Voltage divider for ground

[augggh]

Feels nice to actually have an account on here now after looking at schematics from the forum for about a year! I'm working on a wavefolding fuzz using a tl074, and I'm wondering if it's dangerous to use a voltage divider to get "ground"? I know it works fine if you're using a battery, but if it were to be plugged into a power supply or a daisy chain, would it potentially cause a short circuit since the input signal's ground would be connected to what's actually 4.5V? Thanks

[antonis]

Hi & Welcome..

Could you plz post a schematic..??
(picture is always more enlightening than guess..)

[GibsonGM]

Welcome, glad you decided to join in!

As Antonis says, post up something that shows what you're wondering about.  In any normal battery and PS setup, there isn't a problem - the power supply just replaces the 9V battery "+" (or whatever voltage you're running at).   We'll get you unstuck, no worries

[merlinb]

If you mean this then no, you can't do that as you will get conflicts when plugging in any power source that is shared with another pedal.

[Dormammu]

Feels nice to actually have an account on here now after looking at schematics from the forum for about a year! I'm working on a wavefolding fuzz using a tl074, and I'm wondering if it's dangerous to use a voltage divider to get "ground"? I know it works fine if you're using a battery, but if it were to be plugged into a power supply or a daisy chain, would it potentially cause a short circuit since the input signal's ground would be connected to what's actually 4.5V? Thanks

I think there's a sort of conceptual misunderstanding here. I have always considered this as a bias for the opamp, and as a common wire (ground) is used (-) of power supply. 
Someone need to observe more circuits and think about them — where's the ground, where's "no ground".

[FSFX]

Someone need to observe more circuits and think about them — where's the ground, where's "no ground".

Maybe the confusing thing is that there is more than one ground.
Just off the top of my head I could list these - some are synonymous, others not.
They all provide a reference:
- protective ground;
- chassis ground;
- DC ground;
- signal ground;
- analogue ground;
- digital ground;
- virtual ground;
etc.

[GibsonGM]

A picture is worth 1000 words.

[antonis]

A picture is worth 1000 words.

But, till now, we're speechless..

[GibsonGM]

Patience, Antonis...patience   

[duck_arse]

how many words so far?

draw your battery circuit, the safe one. now erase the battery and replace w/ the dangerous daisy chain connections. what's changed with respect to ground connections? where's the danger?

and welcome. but draw your circuit. and voltages - always post voltages. and pictures of what you've built.

</werd_count>

[Dormammu]

Someone need to observe more circuits and think about them — where's the ground, where's "no ground".

Maybe the confusing thing is that there is more than one ground.
Just off the top of my head I could list these - some are synonymous, others not.
They all provide a reference:
- protective ground;
- chassis ground;
- DC ground;
- signal ground;
- analogue ground;
- digital ground;
- virtual ground;
etc.

In the context of amp and box building.
Can we see at least 1 circuit where all these things are presented in at least 2-3 of the list and not connected to the common wire ?

[augggh]

Sorry for the late reply! Here's the original design and here's an edit I made where I have a "second ground" using a 100uf capacitor to ground. I know that with a battery there's no issue, but I'm worried that if it were to be applied in the context of multiple pedals with one power supply it could cause a short circuit.

[augggh]

The "fold" pot should be going to earth ground, not "GND." Sorry about that

[FSFX]

In the context of amp and box building.
Can we see at least 1 circuit where all these things are presented in at least 2-3 of the list and not connected to the common wire ?

You obviously didn't read or understand exactly what I wrote.

[GibsonGM]

Ground is ground, David    Where do you see a conflict with the power supply?

"Earth ground" is a holdover from mains wiring, literally 'the earth....ground'.   Unless you're building actual amplifiers, it's probably best to not worry about that term right now.   It's the connection from the amp chassis to the mains ground, for safety.   It's the last line of defense - separate from anything we're doing audio-wise (thinking-wise).  It's not part of this - the amp manufacturers took care of that for us.

In your schematic, all points marked ground, or with your 'chassis' symbol, are tied together.  They also connect to battery " - ", the metal box we house the FX in via metal jack connections ('enclosure') and the shield of your guitar cable (back to the amp, but we're not going there right now).    This is the common reference point for our circuitry to operate from.   Plugging in to a properly-wired power supply jack disconnects the battery "+" and replaces it with the power supply "+"...the grounds, the "minuses", connect together yet again.    This holds true for all properly-wired stomp boxes with negative grounds in our pedal chain.  All the enclosures in the chain are at the same potential - ground, via the shield of the guitar cable.  It's one big system.   

Not ALL effects have a negative ground (some fuzz faces, for ex!), some are positive gnd, which DOES cause a problem and requires them to be run off batteries or charge pumps....but most stomps ARE negative ground. The schematic tells us when we are using positive or negative ground once we learn to interpret them correctly...

Did that help?    Once this makes sense, 'we' can talk about 'special cases' or practices that reduce noise that may look like separate grounds (FSFX...), but for now this is the key point.

[augggh]

I think that does help a bit, thanks! Sorry for the possible confusion in saying "earth ground," I just wasn't sure what to call the two symbols. I'm worried that if the sleeves of the input and output cables are connected to a different ground than the power supply, wouldn't it cause a short circuit when connected to other pedals using the same supply? It would be the same thing as connecting 4.5V to ground.
I guess the most important question to ask now before I get into a bunch of work dealing with bias is if that's even necessary. Can you use tl07x op amps with single supply power without worrying about bias, or will that rectify the signal?

[GibsonGM]

Looking a bit closer (I admit, I skimmed your schematic; we're not at the 'does it work' point lol) - are you getting a little mind-warped by the concept of 4.5V REFERENCE VOLTAGE, also called "VRef" and "VR" on schematics?   I see your battery, 10k resistors & cap in your lower schematic, and don't know why they are there.   And I note the 2 100K resistors doing this job in the upper schematic - which is OK for one "Vr", but for several you're better off doing a network.

A bias network is shown here (power supply): https://www.electrosmash.com/tube-screamer-analysis

Following the logic, simply replacing the "+" with anything the same voltage won't change anything (as long as the battery is disconnected, which the power jack does).

 

[GibsonGM]

You ARE biasing the ICs, with the 2 100k resistors on the first input (top image)!  Using a SINGLE supply!      You don't HAVE to bias that way (see link above), but it's valid.

If you were using a dual supply, there'd be either 2 9V batteries joined "+/-", giving + on one end, - on the other, gnd in the middle.....OR you'd have a dual polarity plug-in supply.   Most FX are single supply and require a bias voltage, often but not always 1/2 the DC voltage (4.5V...).

Look at it this way...another step forward....there are no 'many grounds'....the truth is - shields of cables, jack sleeves, battery minuses...your GUITAR strings....all go back thru each pedal, to the amp, and to the amp's chassis and down a safety connection to the literal earth in the power box in the basement (in a properly wired world).    We just don't think about the 'mains' stuff when doing FX at low voltage, we are using DC, it's simple and as long as we follow a few BASIC rules, all goes well    

We're here helping you to find those basic rules, before digging WAY too far in too fast, LOL...May I suggest we start the design over using some of those 'rules'?   

[GibsonGM]

Here, one of the simplest of dirt boxes, a great place to start reading to get some know-how!   https://www.electrosmash.com/mxr-distortion-plus-analysis

Homework - absorb that info, come back and ask questions!  Look for differences from what you've drawn. There are no dumb questions; we like to help ppl learn this awesome hobby!

[augggh]

It's not that it's being used as a reference voltage, it's that it's being used to replace ground that would cause issues. The 10k resistors are acting as a divider to get the "new ground" to set the battery or supply " - " to -4.5V. The 1uf capacitor is part of a basic passive filter between two stages of wave-folding to get a wider array of tones, and to get more focus on the fundamental. For this circuit, I'd just need one "Vr" at about 4.5V to act as the the "ground" for the areas that are biased ~4.5V for shunt clipping and op-amp gain. Thanks for the articles, I'll see what I can get out of them.

Someone need to observe more circuits and think about them — where's the ground, where's "no ground".

This is true, I'm planning on taking a course on circuitry in the fall to get better at building and analyzing circuits. I'm still at the point where I'm pretty helpless when trying to analyze circuits on my own. I know more or less what this circuit will sound like since I've built a pedal on breadboard using a similar wave folder before (it's based on Ken Stone's schematics of the Serge Wave Multiplier module), and I've been using Falstad's in-browser simulator (I really need to learn how to use LTspice).