# Lessons Learned and When the Chips Are Down

#### SparkyCal

Mar 11, 2020
846
Some of you may know that with the help of this forum, I have finally succeeded in building a guitar overdrive stompbox circuit that was beyond me. That thread is here:https://www.electronicspoint.com/forums/threads/a-stretch.293212/

Here's some of the things that I think I learned, and also a question about IC Chips:

I thought it would be important to circle back and try to understand how the circuit worked, rather than just build it like a paint by numbers set. I think I learned the following:

The circuit has three major components. The power supply part (which involves constructing a voltage divider), an IC Chip portion that produces the first stage of distortion by cycling the output into the input, and a third component, which involves sending the distorted signal through a second stage, which involves passing it through at least two diodes and a capacitor. This second stage, adds another layer of distortion, giving the final outputted sound, a more distorted quality.

I also assume that the role of the capaciors and resistors, are to regulate and filter the signal- sometimes to make it cleaner, sometimes to slow down current etc., I am not clear however as to how people decide on the values or what is needed to build this type of circuit.

I also learned that there are single op amps and dual op amps, and when using. dual, it is important to short the additional side of the op amp.

I have three questions:

1. Is my understanding correct?

2. A more general question: I often see capacitors shorted to ground in circuits, including the one I am discussing. My understanding is that a capaciot store power temporarily and then releases it to the circuit. Are capacitors shown as shorting to ground, because electricity really travels from negative to positive?

3. Now that i have learned how to build this circuit, i would liek to experiement with different op amps. I have a socket installed and I undersdtan that i may have to chaneg the wiring to match the pin mapping, depending on the IC's specs. Havings said that, what are your top recommendations for a IC Chip for an overdrive stompbox circuit such as this one. Everyone is welcome to male suggestions. AudioGuru, I assume you'll have some recommendations, although i know you've shared some in the past. There are so many posts, that i foudn it hard to find then, so i thought I'd ask here.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,102
I thought it would be important to circle back and try to understand how the circuit worked, rather than just build it like a paint by numbers set.
Thumbs up for that approach. You struggled afew times, but I think it was worth the effort
I am not clear however as to how people decide on the values or what is needed to build this type of circuit.
Sometimes it is simply experience, at other times it is the application of the correct equations. Knowing what to use is part of the training when you learn electronics (by whatever means).
electricity really travels from negative to positive?
"Electricity" doesn't travel. Except in a battery that's being moved .
We use "voltage" to express the potential difference between different points in a circuit. My favorite analogy is pressure in a pipe system for water. Pressure is the driving force.
We use current to describe the flow of electrons in a conductor (wire). My favorite analogy is the flow of water in a pipe system.
Quite regularly the expression "current flow" is being used instead of current (I know I risk criticism of at least one forum member here). For historical reasons we make a distinction between "conventional" current direction and "physical" current direction. The conventional current direction was defined at a time when th enature of electric current (moving electrons) was not yet established. Physicists the assumed the movement of a positive charge from the "+" ole of a volatge source to ethe "-" pole of a voltage source. Hence converntion current flows from "+" to "-". This is the generally accepted use among electronics engineers.
The physical current is based on the movement of the actual charge carriers (electrons) in a wire which naturally move from their source "-" pole to the sink "+" pole. This definition is almost never (I dare say: never ever) used by electronics engineers.

Question 1: Correct for your first experiences on the journey into the world of electronics. The more you travel onward, the more you will refine your perception and understanding of the details.

Question 2: Beats me. What do you mena by "capacitors shorted to ground"? If it is shorted, the capacitor is without effect. A picture may clarify what you mean.

Question 3: Opamps, though seemingly all the same, vary in many aspects, not only the wiring of the case. Supply voltage, bandwidth, noise, ability to deliver power are only a very, very small subset of the parameters of an opamp. Have you ever wondered why there are so many different types of opamp available. In this application, where the main purpose is distortion of a signal, experimenting with different opamps will probably bring little insight. Imho you'll learn much more in an application where an opamp is used to produce clear sound. There you'll be able to notice differences in e.g. noise behavior, bandwidth etc.

#### ratstar

Aug 20, 2018
485
1. Is my understanding correct?
I don't know, cause I cant read that circuit myself either. =)

2. Capacitors only release energy if they have a loop provided for them to release on.
If I look at the provided circuit I see heaps of ground connects the capacitors will be
constantly releasing on, but i'm not sure if that's just a byproduct and not to do with
the intent of modifying the sound...

3. I don't know I've never used an op-amp in my life, only transistors.

What I actually recommend is cutting the circuit down and only using the bare minimum, then its easier to learn.
A distortion amp is a pre-amp - go through a capacitor (which clips the sound) - then a post amp to speaker... but an even easier one is just put the audio through a diode, and it sounds like excellent distortion already!

#### Audioguru

Sep 24, 2016
3,654
The circuit with one "LM741" opamp and 3 diodes uses the opamp for its voltage gain, not for distortion. It is the diodes that cause the clipping distortion.
If the input signal level from the guitar is too low and/or if the gain of the opamp is set too low then the output of the opamp will have a level too low for the diodes to cause the distortion because a diode conducts when the voltage across it is about 0.7V.

Are you making this circuit now?

#### Attachments

• overdrive circuit.png
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#### kpatz

Feb 24, 2014
334
"Capacitors shorted to ground"... do you mean a capacitor connected between some part of the circuit and ground? Like C5, C6 and C7 in the schematic Audioguru posted above? (I'll be referencing that schematic in my post below for convenience)

C6 and C7 are power supply decoupling capacitors, they help overcome noise and brief fluctuations in the power supply voltage as the load varies. Since the supply rails have some small amount of resistance, and a 9V battery even more so, the voltage can vary somewhat as the circuit operates and the current draw varies, so these caps help smooth this out.

C5 is part of a low pass filter (in conjunction with R6) on the output of the op amp, to roll off some of the high end.

Capacitors inline in a circuit (in series rather than connected to ground) either serve as a DC blocker or a high pass filter (C1 for example).

The distortion is caused by clipping caused by the diodes D1, D2, and D3. Silicon diodes start conducting around 0.6-0.7V so signal below this voltage passes unmolested and anything above that gets clipped. Having 2 diodes in series in one direction increases the clipping threshold so you end up with an asymmetrical waveform, aka even more distortion.

#### SparkyCal

Mar 11, 2020
846
Hi guys.

@Audioguru. unless I am getting my circuits confused, I believe I already built that circuit. Once I did that (or another that i may have it confused with), I went back to the schematic I posted here, and decided to build that one on a PCB.

Two things really helped me breakthrough, and I owe it to people like yourself, Bertus, Martin. Harald and others:

1. I finally realized that my woes revolved around incorrectly interpreting the schematic, where is came to building the voltage divider. Once I found that error, everything else fell into place.

2. I also finally learned how to effectively use my multimeter. Connecting the ground terminal to the negative, allowed me to measure the Pins on the op amp. In this way, i was able to trace back the fact that the voltage divider was mis wired, thereby not producing the proper voltage.

Re: capacitors shorting to ground. What i meant is that I usually see things that look liek thids:
Code:
        |
|
_________+
_________
|
|
|
_____________
________
_____
__
The above is supposed to represent a polarized capacitor who's - lead goes to ground.

So i was wondering; if the point is to store electricity and then release it into the circuit, is the current (voltage) flowing upwards (physical flow) and being released at the + lead of the capacitor into the circuit, or does it flow the other way?

Not sure that question makes sense.

Finally, I am building a PCB board that has three op amp sockets. this will enable me to compare the do-istiorted sound of different op amps used by simply swapping out dupont pins from the various op amps. But if it is the diodes and not the op amps that produce the distortion quality, i may be off course here?

Moderators note : used code tags to preserve spaces

Last edited by a moderator:

#### SparkyCal

Mar 11, 2020
846
"Capacitors shorted to ground"... do you mean a capacitor connected between some part of the circuit and ground? Like C5, C6 and C7 in the schematic Audioguru posted above? (I'll be referencing that schematic in my post below for convenience)

C6 and C7 are power supply decoupling capacitors, they help overcome noise and brief fluctuations in the power supply voltage as the load varies. Since the supply rails have some small amount of resistance, and a 9V battery even more so, the voltage can vary somewhat as the circuit operates and the current draw varies, so these caps help smooth this out.

C5 is part of a low pass filter (in conjunction with R6) on the output of the op amp, to roll off some of the high end.

Capacitors inline in a circuit (in series rather than connected to ground) either serve as a DC blocker or a high pass filter (C1 for example).

The distortion is caused by clipping caused by the diodes D1, D2, and D3. Silicon diodes start conducting around 0.6-0.7V so signal below this voltage passes unmolested and anything above that gets clipped. Having 2 diodes in series in one direction increases the clipping threshold so you end up with an asymmetrical waveform, aka even more distortion.

#### SparkyCal

Mar 11, 2020
846
Very informative. Helps me better understand the design

#### Audioguru

Sep 24, 2016
3,654
Since the diodes produce distortion, not the opamps then the differences in opamps is noise (hiss) and high frequency response (some old opamps like the 741 cannot properly produce the highest octave in hearing, 10kHz to 20kHz).

Original electric guitar amplifiers used vacuum tubes that have a high input resistance for producing the high resonant frequency of guitar pickups and the capacitance of the connecting cable. Modern electric guitar preamp circuit designs say that 1M ohm is the lowest acceptable preamp input resistance. An old 741 opamp has an input resistance as low as only 0.3M which doesn't matter if the listeners are deaf or if no tweeters are used.

Some of the circuits you posted produce "hard" clipping which sounds harsh and other circuits produce "soft" clipping that is more mellow. Since I hate distortion then I do not know which distortion circuit is which.

This thread does not show a circuit, instead it links to the original thread that has many circuits. Maybe you are back to the TL081 circuit that you gave up on? It has a bad tone control circuit that might damage the opamp.

#### bertus

Moderator
Nov 8, 2019
2,858
Hello,

The ascii drawing you show is a grounded capacitor:

This simple drawing is made using this sheet of symbols:

I used the select, copy , paste to create the simple picture.

Bertus

#### SparkyCal

Mar 11, 2020
846
Thanks guys. @Audioguru- it is the schematic in the very first post. But I don't expect you to hunt it down and I don't know how to link directly tot he diagram.

I am in the process of building a modular approach that will enable me to experiment and mix and match opams, diodes and capacitors to see how it changes the sound. Just stumbling through to see if I come across anything I like.

#### WHONOES

May 20, 2017
1,215
All capacitors have impedance which is analogous to resistance. A capacitors impedance is frequency dependent. Rising frequency causes its impedance to diminish whilst falling frequency causes its impedance to rise. It is this aspect of it that is used in the design of filters.
You are right in one respect insofar as capacitors can be used to store a charge and then release it on demand. This aspect is generally used in power supplies.

The impedance of a capacitor may be calculated as follows: Z= 1/(2*PI*f*C)

Where Z is the impedance
PI = 3.142
F is in Hertz
C is in Farads (not uf)
Z will be expressed in Ohms.

Hope that helps

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,102
capacitors shorting to ground. What i meant is that I usually see things that look liek thids:
That is not "shorted to ground". To "short" is usually used as a short hand for "short circuited to" and will be understood as the component being taken out of the circuit by a short circuit across its pins.

This is not an unusual connection, in fact a rather common one. How a capacitor is connected depends on the function it has to perform in the circuit. Therefore no general rule can be given what the function of a capacitor connected to ground is. Some possibilities are:
- power supply buffering,
- signal filtering
- charge storage
- ...

As much as I applaud your persistence in building and understanding these circuits, I really recommend you study some training material to learn the basics of electronics. There's a lot to find in our resource section. Either directly or as a collection of links to other sites.
If you're interested in reading books, here's a collection of books others deem useful.

#### Audioguru

Sep 24, 2016
3,654
I use Microsoft PASTE program to copy and paste schematics.
There is no schematic in this thread but here is the one you gave-up on and was in the video in the other thread:

#### Attachments

• overdrive circuit.png
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#### SparkyCal

Mar 11, 2020
846
Thanks guys. To be brutally honest, it would eb very difficult for me to tackle electronics in a more serious way. If time permitted, I'd love to take electronic course, but my life is such that i have to squeeze time in for hobbies. However, i will be away in a fw weeks for 10 days and i'll need plenty of reading material. So I plan to copy these links and resources and read through what i can. Thanks. AudioGuru, so that i better understand, why remove the tone control? The guy who built said it was necessary to mamnage some of the "fizz" sound.

#### WHONOES

May 20, 2017
1,215
Personally I would put the tone back in. I play a bit of guitar myself and you do need some control over the tone. The circuit that has been removed does actually work.

#### SparkyCal

Mar 11, 2020
846
I put this project together in a wooden box I bought at the dollar store. This pedal is not going to be used on stage at all. It’s just a project. However, I am getting a terrible buzzing noise which almost overrides the sound. I think this is a grounding issue?

as I recall, all my grounds were run to a terminal pin that I soldered in. The negative side of 9 volt battery connects to that pin as well as all of my grounds..

I noticed that when I leaned over and touched the steel toggle switch on my map to turn it off, the buzz got a lot less. How can I fix this issue. Is it because I should have used a metal box?

#### WHONOES

May 20, 2017
1,215
If your project is in a metal box, connect the negative side of the battery to the box. If it is not in a metal box, you could line the inside of your wooden box with cooking foil. Each piece that you put in must be electrically connected to all the others. Ideally there would be no gaps in the foil placement.

#### SparkyCal

Mar 11, 2020
846
I use Microsoft PASTE program to copy and paste schematics.
There is no schematic in this thread but here is the one you gave-up on and was in the video in the other thread:
I think there is some confusion. I built that one. I just put into a wooden box. See post below

#### SparkyCal

Mar 11, 2020
846
If your project is in a metal box, connect the negative side of the battery to the box. If it is not in a metal box, you could line the inside of your wooden box with cooking foil. Each piece that you put in must be electrically connected to all the others. Ideally there would be no gaps in the foil placement.
Do I connect the negative wire to the foil. If so, how?

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