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
Hi & Welcome.. :icon_wink:
Could you plz post a schematic..??
(picture is always more enlightening than guess..)
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 :)
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.
(https://i.postimg.cc/ThjRdM3m/6296.jpg) (https://postimg.cc/ThjRdM3m)
Quote from: augggh on January 12, 2023, 02:29:11 PM
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".
Quote from: Dormammu on January 13, 2023, 04:39:37 AM
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.
A picture is worth 1000 words.
Quote from: GibsonGM on January 13, 2023, 06:13:58 AM
A picture is worth 1000 words.
But, till now, we're speechless.. :-\
Patience, Antonis...patience :)
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>
Quote from: FSFX on January 13, 2023, 05:10:33 AM
Quote from: Dormammu on January 13, 2023, 04:39:37 AM
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 ?
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.
(https://i.postimg.cc/w3MSw7J8/cap-ground.png) (https://postimg.cc/w3MSw7J8)
(https://i.postimg.cc/s1Lbqs9B/divider-ground.png) (https://postimg.cc/s1Lbqs9B)
The "fold" pot should be going to earth ground, not "GND." Sorry about that
Quote from: Dormammu on January 13, 2023, 09:40:55 AM
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.
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.
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?
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 (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).
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'? :icon_lol:
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 (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!
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.
Quote from: Dormammu on January 13, 2023, 04:39:37 AM
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).
The bias voltage (aka 'reference voltage'...Vr) is applied TO the incoming AC signal; they mix (superposition). That signal then rides on a DC level (4.5V)....it's elevated 4.5V ABOVE zero. This is so that we can amplify both the positive AND negative portions of the signal...otherwise, the opamp (or other active device) would clip off that negative half of the wave, like a rectifier. We're making the zero-crossing AC signal able to be worked on, by lifting it up. We 'put it back down' at the end of the process by blocking the DC with an output capacitor (or coupling cap, depending on what we're doing to the signal).
It doesn't change the ground reference a bit. The opamp is working using DC - the ground is still zero volts, to it. It's easier to get this if you look at something like Dist +, which uses input and output caps - that BLOCK the DC voltage. Either side of them is an AC-only signal. Inside their 'loop', you have the AC signal riding on that DC level. Vr replaces the AC's original zero-crossing point, but that's not ground...some call it "AC ground", but that's separate from DC ground (lol). Vr is NOT connected to GROUND...look at Dist +....it has a cap that does go to ground, but DC does NOT pass a capacitor (that cap filters off noise - a different topic). There is still a resistor between Vr and ground in the bias network....
Here's some awesome artwork for you. Top, how the AC looks coming from your guitar. Sort of.
Bottom, jacked up by 4.5V so it doesn't cross zero anymore, and a DC-driven opamp can work with it.
Sorry it sucks, I can't draw with a mouse...
(https://i.postimg.cc/rFjWTJs9/DC-bias.jpg)
Quote from: GibsonGM on January 13, 2023, 03:37:33 PM
Sorry it sucks, I can't draw with a mouse...
And you dare to call yourself "professional painter", Sir..?? :icon_mrgreen:
Looking closely at the Distortion+ is helping a lot, thanks :) The drawing is helpful, I think what I struggle with is understanding is the ending, how pull-down capacitors and resistors actually succeed in their task. If it makes you feel any better, I submitted a drawing of similar quality made on a trackpad for part of a music theory final last semester :icon_lol:
Quote from: FSFX on January 13, 2023, 02:14:21 PM
You obviously didn't read or understand exactly what I wrote.
Someone has an irresistible urge to overcomplicate simple things.
Occam's razor is hopelessly dull ? :-\
I think it makes sense, from "ground" point of view ONLY..!! :icon_wink:
(circuit needs mods like input cap, caps in series with 1k feedback resistors, 100Ohm (R?) value, etc..)
(https://i.imgur.com/nQCDERK.png)
There are no pulldown caps :) Pulldown resistors just reference something to ground rather than an arbitrary floaty thing like "10 mV". Don't worry about that just yet...I suggest getting your mind around what happens when we input an AC signal into an opamp....how the opamp does its job. Looking at the Dist+ makes it much more clear (from my POV anyway).
The R's and C at the end of the Dist+ schematic (power supply) just give the 4.5V needed to jack up the input so we can work with it. It's separate from the actual 'power supply'. No conflict with a power supply jack being used.
You can see input and output caps, that 'keep the DC inside this section' for the opamp to use. That is a next step after the basic ground questions :)
Antonis, my lines become much more straight when my arm is amplified! There is insufficient bandwidth when using a mouse!! :)
QuoteSorry 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.
I think it makes sense, from "ground" point of view ONLY..!! :icon_wink:
(circuit needs mods like input cap, caps in series with 1k feedback resistors, 100Ohm (R?) value, etc..)
The original circuit works, and you might see that configuration in battery powered stuff. However, when you start doing the same thing with effects pedals on a power board local ground will short to -V soon as you connect more than one pedal to the same power supply.
The more common config like antonis' circuit doesn't have that problem - but you need input output caps (and the most of the ground connections should go back to Vref (the orange dots)).
^ This is what I'm nudging him towards, LOL. First let's sort out "ground" :)
It ís possible to 'fake' a bipolar supply from a uni-polar DC input but you need some kind of amplifier to drive this ground. For example like this: (this image shows a battery but a DC adapter works also from experience)
(https://tangentsoft.com/elec/bitmaps/vgrounds/vfb-opa.png)
An opamp can get pretty hot though as it'll need to sink all the current you circuit consumes :)