, and the one that makes me feel especially ignorant (because I feel like I should be able to see it myself just looking at schems), is this:  It has always been my understanding that "ground" is synonymous with "negative".  That is, all grounds tie together and ultimately lead back to the negative supply of your power source.  When looking at schematics, I notice that, usually, grounds end up at the sleeves of the in/out jacks, and also that the negative terminal of the power source is usually connected to the ring of (most often) the input jack.  So, I can only assume that when you insert a plug into the jack, this completes a connection, leading all those grounds back to negative.  Is this correct?  Man, that feels like a really dumb question, but I think it brings me to my second one.

Question two.  I understand that a lot of pedals/circuits are designed so that by inserting or removing a plug into the input jack you're essentially turning the pedal on or off, thereby affecting battery life.  But I fail to see exactly how it works.  Does this have something to do with my first question, and why a stereo plug is often used for the input?  This completes some sort of connection with the bat?  And finally...

Question three.  As I've said, I've been looking at a lot of schematics.  I see patterns, a lot of similarities, I kind of understand some of the basics of what a certain component in a certain location is meant to accomplish, etc.  As I've said, power is usually supplied on the input side, where a stereo jack is utilized.  But I was looking at this schematic of the "Super Hard On" pedal:



I notice the power and stereo jack are on the output "end" of the circuit.  What's the significance of this?  Is there a reason?  I ask because I've also been studying this general layout for bypass switching:



What raises my curiosity is that some of the components (the diodes, transistor, and output cap) in the SHO schematic are polar.  If you used the general switching layout above, would that be an issue?  And what would be the best way to circumvent it?  I think I have this question because I don't really understand how all the different types of switches work.  Would just swapping a couple of positions on the 3pdt switch circumvent the issue?  If there even is an issue, I don't know.  Could you just reverse the polar components?I've been pulling my hair out trying to understand it.  At some point I wondered if you could just "swap ends" in the original circuit, rendering it compatible with this switching set up.  That is, switch the input and output jacks and power supply.  I sketched it up.  Would this have the same effect as the original circuit?  Identical function?



Again, I apologize if I've missed something somewhere, and I'll take and be appreciative of any help I can get.  Thanks.

[Govmnt_Lacky]

Usually, ONLY the battery V- (negative) wire is connected to the Ring of the input jack. When you insert a plug into the Input, it makes the connection between the circuit/enclosure V- (ground) and the battery V- (negative) which completes the circuit and allows the battery to power it.

So you were right all along. It works in that fashion AND is implemented to conserve battery life.

Also, the Input jack is Stereo because of this fact. Mono jack DO NOT have rings. They just have Tips and Sleeves so there is no ability to do this switching of battery power if the Input is a Mono jack.   

Hope that helps. 

[pinkphiloyd]

Okay, that clears that part up then.  Thanks.

[ashcat_lt]

The answer to your 3 stated questions are all yes.

It is not true, however, that ground = negative.  There are circuits with positive ground, as well as bipolar supplies where the ground point is halfway between the power rails.

All voltage is relative to some other voltage.  In most circuits we need to establish a reference voltage, and that's what we call ground.  Many audio circuits actually have multiple reference voltages.  The bottom of the battery maybe the power supply and shield ground, while the "audio ground" is some voltage between the top and bottom of that battery.

It's important, too, to separate th concept of ground from what can be called the "return path".  The sleeve of the jack in your guitar, for example, is not really a ground point until it's connected to something else.  What it is actually there for is to provide a return path, or to complete the circuit from the top of the pickup to the amp (or pedal, or whatever) back to the bottom of the pickup.

[pinkphiloyd]

Excellent, thanks.

[PRR]

> It has always been my understanding that "ground" is synonymous with "negative".

No.

> I'm a biologist

For some biologists, "ground" is synonymous with "feet". Underwater and avian biologists see other situations.

A flashlight has no ground.

A 1948 MG car is positive-ground. Actually, for decades car polarity was pretty random: battery can go either way, lights and thermal gauges don't care, generators and starter motors will work the same on either polarity.

Vacuum tube amps usually make more sense when wired negative ground.

PNP transistor circuits are commonly (but NOT universally) powered positive-ground.

Simple NPN transistor circuits are habitually wired negative ground.

Classic op-amp circuits use TWO power supplies, one pos-gnd one neg-gnd, so that the final output may be either positive or negative and stay there long enough to get a reading. In audio, we don't want steady DC output, and a single supply is cheaper. (The opamp is biased-up halfway so it will swing both ways, a cap blocks the half-voltage from the output.) We habitually power small opamp toys with negative ground.

The "power on jack" thing, with Mono plug in "Stereo" jack, is a Cheap Trick. The parts were NOT designed to work this way. However, it does work. And you need a mono jack anyway, the stereo jack is a dime more, an actual power switch is a buck and another inch of space. Power switches get left on, cords are often un-plugged at the end of the gig: fewer dead batteries. Either jack could be used. Maybe there's an idea that FX-Amp cords may be left in place but musicians always pack their axe and the good cable from axe. Maybe just because Saint Anderton started most plans with battery drawn top-left which happens to be above the input jack.

[pinkphiloyd]

> I'm a biologist

For some biologists, "ground" is synonymous with "feet". Underwater and avian biologists see other situations.

Har dee har har.